P1bL9  Uses of Radiation and Safety

Key Words

Chain reaction - the splitting of a nucleus sets off further splitting of other nuclei.

Decay - unstable nucleus changing to another element by emitting a particle or gamma ray.

Ionise - knocking electrons off atoms.

Irradiated - exposed to large doses of radiation

Nuclear energy - energy obtained by splitting of atoms.

Radiation sickness - a serious illness due to exposure to high doses of radiation

Radiocarbon dating - a technique for identifying age of biological samples by analysing the proportion of carbon-14.

Spent nuclear fuel - nuclear fuel that has given off most of its energy.

Tracer - a radioactive material injected into a flow of water to see how the water flows.

Grade E

Uses of Radiation

Radiation can be used to treat cancer.  Gamma rays from several sources are focused onto the cancer.  The combined dose is fatal for the cancer cells, but cells in each beam don't get too high a dose.

Hospital equipment can be sterilised by exposure to gamma rays which kill bacteria and moulds.  This can be preferable to heating with high pressure steam.

Tracers that emit gamma rays are used to detect leaks in pipes.  The gamma emitter gives of gamma rays that can pass through the ground.  Where there is a leak, the gamma emitter will pool.

Nuclear fission comes about when a neutron is captured by a large and unstable nucleus.  The neutron has to be at the right speed:

• too slow, it bounces off the nucleus;
• too fast, it goes right through.

The neutron "tickles" the nucleus and it "laughs itself to pieces".

As the nucleus splits into a range of other elements, it releases on average three more neutrons, which go on to interact with more nuclei and split them.  Each of these releases three more nuclei, so we end up with 1, 3, 9, 27, 81... nuclei being split.  This is a chain reaction.

If the reaction is uncontrolled, a huge amount of energy is released in an enormous and destructive explosion - an atomic bomb.

If the chain reaction is controlled, it can produce a lot of energy to boil water in a power station.  A nuclear reactor is a boiler.

  Nuclear fission has nothing whatever to do with radioactive decay.

Dangers of radiation

The waste material from nuclear fission is some of the nastiest muck known to man.  There is a whole range of radioactive isotopes that give off alpha, beta, and gamma.

• Alpha is stopped by skin and cannot penetrate from the outside.  However, when taken in (ingested), an alpha emitter will kill and damage cells, leading to irreparable tissue and organ damage.
• Beta can penetrate into the body from outside.
• Gamma can pass through the body easily.

The high energy of these radiations can kill cells.  The injuries are rather like burns.  A lower dose can do damage to the DNA and cause cancer.

There are strict rules on the safe handling of radioactive materials.

Grade C

Other uses of radiation are:

• Medical tracers.  A gamma emitter like iodine-123 is injected into the patient and will show up in the thyroid gland.  This will enable doctors to detect when the thyroid is not working properly.
• Smoke detectors.  Alpha particles from Americium-241 ionise air to form a small electric current.  If smoke gets in, the alpha particles are absorbed by the smoke particles to stop the current.  The alarm sounds.
• Thickness control.  A beta emitter passes high speed electrons through paper as it passes through the paper making machinery.  The beam is reduced as the paper gets thicker, and control circuits alter the pressure on the rollers to make sure the paper stays the same thickness.

High doses of radiation are dangerous.  The radiations ionise molecules in cells which do immense damage.  In high doses, cells and tissues are killed leading to radiation sickness, a condition in which undamaged cells cannot replace the dead cells quickly enough.  Your hair falls out, your skin gets blistered (just like a bad burn), and your organs then fail.  It is an unpleasant death.  70 000 people died of radiation sickness after the Hiroshima bomb in 1945.

Radioactive materials have to be handled with care.  The most radioactive materials are handled remotely with the operators sitting behind thick walls and thick lead glass.

Nuclear waste has to be got rid of carefully:

Grade A

Radioisotope like carbon-14 are found in all living things.  Neutrons from cosmic rays are captured by the carbon nuclei to give the radioactive isotope.  The half life of this beta emitter is about 5700 years.  Once a living thing dies, no more carbon-14 is taken up.

Scientists can date ancient objects up to about 40 000 years.  In this time, there have been 6 half-lives and the activity is very low.

Uranium-238 (half life 4500 million years) is used to date rocks.

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