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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