The Scintillation Response from NaI(Tl) Crystals Under Bombardment with Positive Ions of Energies 60-600 kev

The scintillations of NaI(Tl) under ion bombardment have been investigated, using monoenergetic H, D, He, and Ne ions in the kinetic energy range 60-600 kev. The light output caused electrical pulses in a photomultiplier tube (Type EMI 5311), which were then sorted in magnitude by means of a single channel pulse height analyzer. Single peaked pulse-height distributions were observed for each ion energy. The most probable pulse height was found to increase linearly with energy for each of the ions. The pulse height (most probable) versus energy lines for H, D, and He were found to extrapolate through the origin, with an experimental uncertainty of perhaps 10 kev in the energy intercept. The slopes of these lines, giving the relative scintillation efficiencies, were observed to be in the ratios 1:0.96±0.03:0.75±0.05:0.54±0.03 for the H, D, He, and Ne ions, respectively. It is concluded that the response of NaI(Tl) to protons is approximately the same as for electrons of the same energy, since an extrapolation of the proton pulse-height curve to 661 kev gave the same pulse height as was observed for the photopeak of the ${\mathrm{Cs}}^{137}$ gamma-ray of that energy. The importance of "hard" (i.e., nuclear) collisions, which may not produce scintillations, is brought forward as a factor which may enter into the explanation of the lowered scintillation efficiency for the heavier ions.