1AWhen 5 mm of aluminium is inserted, the count rate is roughly the same as that when a sheet of paper is inserted. Hence, radiation isnot emitted.1AWhen 5 mm of lead is inserted, the count rate is much smaller than that when 5 mm of aluminium is inserted. Therefore, radiation is emitted.1A6SolutionsMarks(a)No,1Athis is because the range of radiation in air is only a few centimetres.1AIt cannot reach the G-M tube even if it is emitted by the source.(b)The radiation recorded is background radiation.1AOnly positive charges (particles) would be deflected downwards by the electric field to positions below Y.1AHowever, the range of particles is too short for them to reach these points. Therefore, no radiation from the source reaches this position.1A
LQ_Radiation(c)As the recorded count rates at Xand Yare both greater than the background count rate, some radiation emitted by the source is detected at these two points.1AAs the radiation detected at Xis deflected towards the positive pole by the electric filed, it must be radiation.1AAs the radiation detected at Yis not deflected by the electric filed, it must be radiation.1ATherefore, the source emits and radiation.(d)The background radiation is counted twice in the sum of the count rates in Figure c.1A(e)Count rate recorded at Yremains unchanged.Count rate recorded at Xdecreases.1A1A
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- Fall '19
- Radioactive Decay, Ionizing radiation, Radioactive contamination, Background radiation, actual count rate