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how does a smoke detector work
a smoke detector uses the radiation from americium-241 oxide . the substance emitts alpha radiation . the alpha radiation ionises molecules in the air inside smoke detectors and this allows electric current to flow . however particles of smoke will absorb the radiation . this stops the electric current and causes the alarm to switch on
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why does a smoke detector use alpha radiation rather than beta or gamma radiation
betas and gammas are not effected by the smoke and they dont have a strong enough ionisng power to be detected , beta and gamma could also be dangerous to humans ,
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explain how the somke detector works in brief
as long as the electric current flows the alarm is quiet , the smoke stops the alphas so no ionisng and no current
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what is tracing
very tiny amounts of radioactive substances can be detected by the radiation they emit . so a tiny amount of a radioistope mixed with the substance canb act like a tag or label , to show what's happening to the substance
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how canb tracing help trace leaks
tiny amounts of radioistopes can be added to fluid in pipes to trace leaks underground . the area around the leak will be come radioactive , which can be discovered using a geiger muller tube and counter
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how can tracing be used in medicine
for example , doctor might suspect that a patient has a blocked kidney . a small amount of I which is radioactive , is injected into the patient . Both kidneys should extract the iodine from the bloodstream in 5 minutes and then pass it into the urine . A geiger counter is held over each kidney and the readings show whether the iodine stays in the kidney or whether it passes out
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what would an unblocked kideny with iodine look like on a graph
 - with count rate on the y axis instead
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what would a blocked kidney with idoine look line on a graph
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how are gamma rays used in medicine
high doses of radiation can kill cells : they are used to kill cancer cells , which are more easily killed than healthy cells . Gamma radiation having the highest penetrating power is used to kill cancer cells . the radioistope of cobalt 60Co , is generally used as the source of gamma radition
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how is radiation used in steralisation
- steralisation is achieved by killing microorganisms with gamma radiation (gamma radiation is used because of its penetrating power) . examples of this use of gamma radiation include the steralisation of
- 1) foods . bacteria , moulds and insects can be killed in foods , even after they are pacakged . this makes the shell life longer , but may also alter the taste
- 2) hospital equioment , especially plastic syringes that would be destroyed by heat
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what is half life
the time it takes for the count rate from a sample containing the isotope to fall to half its initial level
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during radioactive deacy , nuclei disintergrate at
random at a rate which is unaffected by chemical chnage or temperature
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if one half life has elapsed what fraction of the parent isotope is remaining and what fraction of parent radioistope is decayed
- radioistope remaining = 1/2
- radioistope decayed = 1/2
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if 2 half life has elapsed what fraction of the parent isotope is remaining and what fraction of parent radioistope is decayed
- radioistope remaining = 1/4
- radioisotope deacyed = 3/4
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if 3 half life has elapsed what fraction of the parent isotope is remaining and what fraction of parent radioistope is decayed
- remaining = 1/8
- decayed = 7/8
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if 4 half life has elapsed what fraction of the parent isotope is remaining and what fraction of parent radioistope is decayed
- remaining = 1/16
- decayed = 15/16
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what is curve for cout rate and time (for radioactive decay)
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the nost appropriate radioistope for a particular use depends on
- the type of radiation emitted
- the half life
- the important factors to conisder are :-
- how far the radioactivity has to travel to the detector
- the material the radiation has to tavel through
- the hald life
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the longer the half life the
longer the radioactivity will remain
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complete the table
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