Advanced front-end electronics to extend the pulse height spectroscopy range well beyond the ADC analog input range
Professor Gh. Pascovici
Institute of Nuclear Physics,
University of Cologne,
GERMANY
E-mail: gp@ikp.uni-koeln.de
Co-Authors:
A. Pullia, F. Zocca
University of Milan, Department of Physics and INFN-Sezione di Milano, ITALY
D. Bazzacco
INFN-Sezione di Padova,
ITALY
Abstract: Using innovative front-end electronics developed for a
36_fold segmented High-Purity Germanium detectors we were able to
significantly extend the range of spectroscopic measurements well beyond the
fast pipe-line ADC limit. To do that above a certain threshold we are
switching automatically from a standard pulse height analysis to a
Time_over_Threshold [TOT] method (Wilkinson like) and combined we obtain an
unprecedented intrinsic dynamic range as large as 100 dB.
To achieve that performance the structure of the front-end electronics
consists of a very low noise and very high dynamic range charge-sensitive
preamplifier followed by a passive pole-zero cancellation circuit including a
highly accurate Fast_Reset circuit controlled by a fast comparator and zero
crossing detector. A differential buffer Gain/ Anti-Aliasing stage is used to
pass the signal to a 14 bit 100MHz pipe-line ADC. With a thick HP-Germanium
detector we could extend the initial dynamic range measured with a standard
pulse height spectroscopic method from 3 keV - 10 MeV to 3 keV - 170 MeV
(equivalent gamma energy, measured with large pulser signal). The intrinsic
energy resolution (i.e. electronic noise) is 900 eV @ 30 pF detector capacity.
The energy resolution above the comparator threshold measured with the present
TOT method is below 0.08 % @ 100 MeV (equivalent gamma energy i.e. pulse
signals with amplitudes about 10 times higher than the ADC analog input
range). The measured energy resolution is in very good agreement with
analytical calculation and with inter-comparison measurements with normal
pulse height mode only and reduced electronic gain.
The new time-variant circuit technique, proposed for nuclear pulse
spectroscopy, permits a substantial improvement of the energy measurement
dynamic range. This technique can be directly used in many other experimental
pulse spectroscopic methods where the sensor is in a first approximation an
equivalent capacitance.
Brief
Biography of the Speaker:
Gheorghe
Pascovici graduated in 1965 the Polytechnic Institute, Bucharest Faculty of
Electronics and Telecommunications in the field of Engineering Physics. From
1965 to 1989 he worked as scientific researcher at the Institute of Atomic
Physics and from 1989 to 1993 as Director General of the Institute of Atomic
Physics and Ministry Secretary of State he coordinated the Romanian National
Research Program in the field of physics and applied physics. Since 1994 he is
with Institute of Nuclear Physics, University of Cologne, Germany coordinating
the nuclear electronics department. He received the PhD degree in Nuclear
Electronics field in 1976 from the Institute of Atomic Physics, Bucharest.
Fields of interest: - experimental nuclear structure physics, - nuclear
instruments and methods mainly front end electronics in nuclear spectroscopy,
both gamma and charged particles, - pulsing systems for Cyclotron and Tandem
particle accelerators. Key results: - Main coordinator of the nuclear
electronics design for the Miniball Array of Segmented HP-Ge Detectors (CERN),
worldwide first large array of detectors implementing a digital solution (DGF)
in the field of high resolution gamma spectrometry, - Development of the front
end electronics for the core signals in the frame of AGATA Project (Advanced
Gamma Tracking Array, EU Collaboration) and - for charged particles in the
frame of LYCCA Project (GSI Collaboration). He is co-author of more then 100
publications in peer-review journals in the field of nuclear spectroscopy and
nuclear instruments and methods.
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