Nuclear Detection Equipment

7/31/2019 Nuclear Detection Equipment

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RADIOACTIVITY

POLLUTION

SOURCES

EFFECTS ON HUMAN BEINGS

MONITORING TECHNIQUES

By

P.Swarnalatha ( 12MEE0040)

K.Chaitanya (12MEE0030)

B. Ajay Kumar (12MEE0026)


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What Is Radioactive Material?

Radioactivity is a part of nature. Everything is made of atoms. Radioactiveatoms are unstable

that , they have too much energy. When radioactive atoms spontaneously release their extraenergy, they are said to decay. All radioactive atoms decay eventually, though they do not all

decay at the same rate. After releasing all their excess energy, the atoms become stable and

are no longer radioactive. The time required for decay depends upon the type of atom. This

Fact Sheet explains the process of radioactive decay.

The Atom

The explanation of radioactive decay begins with a description of the atom. Atoms are made

up of three subatomic particles: protons, neutrons, and electrons. The protons and neutrons

are packed together in the nucleus at the center of the atom . The space outside the nucleus isoccupied by the electrons. The number of protons in the nucleus determines what material, or

element, the atom is. For example, if the nucleus contains 8 protons, the atom is oxygen. If

the nucleus contains 17 protons, the atom is chlorine.

Isotopes and Nuclides

While all atoms of the same element contain the same number of protons, the number of

neutrons may be different. For example, carbon atoms have six protons. If a carbon atom also

has six neutrons, it is Carbon-12. If it has seven neutrons, it is Carbron-13. A carbon atomcontaining six protons and eight neutrons is Carbon-14. This form, or isotope of carbon is

radioactive. Carbon-14 is radioactive while Carbon-12 and Carbon-13 are stable. The term

nuclide is used to refer to any type of atom, so that Carbon-12 and Hydrogen- 2 are nuclides.

They are not isotopes of each other because they differ in the number of protons that they

each have in their nucleus. The prefix radio- can be added to either term, making

radioisotope or radionuclide, whenever the atom referred to is radioactive.

Radioactive Decay

When the nucleus of a radionuclide spontaneously called ionizing radiation. Ionizing

radiation may take the form ofalpha particles, beta particles, or gamma rays. The process

of emitting the radiation is called radioactive decay.

Half-Life

It is not possible to predict exactly when a particular radioactive atom will decay. However,

scientists have determined the time required for half of a large number of identical

radioactive atoms to decay. This time is calledthe half-life.


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Radioactive substances within the meaning of the Atomic Energy Act are:

Nuclear fuels, i.e.

a) plutonium 239 and plutonium 241,

b) uranium enriched with the isotopes 235 or 233,

c) any substance containing one or several of the substances mentioned in a) and b),

d) substances which can be used in a suitable plant to maintain a chain reaction

which initiates its own repetition and which are determined in an ordinance

having the force of law.

Other radioactive substances which - without being nuclear fuel

a) spontaneously emit ionizing rays,

b) Contain one or several of the substances mentioned in a) or are contaminatedwith such substances.

What is Radioactive Pollution?

Radioactive pollution, like any other kind of pollution, is the release of something

unwanted into the environment and, in this case, the unwanted thing is radioactive

material.

The radioactive pollution can also be defined as the physical pollution of air, water

and the other radioactive materials. The ability of certain materials to emit theproton, gamma rays and electrons by their nuclei is known as the radioactivity.

There are many causes of radioactive pollution, which can significantly harm the

environment.

Sources of radioactive contaminants:

Following are the major sources where most of the radioactive waste is generated and is

responsible for causing radioactive pollution:

o Production of nuclear fuel

o Nuclear power reactors

o Use of Radionuclides in industries for various applications

o Nuclear tests carried out by Defense Personnel

o Disposal of nuclear wast

o Uranium Mining


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Impact of Radioactive Pollution on human health

The effects of radioactive pollution or exposure to nuclear radiations were first

reported in early 20th

century when people working in uranium mines suffered from

skin burn and cancer.

The effects vary from organism to organism and from level of radioactivity of

nuclear isotopes and it largely depends on the level of exposure to the emissions.

The radiations destroy the Radioactive particles forms ions when it reacts with

biological molecules. These ions then form free radicals which slowly and steadily

start destroying proteins, membranes, and nucleic acids.

The rapidly growing cells like that of the skin, bone marrow, blood, intestines, and

gonads, are more sensitive towards radioactive emissions. On the other hand, cells

that do not undergo rapid cell division like bone cells, muscle cells, and nervous cells,

cannot be damaged so easily.

It has a serious threat to various systems of the body that include the cardiac system,

neurological system and reproductive system.

The radioactive rays can cause irreparable damage to the DNA molecules and lead to

a life-threatening condition. It causes genetic mutations that promote the growth of

cancerous cells in the body.

People with heavy radiation exposure are prone to skin cancer, lung cancer, thyroidcancer, etc. The effects of genetic mutation tend to pass on to the future generations as

well. In other words, if the parents are exposed to nuclear radiation, then their child

could be born with genetic birth defects and retardation.

A longer exposure to radioactive radiations can damage the DNA cells that results in

cancer, genetic defects for the generations to come and even death. cells in human

body and causes

Through the Environment

soil gets contaminated by radioactive substances, It can lead to genetic mutation of

the plants' DNA and affect its normal functioning.

Some of the plants may die after such exposure while others may develop weak

seeds.When any part of the contaminated plant, including the fruits are consumed by

human beings, then it causes serious health risks.

Radioactive emissions from nuclear weapons are considered as the most harmful for

the environment, as they stay in the atmosphere for as long as a hundred years.

Thus, it affects several generations. Similarly, the radioactive substances from the

land surface that flows down to the water bodies remain there for years to come


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Radioactive Waste Management

Geological disposal

This is, effectively, the burying of radioactive material.Large geologic formations are locatedand tunnels as deep as 1000m underground are drilled. Rooms are then excavated at the

bottom of these and radioactive material is stored here until it has decayed enough to not be

dangerous any more.

Transmutation

Transmutation of radioactive waste is the process of consuming this radioactive waste and

turning it into less harmful waste.This is currently not used very often due to high costs,

however, research is being done to make the process more efficient and more economically

viable.This currently is our most environmentally friendly radioactive waste management

technique and, as such, when perfected will effectively solve the problem of radioactive

waste.

Re-use of radioactive waste

Some radioactive isotopes, such as strontium-90 and caesium-137 are able to be extracted for

use in other industries such as food irradiation. The re-use of radioactive waste means that the

quantity of waste produced is reduced, so this serves as another good environmentally

friendly management scheme.

Space disposal

Space disposal is not currently used to reduce radioactive pollution, due to the potential

problems which could occur when attempting to carry out the procedure. If, for example, a

rocket used to launch the waste fails (and bear in mind that many rockets would have to be

used due to the large amount of radioactive waste) then huge amounts of radioactive material

would be released into the atmosphere, causing significant health risks to people within

thousands of miles of the launch.Sometime in the future this may be possible, however, for

now, it is best for us to avoid space disposal.


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RADIOACTIVE CONTAMINATION CONTROLLING

AND MONITORING

The radioactive pollution can be controlled by number of ways. It includes the stoppage of

leakage from the radioactive materials including the nuclear reactors, industries andlaboratories. The disposal of radioactive material must be safe and secure. They must be

stored in the safe places and must be changed into harmless form. The wastes with a very low

radiation must be put into the sewage. The nuclear power plants must follow all the safe

instructions. The protective garments must be worn by the workers who work in the nuclear

plants. The natural radiation must be at the permissible limits and they must not cross it.Part

of the reason that radioactive pollution is a problem is that radiation can remain for up to a

million years if levels of certain isotopes are high enough. For this reason radioactive waste

management is very important and plans stretch up to around 100 years in the future, with

ongoing evaluations and research into these to make sure radioactive pollution affects us aslittle as possible.Human senses cannot detect ionizing radiation. However, excess and long-

term exposure may cause adverse health effects. Hand-held radiation measuring instruments

are the tools used as a first line of defense in the detection of the presence of such radiations

and are often used to avoid unwarranted exposure to radiation. Using the right type of

radiation detection equipment provides an effective means of limiting exposures and assists

in minimizing doses.

Basic terminology associated with measuring instruments , principal types

and respective applications to a radiological event.

If subjected to gamma radiation, different materials will in general absorb different amounts

of energy. Because both physical and chemical changes can occur as a result of this absorbed

radiation, the absorbed energy most often described as energy per unit mass. This then is

referred to as absorbed dose or simply dose.A fundamental distinction exists between

radiation or radioactivity and dose. In general, radioactivity is measured in counts per minute

(which when a correcting factor called efficiency is applied) and can be converted to

disintegrations per minute. In general, the higher the activity, the higher the absorbed dose.

However, it is not a one to one relationship. In fact, the absorbed dose will be a reasonable

measure of the chemical or physical effects created by absorbed energy of a radioactive

source. Again, the radiation source is measured in counts per unit time (usually counts per

minute), and the absorbed dose is a measure of a specific amount of energy absorbed by the

human body [usually measured in roentgen equivalent man (rem) or Sievert (Sv)]. In short,

some types of detectors count radiation events, whereas others measure the dose to a

human.It is vital that correct radiation monitoring is carried out when there is likelihood for

radiation exposure. It is equally important that the correct monitoring instrument is selected

and used in an emergency setting. Competent user training is also essential for correct

interpretations on the results obtained bythe instrument and for assessing appropriate doses

received by humans.


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3.Nuclear rate meter for measuring surface contamination, which indicates the potential

internal exposure when a radioactive substance is distributed over a surface

4.Dose rate meters for measuring an immediate external human exposure to radiation

Dosimeters

Dosimeters measure the total energy absorbed as a consequence of exposure to ionizing

radiation. Several types of dosimeters are available, including thermoluminescent dosimeters

(TLDs), optically stimulated luminescence (OSL), electronic dosimeter, film dosimeter, and

direct ion storage. TLD store radiation energy in a crystal such as lithium fluoride that is later

read by heating the crystal and measuring the glow of light that is proportional to the

radiation level that first struck the crystal.A dose rate meter measures external hazards in

units of dose equivalent rate. Dose rate meters provide direct measurements of externalexposure.OSLs are a relatively new technology that differs from TLDs in that trapped

charges are released using optical rather than thermal energy.Electronic dosimeters measure

radiation exposure on a real-time basis and provide immediate dose rate readings. Depending

on the environment, parameterscan be set on the device to warn individuals that they are

approaching a certain limit of exposure.Film dosimeters are processed in the sameway as

photographic film. A calibrated light source and sensitive detectors are used to measure the

amount of light that can pass through the film. This information determines the quantity and

type of radiation exposing the film.Direct ion storage measures radiation by absorbing

charges into a miniature (MOSFET) ion chamber. The dosimeter can be instantaneously

processed and read by an on-site reader. Personnel dosimeters should be worn by all


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Personnel dosimeters and integrating dose rate meters have the ability to measure the

dose equivalent caused by an external hazard that is rapidly changing. Dosimeters,

however,provide a measurement of cumulative exposure to radiation.

emergency responders while in a radiological zone to assess their radiation exposure. Passive

dosimeters routinely monitor cumulative doses that result from an external exposure. Active

dosimeters provide an immediate reading of the dose in microsieverts (mSv) and may also

provide an immediate alarm signal when the measured dose approaches a value preset by the

manufacturer or the health physics specialist. Integrating dose rate meters and dosimeters can

be used to assess an external exposure which is rapidly changing, for example:(1) A task of short duration has to be carried out in the presence of high dose rates, and

(2) The source [e.g., high dose rates while near the release point of a radiological dispersion

device (RDD)] emits radiation within a short distance of a radiological device

AIRBORNE CONTAMINATION METERS AND GAS MONITORS

Airborne contamination meters are used to detect radioactive aerosols that may be present

after a nuclear detonation or a chemical explosion involving a RDD. These may be dispersion

aerosols (dusts), condensation aerosols (smoke), or liquid aerosols (mists). Fallout particles

from a nuclear weapons detonation or improvised nuclear device (IND) liberate large

particles from 50 to 200 mm (1/1000th of a millimeter). This means that fallout from nuclear

weapons or INDs can be easily filtered and/or blocked from entering a shelter or well-sealed

house. Particles from an RDD can be on the submicron level which means that Hepa filters

must be used to remove them from contaminated air. Submicron particles also present a

mechanism for easily entering the lungs. Thus, although an RDD presents a much smaller

activity level than an IND or nuclear detonation, the harm on a very localized scale can be

more severe to those who breathe these much smaller particles.Instruments for monitoring

airborne contamination normally draw suspect contaminated air at a constant rate through a

filter or past a detector with instantaneous feedback. The problem with the former is that


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Surface contamination meters are used to detect and measure radioactive substances on

surfaces. A surface contamination meter can indicate a potential for uptake and

internal exposure to radiation.

Measurements must be made using a calibrated instrument with the best available,

predetermined detection efficiency for the contaminant. The measurements, in counts persecond (cps or s1), need to be converted to becquerels per square centimeter (Bq/cm2).Some

surface contamination meters are programmable. The user sets the instruments likely

response to the radionuclide in use and obtains a direct measurement of surface

contamination (in Bq/cm2).

DOSE RATE METERS

A dose rate meter measures absorbed energy from penetrating radiation. A suitable and

efficient instrument that is matched to the specific task should be capable of providing direct

readings of the dose equivalent rate in microsieverts per hour (mSv/hr or mSv/hr). A smallernumber of instruments indicate the absorbed dose rate in micrograys per hour (mGy/hr).

These instruments usually respond only to X-rays, gamma, and/or beta radiations.

A dose rate meter measures external hazards in units of dose equivalent rate. Dose

rate meters provide direct measurements of external exposure

Specialized instruments are necessary to measure neutron dose equivalent rates. Older units

of dose ratemillirem per hour (mrem/hr), millirad per hour (mrad/hr), and milliroentgen perhour (mR/hr)are still displayed on some instruments (10 mSv/hr is equivalent to 1


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mrem/hr).Dose rate meters may not be able to provide an accurate response to

rapidlychanging or pulsed radiation fields. Integrating dose rate meters and dosimeters are

more appropriate in such circumstances

Different types of detectors

Gasfiller detctors

Since we cannot see, smell or taste radiation, we are dependent on instruments to indicate the

presence of ionizing radiation`n. The most common type of instrument is a gas filled

radiation detector. This instrument works on the principle that as radiation passes through air

or a specific gas, ionization of the molecules in the air occur. When a high voltage is placed

between two areas of the gas filled space, the positive ions will be attracted to the negative

side of the detector (the cathode) and the free electrons will travel to the positive side (the

anode). These charges are collected by the anode and cathode which then form a very smallcurrent in the wires going to the detector. By placing a very sensitive current measuring

device between the wires from the cathode and anode, the small current measured and

displayed as a signal. The more radiation which enters the chamber, the more current

displayed by the instrument.

Proportional Counter

A gas-filled discharge device for the detection of ionizing particles and quanta. The counter

produces a signal with an amplitude proportional to the energy of the particle being detected.

On passing through the gas inside the counter, a charged particle produces in its path ion-electron pairs, the number of pairs depending on the energy lost by the particle in the gas.


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When the particle is brought to a full stop in a proportional counter, the impulse is

proportional to the particles energy. As in the ionization chamber, an electric field sends the

electrons toward the anode and the ions toward the cathode. In contrast to the ionization

chamber, the field near the anode of the proportional counter is so strong that the electrons

acquire energy sufficient for secondary ionization. As a result, instead of a single primary

electron, an avalanche of electrons arrives at the anode, and the total number of electrons thuscollected far exceeds the number of primary electrons. The ratio of the total number of

collected electrons to the number of primary electrons is called the gas amplification factor

(ions also take part in the formation of the impulse).A cylinder usually serves as the cathode

in a proportional counter, and a fine (10100 ) metal wire, stretched along the axis of the

cylinder, serves as the anode . Gas amplification occurs near the anode at a distance

comparable to the wires diameter; beyond this region, the electrons drift under the action of

the electric field without multiplication. Proportional counters are filled with an inert gas

(the gas must not absorb drifting electrons) with the addition of a small amount of a

polyatomic gas, which absorbs the photons formed in the avalanches.

Proportional counters usually have a gas amplification factor of ~103-10

4(which may reach

106

or more) and and an impulse amplitude of ~10-2

V when the capacitance of the

proportional counter is about 20 picofarads. An avalanche develops in ~10-910

-8sec, but the

instant at which a signal appears at the output of the proportional counter depends on the path

of the ionizing particle, that is, on the time required for the electrons to drift to the wire. At a

radius of approximately 1 cm and a pressure of approximately 1 atmosphere, the delay time

of the signal with respect to the particles passage is ~106 sec. The sensitivity of the

proportional counter surpasses that of the scintillation counter but is less than that of the

semiconductor detector. However, proportional counters allow work in the energy rangebelow 1 kiloelectron volt, where semiconductor detectors cannot be used.Proportional

counters are used to detect all types of ionizing radiation. There are counters designed to

detect, for example, alpha particles, electrons, nuclear fission fragments, neutrons, gamma

quanta, and X-ray quanta. In the case of proportional counters that detect neutrons, gamma,

and X-ray quanta, interactions with the gas filling the counter are employed to produce

secondary charged particles that lend themselves to detection. The proportional counter,

together with the ionization chamber, played an important role in nuclear physics in the

1920s and 1930s as virtually the only spectrometric detector.In the late 1960s, the physics

of high-energy particles found a new use for the proportional counter in the form of a

proportional chamber, which consists of a large number (10210

3) of proportional counters

arranged in coplanar fashion in a gas-filled enclosure. Such a device makes it possible not

only to measure the ionization of a particle in each individual counter but also to locate the


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track of the particle. Typical parameters of proportional chambers are a distance between

adjacent anode wires of ~ 12 mm, a distance between anode and cathode planes of

approximately 1 cm, and a resolution time of ~ 10-7

sec. The development of microelectronics

and the introduction of electronic computers in experimental techniques have made possible

the development of systems consisting of tens of thousands of individual wires connected

directly to a computer, which stores and processes all information from the proportionalchamber. Such systems thus function simultaneously as both high-speed spectrometers and

track registration detectors.The drift chamber, which uses the drift of electrons preceding the

formation of an avalanche to measure the track of a particle, appeared in the 1970s. By

alternating the anodes and cathodes of the individual proportional counters in one plane and

measuring the drift time of electrons, it is possible to measure the track of a particle through

the chamber with a high degree of precision (~0.1 mm) with only one-tenth as many wires as

in a proportional chamber.Proportional counters are used not only in nuclear physics but also

in such fields as the physics of cosmic rays, astrophysics, engineering, medicine, geology,

and archaeology. For example, an X-ray fluorescence analysis of the lunar soil was carried

out by means of a proportional counter mounted on Lunokhod 1.

Geiger-Muller Counter

Also called a Geiger counter or Geiger tube, an instrument for detecting the presence of and

measuring ionizing radiation such as alpha particles, beta particles, and gamma rays. A

Geiger-Mller counter an count individual particles at rates up to about 10,000 per second

and is used widely in medicine and in prospecting for radioactive ores.

A fine-wire anode runs along the axis of a metal cylinder which has sealed insulating ends,

contains a mixture ofargon or neon and methane at low pressure, and acts as the cathode, the

potential between them being about 1,000 volts. Particles entering through a thin window

cause ionization in the gas; electrons build up around the anode and a momentary drop in the

inter-electrode potential occurs which appears as a voltage pulse in an associated counting

circuit. The methane quenches the ionization, leaving the counter ready to detect further

incoming particles.
http://www.daviddarling.info/encyclopedia/I/ionizing_radiation.htmlhttp://www.daviddarling.info/encyclopedia/A/alphapart.htmlhttp://www.daviddarling.info/encyclopedia/B/beta_particle.htmlhttp://www.daviddarling.info/encyclopedia/G/gamma_rays.htmlhttp://www.daviddarling.info/encyclopedia/A/anode.htmlhttp://www.daviddarling.info/encyclopedia/A/argon.htmlhttp://www.daviddarling.info/encyclopedia/N/neon.htmlhttp://www.daviddarling.info/encyclopedia/M/methane.htmlhttp://www.daviddarling.info/encyclopedia/C/cathode.htmlhttp://www.daviddarling.info/encyclopedia/E/electron.htmlhttp://www.daviddarling.info/encyclopedia/E/electron.htmlhttp://www.daviddarling.info/encyclopedia/C/cathode.htmlhttp://www.daviddarling.info/encyclopedia/M/methane.htmlhttp://www.daviddarling.info/encyclopedia/N/neon.htmlhttp://www.daviddarling.info/encyclopedia/A/argon.htmlhttp://www.daviddarling.info/encyclopedia/A/anode.htmlhttp://www.daviddarling.info/encyclopedia/G/gamma_rays.htmlhttp://www.daviddarling.info/encyclopedia/B/beta_particle.htmlhttp://www.daviddarling.info/encyclopedia/A/alphapart.htmlhttp://www.daviddarling.info/encyclopedia/I/ionizing_radiation.html


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SCINTILLATION COUNTERS

The essential components of a scintillation counter are as follows:

SScintillator. A phosphor contained within a nontransparent enclosure.Ionizing radiations

interact with the scintillator, which in turn immediately converts some absorbed energy into

photons.

LLight guide transfers the scintillation to the photocathode (C) of the photomultiplier tube

(M).

CPhotocathode is a type of vacuum tube that is translucent, with a lightsensitive coating of

material (e.g., antimony doped with cesium) on the photomultiplier window. When light is

absorbed, it produces electrons that cascade down the dynodes and are multiplied by a factor

of 1E6 to 1E7.

MPhotomultiplier tube includes electrodes called dynodes. A successively increased

potential difference (about 2000 V overall) draws electrons to each dynode in turn. The

number of electrons increases at each dynode. The number of electrons is multiplied by afactor of 1 million to 10 million.

Scintillation devices on the front side of the photomultiplier tube turn the light into electrons.

They include materials such as solid organics (anthracene and stilbene), liquid scintillants,

and solid plastic scintillants and activated inorganic crystals such as sodium iodide and

cesium iodide, which are activated by trace amounts of thallium [NaI(Tl) and CsI(Tl)].

SOLID STATE DETECTORS

Solid-state detectors are made of semiconductor materials such as high-purity silicon and

high purity germanium. Two groups of detectors are junction detectors and bulk conductivitydetectors.

Principles of surface barrier solid-state counter

shown enlarged and in section.Solid-state counters contain semiconductor devices


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