5. Nuclear physics
A section of Physics, 5054
Listing 10 of 279 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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The proton number (atomic number) of the element lead is 82. The isotope lead-209 (209 82Pb) is radioactive and decays by the emission of beta-particles. Describe the composition and structure of a neutral atom of lead-209. A nucleus of lead-209 emits a beta-particle. State how the composition of the nucleus produced differs from the original nucleus. Complete the table in to show the relative ionising effects of the three types of ionising radiation produced by radioactive decay. least strongly ionising most strongly ionising A sample containing lead-209 nuclei is used to produce a beam of beta-particles. The beta-particles enter a magnetic field. The magnetic field is perpendicular to the direction of travel of the beta-particles. The beta-particles travel from left to right. shows that the direction of the magnetic field is out of the page. magnetic field out of the page beam of beta-particles On , sketch the path of the beta-particles in the magnetic field. An industrial technician uses a detector to measure the background count rate in a laboratory. State what is meant by background radiation. Suggest two major sources of background radiation. 1. 2. The average reading for the background count measured by the technician is 16 counts / minute. He then brings a sample that contains a radioactive isotope of lead close to the detector and he finds that the new count rate is 92 counts / minute. The half-life of this isotope is 3.3 hours. Determine the count rate measured using the detector after 6.6 hours. count rate =
5054_w15_qp_22
THEORY
2015
Paper 2, Variant 2
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Plutonium-238 is a radioactive isotope that decays by alpha-particle emission. It also emits gamma-rays. The nuclide notation for plutonium-238 is 238 94 Pu. Describe the structure and composition of a neutral atom of plutonium-238. Alpha-particles, beta-particles and gamma-rays all cause ionisation. The ionisation of substances in the human body can be hazardous. State how the ionising effect of beta-particles compares with 1. the ionising effect of alpha-particles, 2. the ionising effect of gamma-rays. State two precautions that are taken when radioactive substances are moved in a safe way. 1. 2.
5054_w16_qp_22
THEORY
2016
Paper 2, Variant 2
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Questions Discovered
279