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DETECTION & USES DETECTION & USES OF RADIATIONOF RADIATION

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Detection of radiation

Small packets of photographic emulsions are routinely used by workers to monitor radiation exposure.

1. Photographic film

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2. CLOUD CHAMBERS

Used to track charged particles, it contains a vapour, usually an alcohol. The vapour is cooled so that it becomes supersaturated. A charged particle enters the chamber and ionises air or alcohol vapour atoms. Vapour in the chamber condenses around these ions, forming droplets. The droplets are what form the trail.

More information about the particles that are present can be found out by placing

the chamber in a magnetic field.

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CLOUD CHAMBERS

ALPHA TRACKS

BETA TRACKS

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μA

radiation --

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3. IONISATION CHAMBER

Radiation ionises the air between the metal plates. This provides a mechanism for a current to flow.

The ionisation current is proportional to the intensity of the radiation.

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4. GEIGER MÜLLER TUBE

The tube is filled with Argon gas at low pressure. About +400 Volts are applied to the thin wire in the middle. When a particle enter the tube, it ionises an Argon atom. The electron produced is attracted to the central wire anode, at high speed and ionises further Argon atoms, causing an "avalanche". Thus one single incoming particle will cause many electrons to arrive at the anode, creating a pulse which can be amplified and counted.

+ve 400V

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+ve 450V

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t u b eoutput

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Smoke Alarm

Radiation ionises the air between the metal plates.

This provides a mechanism for a current to flow.

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Americium source emits ionising alpha particles which pass through the mesh.

Am-241

Smoke particles attach to the charged ions and restore them to a neutral electrical state. This reduces the flow of electricity between the two plates in the ionization chamber. When the electric current drops below a certain threshold, the alarm is triggered.

+ +

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DETECTION OF CRACKS AND LEAKS

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Monitoring Thickness

RADIOACTIVE SOURCE

DETECTOR

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“THE ICE MAN” FOUND IN A MELTING AUSTRIAN GLACIER IN 1991

DATED USING RADIO CARBON – 14 DATING TO THE COPPER AGE, 5300 YEARS OLD

Nitrogen 14 atoms in the atmosphere absorb neutrons that have been released by cosmic bombardment.

One carbon 14 atom exists in nature for every 1,000,000,000,000 Carbon 12

Plants and animals which utilise carbon in biological foodchains take up C-14 during their lifetimes. They exist in equilibrium with the C14 concentration of the atmosphere, that is, the numbers of C14 atoms and non-radioactive carbon atoms stays approximately the same over time. As soon as a plant or animal dies, they cease the metabolic function of carbon uptake; there is no replenishment of radioactive carbon, only decay. A carbon 14 count enables an analyst to determine when the sample died.

HCNnN 11

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Carbon 14 is a beta (–) emitter, half life about 5600 year eeNC

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FOOD IRRADIATION

GAMMA RAYS

Cobalt 60

The gamma rays passing through the food is enough to destroy

many disease-causing bacteria as well as those that cause food to

spoil, but is not strong enough to change the quality, flavour or

texture of the food.

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Radio isotopes to be used as tracers are produced by neutron bombardment in a nuclear reactor.

e.g. Sodium 24 is made by bombarding sodium with neutrons

NanNa 2411

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2311

Sodium 24 is a beta/gamma emitter and is used to trace blood circulation in animals.

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Normal Cells Cancer Cells

MEDICAL USESTHERAPEUTIC DIAGNOSTIC

High-energy radiation from x-rays, gamma rays or neutrons is used

to kill cancer cells and shrink tumours. Radiation may come

from a machine outside the body (external-beam radiation therapy), or it may come from radioactive material placed in the body near cancer cells (internal radiation

therapy, implant radiation).

Tracers In tracer techniques a radioactive isotope, such as Technetium 99m, is injected into the body. The signals coming from the ensuing radiation can be detected with a gamma camera.

PET scans A radio isotope which decays by positron emission, is

injected. When a positron encounters an electron they annihilate each other,

emitting two photons. The energy and path of these photons leaving the body can then be used to give an accurate picture of the area where the isotope

was absorbed.

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MEDFLY

Mediterranean Fruit Fly

The Sterile Insect Technique (SIT) involves producing a large number of insects then irradiating them with gamma radiation before hatching, to sterilise them. The sterile males are then released in large numbers in the infested areas. When males mate with females, no offspring are produced. Repeated releases of sterilised males ensures the population of the insect pest in a given area is drastically reduced.

PEST CONTROL

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Agriculture: Radioactive isotopes are used as tracers in plants. Radioisotopes are added to fertiliser in small but known quantities. The uptake of the fertiliser can be measured by the researcher measuring how radioactive a plant has become. This technique is largely a research tool. Examples of isotopes used for this purpose include phosphorous32 and nitrogen15.

radio phosphorous

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RADON

50%

GROUND & BUILDINGS 14%

MEDICAL 14%

FOOD & DRINK 11.5%

COSMIC 10%

NUCLEAR POWER & WEAPONS 0.3%

OTHER 0.2%

BACKGROUND RADIATION (UK)