Ionising Radiation and Living Things

Ionising Radiation and Living Things - Transcript

Standard Grade Physics Health Physics The Effects of Radiation on Living Things

From this lesson and for the exam you should be able to
State that radiation can kill living cells or change the nature of living cells State that radiation energy may be absorbed in the medium through which it passes State that the dose equivalent is measured in sieverts State that for living materials the biological effect of radiation depends on the absorbing tissue and the nature of the radiation Understand that the dose equivalent measured in sieverts takes account of the type and energy of radiation

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

Radiation may be absorbed by the medium it passes through Radiation can kill living cells or change the nature of living cells
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

The Effects of Ionising Radiation
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

Short Term Effects of Radiation

Short term effects usually occur when there s a large amount of exposure to radiation

WW2 Hiroshima and Nagasaki
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

Chernobyl Nuclear Power Station
There was also a huge nuclear accident at the Chernobyl Nuclear Power station in the former USSR in 1986 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
135 000 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

Long Term Effects of Radiation
These effects take longer to become apparent and can be caused by much lower levels of radiation One of the most important long term effects of radiation is that of cancer in various parts of the body 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

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

Radiation Alpha particles Beta particles Gamma rays

Quality Factor Q 20 1 1

From this it can be seen that alpha radiation is the most ionising radiation out of the three types

Dose Equivalent
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

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

The DOSE EQUIVALENT is measured in sieverts Sv

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

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

Natural Sources of Radiation
Source Radon and thoron gas from rocks and soil Gamma rays from ground Carbon and potassium in your body Cosmic rays at ground level Total Annual Dose Sv 800 400 370 300 1870

Man Made Sources of Radiation
Source Medical uses x rays etc Chernobyl first year Fall out from weapons testing Job average Nuclear industry e g waste Others TV aeroplane trips etc Total Annual Dose Sv 250 50 10 5 2 11 328

Death Risk Cause
Death Risk Cause All causes Smoker 10 per day Road accidents Home accidents Work accidents All radiations Medical Radiations Death Risk 40 Year Old 1 per 500 1 per 2000 1 per 5000 1 per 10 000 1 per 20 000 1 per 27 500 1 per 240 000