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p6 (half life basics (radioactive decay is a random process, so you…
p6
half life basics
radioactive decay is a random process, so you can't predict when a particular nucleus will decay
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radioactive isotopes decay at different rates, number of unstable nuclei that decay in a given time is called the activity, measured in becquerels, number of nuclei that decay each second
radiation emitted from a decaying nucleus can be detected using a Geiger Muller tube, measures count rate in counts per minutes or second
as more unsable nuclei decay, the activity of the source as a whole decreases
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contamination
if a radioactive source ends up on or in the object, it is contaminated, eg if you touch a radioactive source, some atoms might rub off onto your hand and contaminate you
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if source if solid, no risk if object doesn't touch, if a gas, could move and come into contact with object, increases risk
gases are very dangerous for people, can be inhaled, contaminates from inside
if an object is contaminated, irradiation risk is very high as the distance between source and object is so small
contamination lasts longer, if the original source is taken away, the atoms causing the contamination are left behind, causing more harm
radiation
outside the body, beta and gamma are the most dangerous
can still get inside to the delicate organs, pass through skin
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inside the body, an alpha source is the most dangerous because they're the most ionising and do all their damage in a very localised area
beta and gamma sources are less dangerous because they are less ionising, and gamma will mostly pass straight out without doing much damage
irradiation
if the radiation from a radioactive source reaches an object, the object is said to be irradiated
the risk of irradiation from a source is how likely that an object will be irradiated by the source, depends on distance from the source and the type of radiaiton
as the distance from the source increases, the amount of radiation reaching that point decreases, so the irradiation risk for any source is lower and larger distances
alpha radiation has shorter range, lower risk
temporary, if the source if taken away, and irradiation it is causing stops
tracers
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need a shortish half life eg a few hours, so the radioactivity quickly disappears, but long enough that it emits enough radiation when it reaches the right place
all gamma, can penetrate tissue, pass out of the body, are detected, alpha can't and is more dangerous in the body
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hazards
lower the activity of the source, the safer it is to be around
if two sources with different half lives contain the same number of radioactive nuclei, the source with the longer half life will have lower activity
if two sources with different half lives start off with the same activity, the activity of the sample with the shorter half life will fall faster, so after a while the source with longer half life will have a higher activity and will be more dangerous
when choosing a radiactive source, it is important to find a balance between a source that has a high enough activity to be useful but that won't be dangerous for too long
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half life
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short half life means activity falls quickly, lots of nuclei decay in a short time
long half life means activity falls more slowly because most of the nuclei don't decay for a long time
radiotherapy
high doses of radiation will kill living cells, can be used to treat cancers
radiation directed carefully and at a specific dosage, depends on size and type of tumour, size and age of patient, kills the cancer cells without damaging too many normal cells
some damage to normal cells, makes patient feel ill