5.2. Radioactivity
A subsection of Physics, 5054, through 5. Nuclear physics
Listing 10 of 187 questions
A smoke detector containing an alpha-particle source is fixed to the ceiling in a room. The alpha-particles ionise the air between two metal plates so that a battery produces a current between the plates. If smoke enters the detector, it reduces the current between the plates and an alarm sounds. shows the arrangement. ceiling ionised air alpha-particle source to alarm circuit metal plates A technician removes the source from the smoke detector and measures the count rate of the source. Suggest two precautions that the technician should take when working with the source. 1. 2. The technician measures the count rate, in counts / s, five times. On each occasion, the arrangement of the equipment is the same. The values obtained are: 81 77 80 83 and 79. Suggest why the values are different. Radioactive sources that emit beta-particles or gamma-rays are not used in smoke detectors. State and explain two reasons for this. 1. 2. .
5054_w13_qp_22
THEORY
2013
Paper 2, Variant 2
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shows the proton number and the nucleon number of the nuclei of five neutral atoms. neutral atom 1 neutral atom 2 neutral atom 3 neutral atom 4 neutral atom 5 proton number nucleon number State the two atoms in that are different isotopes of the same element, contain the same number of neutrons, contain the same number of electrons. The nucleus of atom 1 is radioactive and when it decays, it emits a beta-particle. State, for the nucleus produced by this decay the proton number, proton number = the nucleon number. nucleon number = A sample contains a large number of radioactive nuclei that emit beta-particles. The sample is placed near to a radiation detector in a laboratory and the count rate is recorded over a long period of time. shows the count rate recorded by the detector during this period. time / days count rate counts / minute Suggest two major sources of background radiation. 1. 2. Using , 1. determine a value for the background count rate in the laboratory, background count rate = 2. determine the count rate, at time = 0, due to the sample on its own, count rate due to sample = 3. estimate the half-life of the radioactive atoms in the sample. half-life = A student suggests a change to the experiment in . He suggests completely encasing the radiation detector in lead before the sample that emits beta-particles is placed near to it. The effect on the count rate of background radiation may then be ignored. Describe and explain the effect on the background count rate recorded by the detector of completely encasing the radiation detector in lead. State and explain whether the student’s suggestion is a sensible one.
5054_w15_qp_21
THEORY
2015
Paper 2, Variant 1
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Questions Discovered
187