1 - IAEA Nuclear Data Services

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The possibilities of threshold reduction in leading edge timing with
pulse transformers between detector and preamplifier have been studied
by means of a fast low-noise preamplifier for the time signals £?_7.
Since this method proved to be insufficient for large volume ger­
manium detectors a timing circuit was developed which is applied be­
tween charge-sensitive preamplifier and main amplifier /~8_7. The
timing system has no influence on the energy resolution of high pre­
cision semiconductor spectrometers.
High-resolution studies with semiconductor counters are now aiming
at an accuracy of 100 eV or better in the particle or gamma-ray
energy /~9_7. For calibration and/or gain stabilisation such measure­
ments require pulse generators of extremely high linearity and
stability. A precision puiser has been developed which has an accuracy
and stability of 20 ppm and better £~"\0_J.
5.2.3 New Spectrometers
For applications in radiative neutron capture spectroscopy a Ge(Li)
anti-comptonspectrometer has been designed for the energy range up
to 3 MeV £3 J. The instrument allows for the special conditions of
(n,y) spectroscopy and gives improved performance compared to pre-
vious devices. The system consists of a planar ^f.9 cm Ge(Li) diode,
a 50 cm dia. x kO cm plastic scintillator and a ^ dia. x 6 Nal (TI)
detector at scattering angle 0 . The anti-coincidence method together
with a ulse-shape discrimination technique very effectively suppress
the compton background under the peaks. The energy resolution is 2.15
keV fwhm at 662 keV.
A new type of internal pair formation spectrometer has been developed
which makes use of the high-resolution capabilities of semiconductor
diodes £'11J'. The instrument consists of two silicon detectors for­
ming a dE/dx + dE telescope for the positron-electron pair and two
Nal (Ti) scintillation counters for detecting the positron annihi­
lation quanta, with present techniques the optimum energy resolution
is 0.07 % at 10 MeV. The spectrometer has been designed for appli­
cation in neutron capture spectroscopy.