Radioactivity

Section 114

Show an awareness of the existence andorigin of background radiation, past and

present

BACKGROUND RADIATIONThere are radioactive substances all around us, from:

the air (the radon in the air accounts for over half the total) the rocks, soil and hence building materials seawater plants and hence in foodfrom space

The radiation from all these sources is called background radiation. The level of background radiation is higher in some places than in others . For example Radon gas is released from granite rocks. Radon is also released from building materials made using this rock.

Is the emission of light energy from some minerals and certain other crystalline materials.

When pottery is exposed to radiation the electrons of the atoms that make up the pottery, absorb energy and move to higher energy levels, where they become trapped.

Heating the substance at temperatures of about 450° C enables the trapped electrons to return to their normal positions, resulting in the release of energy (extra) in the form of light.

The intensity of the emission can be correlated to the length of time that a given substance was exposed to radiation.

Thermoluminescence

The rock to the left has been exposed to more radiation than the one to right. Upon heating the left rock glows more brightly than the right

Section 115Investigate and recognise nuclear

radiations (alpha, beta and gamma) fromtheir penetrating power and ionising ability

An alpha particle is made from 2 protons and 2 neutrons.Here is an alpha decay example. An isotope of Uranium (238U) gets transformed into Thorium (234Th).

Alpha decay

An alpha particle is a helium nucleus

A beta particle is a fast moving electron

Beta decay

Gamma decayAs a result of the emission of an alpha or beta particle the nucleus is often left in an excited state (It has excess energy). This energy can be released in the form of electromagnetic radiation; that is a gamma ray.

In the example the boron nucleus releases a beta particle to form a carbon nucleus (excited) the energy is released in the form of a gamma ray. Note the final nucleus is still a carbon nucleus but it has less energy.

A gamma ray is an electromagnetic photon

http://upload.wikimedia.org/wikipedia/commons/c/c4/Table_isotopes_en.svg

Alpha and beta particles of the same energy produce about the same total number of ion pairs.

However, the ionisation of alpha particles per cm is much higher than that of beta particles. This means they will lose all their energy in a shorter distance than will the beta particles.

In other words alpha particles  will have a smaller range than beta particles 

Radiation name and symbol

Charge / C Mass/kg Mass/ u Mass / MeV c-2

Penetration in air

Stopped by Deflected by magnetic and electric fields

Ion pairs created per cm in air

Typical energy

Alpha 3.2 x 10-19 6.64 x 10-27 4.02603 3728 a few cms A sheet of Paper yes 50 000 3 to 7 MeV

Beta 1.6 x 10-19 9.11 x 10-31 0.00055 0.511 A metreA few mm of aluminium yes 100

200 keV to 3 MeV

Gamma none 0 0 0 many kmsMany cms of

lead no less than 1 3 keV to 3 MeV

Table of data for alpha, beta and gamma

Link between ionisation ability and penetration power

AlphaBetaGamma

http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/radiation/radioactiverev2.shtmlBBC intro

http://www.furryelephant.com/content/radioactivity/alpha-beta-gamma-radiation/ interactive

http://www.youtube.com/watch?v=ec8iomUS34U 30 second demo

http://www.youtube.com/watch?v=4OkR-B4BpvA&feature=related differentiate and http://www.s-cool.co.uk/a-level/physics/radioactivity/revise-it/what-is-ionising-radiation scool

Section 116

Describe the spontaneous and randomnature of nuclear decay

http://www.walter-fendt.de/ph14e/decayseries.htm Decay series

Section 117Determine the half lives of radioactive

isotopes graphically and recognise and usethe expressions for radioactive decay:

dN/dt =-λN, λ= ln 2/t½ and N = N0 e-λt

RADIOACTIVE ELEMENTS – HALF LIFE The radioactive elements decay, i.e., lose their activity with time. The decay is measured in half-life, i.e., the time required for the radioactivity to reduce to half.

The half-life of some of the elements are shown below:

RADIOACTIVE ELEMENTS – HALF LIFE

Element Half life Uranium-235 Billions of years Carbon-14 5730 years Strontium-90 28 years (beta) Ce-137 30.2 years Co-60 5.27 years

http://phet.colorado.edu/en/simulation/radioactive-dating-game

http://www.youtube.com/watch?v=fToMbj3Xz2c&feature=related experiment

Section 118

Discuss the applications of radioactivematerials, including ethical and

environmental issues

SOME PEACEFUL USES OF NUCLEAR ENERGY AND RADIOACTIVE ISOTOPESThere are many beneficial uses of ionizing radiation in medicine for diagnosis and treatment of many diseases. Radioisotopes have found a large number of applications. They include:

Generate electricity Power for spacecrafts Power for ocean vessels Wear testing (auto-engines, tires) Thickness gauges Sterilization of medical supplies Medical diagnosis Synthesis of new elements Chemical analysis (by neutron activation) Sterilization of insects Preservation of food Smoke detectors Bomb detectors at airports Manufacture of semiconductors Manufacture of radioisotopes Carbon-dating

Medical applications

For example more than 20 radioisotopes are used for medical applications.

ISOTOPE HALF-LIFE USES

Carbon-11 20.3m Brain scansChromium-51 27.8d Blood Volume determinationCobalt-57 270d Measuring vitamin B12 uptakeCobalt-60 5.26y Radiation cancer therapy Gadolinium-153 242d Determining bone density Gallium-67 78.1 Scan for lung tumours Iodine-131 8.07d Thyroid therapy Iridium-192 74d Breast cancer therapy Iron-59 45d Detection of anaemia Phosphorous-32 14.3d Detection of skin cancer or eye tumours Plutonium-238 86y Power for pacemakers Radium-226 1600y Radiation therapy for cancer Slenium-75 120d Pancreas scansSodium-24 15.0h Locating obstructions in blood flowTechnetium-99 6.0h Imaging of brain, liver, bone marrow, kidney, lung or heartThallium-201 73h Detecting heart problems with treadmill stress testTritium 12.3y Determining total body waterXenon-133 5.27d Lung imagingY = year, d = days, h = hours, and m = minutes

The problem with Planck's curve is that it does not agree with Rutherford's model of the atom. Atoms absorb and emit light through a process called scattering. Photons fly near the atoms and are deflected. Sometimes their motion pushes the atom (where push means electromagnetic forces), and the photon loses energy (i.e. becomes redder). Sometimes the atom pushes the photon, and the photon gains energy (i.e. becomes bluer). However, even the nature of atoms, the photons should receive more energy than the atoms, so there should be more and more blue photons, but clearly the Planck curve drops off at short wavelengths. This is called the UV catastrophe, which was resolved by quantum physics.