# Half life - Physics GCSE

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#1
Hi,
With radioactive half life decay, just wondering what will be picked up on a Geiger Muller, will only half the radiation now be present - hence you know you reached half life, or will the half that decayed still be emmiting some radiation.

~ or does it depend on the isotope, some isotopes will decay and no longer emit radiation, where isotopes of a different element might decay and still be emitting radiation? - thanks
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10 months ago
#2
The count rate is directly proportional to the amount of radioactive material left. The actual radioactivity of the material on a specific basis doesn't change, but the count rate will fall as there is simply less material decaying. Half the material = half the radiation count rate = 1 half life

Think of it as a crowd at a concert. The noise of one person would be the "radioactivity", and the total noise is the "count rate/intensity" in this example. A huge crowd will be loudest and have a greater count rate, whereas a group half the size will have a smaller one. However, there is still "radiation" being emitted, albeit a lower level. As the crowd size halves over and over there is always radiation/noise, it just falls in intensity as there are less individual emitters (radioactive nuclei).

Until all of the material is gone radiation is still being emitted
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#3
(Original post by tmr19)
The count rate is directly proportional to the amount of radioactive material left. The actual radioactivity of the material on a specific basis doesn't change, but the count rate will fall as there is simply less material decaying. Half the material = half the radiation count rate = 1 half life

Think of it as a crowd at a concert. The noise of one person would be the "radioactivity", and the total noise is the "count rate/intensity" in this example. A huge crowd will be loudest and have a greater count rate, whereas a group half the size will have a smaller one. However, there is still "radiation" being emitted, albeit a lower level. As the crowd size halves over and over there is always radiation/noise, it just falls in intensity as there are less individual emitters (radioactive nuclei).

Until all of the material is gone radiation is still being emitted
Thanks very much for the reply, understand it now, have a good night
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