SG Health Physics Worksheets

8/7/2019 SG Health Physics Worksheets

1/80

Knox AcademyPhysics DepartmentStandard Grade

Health PhysicsPupil Worksheets

lens whitescreenaDcm

Do not removeFrom the PhysicsDepartment


2/80

HEALTH PHYSICS STUDY GUIDESection 1 - - - The use of Thermometers

Thermometers are useful in medicine to help check the health of apatient. In this section you will investigate some different types ofthermometers.

(Copy) A t th e end of the section I should be able to:

1. state what all thermometers have in common2. describe how a mercury thermometer works3. describe the main differences between a clinical thermometer and an ordinarythermometer4. describe how body temperature is measured usinq a clinical thermometer5. explain why doctors measure body temperature

The following Activities (Activlties 1 - 4) can be done in any order.Remember to return the apparatus from one activity before you start another.


3/80

HEALTH PHYSICS ACTIVITY 1Mercury Thermometers

(What you need)"Ordinary" mercury thermometer, clinical mercury thermometer, stopclock.

C , : , ! 1\."ordinary" thermometer clinical thermometer

(What to dO )1. Copy this table:

Ordinary

MinimumTemperature MaximumTemperature BodyTemperature Reading after60 secondsThermometer

Clinical

2. Look at the scale on the ordinary thermometer. Note, in the table, the maximum andminimum temperatures which can be recorded on this thermometer.

3. Put the bulb of the ordinary thermometer under your arm.4. Leave it there for 1 minute and, without removing the thermometer, record the bodytemperature in the table.5. Now place the ordinary thermometer on the bench. Leave it for 60 seconds and recordthe temperature in the table.6. Repeat steps 2 to 5 using the clinical thermometer.

( Questions)1. Apart from the different temperature range describe two more important differences youdiscovered between the ordinary and the clinical thermometer?2. Why is the clinical thermometer easier to use when finding body temperature?3. What changes in the thermometers to indicate a temperature change?4. Read 'Physics Through Applications" pages 66 and 67. Write a note on normal bodytemperature and the significance of temperatures both above and below this value.


4/80

HEALTH PHYSICS ACTIVITY 2Digital Thermometers

(What you need)"Ordinary" digital thermometer, clinical digital thermometer, kettle, beaker, ice.

"cr'dinary=digital thermometer clinical digital thermometer

(What to dO )1. Use the ordinary digital thermometer to find the temperature of as many of thefollowing as possible. (Each time, wait until the reading becomes steady beforerecording the temperature.)

(a) Hot tap water(b) A room for working in(c) An iced drink(d) Outdoors(e) Cold tap water(f) Water poured from a kettle which has just boiled(g) Yourself

2. Produce a table of your results showing the situation tested and the temperaturerecorded. Place the readings in order, hottest to coolest.3. Find out how many of the above temperatures you can measure using the clinicalthermometer.

list those places which you can measure using the clinical thermometer in yourjotter.

(Question)1. What advantage does the digital thermometer have over the mercury

thermometer?


5/80

HEALTH PHYSICS AC1-'IVITY 3Crystal Strip Thermometer

(What you neeVCrystal strip thermometer (thermochromic thermometer).

(What to d O )1. Read the instructions on the crystal strip thermometer.2. Use the thermometer to find the temperature of the hottest and the coldest parts of theroom.

Record your findings in your jotter.

(Questions)

1. In some parts of the country, the Social Work Department have given crystal striproom thermometers to elderly people. Why do you think they have done this?2. Would a pensioner be comfortable and safe sitting all day in a room where thetemperature was the same as the coldest part of your classroom?3. Find out the name of the medical condition which can cause death as a result oflowered body temperature.4. What changes in the strip to indicate a change in temperature? (Your SummaryNotes may help)


6/80

HEALTH PHYSICS ACTIVITY 4Bimetallic Strip and rotary Thermometer

(What you need)Bimetallic strip, bunsen burner, safety goggles, tongs.

bimetallic strip

(What to do ) rotary thermometer1 . Using a ruler, draw a labelled diagram of the bimetallic strip when it is cold.2. Heat the strip in the bunsen flame.3. Draw a labelled diagram of the bimetallic strip when it is hot.4. What can you say about the metal on the outside of the curve compared to the metalon the inside of the curve?

Ask you teacher to show you the rotary thermometer,(It is a bimetallic strip which is curled up)(Questions)1. What happens to the strip when it is put into the flame?2. Why does this happen?3. How does the rotary thermometer work?(What to do )1. Use the answer file to check that your answers to the activity questions are correct. Ifyou get any wrong, copy down the full correct answer. You must ask your teacherif there is something you still don't understand.2. Read pages 1 - 3 of your summary notes. Ask your teacher to explain any part you donot understand.3. Collect a copy of 'Problems for Standard Grade Physics'. Answer the questions onpage 17 in your jotter.


7/80


8/80

HEALTH PHYSICS STUDY GUIDESection 2 * - - Using Sound

Doctors can listen to sounds from inside the body. This can help them todecide i f a patient is ill.Sound waves can be used to give pictures of the inside of the humanbody. For example, they can be used to give a picture of an unbornbaby, or to discover i f a tooth needs filling.Some sounds can damage your hearing.In this section you will find out about the use of sound in medicine, anduse a sound level meter to measure sound.

~ At the end of the section I should be able to:

1. state what sound can travel through2. explain how a stethoscope works3. state what ultrasound is4. give an example of ultrasound in medicine5. give two examples of noise pollution6. give examples of sound levels in decibels

I might also be able to:7. explain a use of ultrasound in medicine


9/80

HEALTH PHYSICS AC'fIVITY 5Using a Stethoscope

Stethoscopes are used to listen to sounds made inside the body. These sounds canhelp doctors to diagnose various diseases.

Teacher Demonstration

vmodem stethoscopewith bell-shaped andflat chest pieces

(What to d O )1. With help from your teacher place the bell of the stethoscope on your partner's backand listen to your partner's heartbeat2. If you can, count the number of beats per minute.3. Place the bell of the stethoscope on the bench and listen to your partner scratch thebench lightly with a pencil.

( Questions)

1. Describe the sound of your partner's heartbeat.2. What was the number of beats per minute?3. When your partner scratches the bench, how does the sound heard through thestethoscope compare with the sound heard without it?


10/80

HEAL TH PHYSICS ACTIVITY 6The Stethoscope

Read the information below and, if possible, "Physics Through Applications" pages 68 and 69.

The stethoscope can be thought of as a hearing aid which allowsthe doctor or nurse to listen to sounds made within the body. It ismost often used to listen to the heart and the lungs. These soundscan be useful in the diagnosis of various diseases.Until 1816, a doctor couid listen to the sounds from inside thepatient, only by placing his ear directly on the patient's chest.However, in 1816, a French doctor, Rene Laennec, experimentedwith pieces of paper roJledinto a cylinder. He observed that,when he held his ear to one end of the cylinder and placed theother end on the patient's chest, the results were greatlyimproved.

Dr Laennec'sstethoscope

o f 18 i6

This encouraged Laennec to improve the method. He eventually developed a hollow woodencylinder about 30 cm long. He named this the "stethoscope", and went on to use it to investigatethe different sounds from the hearts and the lungs of healthy and ill people.

The stethoscope used today is stili based on the original one. Below is a simplified diagram of amodern stethoscope.

closed bell

valva


11/80

HEALTH PHYSICS ACTIVI1'Y 6 cont.The main parts of the modern stethoscope are the chest piece, the tubing and the ear pieces.The chest piece has two "bells", one open and the other closed by a thin diaphragm (a semi-rigid disc). A valve can be turned to change from the open to the closed bell.The open bell is used to listen to heart sounds. The closed bell is used to listen to soundswhich have a higher frequency than heart sounds such as the lungs. Sounds picked up by theopen bell or the diaphragm are transmitted to the ear pieces through the air in the tubing. Theeardrum of the listener is also a pressure sensitive diaphragm. To create sufficient pressurechange at the ear for a given movement of the diaphragm it is important to have a bell with assmall a volume as possible. The volume of the tubes should also be small and this requires thetubes to be short with a small diameter. However, we also need to have very little sound lossdue to friction and this requires large tube diameters. A compromise is achieved by using tubesabout 30 cm long and 0.3 cm in diameter. The ear pieces have to be a good fit with the ears toavoid sound losses and to prevent background sounds from interfering with those from the heartand lungs.

@uestiony1. What do doctors use a stethoscope for?2. What is a diaphragm?3. Explain why a doctor would sometimes use the closed bell and sometimes the open bell.4. Why should the volume of the tubes and bell be so small?5. To reduce friction, the tubes should be of a large diameter. Exactly where is the soundlost due to friction?6. Why do the ear pieces require to be a good fit?


12/80

HEALTH PHYSICS ACTIVITY 7The Range of Human Hearing

Most signal generators have two frequency controls. One (the COARSE control) changesthe frequency in large steps. The second control (the FINE control) adjusts the frequencymore accurately within the range set by the coarse control. In this activity, you will probablyrequire to use both of these controls.

Teacher DemonstrationListen Carefully to your teacher as he explains about the range of human hearing.Your teacher will then give you a note about what you have discovered.


13/80

HEALTH PHYSICS ACTIVITY 8

Young people can hear vibrations to about 20 000 Hz. Above this frequency, the vibrationsare called ultrasound or ultrasonic vibrations.Ultrasound can be used to take pictures of the inside of the body. In this activity you will usea simple ultrasonic transmitter and receiver to try to find an object hidden inside a coveredframe.

Ultrasonic transmitter and receiver connected to computer, covered frame, a brick

Searching with Ultrasound

(What you n e e V

coveredframe transmitter andreceiver/ computer(What to do)

1. Copy the above diagram2. Listen to your teacher as he explains the above experiment.

o

Your teacher will now give you a note which will explain thesignificance of this experiment.


14/80

HEALTH PHYSICS ACTIVITY 9aUltra Sound in Medicine

&hattod)1. Read the information below and, if possible, "Physics Through Applications" pages 70and 71.

Ultrasound and X~raysare both used in medicine to examine various parts inside the body.However, a long exposure to X-rays can damage the cells of the body and so are not suitablefor continuous examinations. Fortunately, low intensity ultrasound does not damage the bodycells and so narrow beams of these waves can be used with safety.

Ultrasonic pulses are sent into the body from a transmitter placed in good contact with the skin.A gel is placed between the skin and the transmitter to expel any air. This prevents the wavesbeing reflected off the skin before they enter the body. The waves are also reflected when theypass from one type of tissue to another, e.g. from muscle to bone. By using a scan of ultrasonicwaves, a picture of the inside of the body can be built up because the reflected signals takedifferent times to return from objects at different distances from the source. In the 1950's, thistechnique was introduced into medicine by Professor Ian McDonald in Glasgow.

Look at the ultrasound images shown on page 71 of"Physics through Applications",The frequency of the ultrasonic waves used in medicine is several megahertz (MHz) and thespeed of sound in soft biological tissue is about 1500 metres per second. As the depthconcerned is around 150 mm, the echo time is about 1/5000 of a second.

(Questions)1. What is Ultrasound?2. Why is ultrasound used in preference to X-rays to scan unborn babies?3. Where is ultrasound reflected in the body?4. Why must the transmitter be in good contact with the skin?


15/80

HEAL TH PHYSICS ACTIVITY 9bUltrasound Tutorial

1, Ultrasound travels at a speed of 1500 ms"1 in body tissue,(a) Calculate the time taken for the sound to reach a baby 100 mm below the mother'sskin,(b) Calculate the time taken for the sound to reach the skin after being reflected by thebaby,(c) Calculate the total time that the ultrasound spends in the body,

2, Boats use ultrasound in order to calculate thedepth of the water they are in. The boat shownin the diagram sends an ultrasound signaldown to the sea bed. The transmitted signaltakes 0.1s to reflect back up and be detectedby the boat. (See diagram)

1 0 I~ - - I- J - - - - -

transmittedsignal reflectedsignal, - (a) If the speed of sound in water is

1500 m8-1, calculate the depth of thewater below the bottom of the boat.(b) Calculate the wavelength of the

ultrasound used in the water jf it has a frequency 10 MHz, (10 x 1Q6 Hz.)

3. A doctor wants to scan a patient's heart. The sensor is placed below the patient'srib cage and can 'see' the heart using ultrasound. A computer measures the delay timebetween the transmission and reception of the ultrasound pulses to be 1OO~IS( 100 x 10"6s).How far away is the heart from the sensor if the speed of ultrasound in the body is1500 ms-t ?

4. A scientist wants to measure the speed of sound in an aluminium bar. She sets up anultrasonic transmitter and receiver at one end of the bar which is 1m long. A short pulseof ultrasound is sent down the bar, and is reflected back off the far end. The pulse isdetected by the receiver 380 us (380 x 10-6s) after transmission.Calculate the speed of sound in the aluminium.


16/80

HEALTH PHYSICS 10ACTIVITYSound Travels

Sounds from inside a patient's body travel through a stethoscope to the doctor's ear.Ultrasound travelling through a patient's body can be used to make a picture of the inside ofthe body.In this set of activities, you will find out about sound travelling through different materials.

Consider the following questions before the experiments are carried out.

Part OneCan sound travel through a vacuum?

radio

Part Two

Can sound travel through solids?


17/80

HEALTH PHYSICS ACTIVITY 10 cont.Part Three

Does sound travel quicker through solids or gases.

, I l l I ! i l l I ~Part Four

Can sound travel through liquids?

./ ...." pieces of metal

bucket of water - - - - - - - - - - - f / L i - ear


18/80

HEALTH PHYSICS ACTIVITY 11Measuring Sound Level

The human ear is a sensitive detector of sound. It can be damaged by very loud sounds. Inthis activity, you will measure the loudness of some different sounds using a sound level meter.This meter measures the sound level in decibels (dB).CWhat you need)A sound level meter which measures sound in decibels (dB), a radio.

sound level meter

This is a class experiment which you will do with your teacher.

(What to do)1. Switch on the sound level meter and record the readings in the followingsituations by pointing the detector at the source of the sound.

(a) A quiet room or corridor.(b) A noisy room or corridor.(c) Electric bell (several metres from the bel!).(d) A person talking (1 metre from the meter).(e) A person yelling (1 metre from the meter).(f) A radio.(g) A situation of your own choice.(h) Another situation of your own choice.

2. Draw up a table of results showing location and meter reading (dB) in your jotter.


19/80

HEALTH PHYSICS AC1"'IVITY 12Noise Pollution

Very loud sounds can be unpleasant and cause damage to the ear.Loudness is measured in decibels (dB). The following table gives a rough guide to the decibelleve l of typical sounds.Decibels Typical Sounds

150 Sound at speech frequencies can burn the skin.140 Threshold of pain.130 Jet engine at 35 metres.

Pneumatic driver. Hydraulic press at 1 metre.120 1 billion times greater that the least audible sound.Jet aircraft at 175 metres. Inside boiler factory.110 Motor horn at 6 metres. Pop group at 1 metre.Power mower at 1 metre. Train whistle at 15 metres.100 Food blender at 05 metres. Inside train when when dooris slammed. Lorry which has passed MOT test of 92 dB at8 metres measured in narrow street at 4 metres (furthest

distance to which a pedestrian can retreat).90 Heavy truck. Automatic lathe. Underground train.80 Danger Level.

Inside small car. Noisy office. Alarm clock.70 Busy street. Large shop. Building noise.60 Normal conversation at 1 metre.50 Quiet street. Inside average home.40 Quiet office. QUiet conversation.ReSidential area at night.30 Tick of watch. Rustle of paper. Whisper.20 Quiet country lane.

10 Leaves rustling in a light breeze.o Threshold of hearing.


20/80

HEALTH PHYSICS ACTIVITY 12 cont.(What to d~1. Use the table on the last page to complete the second box on page 5 of your summary

notes.Remember you must learn a selection on these values in dB.

2 . Use Physics Through Applications page 72 and 73 if available, the table on the previouspage and the information below to answer the questions at the end of this activity.

In factories and other noisy workplaces, in heavy vehicles or tractors and near pneumatic drillsor aircraft, the noise level can be over 100 dB. In these circumstances, ear protectors should beworn since sound level over 100 dB can cause permanent damage to the ears. A ringing soundheard after exposure to noise is a warning that the sound level has been too high. Theinternational Organisation for Standards (ISO) has recommended that a worker, over the wholeday, should not be exposed to a noise level above 90 dB.

Ear damage due to loud noise is only one cause of hearing difficulty. Disease, defects at birth, oraccidental damage to the ear mechanism can cause total deafness. Slight hearing loss oftencomes with age. Partial deafness is not uncommon, but is often not recognised. Many childrenhave been thought to be slow learners when, in fact, their hearing was some way below normal.

For many people with impaired hearing, their hearing loss is greater at certain frequencies.

High frequency deafness, for example, is quite common. In such cases, the hearing aid has toamplify high frequencies more than low frequencies.

Frequencies below 1 kilohertz (kHz) are called base frequencies and those above 1 kHz arecalled treble frequencies. In some audio equipment there are separate base and treble controlswhich can vary the amplification of these frequency ranges. Newer hi-f systems have graphicequalisers. These are also controls for amplifying certain frequencies. There are usually threeor five different ranges which can amplified separately.


21/80

@uestion~HEAL TH PHYSICS ACTIVITY 12 cont.

1. Why is it important to be able to measure loudness?2. Describe where you recorded any sound level over 90 dB when carrying out Activity 11.3. Explain clearly the term Ihigh frequency deafness'.4. In which way would a person with high frequency deafness alter the controls of a hi-fisystem to improve the quality of the sound heard?5. Give two examples of noise pollution.6. Copy and complete this sentence.

Excessive can damage _

(What to do)1. Use the answer file to check that your answers to all the questions in activities 5 - 12 arecorrect

Copy out the correct answer i f you were wrong and ask your teacher if you still do notunderstand.

2. Read pages 4 and 5 of your summary notes. Again speak to your teacher if there areparts you do not understand.

3. Collect a copy of 'Problems for S.G. Physics'. Answer the questions on page 18 in your[otter. (Omit question 2a)Some questions need you to have completed the "Telecommunications" section first. Ifyou have not, ask your teacher which questions to miss out.

4. Ask your teacher for Health Physics Homework 1.


22/80

HEALTH PHYSICS STUDY GUIDESection 3 - - - Light and Sight

The activities in this section will help you to understand how your eye works. Youwill find out how glasses can help some people with poor eyesight, and howdoctors are able to see inside a patient's stomach.


1. describe how light is focused on the retina of the eye2. state what is meant by refraction of light3. draw diagrams showing what happens to light when it passes from air intoglass, or glass into air4. describe the shapes of convex and concave lenses5. state what is meant by long and short sight6. describe how various lenses affect rays of light7. state how long and short sight can be corrected8. measure the toea/length of a lens9. state what can be used to produce a "cold light" source inside the body

I might also be able to:10. use the terms angle of incidence, angle of refraction and normal11. explain how long and short sight can be corrected12. carry out calculations involving lens power and tocal length13. explain how fibre optics are used in a fibrescope


23/80

HEALTH PHYSICS Ac'rIVITY 13Bending LightAn image is formed on the retina of the eye because light is bent when it enters the eye.This bending is called refraction.In this set of activities you will see how light is refracted as it passes through differentpieces of glass.

(What you need)Low voltage supply, ray box, single and triple slits, sheets of paper, ruler, protractor,rectangular glass block, semi-circular glass block.

Part One Setting up the ray box

ray box ray of light~~,,--~x~--/---*x---

to power supply slit

(What to d O )1. Place the ray box on top of the paper.2. Connect the ray box to the low voltage supply (12V a.c. or d.c.) and put the single slitin front of the ray box to give a single ray.3. Make crosses on the paper to mark the line of the ray and join them up with a ruler.

This is an important skill. You will be using this method to 'draw' light rays later.


24/80

rectangular block/HEALTH PHYSICS ACTIVITY 13 cont.Part Two Rectangular block

~------~---------/

(What to d O )1.. Turn the paper over and trace round the rectangular glass block while positioned asin the diagram above.2. Mark the rays which enter and leave the block with crosses.3. Remove the block and draw in lines to represent the rays.4. Add a third line which represents the ray through the block.5. Put an arrow on each ray to show its direction.

@uestion)1. What is the relationship between the ray entering and the ray leaving the block?

Hint: will the rays meet.

The changing of direction that takes place when a ray of light travels from onesubstance (medium) to another is called refraction.


25/80

HEAL TH PHYSICS ACTIVITY 13 cont.Part 3 Measuring Refraction(What to d~

Angle ofRefraction (r)Angle ofIncidence (i)1. Copy this table.

2. Place semi circular block on the paper.3. Trace a line round the semi-circular block and mark a point half way alongit's straight edge.4. Mark a dotted line at right angles to the straight edge at the half way markas shown.

This line is called a "normal"

~normal->:7kdJ .from ray box ~

5. Send a single ray into the block as shown.6. Measure the angle i. This is called "the angle of incidence",7. Measure the angle r. This is called "the angle of refraction",8. Repeat for different angles and complete the table.


26/80

HEALTH PHYSICS ACTIVI1"Y 13 cont.

1. How do the angles of incidence compare with the angles of refraction?2. How would the angles compare if the block was made from a materialwhich caused more refraction?

Perspex and glass are denser than air. When refraction takes place the rayof light bends towards the normal in the denser material and away fromthe normal when it enters a less dense material.

1. Repeat the above experiment once more by passing the incident rayinto the block along the normal.Did the ray change direction as it entered the block?Can you explain this?

2. Did the ray change direction as it left the semi-circular block this timeor for any of the above readings?Can you explain this?


27/80

HEALTH PHYSICS ACTIVITY 14Lenses

(What you need)

Low voltage supply, ray box, ray box lens, single and triple slits, sheets of paper, ruler,selection of lenses.Part One Concave Lens

Concave lenses come in two forms. Some have onlyone surface cuved, others have both surface curved.They both, however give the same results.Some people easily remember the name of this type oflens because the surface curves inwards like a cave.

1. Connect the ray box to a 12V power supply.2. Place the triple slit into the front of the ray box so that the rays spread out.3. Place a concave lens infront of the raybox so that all three rays can pass through.(See diagram below.)

4. Copy the above diagram and carefully continue the rays to show what happenswhen diverging rays pass through a concave lens

5. Slot a ray box lens half way along the ray box. This has the effect of making the threerays parallel.

6. Copy the above diagram and again complete the ray paths.


28/80

HEALTH PHYSICS AC1'IVITY 14 cont.(QuestionS)1. Does the fact that the incoming rays can be parallel or diverging have an

effect on the rays after passing through the lens.

Since a concave lens causes the rays of light to diverge (spread out), a concavelens is sometimes called a diverging lens.

Part Two Convex Lens

Convex lenses also come in two forms.Again both shapes do the same job.

(What to dO)

1. Set up your ray box with three parallel rays.2. Compare the effects on the rays of placing a thin and thick convex lens in the rays.3. Draw accurate diagrams to show the paths of the rays each time.

4. Remove the ray box lens so that the rays spread out.


29/80

HEALTH PHYSICS ACTIVITY 14 cont.5. Investigate the effects on the rays by the thick and thin lenses.6. Does it matter how far the ray box is from the lens.7. Draw accurate diagrams to show any differences.

(QuestionS)1. Can each of the lenses make parallel rays come together?2. What is the difference between the effects of the two lenses on the parallel rays?3. What effect do the lenses have on rays which are spreading out?

Since a convex lens causes the rays of light to converge (come together), aconvex lens is sometimes called a converging lens.


30/80

HEALTH PHYSICS 15ACTIVITYThe Eye

Our eyes tell what is going on in the 'outside world'. They enable us to grasp or touch objects,

warn us of dangers and allow us to tell the shape, size and colour of objects.

comea

opn c ne rv e

aqueoushumour

pupil ---,.+_iris(coloured)

ciliary muscle:a r ing 01 muscle to which thelens is attached by ligaments

In the eye, the lens system works in a similar way to a camera. It focuses an image on a screencalled the retina. This consists of about 100 million tiny nerve endings (cells) caJledrods andcones. The rods are sensitive to small amounts of light and are used in night vision. Thecones give us colour vision and help us to see detailed sharp images. In poor light, the conesdo not function and we tend to see things in shades of grey.

The area of sharpest vision is called the fovea or yellow spot. It is packed with cones andtherefore responds well to sharp, bright, coloured images.

Electrical signals pass along the nerve fibres to the brain. The part of the retina where thenerve fibres leave the retina contains no light-sensitive cells and is therefore a blind spot onthe retina.The optical system of the eye is a remarkable compound lens which combines a fixed focuspart and an adjustable part. The front part of the lens is called the cornea. Behind it there is aclear liquid called the aqueous humour. Together the cornea and aqueous humour form the


31/80

(a) when you are looking at a distant hill and(b) when you looking at a page of type,

HEALTH PHYSICS ACTIVITY 15 cont.fixed-focus lens, However, in order to focus on near and on distant objects, an adjustable lensis needed, This is provided by the eye's 'jelly' lens.

This lens tends to bulge - as would a balloon - when it is free to do so. However, it is held roundthe edges by suspensory ligaments which, in turn, are connected to the ring-like ciliary muscles.These muscles control the shape of the lens, The lens is thin when looking at distant objectsand fatter when looking at near objects. The ability to change the lens shape is calledaccommodation. When the eye is relaxed, it is focussed on distant objects. The nearest point on

which your eye can focus is called the near point. It is usually between 10 cm and 30 cm away,The iris is an adjustable diaphragm with a central hole, the pupil, through which light enters theeye. The size of the pupil changes automatically with the amount of light coming to the eye.

Reading, "Physics through applications", pages 74 and 75, may also help you toanswer the following questions.

@uestion>1. What is the name of the screen where the light strikes the back of the eye?2. The lens shown here represents the lens of your eye. Draw its shape

3. (a) What is the name for the part of the retina where the signals leave the eye?(b) Why can you not see anything at this point?4. What is the point on the retina at which objects can be seen most sharply?5. (a) Which cells are used to see colour?(b) Which are used at night?6. Draw diagrams showing the iris size

(a) in bright light and (b) in dull light.


32/80

HEALTH PHYSICS Activity 16Image Formation

Part 1

@"hat you nee~Bulb in bulb holder, Mounted letter IF', Circular lens in holder, Screen.

1. Set up the following, placing the screen 80cm from the IF',

whitescreenlens80 em

2. Move the lens until a sharp image of the 'F' is produced on the screen.3, Draw the above picture into your jotter showing the correct position of your lens.

@uestions)

1. Is the image larger, smaller or the same size as the object (letter 'F)?2. Is the image the correct way up or has is been turned upside down (inverted)?3. Is the image back to front or is it the same way round as the object?


33/80

HEALTH PHYSICS Activity 16 cont.Part 2 - The Camera

0'hat you nee)Bulb in bulb holder, Mounted letter 'F', Model Camera, Camera screen.

Camera screenletter 'F' Camera

2m

1. Place the plastic camera screen, (which represents the photographic film), into theback of the camera and set up the apparatus as shown above making sure thecamera is 2m from the 'F'.

2. Point the camera at the 'F' and push the lens in until a sharp image of the 'F' is seenon the screen.3. Reposition the camera so that it is now 60 cm from the letter 'F'.4. Move the lens until the image is again focussed.

@uestions)

1. Describe the position of the lens relative to the film when focussed on a distantobject.2. Describe the position of the lens relative to the film when focussed on a closeobject.


34/80

HEALTH PHYSICS Activity 16 cont.Part 3 - The Eye

In our eyes, the distance from the lens to the screen (retina) cannot be changed as in thecamera. It is the shape of the eye lens which changes

~hat you neeC0Bulb in bulb holder, Mounted letter 'F', 2 model eyes (1 with thick lens and 1 with thin lens),

fixed length. . . . f > -letter 'F'Othick lens I ; s c r e e n( ] t h i n l e n s I

1. Hold both model eyes as if you were looking through a pair of binoculars. (Thelenses should be pointing towards the object and you should be looking at the whitescreens on the back of the models).2. Move very close to the object until a focussed image of the 'F' is focussed on one of

the screens.3. Note which model has focussed the image. (Thick or thin lens)4. Still looking through the model eyes walk backwards until a focussed image is seenon the other screen and again note the model being used.

Answer the questions on the next page.


35/80

HEAL TH PHYSICS Activity 16 cont.@uestions)

1. Which shape must the eye lens be when looking at close up objects. (e.g. reading)2. What shape must the eye lens be when looking at a distant object. (e.g. lookingacross the playing fields.)3. Draw a ray diagram to show how the eye forms an image on the retina. (You mayfind, "Physics Through Applications" page 74 useful.)4. Draw a ray diagram to show how the lens of the eye forms an image when the objectis

a) far from the eye. b) close to the eye.(You may find, "Physics Through Applications" page 75 usefuL)

Ask your teacher for Health Physics Homework 2.


36/80

HEAL TH PHYSICS ACTIVITY 17Focal Length

Some lenses bend light more than others. One way to indicate the amount of refraction is togive the focal length of the lens.A convex lens can make rays of light come together to a point after they have passedthrough the lens. The point where the rays meet is called the "focus". The position of thefocus depends on where the rays come from.

Rays come from point close to lens - focus is far from lens.

Rays come from point further from [ens - focus nearer to lens.focal length

principal focus

When the rays come from a point which is so far away that the rays seem parallel, thefocus is even nearer to the lens.In this case, the focus is called the principal focus.The distance from the lens to the principal focus is called the focal length.

1 this is the symbolfor a convex lens. Ithis is the symbolfor a concave lens.NOTE


37/80

HEALTH PHYSICS ACTIVITY 17 cont.Measuring Focal Length

(What you need)Ruler, convex lenses, white screen.

/(What todo)

~ this table Lens shape Focal length(em)

thickmediumthin

1. Choose a convex lens and use it to produce a sharp image of a distant object (forexample, a window) on the white screen.

2. Measure the distance from the lens to the image. (This is the approximate focallength)3. Repeat using different lenses and complete the table.

(Questions)1. In which way do lenses with a short focal length look different from those with a longfocal length?2. Does the focal length affect the image in any way?(Whattodo)1. Collect a copy of 'Problems for Srandard Grade Physics".2. Answer questions 1, 2, 3, 4 and 7 from page 19 in your jotter.


38/80

HEALTH PHYSICS ACTIVITY 18Long and Short Sight

Teacher DemonstrationListen and watch carefully as your teacher explains about two common eye problems.


39/80

HEALTH PHYSICS Activity 19Lens Power

People who have severe eye defects may need stronger (more powerful) lenses to correcttheir eyesight than those who have only slight defects.(A more powerful lens is one which causes more refraction.)An optician must therefore have a range of lenses to suit different individuals' needs.The power of these lenses could be indicated by giving their focal lengths - the mostpowerful lenses having the shortest focal lengths. Another way to indicate the amount ofrefraction caused by a lens is to calculate its power from the following relationship:

1power = focal length (in metres)

It is useful to note that the opposite is also true. Le.

1focal length (in metres) = power

If the focal length is measured in metres, then power is given in dioptres (0).

Converging (convex) lenses have positive powers (e.g., + 10 0, + 17 0)Diverging (concave) lenses have negative powers (e.g., - 10 0, - 17 D)

Example: A convex lens has a focal length of 10 cm. Find its power.1power = .focal length (In metres)

power =_10.1

power = + 10 dioptres


40/80

HEALTH PHYSICS Activity 19 cont.(Questions)

1. A convex lens has a focal length of 5 cm. What is its power?

2. A concave lens has a focal length of - 20 cm. What is its power?

3. A convex lens has a power of +3D. What is its focal length?

4. A lens has a power of -14 D. a) What type of lens is it?b) What is its focal length?


41/80

HEALTH PHYSICS Activity 20Optical Fibres in MedicineCWhat you need)

Display of optical fibres.(What to do)1. Discuss with your teacher how optical fibres work.2. Read the following passage before answering the questions below.

The total internal reflection of light inside a narrow perspex rod lets the light travel fromone end to the other even if the rod is bent.

T otal in te rn al re fle ctio n o cc urs w he n lig ht h itsthe inside surface o f the ro d at la rge angle s .

In telecommunications, the total internal reflection of light inside optical fibres is used tocarry signals. Another important application of total internal reflection is in medicine.Doctors can pass thin optical fibres inside a patient and examine, for example, damage tothe stomach.

image guide)

scopa lip

The instrument used for this, called the fibrescope, is shown in the diagram above.Inside the protective sheath there are two separate fibre optic bundles. Each bundle iscomposed of tens of thousands of very thin glass fibres. One bundle - the light guide - isused to shine light inside the patient.

pass light downfrom lamp(light guide)


42/80

HEALTH PHYSICS Activity 20 cont.The heat from the lamp does not pass down the fibres. This means that the other end ofthe guide is cold. This is safer for the patient.

The second bundle - the image guide - aJlowsthe doctor to see inside the patient. This ispossible because each of the thousands of fibres is coated and transmits light separately..;A lens at the tip of the fibrescope focusses the light from the fibres to produce an image.To focus on objects at different distances, the lens at the tip must be moved in or out. Thismovement is usually controlled remotely at the eyepiece section. A separate adjustmentat the eyepiece is necessary to allow for differences in eyesight.

Fibrescopes usually have a controllable bending section near the tip so that the observercan direct the scope during insertion and be able to scan an area once inside.

Fibrescopes, in medicine, are are also called Endoscopes. A Gastroscope is aspecial type of endoscope used for looking into the stomach for example.

Answer the questions on the following page using the information above. Reading,"Physics Through Applications", page 79 may also help.


43/80

HEAL TH PHYSICS Activity 20 cont.( Questions)

1. (a) Copy and complete this diagram to show how light travels down a glass rod.

(b) What name is given to this method by which light travels?

2. Why is the end of the tube "cold" and why is this useful?

3. Which parts of the body do doctors study, using an fibrescope?

4. Explain why two separate bundles of fibres are used.

5. Why is the end of the tube flexible?

6. What in medicine is the other name by which fibrescopes are known?

7. Draw a diagram of how a gastroscope is used to examine the inside of a patient'sbody.

&hat to d O )1. Use the answer file to check that your answers to all the questions in activities 13 - 20are correct.

Copy out the correct answer if you were wrong and ask your teacher i f you still do notunderstand.2. Read pages 6 to 9 of your summary notes completing them where nessecary. Againspeak to your teacher if there are any parts you do not understand.3. Collect a copy of 'Problems for S.G. Physics". Answer the remaining questions

from page19 in your jotter.


44/80

HEALTH PHYSICS STUDY GUIDESection 4 ~ ~ ~ Using Light, X-rays Infrared and Ultraviolet Radiation

Doctors can use a number of different types of rays to treat variousillnesses. In this section you will find out about the medical uses oflasers, X~rays, and infrared and ultraviolet radiation.


1. describe a use of the laser in medicine2. describe a use of X-rays in medicine3. state how X-rays can be detected4. describe the use of infrared and ultraviolet radiation in medicine5. state the danger of too much ultraviolet radiation

I might also be able to:6. describe the advantages of computer assisted tomography


45/80

HEALTH PHYSICS ACTIVITY 21Lasers

The first laser was made in 1960 by Theodore Maiman. Although it was then described as a,"solution looking for a problem", the laser now has many uses. They are used incommunication, surveying, nuclear physics, photo-chemistry, hologrophy and entertainment.In medicine the laser has not replaced the scalpel to the extent some surgeons had predicted.One reason for this is that the cost of a medical laser can be as much as 100 000.

In medicine, the laser is used to produce extreme heating in a very small piece of tissue. Oftenthe laser beam is transmitted through a fibrescope to an inaccessible part of the body.

Tissue PenetrationWhen a laser beam strikes tissue, some of it is reflected, some absorbed and some transmitted.Many factors affects the way the laser beam reacts with the tissue. These include the type oftissue - it's colour and internal structure - the power of the laser beam and it's wavelength. Anindication of the penetration of different laser beams is shown below.

la se r b eam

Carbon Dioxide LaserAs the carbon dioxide laser beam is almost totally absorbed in the first tenth of a millimetre, it isparticularly suited for use as a 'laser scalpel'. The shallow penetration makes it ideal fortreating areas where it is important not to damage underlying structures. Malignant tumours ofthe larynx can be vapourised without scarring the vocal cords. In gynaecology, early cancer ofthe cervix (neck of the womb) can be treated with this Jaserand the fallopian tubes can beenunblocked in an attempt to cure infertility.


46/80

HEALTH PHYSICS 21 cont.ACTIVITYArgon LaserEye surgery is the best known application of Argon Lasers. The retina of a diabetic personsometimes does not get enough oxygen from the blood vessels. To compensate for the lack ofoxygen, abnormal vessels grow forwards and bleed into the eye. Vision at the edge is alteredand the patient can eventually go blind.

The eye surgeon uses the argon laser to photocoagulate the less important areas of the retina.This heats the blood vessels to the point where the blood clots and blocks the vessel, asshown below. Although this reduces the patient's field of viston, the retina now requires lessoxygen than before and the patient is much less likely to go blind.

A laser beam is focussedby the cornea and lens toa small spot on the retinawhere it photccoagulatesa small blood vessel

laser beamoptic

blind spot -,

Photocoagulation is also useful for repairing retinal tears and holes which develop prior to theretina coming away from the back of the eye.

Argon lasers transmit blue-green light which is strongly absorbed by the red part of the blood.Such lasers are therefore particularly suitable for sealing blood vessels. Argon lasers areused to remove 'port-wine' birthmarks from patients faces. Both the surgeon and patient wearprotective glasses. Since the laser energy is concentrated in a narrow beam for long distances,even a reflected beam can be a hazard. Walls and other surfaces in laser installations shouldtherefore be painted with matt black paint.(What to d O )Use this passage to answer the questions on the following page. "Physics ThroughApplications" pages 80 and 81 may also help.


47/80

ACTIVITY.HEALTH PHYSICS 21 cont.Cuestions)1. Give 3 examples of the use of lasers in medicine.

2. How can a laser be used to seal blood vessels?

3. Why is this called "bloodless" surgery?

4. How is the laser beam sent into parts of the body that cannot otherwise be easilyreached?

5. Why is an argon laser useful in eye surgery?

6. What precautions must be taken in using the laser in hospital treatment?


48/80

HEALTH PHYSICS ACTIVITY 22Infrared Radiation

(What you need)Metal container with shiny and dull surfaces, infrared sensor, digital voltmeter

Infra-reddetectorshiny voltmeter

Part One

(What to d O )1. Fill the container with very hot water from either the tap or the kettle.2. Try to detect the infrared radiation from the shiny surface and from the dull surfaceby placing your hand near each surface.3. Repeat step 2 uslnq the infra-red detector. Note any readings in your jotter.4. Switch off the voltmeter and the power supply.

(Questions)

1. You have been asked to try and detect infra-red radiation. What other name haveyou used instead of infra-red radiation in the past?

2. Did you detect the infra-red radiation with your hand?

3. Did you detect the infra-red radiation with the detector?

4. Which surface gave off the greatest amount of infrared radiation?


49/80

Part Two

HEALTH PHYSICS ACTIVITY 22 cont.All hot objects give invisible 'heat rays' called infra-red radiation. Infra-red belongs to thesame family of waves as visible light which is known as the Electromagnetic Spectrum.Infra-red radiation has a slightly longer wavelength than visible light. Special infra-redcameras can be used to take colour photographs called thermograms using this radiationinstead of light.

In medicine, thermograms of a patient's body show areas of different temperature. Thethermogram below shows a patient's face.

Coloured thermograms of a hand can be seen on page 85 of "Physics Through Applications".

In these colour photographs, each colour indicates a different temperature. Doctors havefound that malignant tumours are warmer than healthy tissue and show up clearly onthermograms.

Infra red radiation is used in a different way by physiotherapists. They use this radiation topenetrate the skin and heat the muscles and tissue. Heat causes healing to occur morequickly.


50/80

ACTIVITY 22 cont.HEALTH PHYSICS(Questions)

1. How does the wavelength of infra-red compare with the wavelength of visiblelight?

2. How do doctors detect different temperatures on the body using a thermogram?

3. Why is infrared radiation useful to a physiotherapist?

(What to dO )1. Collect a 'Thermogram Sheet' from your teacher.2. Follow the instructions on the sheet

Once completed the thermogram can be glued or stapled into your jotter.If you have time you can complete this in class but you may want to do it at home.


51/80

ACTIVITY 23HEALTH PHYSICSUltra violet Radiation

Ultraviolet is another type of invisible radiation. The wavelength of ultraviolet rays is shorterthan the wavelength of infra-red or visible light.To keep healthy, our bodies need the ultraviolet radiation in sunlight. When ultraviolet isabsorbed by the skin, vitamin 03 is produced. Visible light does not cause this to happen.

Vitamin 03 helps the body to obtain calcium from food. Patients who have to stay in hospital fora long time are often asked to sit in front of ultraviolet lamps to compensate for their lack ofsunlight. The lamps used in sunbeds also produce ultraviolet rays.

Too much ultraviolet light on the skin produces sunburn and can cause the skin to turn red andbe very painful. Suntan lotians and creams absorb the higher frequency ultraviolet rays whichcause the burning, but they allow the lower frequency rays to reach the skin and to produce atan. The tan is due to a pigment called melanin being produced. Excessive use of sunbedsmay cause melanoma, a form of skin cancer.

Ultraviolet radiation is used in the treatment of certain skin diseases such as acne. Care mustbe taken to ensure that over-exposure does not cause burning of the skin. Suitable gogglesmust be worn to protect the patient's eyes.

(Questions)

1. How does the wavelength of ultraviolet light compare to the wavelength of visible light?2. Why is ultraviolet light needed by the body?3. Why can excessive exposure to ultraviolet radiation be dangerous to a person's health.

DemontrationYour teacher will show you how ultraviolet radiation can be detected and give you a short note.


52/80

HEALTH PHYSICS ACTIVITY 24X-ray Photographs

(What you need)Medical X-ray transparency

(What to do )

1. Hold your X-ray transparency up to a window or to an artificial light source.2. Try to identify which part of the body has been X-rayed. You should be able to makeout bones and also some of the surrounding softer tissue (e.g. muscle or lungs).

(Questions)

1. Are the bones which show up on your transparency lighter or darker than thesurrounding tissue?

2. X-rays blacken the photographic film when they hit it. What effect have the bones hadon the X-rays which were passed into the body?

3. Healthy lungs always appear fairly dark on X-ray transparencies. Can you work outwhy this is?


53/80

Medical X..raysHEALTH PHYSICS ACTIVITY 2 5

There is a good chance that part of your body has been X-rayed at some time. Doctors use x -rays to "see inside" your body, and dentists sometimes use X-rays to examine the roots of yourteeth. These X-rays are called "soft" X-rays. This type is usually used for diagnosing illness ordetecting breaks in bones. As long as you are not exposed to too many of these X-rays nodamage should be caused to your body.

x-rays, like ultraviolet, infra-red and visible light, are part of the electromagnetic spectrum.X-rays, however, have a smaller wavelength than the others. They are made by high voltageelectrical machines and they may be detected by photographic plates.

photographic plateX-ray tube

X-rays

There use in medicine depends on the fact that they pass through body tissues like skin, fatand muscle fairly easily, but are more easily absorbed by denser substances such as bones.This makes them more.useful than visible light for looking inside the body. If you hold the palmof your hand up to the light, you can't see the bones inside. Most of the light is reflected off theskin or absorbed by it.

With X-rays, hardly any is reflected. It all either passes straight through or is absorbed.Different types of tissue absorb different amounts. Imagine X-rays being fired at part of the arm.The X-rays start out with equal strengths, but those going through the muscle are slightlyabsorbed, and of those aimed at the bone only a small proportion pass through.

See diagram on next page.


54/80

HEALTH PHYSICS ACTIVITY 25 coot.arm bone

X-rays

.. '>."'::", ..; .: ./ ' ".--~ " "( L ) l.. ')\ ~ ), " _ " .. ".. . . . . . , ; . . . . , .

-- dark on plate

- light

arm muscle photographicplateWhen X-rays hit the photographic plate on the other side of the patient, they affect thephotographic emulsion and blacken it. The image of the arm, therefore, will be fairly dark, withlighter areas for the bone. Any break in the bone lets X-rays through and may show up as adark crack.

X-ray photos may also be used to look for problems in organs like the lungs, the brain or thegut. Sometimes patients may be asked to swallow a liquid which absorbs X-rays - a 'bariummeal". This shows up parts of the digestive system very clearly. The swallowing may even bewatched by doctors on a TV-type monitor. Here, the X-rays do not fall on photographic platesbut on a screen made up of a special paint which, when struck by X-rays, gives off flashes oflight called scintillations. These are detected electronically, processed by a computer andproduce an image on the monitor. Very detailed X-ray pictures may be produced by suchmachines and permanent photographic records can also be made.Computed TomographyComputed tomography uses a sophisticated X-ray machine known as a CAT (or CT) scannerto give a clear image of a selected slice through the body. The body is taken to be a series ofhorizontal slices a few millimeteres thick. Some of these are shown in the diagram below.

detector

~"W-~I '-' , yI " . . . . ' ,L ,fMh. ..l, r ~ ,, ,, - , .

~. .. , - '\ , . , : - -s ~ F..v ,'-i ".J ,..r- '.r;"\ '-l( ':~ ," ~'", -c- "'. " . I"" ' " , I. . . . . . , . , . . , ~,

'0Hn,:.T.I . +- X-rays1t11T '"11 1z,nu

o


55/80

For each slice, a beam of X-rays is passed from one side of the body to the other. The X-raystravel at right angles to the body's length as shown below, and the source and detector rotatearound the body to give readings for all directions.

ACTIVITY 25 cont.HEALTH PHYSICS

detector

A total of about 300 000 readings are taken for each slice. The data is fed into a computerwhich then builds up a picture of the organs in each slice. The picture is then diplayed on a TVscreen. The main advantage of computed tomography compared with normal X-rayphotographs is that a series of slices gives a three dimentional picture of the part o f the bodybeing studied.(Questions)The following questions will require more than just one sentence answers. Try to write a smallparagraph for each using as many of your own words as possible.1. What are X-rays used for in medicine?2. How is an X-ray image detected?3. What happens when X-rays enter the body?4. How are X-rays used in CT scanners?5. What are the advantages of Computed Tomography?(What to do )1. Use the answer file to check that your answers to all the questions in activities 21 - 25

are correct. Copy out the correct answer if you were wrong and ask your teacher i f stilldo not understand.2. Read pages 10 and 11 of your summary notes. Speak to your teacher if there are any

parts you do not understand.3. Collect a copy of 'Problems fo r 8.G. Physics'. Answer the questions 1,2,5,6 & 7 from

page 20.4. Ask your teacher for Health Physics homework 3.


56/80

HEALTH PHYSICS STUDY GUIDESection 5 ~ ~ - Nuclear Radiation M Humans and Medicine

Radioactive materials have a number of uses in medicine.A radioactive substance can be put inside a patient's body to help adoctor to diagnose illness. Other radioactive sources can be usedoutside the body to kill unwanted cells.In this section you will find out about medical uses of radiation. Youwill also learn about some of the properties of this radiation, and thesafety precautions needed when using radioactive materials.

At the end of the section I should be able to:1. state the effect of nuclear radiation on living cells.2. describe a medical use of radiation which involves killing cells.3. describe how the fact that radiation is easy to detect can beused in medicine.4. describe the range and absorption of alpha, beta and gamma radiation5. state what happens to radiation energy when radiation passes through a material6. describe a model of the atom7. state which type of radiation causes the most ionisation8. give one effect of radiation on non-livmq things9. state the unit used to measure the activity of a radioactive source10. state what happens to the activity of a source as time passes11. describe safety precautions needed when handling radioactive substances12. state the unit used to measure dose

I might also be able to:13. explain the term ionisation14. Describe how one of the effects of radiation is used in a detector15. state what is meant by half-life16. describe an experiment to measure belt-ilte17. calculate half-life18. state two factors which affect the biological effect of radiation


57/80

HEAL TH PHYSICS 26ACTIVIl'YUsing Radiation in Medicine

TREATMENT

Cancer - Radiation TherapyCancers are growths of cells which are out of control. The object of the radiation treatment isto cause damage to the cancer cells which then stop reproducing. The cancer or tumour thenshrinks.

Unfortunately, also healthy cells can be damaged by radiation, and so the applied dose hasto be very accuratey calculated so that sufficient damage is done to the cancer cells withoutoverdoing the damage to other cells.Some localised tumours (e.g. a bone tumour) can be treated by irradiation with high energyX-rays (hard X-rays) or gamma rays.

The gamma rays are emitted from a Cobalt-60 source - a radioactive form of Cobalt. Thecobalt source is kept within a thick, heavy metal container. This has a slit in it to allow anarrow beam of gamma rays to emerge.

The X-rays are generated by a linear accelerator. This machine fires high energy electronsat a metal target and when the electrons strike the target, X-rays are produced. The X-raysare shaped into a narrow beam by movable metal shutters.

With either tequnique, the apparatus is arranged so that it can rotate around the couch onwhich the patient lies. This allows the patient to be irradiated from different directions. Thetumour receives a maximum radiation dose from the beam, while the skin and other tissuereceive as little unwanted radiation as possible.

~ source rotates, butstays aimed at cancer

tumour


58/80

Other Methods of TreatmentThere are other ways in which radiation can be used to treat cancer. For example, a tumourin the bladder wall can be treated by a permanent implanting of a piece of radioactive goldcalled a 'gold grain'. This emits gamma rays and it's radioactivity decreases almostcompletely to background levels after about two weeks. The gold itself does no harm to thepatient. The amount of radiation needed for a tumour of a certain size can be accuratelycalculated, and a gold grain of the correct size is then implanted.

HEAL TH PHYSICS ACTIVITY 26 cont.

DiagnosisFor some medical conditions, radioactive tracers can be injected into the body. Thesetracers can be followed in their path through the body because of their radioactivity. Thesubstances used are chosen so that:

1. they will concentrate in the organ which is to be examined2. they lose their radioactivity quickly3. they emit gamma rays which can be detected outside the body

Kidney Examination using TracersOne of the most common uses of tracers is to examine the working of the kidneys. Thetracer used is a radioactive form of the rare element technetium, The tracer solution isinjected into the patient and a device called a gamma camera is positioned above thepatient's body. OSCi l l iscope

I I1 _I-- electronics1----1 detectorcollimatorI q I 1 . 1

radioactive tracer ---r:..-"\~::::::::~R:----__fillin patient's lungs \. __ --::::~~ +-': JJ \ .

gamma raysWhen a gamma ray has been detected, the electronics of the camera send a signal to themonitor screen. Different points of the patient's kidneys are matched up with different pointson the screen so that the image of the kidneys is seen. The image may consist of differentcolours - each colour indicating a different concentration of gamma rays. The completedpicture will be made up by around a million dots on the screen - each produced by agamma ray.


59/80

HEALTH PHYSICS ACTIVITY 26 cont.STERALISA TIONAs radiation can be used to kill cells, it can also be used to kill bacteria or germs. In the past,medical instruments such as syringes had to be steralised by heat or chemicals. Now cheap,plastic, throw-away syringes can be used. They are prepacked and then irradiated by anintense gamma ray source. This kills any bacteria but does not make the syringe radioactive.

Other medical equipment such as scalpels and bandages can be steralised by the samemethod.

( What to d O )Use the information above to write your own notes about using radiation in medicine.Your notes should be in your own words - don't just copy bits from the information sheet.They should cover all the things listed below. A paragraph or two on each topic should beenough.

1. Radiation can kill or change living cells.2. Treatment of cancer: X-rays, gamma rays, tumour, rotating patient and implants.3. Diagnosing illness; injecting radioactive substances (tracers), concentration in partsof the body, emitting gamma radiation, gamma camera.4. Sterilising instruments.


60/80


61/80

HEALTH PHYSICS 27 cont.The process of ionisation by an alpha particle is shown in the diagram below. In (a) thealpha particle is approaching the neutral atom and in (b) it has passed by creating an ion.

(a) (b)positve ion

. , . +alpha /

+. , .+-The relatively slow-moving alpha particle will go on to create many more ions during itsjourney through the gas.

Beta radiation is a stream of fast moving electrons. As these have the same negativecharge as the electrons near the outside of the atoms in the air, they exert electrical forces onthese outer electrons, this time repelling them and allowing them to break free and createions.

Gamma radiation is uncharged - it is made up of electromagnetic radiation of very shortwavelength. However, it can also affect the electrons in the atom and knock them away tocreate ions.

The alpha particle emissions from a radioactive source cause much greater ionisation thanbeta or gamma - they pull electrons off atoms much more effectively than the other radiationsdo.

In Activity 33 you will see a video which shows experiments which look at the effects ofionisation. The Geiger-Muller tube is an example of a detector which uses ionisation tomeasure the amount of radiation given off from a source. You will also see a cloudchamber in use. This lets us see trails of radiation being given off from a source. Bothdetect alpha radiation most easily because it is the most strongly ionising.


62/80

HEALTH PHYSICS ACTIVITY 27 cont.Geiger-Muller Tube

metal rodatG-M high voltage

I I I I Iometal casing 000counter

The central wire inside the cylidrical tube is kept at a voltage of about +400V compared to theouter case. When radiation enters the tube it produces a few ions. These ions areaccelerated towards the central wire. This movement of charged particles between thecasing and the central wire is in fact a pulse of current. Each pulse is counted electronicallyby the counter and so the amount of radlation detected by the G-M tube is measured.

Photographic FoggingPhotographic film has a thin layer of silver-based chemical on the surface of the plastic orpaper. Normally, this silver salt is affected by light falling on it. Wherever the light lands, itchanges the chemical and blackens or fogs the film surface. Alpha, beta and gammaradiations have a similar effect on this film, and so it is used to detect them.Workers who use radioactive materials, such as health physicists in hospitals and engineersin nuclear power stations, wear film badges throughout the day. They use the badges tocheck how much radiation they have been exposed to. When the film is developed, theamount of fogging gives a measure of the radiation exposure.

ScintillationsSome substances, such as zinc sulphide, are fluorescent. This means that they absorbradiation and give out the energy again as a tiny burst of light. These flashes of light arecalled scintillations, and they may be observed by the naked eye or counted by a lightdetector. These scintillation counters are used in many modern instruments including thegamma camera discussed in the last activity.

burst of light. . . _ _ _ _ _ zinc sulphidecoatingradiation fromradioactive source


63/80

(What to do)HEALTH PHYSICS 27 cont.

Use the above information to help you write a short note on each of the following topics inyour jotter.

1. the nuclear model of the atom - draw a diagram showing nucleus, electrons,protons, and neutrons. Give some information about each of the particles(e.g. charge)2. ionisation of gases - what is meant by this and how radiations cause it3. the Geiger-Muller tube4. the fogging of photographic film and film badges5. scintillations and the scintillation counter


64/80

HEALTH PHYSICS Activity 28Measuring Background Radiation

(What you need)

Geiger-Muller tube, counter, stopcock.

metal rod atG-M high voltage I I I I Iometal casing 000

counter

(What to do)

1. Copy the following table into your jotter.Sample Background Radiation (counts per minute)

123

Averaseb

Your teacher will set up the apparatus for you and give youinstructions for operating the counter and resetting it to zero.

2. Switch on the counter for one minute and measure the amount of radiationdetected in the lab during this time. Enter the result in your table.3. Reset the counter and repeat twice more to give you three readings.4. Calculate the average count rate for background radiation.5. In your [otter, write a brief report on the experiment


65/80


66/80

HEALTH PHYSICS Activity 29 cont.Information Sheet - Safety with Radioactivity

cylindricallead castlefor storage/"t----+-ir-- 4mm piugholder

act ivematerial

wire gauze protection

1. Always use forceps or a lifting tool to remove a source. Never use barehands.2. Arrange a source so that its radiation window points away from the body.3. Never bring a source close to your eyes for examination. It should beidentified by a colour or number.4. When in use, a source must always be attended by an authorised personand it must be returned to a locked and labelled store in its specialshielded box immediately after use.S. Never eat when radioactive sources are being used.6. After any experiment with radioactive materials, wash your handsthoroughly before you eat. (This applies particularly to the handling ofradioactive rock samples and all open sources.)7. In the U.K. , students under 16 years old may not normally handleradioactive sources.


67/80

HEALTH PHYSICS ACTIVITY 30Absorption of Radiation

(Copy) the following Table.AbsorptionMaterialType ofRadiation Range inair (em)

a (alpha)f 3 (beta)y (gamma)

(What to dO )Watch the video on radioactivity, then complete the table.

( Questions)

1. Name the type(s) of radiation that are absorbed by several em , oflead.2. Name the type(s) absorbed by a few mm. of aluminium.3. Name the type(s) absorbed by a thin sheet of paper.4. Do you think that a-radiation would be able to pass through a layer ofskin?

Give a reason for your answer.5. Which type of radiation is most penetrating?6. As c-radiation is least penetrating does this make it the safest form ofradiation?7. What type of damage does it cause in animals such as humans?


68/80

HEALTH PHYSICS 31ACTIVll~YThe Biological Effects of Radiation

All living things, plant or animal, are made of cells. Cells are very small and can only be seenusing a microscope. Humans have many different kinds of cell which perform different jobs:skin cells, red blood cells which carry oxygen, white blood cells which fight infection, nervecells, muscle cells and so on.

Ionising radiation may damage the cells they pass through. The damage caused may besevere and cause immediate effects, or it may be more subtle and have effects which are notseen for a long time. The effects depend on both the type of radiation and the part of the bodythe radiation is going through.

Short-Term EffectsThe short-term effects usually happen when there is a large amount of exposure to radiation.When the nuclear bombs were dropped on Hiroshima and Nagasaki during the Second WorldWar, many people nearby who survived the blast were exposed to a large sudden dose ofradiation. This caused severe damage to cells all over the body, but especially in the skin,blood, bone tissue and gut. Many of these people died within a few weeks. Most of those withsmaller doses recovered from the immediate effects.More recently, there was an accident at the Chernobyl nuclear power station in the then USSR.A fire there caused a number of firemen to be exposed to very large amounts of radiation, andaround thirty died as a result.

We also make use of the short term effects in nuclear medicine. When people with cancer aregiven radiation therapy, the radiation is directed at the cancerous cells to kill or severelydamage them. The secret is in being able to do this to the cancer cells but not to do too muchdamage to the healthy cells about it.

Long-term EffectsThere are other effects of radiation which take much longer to show. In some ways these aremore important to us because they can be caused by much lower levels of radiation.

The most important long-term effect is to cause cancers in various parts of the body. We havelots of evidence of these effects. Uranium miners tended to get lung cancer due to breathing in


69/80


70/80

The effect of radiation damage also depends very much on the absorbing tissue. Sometissues ~such as the bone marrow or blood - are more affected than other parts of the bodysuch as muscle.

HEALTH PHYSICS ACTIVITY 31 cont.

So the total effect of the radiation is a combination of:

a) the type of radiation.b) the type of body tissue which absorbs it.c) the total amount of energy absorbed.

Dose equivalentThe biological risk caused by the radiation is represented by a quantity called "doseequivalent". It is measured in a unit called the sievert (Sv), although we often talk of doses inmillisieverts (mSv) or microsieverts (!ASv) (A milJisievert is a thousanth of a sievert and amicrosievert is a millionth of a sievert.

A sievert is a very large dose of radiation and could only happen as a result of a very seriousaccident or after a nuclear explosion.

How dangerous is a dose equivalent of 1 Sv? - It is impossible to say for anyone person.However, suppose that 100 people all receiee a dose equivalent of 1 Sv spread over theirwhole body. It is estimated that, of the 100 people, on average 4 of them would eventually dieas a result of the radiation. But precisely who would die or when they would die or what illnessthey would die of, can not be predicted.

Background RadiationIn Activity 28 we saw that there is radiation all around us - our detectors in the lab pick upradiations even when no direct sources are near. This is known as background radiation andit is almost all from natural sources. The tables on the next page show the typical doseequivalent we get every year from background radiation and other sources. They are averagefigures, and vary a lot on our job and where we live.


71/80

HEALTH PHYSICS 31 cont.ACTIVITYTABLE 1 - NATURAL SOURCES

Source Annual Dose (f.t,Sv)Radon & Thoron gas from rocks and soil 800Gamma rays from the ground 400Carbon and Potassium in body 370Cosmic rays at ground level 300

Total = 1870 f,tSv

TABLE 2 - MAN-MADE SOURCES

Source Annual Dose (u Sv)Medical uses - X rays etc 250Chernobyl (first year) 50Fall-out from weapons testing 10Job (average) 5Nuclear Industry (e.g. waste) 2Others (TV, aeroplane trips, etc) 11

Total = 328 f,tSv

Remember that the unit used is the I-tSv which is one millionth of a sievert. You can see thatnatural radiation is by far the biggest influence on us.

The total annual dose equivalent in the UK averages about 2000pSv = 2mSv. However,there is a big variation from person to person. If you take several aeroplane trips across theAtlantic each year you are getting more than your fair share. If you live in Aberdeen orespecially Cornwall where the granite rocks are giving off radioactive radon gas, you aresubjected to a much higher background rate.


72/80

Protection from RadiationHEAL TH PHYSICS ACTIVITY 31 cont.There are people who, as a result of their work, are exposed to ionising radiations. Thesepeople include medical workers using X-rays in hospitals, dentists and vets, research workersusing radiation sources in their experiments and people who work in the nuclear powerindustry.

These "radiation workers" obviously must be protected from the radiation.

Distance is the simplest way of obtaining protection. Twice the distance away means you willreceive one quarter of the radiation.

Shieldi ng a source of radiation with an appropriate thickness of absorber can reduce the risk.For example, a radiographer wears a lead impregnated apron.Measurement of the amount of radiation received by workers is carried out to check that noworker goes above the safe limit. Monitoring devices such as photographic film badges canrecord radiation exposure during a working day. Special monitors check for traces ofradioactive contamination on hands, feet and clothing.

@ u e s t i o n )1. Choose, from the passage, two effects that ionising radiation have on humans.

Describe what the effects are and explain how they are produced.2. What three factors combine to produe these effects?3. What does the term "dose equivalent" mean and how is it measured?

4. Give three common sources of background radiation and explain why differentpeople can experience different dose equivalents.

5. Describe two methods used to protect workers who work with radiation.


73/80

HEALTH PHYSICS ACTIVITY 32Introduction to Half-Life

You saw on the video for activity 30 that it is impossible to say which particular atom in aradioactive element will disintegrate next - i.e. the decay is random.

In this activity we will simulate this random decay using cubes to represent radioactive atoms.Each cube has one face painted black and when that face is on top it will represent a decayedatom and can be removed.

(1) Copy the table below into your jotter.(2) Count the number of atoms and enter the number in the table.(3) Tip them out onto the bench and remove and count the "decayed"

(black) ones. By subtraction work out the number remaining andenter this in the table.

(4) Repeat step (2) with the remaining "undecayed atoms" until all the"atoms" have "decayed".

Method:

oatoms"No. ofNo. ofthrows "radioactive

1234566789101 I12

No. of"radioactiveNo. ofthrows atoms"1314

(5) Plot a graph of number of "radioactive atoms" against number of throws.(6) From the graph, how many throws did it take for the number of radioactive atoms tohalf?(7) How many more throws did it take for the number of radioactive atoms to half again?(8) How did the answers to questions 6 and 7 compare? Discuss this with your teacher.


74/80

HEALTH PHYSICS ACTIVITY 33Radioactive Decay

The Activity of a Radioactive Source

The activity of a radioactive source is a measure of how much radiation it is giving out. Thisdepends on the number of radioactive atoms which break up every second and give outradiations.The unit of activity is the becquerel (Bq). A source has an activity of 1 8q if one of its atomsdisintegrates each second and gives out a particle of radiation.In real life, the becquerel is a very small unit. Radioactivity sources used in medicine haveactivities measured in megabecquerels (MBq).

One MBq = one million 8q or 1 MBq = 106 8qPart One

~ the table below

Time onclock (a.m.) Count rate (c.p.m.)

9.3015

Time from start(minutes)9.00 o 5569.15


75/80

HEALTH PHYSICS ACTIVITY 33 cont,You are going to watch part of a video programme on radioactivity.In the programme, radioactive INDIUM is used and its count rate measured over a 3 hourtime period.Complete your table as the experiment takes place.

(Questions)1. Why was the indium placed inside a lead box?2. Which two pieces of apparatus were connected together to measure its count rate?3. Why were 2 clocks necessary?

Part Two

1. On graph paper, plot a graph of activity against time for the decay of indium.2. In your jotter, write up this experiment. Make sure you include.

(a) a suitable title(b) a diagram(c) a method(d) a results table (already done)(e) your graph (already done)(f) what you conclude from the experiment ""

"" If you find (f) difficult, answer the following questions first-

(i) What happens to the count rate as time increases?(ii) Use your graph to find out how long it takes for the activity to fall from

(a) 556 cpm to half this value (278 cpm)(b) From 278 cpm to half this value (139 cpm)(c) From 139 cpm to 69 cpm

(iii) What can you say about the time taken for the activity to half?


76/80


77/80

HEALTH PHYSICS ACTIVITY 35Half-life Graphs

(Questions)

1. Values of count rate against time for a source are given below, uncorrected forbackground radiation.Time (minutes) 0 2 3 4 5 6Count rate (per minute) 180 135 100 77 60 48 40

The background count rate is measured at 20 counts per minute.a) Copy out the table but include a third row which shows Corrected CountRate (per minute)b) Plot a graph of Corrected Count Rate against time and use this tocalculate the half life of the source.

2. The table below shows how the count rate of a radioactive source varies with time.Correction has been made for background radiation.Time (minutes) 0 2 4 6 8 10Count rate (per second) 72 45 28 18 ]2 8

Draw a graph and determine the half-life of the source.

3. The measured activity of a radionuclide was taken at 3-day intervals. The followingreadings are uncorrected for background radiation.Time (days) 0 3 6 9 12 l5Count rate (per minute) 145 100 71 52 39 30

The count rate was measured again 2 months after the first reading and found to be 12counts per minute.(a) Estimate the background count rate.(b) Assuming your answer to part (a) is correct, draw a graph and calculate thehalf-life of the radionuclide.


78/80

HEALTH PHYSICS ACTIVITY 36Half-life Calculations

It is possible to calculate the half-life of some substances without using graphs. Otherinformation is also important such as the count rate after a certain time or how much of aradioactive source is left after a certain time.Your teacher will now show you how to carry out some of these calculations.Make careful notes as you will have to carry out the questions below yourself.

(Questions)

1. A radioactive substance has a half-life of 6 hours.What fraction of the original activity is left after one day?

2. The activity of a source starts at 80 MBq. After 10 days it has fallen to 2.5 MBq.Calculate the half-life.

3. What is the half-life of a radioactive substance if its activity falls from 400 kBq to 100kBq in 12 days?4. What is the half-life of a radioactive isotope if the activity falls from 3200 kBq to 200kBq in 20 days?5. On a day when the background count is 15 counts per minute, a radioactivesubstance gives a count rate of 275 counts per minute.

What is the half-life of the substance if the count rate, 18 minutes later, is 80 countsper minute?6. The half-life of Cobalt-60 is 5 years. A school bought a source 15 years ago ofactivity 300 kBq.

What would its activity be now?T An isotope has a half-life of 50 s.

How long does it take for the activity to fall to 1/64 of the starting value?8. The half-life of a radioisotope is 30 days. One hundred and twenty days after itsmanufacture, its activity is measured at 100 kBq.

Find its initial activity.


79/80

HEALTH PHYSICS ACTIVITY 36 cont.Alternative method in Half-Llfe Calculations

If you are good at maths, you may prefer this shorter method.In the questions you have just completed you saw how fractions of the original activity can befound. Here is a summary - Copy out the table and fill in the blanks:-

1you can see that the activity is equal to 2n where n = = no. of half-lives

A radioactive source has a half-life of 4 days, what fraction of the original activity will remainafter 20 days?20 days = = ~o = = 5 half lives = = > Fraction remaining = = 21 5 = = 3 bTry some of the problems on the previous page again using this method, to see which methodyou prefer. (Question 5 may be difficult to do this way)

2

1/'256

No. of half-lives Fractiono 1

3 l/S45678

Since 2 can be written 214 can be written 228 can be written 2316 can be written 24, etc.

EXAMPLE


80/80

HEALTH PHYSICS ACTIVITY 37Carbon Dating

Radiation from outer space (cosmic radiation) is always bombarding the earth's atmosphere.One effect of this is to make a radiactive form of the element carbon, called Carbon-14. ThisCarbon-14 gives out beta radiation when it decays. It loses its activity slowly as it decays. It hasa half life of 5600 years.

This radioactive carbon quickly finds its way into the web of living things. Plants "breathe" it in inthe form of carbon dioxide gas. Animals eat it in their food and so we all have a small proportionof radioactive carbon in us. We are all a little bit radioactive.

This stops when we die because then we don't take in any more food. The Carbon-14 whichdecays is no longer replaced. The activity of the carbon in us will gradually decrease.

Most living things are quickly broken up (often eaten up) when we die. But some parts maysurvive for a very long time. Old furniture, battle axe handles and Egyptian paper, for example,were all once part of living trees. The age of these things can be estimated by measuring theactivity of the carbon they contain and comparing this to activity of say a living tree.

Use the above information to answer the following problem in your jotter.

The Problem

Suppose you are a physicist.An archaeologist comes to you and says that she has found a man's body, preserved forthousands of years in a peat bog where it didn't break up. Use the information above to say

Date post:	08-Apr-2018
Category:	Documents
Upload:	knoxphysics
View:	227 times
Download:	0 times

SG Health Physics Worksheets

Documents