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Performance of the Ultra-High Rate Germanium (UHRGe) System

About: The article was published on 2013-12-01 and is currently open access. It has received 2 citations till now. The article focuses on the topics: Germanium.

Summary (2 min read)

2.2 Preamplifiers

  • Preamplifier development was a significant effort for the UHRGe project.
  • The preamplifier development was previously reported in PNNL-22164.
  • The final UHRGe test bed operates two detectors, one instrumented with a modified PGT RG-11 that can operate with feedback voltage swing up to -60V and the other with a custom PNNL high-swing preamp dubbed the XS-11 which can operate with feedback voltages as high as -100V.

2.2.1 Modified RG-11

  • The modification to the RG-11 is rather simple using the proprietary schematics available from the manufacturer 1 .
  • The supply rail for the feedback node in the standard circuit is -24V entering through a current regulating diode (CR2).
  • The supply side of this element was lifted from the -24V rail and connected to an external voltage source operating at up to -60V.
  • The connection to R34 was cut to prevent this high voltage from propagating to the current sense pin on the DB-9 (preamp power) connector.
  • The voltage that can be applied is limited by the ratings of the current regulating diode, an IN5312, and the transistor Q5, a 2N5087 that are rated at 50V.

2.2.2 Modified XS-11

  • Rev. 1 includes fixes for the above defects, re-designs the output stage for significantly lower noise, and includes a novel ultra-linear ultra-low noise JFET source follower shaper "pick-off" amplifier (similar to an oscilloscope input amplifier but far more linear).
  • A totally new printed circuit board layout was required, which was carefully optimized for the required ultra-high signal integrity and precision high speed settling time, while retaining the 125V charge-sensitive amplifier output swing.
  • The charge sensitive amplifier is an entirely discrete transistor design with no integrated circuits as no >70V swing IC amplifiers commercially available are anywhere near as fast as the XS-11.

2.3 Data Acquisition Systems

  • Finally, the authors were able to evaluate a 4DSP VP680 VPX card with an FMC108 digitizer module (16-bit, 250 MHz) system that was obtained as part of a PNNL internally funded Laboratory Directed Research and Development project .
  • This system performed comparably to the AlazarTech system.

2.4 Digital Signal Processing in the FPGA

  • Example of multiple energy filters in parallel.
  • Each event is matched with the longest filter that completes before the next event occurs.

3.1 Results obtained with offline analysis

  • The three plots below are results for operation at incoming event rates in the range of 0.2-1.1 Mcps.
  • Data are analyzed for four different values of fast trigger rise times l as denoted in the legends.
  • The improvement is most pronounced at the highest rates where pileup during this short window is most probable.
  • The length of their shortest filter is dominated by the need to accommodate slow rising pulses in their large HPGe detector.
  • Energy resolution is measured as the full-width at halfmaximum (FWHM) of the 137 Cs 662 keV peak.

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PNNL-23084
Prepared for the U.S. Department of Energy
under Contract DE-AC05-76RL01830
Performance of the Ultra-High Rate
Germanium (UHRGe) System
JE Fast, MP Dion, DC Rodriguez, BA VanDevender, LS Wood, ME Wright
December 2013

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(9/2003)

PNNL-23084
Performance of the Ultra-High Rate
Germanium (UHRGe) System
JE Fast, MP Dion, DC Rodriguez, BA VanDevender,
LS Wood, ME Wright
December 2013
Prepared for
the U.S. Department of Energy
under Contract DE-AC05-76RL01830
Pacific Northwest National Laboratory
Richland, Washington 99352

PNNL-23084
iii
Executive Summary
This report describes the final performance achieved with the detector system developed for the Ultra
High Rate Germanium (UHRGe) project. The system performance has been evaluated at low, moderate
and high rates and includes the performance of real-time analysis algorithms running in the FPGA of the
data acquisition system. This performance is compared to that of offline analyses of streaming waveform
data collected with the same data acquisition system the performance of a commercial Multi-Channel
Analyzer designed for high-resolution spectroscopy applications, the Canberra LYNX.
The UHRGe system was successfully operated at input count rates exceeding 1 Mcps with 40% live time
using a 722 µCi
137
Cs source. Energy resolution at high rate was degraded, but remained better than 1.5%
full-width at half maximum (FWHM). This can be compared with the best performance achieved with the
fast scintillator LaBr of 3.6% FWHM at 662 keV at 70 kcps with relatively little degradation in resolution
at rates up to 2.6 Mcps, but with ~2% gain shifts originating from current flow in the PMTs at high rates
[Nocente]. Future system-level improvements, particularly the utilization of a lower capacitance detector
electrode configuration, are expected to improve the energy resolution at high rates while faster charge
collection times in planar detectors will enable higher live time and throughput. Improvement in
throughput is accompanied by only modest compromise in energy resolution.
In addition to system-level investigations of analog and digital signal processing and analysis algorithms
performed with a small semi-coaxial detector, the UHRGe project investigated the performance of a novel
HPGe pixel detector. This detector is 70 mm in diameter and 10 mm thick with 7 electrodes fabricated by
PhDs Co. This was the first detector of this kind ever produced. This detector was able to achieve an
energy resolution of 2.87 keV FWHM at 662 keV for a collimated source over the pixels and 6.75 keV
FWHM for uniform illumination of the entire detector surface. The corresponding results for the 59 keV
gamma-ray from
241
Am are 1.42 keV and 3.13 keV, respectively. While we have no direct evidence, we
believe that inhomogeneous charge collection (e.g. between low and high field regions), leads to the
broadening of the photoelectric peaks for uniform illumination. The electrode configuration was found to
be non-ideal for high-rate applications as it generates regions of the detector with long drift times. Thus,
while the charge pulses have short durations, as expected from a point contact configuration and desirable
for this application, the long drift times make it impossible to time-order energy depositions at high rates
making it impossible to build events from Compton scattered events. Alternative electrode configurations
have been conceptually developed to eliminate this issue and these will be further studied in the future.
The technology described in this report is being further developed in a new project “PL14-
NDASpentFuel-PD2Ja_FY14” that will be targeted toward the assay of high burnup fuel and its need for
ultra high rate gamma ray spectroscopy to perform isotopic analysis. The Office of Defense Nuclear
Nonproliferation Research and Development (NA-22) is also funding the new project.


Citations
More filters
Journal ArticleDOI
TL;DR: An experimental demonstration of an isotope-sensitive warhead verification protocol capable of detecting tampering with a warhead’s material or geometry with high statistical confidence in realistically attainable measurement times, while simultaneously protecting sensitive warhead design information is presented.
Abstract: Future nuclear arms reduction efforts will require technologies to verify that warheads slated for dismantlement are authentic without revealing any sensitive weapons design information to international inspectors. Despite several decades of research, no technology has met these requirements simultaneously. Recent work by Kemp et al. [Kemp RS, Danagoulian A, Macdonald RR, Vavrek JR (2016) Proc Natl Acad Sci USA 113:8618–8623] has produced a novel physical cryptographic verification protocol that approaches this treaty verification problem by exploiting the isotope-specific nature of nuclear resonance fluorescence (NRF) measurements to verify the authenticity of a warhead. To protect sensitive information, the NRF signal from the warhead is convolved with that of an encryption foil that contains key warhead isotopes in amounts unknown to the inspector. The convolved spectrum from a candidate warhead is statistically compared against that from an authenticated template warhead to determine whether the candidate itself is authentic. Here we report on recent proof-of-concept warhead verification experiments conducted at the Massachusetts Institute of Technology. Using high-purity germanium (HPGe) detectors, we measured NRF spectra from the interrogation of proxy “genuine” and “hoax” objects by a 2.52 MeV endpoint bremsstrahlung beam. The observed differences in NRF intensities near 2.2 MeV indicate that the physical cryptographic protocol can distinguish between proxy genuine and hoax objects with high confidence in realistic measurement times.

21 citations


Cites background from "Performance of the Ultra-High Rate ..."

  • ...This increase may be mitigated by reducing the detector sizes and the operating with more detectors, by optimizing the balance of the detector event rate and the available measurement time, or by taking advantage of future developments of highrate HPGe detectors capable of operating at MHz rates (26)....

    [...]

Journal ArticleDOI
TL;DR: In this article, a high-resolution high-throughput real-time adaptive digital pulse processing system was developed for high count rate gamma-ray spectroscopy applications, which includes a pulse deconvolver, adaptive shaping filter, timing filter, baseline restorer, and pile-up rejecter.
Abstract: A high-resolution high-throughput real-time adaptive digital pulse processing system is developed for high count rate gamma-ray spectroscopy applications. The adaptive digital pulse processing algorithms are implemented on a reconfigurable FPGA and include a pulse deconvolver, adaptive shaping filter, timing filter, baseline restorer, and pile-up rejecter. Digital pulse deconvolution is implemented to reconstruct the original detector signal from the preamplifier signal, which reduces the resolution deterioration due to pulse pile-up. The deconvoluted signal is shaped with a trapezoid filter and the shaping parameter is selected adaptively based on the time separation between successive input pulses. Experimental measurements are performed with a 137 Cs source under varying count-rate conditions and using germanium detectors equipped with resistive feedback and transistor reset preamplifiers (TRP). The results demonstrate that when using a TRP, adaptive digital signal processing allows handling 10 6 counts/s. In addition, the implementation of a deconvolution approach limits resolution deterioration for throughput rates that are 4 to 10 times better than achievable in typical digital and analog gamma-ray spectroscopy systems.

11 citations

References
More filters
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TL;DR: In this paper, an efficient recursive algorithm was proposed for real-time implementation of a shaper that can produce either trapezoidal or triangular pulse shapes. But this algorithm is not suitable for high-count rate pulse spectroscopy.
Abstract: Techniques have been developed for the synthesis of pulse shapes using fast digital schemes in place of the traditional analog methods of pulse shaping. Efficient recursive algorithms have been developed that allow real time implementation of a shaper that can produce either trapezoidal or triangular pulse shapes. Other recursive techniques are presented which allow a synthesis of finite cusp-like shapes. Preliminary experimental tests show potential advantages of using these techniques in high resolution, high count rate pulse spectroscopy.

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TL;DR: The ADONIS (Algorithmic Development framewOrk for Nuclear Instrumentation and Spectrometry) system is a new γ spectrometer which addresses high count rate metrology, developed for count rate up to 106 cps and beyond on HPGe detectors.
Abstract: The ADONIS (Algorithmic Development framewOrk for Nuclear Instrumentation and Spectrometry) system is a new γ spectrometer which addresses high count rate metrology. It has been developed for count rate up to 106 cps and beyond on HPGe detectors. The ADONIS system has been designed in order to: (1) maximize the (pile-up free) output count rate (OCR), (2) achieve both qualitative (i.e. Gaussian shape of spectrum peaks) and quantitative (i.e. reliable metrology) spectrometry, and (3) maintain these results even with time-varying activities. The actual instrument is based on a PC, hosting a PCI acquisition board, together with the standalone analog and digital front end module. The system allows data storage on hard disk for eventual off-line signal analysis. One of the main advantage of such a system is that there is no tuning depending on both input count rate (ICR) and charge collection duration. The accuracy of energy estimation naturally decreases as ICR increases. The same performances as conventional systems are reached at low ICR. For the user no trade-off between resolution and throughput has to be made.

11 citations