Assignment:
1. When operated at a gas multiplication factor of 1000, estimate the pulse amplitude produced by the interaction of a thermal neutron in a He-3 tube of 100 pF capacitance.
2. Sketch the pulse height spectrum expected from a boron-lined proportional tube for thermal neutrons if the boron thickness is small enough so that energy loss of the reaction products in the layer can be neglected.
3. Why is it not possible to increase the counting efficiency of a fission chamber indefinitely simply by increasing the thickness of the fissional deposit?
4. Show that the angle (in the laboratory frame) between a recoil proton and the corresponding scattered neutron is always 90 degree.
5. What length of conventional coaxial cable is necessary to shift the position of the prompt coincidence peak in a time spectrum by 100 ns?
6. Two NaI detectors are arranged to count one each of two gamma rays emitted in coincidence with no angular correlation by a radioactive source. In each of the cases listed below, describe the effect of the indicated change on the ratio of true coincidence to chance coincidence counting rates, and indicate the practical limits to which each of the changes may be carried in order to improve this ratio.
a. Moving the detector positions to change the solid angle subtended by each
b. Varying the amount of source material
c. Changing the coincidence circuit resolving time
d. Varying the pulse height window width used to select a given gamma energy