Glossary of Cyberphysics - Radioactivity2

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What causes 'background radiation' in the UK?
Most of the background radiation dose we receive in the UK is from natural sources (about half is inhaled as radon gas).
What factors affect your annual radiation dose?
The radiation dose you get in a year depends on:
- where you live (the rock type in your locality), o your state of health (whether you require treatment or investigation in hospital that involves ionizing radiation ),
- your diet (salt substitutes contain potassium rather than sodium and the percentage of potassium that naturally occurs in the radioactive form is higher than that of sodium),
- your occupation (do you work in an environment that exposes you to nuclear radiation?)
Why are some rocks radioactive?
Radioactive rocks contain atoms of radioisotopes such as thorium or uranium. Uranium has a very long half-life so deposits of it are still quite abundant around the world. It is an alpha and gamma emitter so it is not dangerous to living things when it is outside the body. However, tiny particles of rock are dissolved in water or broken off by the wind during the process of erosion. These tiny alpha emitters can be ingested (drank or eaten) or inhaled (breathed into the lungs). Alpha emitters inside the body are very dangerous. If a rock contains a vein of uranium ore the concentration of uranium can be as great as 5000 parts per million but in general the levels are much lower.
What type of rock tends to have the most radioactive source particles in it?
Igneous - granite
What are cosmic rays?
Cosmic rays originate out in space.

They are high energy particles produced by our Sun (when they are called the solar wind), stars, supernovae, neutron stars and black holes.
# They travel at very fast speed indeed - very close to the speed of light.
# Cosmic rays are made up from a stream of high-energy particles that are generally ionised atoms (ions), ranging from a single proton, up to an iron nucleus and sometimes an even heavier one!
Cosmic rays have been detected with very high energies, we believe that they originate from quasars and active galactic nuclei. We do not know where these particles are coming from but a lot of exciting research is going on in that area. We have not got detectors that are able to detect cosmic rays of even higher energy but scientists are sure that super-energy Cosmic rays exist…. we just can't 'see' them with any instrument we have devised yet.
Why does your radiation dose increase if you go up to a high altitude (or up in a plane)?
If you live at a high altitude or go up in an aeroplane your radiation dose increases because you are hit by more cosmic rays!
Why does your radiation dose increase if you go nearer to the poles?
If you live nearer the poles you will receive a higher dose of cosmic radiation because the earth surface rotates more quickly at the equator than at the poles… also the atmosphere is deeper at the equator than at the poles.

The atmosphere shields you from radiation.
What is the danger from an alpha source?
An alpha source outside the body can do little harm. The alpha particles do not even penetrate the outer layer of dead skin cells on the body. But once inside the body (for example inside the lungs) they are very dangerous indeed.

Each alpha particle causes a series of ionisations as it rips through matter. As they are so highly ionising they cause a lot of localised damage.

E.g. A tiny speck of uranium dust contains millions of atoms (one millionth of a gram contains 2,500,000,000,000,000 atoms!). Over a long period of time these atoms decay, their alpha particles doing considerable damage in a region very close to the source. Alpha rays can only penetrate about 0.1mm into tissue, therefore a lot of localised damage occurs and the chance of a tumour developing or serious damage due to cell death is much higher than if the damage was more widely (and sparsely) spread.

Once inside the body alpha sources are very difficult to detect because the rays do not get out to the detector! You could swallow an alpha source and it would not register on a Geiger counter.

Thus alpha sources are very hazardous and are never used for medical applications. They are particularly dangerous in powder form - the danger of inhaling or ingesting them is then higher. Look at - it is an animated gif showing the spread of damage through the lung from an inhaled grain of Plutonium.
What is the danger from a beta source?
Beta particles are more penetrating than alpha particles. They therefore cause less localised damage. However they are still very dangerous. An outside the body source of beta particles would be able to penetrate the skin and a source inside the body would be able to penetrate about 1mm into tissue.

All nuclear radiation carries the risk of causing mutations to DNA or tumours. In high doses there is an increased risk of cell death.
What is the danger from a gamma source?
Gamma rays hardly interact with matter at all. They are very penetrating. Therefore if the intensity is low they are used with a gamma camera for medical applications

If the intensity of the source is high gamma ray sources are very high they are dangerous inside or outside the body. Just as intense ultra violet rays can cause sunburn, they can cause radiation burns. But, these burns do not only occur on the skin's surface, they also occur within organs deep in the body, resulting in sickness and nausea and considerable pain and discomfort.

All nuclear radiation carries the risk of causing mutations to DNA or tumours. In high doses there is an increased risk of cell death.
What is DNA and what affect does ionizing radiation have on it?
Deoxyribonucleic Acid - double helix molecule that forms the genetic material of all living cells. It controls the structure and function of cells and is the material of inheritance; therefore damage to the coding can cause mutation.

Ionizing radiation can cause damage to the structure of DNA so that on division the new cell is altered (mutated). Repair to damage to DNA is carried out by 'repair enzymes'. If mutants that lack such a facility are more susceptible to radiation damage and to express the damage so produced.

Nuclear radiation therefore can have harmful effects on living matter, resulting in mutations and cancer (tumours). Very high dose can cause cell death.
Cells and cancer
Cancer is a disease that originates in our own cells. A change in the DNA causes a special gene called an oncogene to be switched on. This leads to uncontrollable cell reproduction by mitosis. And this is a cancer.
How is radioactivity detected?
Radioactivity can not be detected with our five senses, special detectors are needed to tell us we are being exposed to it therefore it is particularly dangerous. People may unknowingly be exposed to it for prolonged periods of time with a detrimental effect on their tissue and genetic material.

Several devices have been developed to detect radioactivity, with the earliest being an unexposed photographic plate placed in the vicinity of a source being detected. Other devices include the cloud chamber, electroscopes, ionizing chambers, the Geiger-Müller tube,
o liquid and electronic bubble chambers, scintillation detectors (spinthariscope), and solid state semiconductor devices.
The most commonly known one is the Geiger counter.
How is radioactivity measured?
The rate of decay is the number of radioactive atoms that emit nuclear radiation in one second. This is effectively the same as the activity of the sample. It is measured in becquerel (Bq) or counts per second. It is sometimes referred to as the 'count' for a sample.
What is a 'half-life'?
The activity of radioisotopes decreases exponentially with time. After a given time period the amount that has yet to decay is halved. This is the case no matter when you start to measure the activity of the sample. The time taken for this 'halving' of activity is called the half-life. So a half-life is the time taken for half of the atoms in a sample to decay or the time taken for the activity of a sample to halve.
How long is a half-life?
Half-lives vary widely from microseconds to millions of years!

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