Dr. Tovey et al., MEASUREMENT OF SCINTILLATION EFFICIENCIES AND PULSE-SHAPES FOR NUCLEAR RECOILS IN NAI(TL) AND CAF2(EU) AT LOW ENERGIES FOR DARK-MATTER EXPERIMENTS, Physics letters. Section B, 433(1-2), 1998, pp. 150-155
Measurements have been performed with a 2.55 MeV mono-energetic neutro
n beam of relative scintillation efficiency and pulse-shape for nuclea
r and electron recoils in NaI(T1) and CaF2(Eu). Scintillation efficien
cies in NaI(T1) relative to 60 keV gamma events were found to be 27.5
+/- 1.8% for Na recoils (recoil energy E-rec > 4 keV) and 8.6 +/- 0.7%
for I recoils (E-rec > 10 keV). Relative scintillation efficiencies i
n CaF2(Eu) for Ca and F recoils show some evidence for a fall with ene
rgy (17% to 8% for F) for 10 keV < E-rec < 100 keV. Pulse-shape analys
is of NaI(Tl) data gives a mean photo-electron arrival time ((t) over
bar(i)) of 263 +/- 15 ns for Na events (visible energy E-vis in the ra
nge 2-8 keV and 272 +/- 10 ns for I events (2 keV < E-vis < 5 keV). Th
e [(t) over bar(i)] of 4 keV < E-vis < 54 keV electron events in NaI(T
I) is found to rise with energy (320 ns to 440 ns). Similar analysis o
f CaF2(Eu) data shows [(t) over bar(i)] for 2 keV < E,, < 33 keV Ca, F
and electron events to rise with energy (660 ns to 850 ns) with no ev
idence for pulse-shape differences. (C) 1998 Elsevier Science B.V. All
rights reserved.