DETECTION & USES OF RADIATION © JP

Detection of radiation 1. Photographic film Small packets of photographic emulsions are routinely used by workers to monitor radiation exposure. © JP

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. © JP

CLOUD CHAMBERS ALPHA TRACKS BETA TRACKS © JP

3. IONISATION CHAMBER μA - + radiation 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. © JP

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 0V source +ve 450V 0V C R t u b e output © JP

Smoke Alarm Am-241 Americium source emits ionising alpha particles which pass through the mesh. - + + - Radiation ionises the air between the metal plates. This provides a mechanism for a current to flow. 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. © JP

DETECTION OF CRACKS AND LEAKS Radioactive Tracer DETECTION OF CRACKS AND LEAKS © JP

Monitoring Thickness DETECTOR RADIOACTIVE SOURCE © JP

“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 Carbon 14 is a beta (–) emitter, half life about 5600 year 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. © JP

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. © JP

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

MEDICAL USES THERAPEUTIC DIAGNOSTIC 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. Normal Cells Cancer Cells 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). 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. © JP

MEDFLY Mediterranean Fruit Fly PEST CONTROL 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. © JP

Agriculture: Radioactive isotopes are used as tracers in plants 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 © JP

BACKGROUND RADIATION (UK) RADON 50% GROUND & BUILDINGS 14% MEDICAL 14% FOOD & DRINK 11.5% COSMIC 10% NUCLEAR POWER & WEAPONS 0.3% OTHER 0.2% © JP