The Effects of Radiation on Living Things Health Physics

What types of radiation are harmful? Why is ionising radiation harmful? Radiation

Radiation may be absorbed by the medium it passes through. All living things contain living cells. We have many different types of cells which perform different functions including: Skin cells. Red blood cells (they transport oxygen around the body) White blood cells (they fight infection). Nerve cells. Muscle cells. Brain cells. Radiation can kill living cells or change the nature of living cells.

Ionising radiation can kill or change the nature of living cells. The effects of the damage inflicted by the ionising radiation may: be severe and cause immediate effects, or not become apparent for a long time. The biological effect of radiation depends on: The type of radiation. The type of body tissue or body organ that absorbs the radiation. The total amount of energy absorbed. The Effects of Ionising Radiation

During the Second World War, two atomic bombs were dropped on Hiroshima and Nagasaki in Japan. Those people who survived the blast were exposed to a large dose of radiation. Such doses caused severe damage to cells all over the body, especially in the skin, blood, bone tissue and gut. Many of these people died within a few weeks. Those people who were exposed to a smaller dose recovered from such immediate effects. WW2 – Hiroshima and Nagasaki

There was also a huge nuclear accident at the Chernobyl Nuclear Power station in the former USSR in Workers there were carrying out experiments on the reactor rods which caused fires to start. A number of firemen were exposed to very large amounts of radiation and 30 people died as a result. The damage to the power station was extensive but the radiation effects over a wide area were considerable. Chernobyl Nuclear Power Station

people were removed from an area within a radius of 30 km. The smoke and radioactive debris reached a height of 1200 m and travelled across Russia, Poland and Scandinavia. A cloud of material from the accident reached the UK and, with heavy rain, there was material deposited on parts of north Wales, Cumbria and Scotland. This caused certain farm animals (e.g. lambs) to be banned from sale as they had absorbed radiation from the grass. Chernobyl Nuclear Power Station

Long-Term Effects of Radiation These effects take longer to become apparent and can be caused by much lower levels of radiation. Uranium miners tended to get lung cancer due to breathing in gases which emitted alpha particles. People who painted the dials of clocks with luminous paint developed one cancer from using their lips to make points on the brushes. One of the most important long-term effects of radiation is that of cancer in various parts of the body.

Exposure to ionising radiation does not necessarily cause cancer The mechanisms for cancer occurring are poorly understood at the moment. One theory is that the ionising radiation affects the DNA material within us – our genetic make-up. Our DNA contains genetic instructions which control the operation and reproduction of the cells. If ionisations caused by ionising radiations alter these instructions in the DNA, there is a chance that cancer will develop. Genetic damage can be caused to cells by radiation, including cells which are involved in reproduction.

Quality Factor Different types of radiation have different effects on living cells. Even though the same type of tissue may receive the same dose, the biological effects of different radiations will be different. To take this into account, a quality factor is assigned to all types of radiation. The quality factor, Q, allows the effects that different radiations have on living cells to be compared.

Quality Factor The quality factor for each type of radiation is shown below: RadiationQuality Factor (Q) Alpha particles20 Beta particles1 Gamma rays1 From this it can be seen that alpha radiation is the most ionising radiation out of the three types.

Dose Equivalent The DOSE EQUIVALENT is a measure of the biological effect of radiation and it takes account of the type and energy of the radiation as well as how the radiation is distributed. REMEMBER, the biological effect of radiation depends on: The type of radiation. The type of body tissue or body organ that absorbs the radiation. The total amount of energy absorbed.

Because 1 Sv is a very large dose of radiation which could only happen as a result of a very serious nuclear accident or explosion, doses are given in millisieverts (mSv) or microsieverts (  Sv). The DOSE EQUIVALENT is measured in sieverts (Sv). Rolf Maximilian Sievert (1896 – 1966)

Suppose that 100 people all receive a dose equivalent of 1 Sv spread over the whole body. It is estimated that, of the 100 people on average 4 of them would eventually die as a result of the radiation. But precisely who would die, or when they would die, or what illness they would die of, cannot be predicted.

Background Radiation Radiation is all around us! Background radiation is radiation that is naturally occurring. The limits on effective dose (dose to the whole body) introduced by the IRR99 to replace the limits set previously by the IRR85 are: for employees aged 18 years or over, 20 millisieverts in a calendar year (except that in special cases employers may apply a dose limit of 100 millisieverts in 5 years with no more than 50 millisieverts in a single year, subject to strict conditions); for trainees, 6 millisieverts in a calendar year; and for any other person, including members of the public and employees under 18 who cannot be classed as trainees, 1 millisievert in a calendar year. The dose limit for the skin now applies to doses averaged over an area of skin not exceeding 1 cm2.

Natural Sources of Radiation SourceAnnual Dose (  Sv) Radon and thoron gas from rocks and soil 800 Gamma rays from ground400 Carbon and potassium in your body370 Cosmic rays at ground level300 Total =1870

Man-Made Sources of Radiation SourceAnnual Dose (  Sv) Medical uses – x-rays, etc.250 Chernobyl (first year)50 Fall-out from weapons testing10 Job (average)5 Nuclear industry (e.g. waste)2 Others (TV, aeroplane trips, etc.)11 Total =328

Radiation Dosage The limits on effective dose (dose to the whole body) are: For employees aged 18 years or over, 20 millisieverts in a calendar year (except that in special cases employers may apply a dose limit of 100 millisieverts in 5 years with no more than 50 millisieverts in a single year, subject to strict conditions) For trainees, 6 millisieverts in a calendar year Any other person, including members of the public and employees under 18 who cannot be classed as trainees, 1 millisievert in a calendar year.

Death Risk - Cause Death Risk – 40 Year Old All causes1 per 500 Smoker – 10 per day1 per 2000 Road accidents1 per 5000 Home accidents1 per Work accidents1 per All radiations1 per Medical Radiations1 per