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NCSD provides communication among nuclear criticality safety professionals through the development of standards, the evolution of training methods and materials, the presentation of technical data and procedures, and the creation of specialty publications. In these ways, the division furthers the exchange of technical information on nuclear criticality safety with the ultimate goal of promoting the safe handling of fissionable materials outside reactors.
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Latest News
Can hydrogen be the transportation fuel in an otherwise nuclear economy?
Let’s face it: The global economy should be powered primarily by nuclear power. And it probably will by the end of this century, with a still-significant assist from renewables and hydro. Once nuclear systems are dominant, the costs come down to where gas is now; and when carbon emissions are reduced to a small portion of their present state, it will become obvious that most other sources are only good in niche settings. I mean, why use small modular reactors to load-follow when they can just produce that power instead of buffering it?
Xianfei Wen, Dante Nakazawa, Mat Kastner, Jason Pavlick, Haori Yang
Nuclear Technology | Volume 194 | Number 1 | April 2016 | Pages 117-125
Technical Note | doi.org/10.13182/NT15-113
Articles are hosted by Taylor and Francis Online.
Pulsed photonuclear techniques are commonly used in homeland security and nuclear safeguards applications to achieve enhanced detection sensitivity. For example, photoneutrons generated by a pulse-mode linear accelerator (linac) are commonly utilized to produce characteristic capture gamma rays for the detection of nitrogen-rich explosives. Recently, in an effort to develop innovative systems with increased sensitivity to detect diversion and prevent misuse, the authors proposed to assay used nuclear fuel for its plutonium content using a photofission technique, in support of nuclear material management in the U.S. fuel cycle.
Passive spectroscopy measurements in the presence of intense background from fission products could be very difficult. Focusing on high-energy delayed gamma rays emitted by short-lived products from photofission presents a much more promising solution. However, as discovered in this study, a commercially available standard high-purity germanium (HPGe) preamplifier can be easily saturated for tens of milliseconds after each linac pulse. This greatly reduces the live time of the system especially when the linac repetition rate is high. On the other hand, although significantly reduced by increasing the lower-level threshold, the input count rate can still easily reach 106 cps (counts per second). Developing a gamma spectroscopy system that can handle such a high count rate has been a major challenge.
In this work, a commercial HPGe preamplifier was modified to reduce the saturation time and tail time to improve its high-rate performance in a pulsed photonuclear environment. Results of the modifications were evaluated via both simulations and experiments and proven to be effective without significant degradation of energy resolution. The field-effect transistor (FET) and feedback components were first moved to the warm side to enable the modifications. The saturation time of the preamplifier following a linac pulse was greatly reduced by decreasing the value of the feedback resistor. The effect of reducing the tail time of the output signal was also studied. A traditional trapezoidal shaping approach was then employed to study the impact of the modifications on energy resolution.