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The Uses of RADIOISOTOPES

Form 5 Physics (SPM)

Health Physics

GEE KUANG BENGSMK METHODIST

2012

From this lesson and for the exam, you should be able to: State what radioisotopes are and give examples

Describe applications of radioisotopes in the field of

> Medicine

> Agriculture

> Archaeology

> Industry.

RADIOISOTOPES are unstable isotopes which decay and gives out radioactive emissions.

Radioisotope Nuclide notation Radioactive emission

Half-life

Tritium-3 β 12.33 years

Carbon-14 β 5730 years

Sodium-24β , γ

15 hours

Cobalt-60β , γ

5.27 years

Technetium-99m γ 6.01 hours

Iodine-123γ

13.2 hours

H31

C146

Na2411

Co6027

Tcm9943

I12353

Medicine

Sterilising

Gamma rays are used to sterilise hospital equipment, especially plastic syringes that would be damaged if heated.

Radioactive Tracers

Radioisotopes are used for checking for a blocked kidney.

To do this a small amount of Iodine-123 is injected into the patient.

After 5 minutes 2 Geiger counters are placed over the kidneys.

Cancer Treatment

"Radiotherapy” is using Gamma rays to kill cancer cells.Cancer cells can't repair themselves when damaged by gamma rays.

AgricultureWhat Is Food Irradiation?

Food irradiation is the process of exposing food to controlled levels

of ionizing radiation to kill harmful bacteria, pests, or parasites, or to preserve its

freshness.

AgricultureRadiation can be used to

Control insects in grains and fruits Inhibit sprouting in tubers Delay the ripening of some fruits/vegetables Reduce the problems of parasites in products of animal

origin, (e.g., trichinella spiralis in pork) Control Salmonella, Shigella, Campylobacter, Yersinia,

Listeria and E. coli in meat, poultry, and fish Delay mold growth on strawberries and other fruits Kill microorganisms and insects in spices Commercially sterilize foods, destroying all

microorganisms of public health concern (i.e., special diets for people with weakened immune systems)

Even after it has been packaged, gamma rays can be used to kill bacteria, mould and insects in food.

This process prolongs the shelf-life of the food, but sometimes changes the taste

The International Food Irradiation Symbol – The

Radura

Archaeology

Radioactive (Carbon) Dating Animals and plants have a known proportion of Carbon-14 (a radioisotope of Carbon) in their tissues.When they die they stop taking Carbon in, then the amount of Carbon-14 goes down at a known rate (Carbon-14 has a half-life of 5730 years). The age of the ancient organic materials can be found by measuring the amount of Carbon-14 that is left.

Carbon dating tells us when this mammoth died

Radiocarbon is first produced in the atmosphere by collisions of neutrons with nitrogen atoms (Nitrogen has 7 protons and 7 neutrons in its nucleus).

The neutron will knock out a proton from the nitrogen atom’s nucleus, replacing it with a neutron. The proton number is reduced by 1 (it is now 6), but the mass number remains the same (14).

The atom will now have 6 protons and 8 neutrons in its nucleus and form the isotope 14C (radiocarbon). C-14 is radioactive and decays with a half-life of 5730 years back to Nitrogen (14N).

The 14C atoms rapidly form CO2 gas and then exchanged between the atmosphere, hydrosphere and biosphere. As long as the organism is alive it will continually exchange carbon within its reservoir and remain in equilibrium as new carbon is replenished. After the organism dies the 14C clock is set as the ratio of 14C/stable carbon (12C and 13C) decreases as 14C decays to 14N.

Carbon Dating• Try this: An artifact

recovered from an archaeological site was found to have 1/64 of its initial amount of radioactive carbon. If the half-life of the radioactive carbon 5730 years, determine the age of the artifact.

The age of the artifact is

34,380 yrs

Industry

Smoke Detectors

Smoke alarms contain a weak source made of Americium-241.Alpha particles are emitted from here, which ionise the air, so that the air conducts electricity and a small current flows. If smoke enters the alarm, this absorbs the a particles, the current reduces, and the alarm sounds. Am-241 has a half-life of 460 years.

Thickness Control

In paper mills, the thickness of the paper can be controlled by measuring how much beta radiation passes through the paper to a Geiger counter.

Radioactive Tracers

Radioisotopes are used in industry, to detect leaking pipes.To do this, a small amount is injected into the pipe. It is then detected with a GM counter above ground.

Radioactive Tracers A solution of phosphate, containing radioactive phosphorus-32, is injected into the root system of a plant. Since phosphorus-32 behaves indentically to that of phosphorus-31, the more common and non-radioactive form of the element, it is used by the plant in the same way. A Geiger counter is then used to detect the movement of the radioactive phosphorus-32 throughout the plant. This information helps scientists understand the detailed mechanism of how plants utilized phosphorus to grow and reproduce.

Checking Welds

If a gamma source is placed on one side of the welded metal, and a photographic film on the other side, weak points or air bubbles will show up on the film, like an X-ray.

THE END

…..the beginning ?