A radioactive source is positioned 20 mm from a radiation detector, as shown in Fig. 11.1. The detector first records a count rate of 150 counts/s. A sheet of paper is inserted between the source and the detector. The detector count rate then drops to 60 counts/s. Keeping the paper in position, a magnetic field is applied at right angles to the direction of the radiation. The detector count rate then drops to 20 counts/s. The count rates have not been background-corrected. The background count is 20 counts/s.
(a)[5]
State the evidence showing whether each kind of radiation is present in, or absent from, the radiation emitted by the source: $\alpha$-particles, $\beta$-particles, $\gamma$-rays.
(b)[2]
Determine how much of the initial count rate of 150 counts/s, if any, comes from each type of radiation: $\alpha$-particles, $\beta$-particles, $\gamma$-rays.
Worked solution & mark scheme
This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Alpha and beta are present” …