Applied Nuclear Physics

Principal investigators: E.B. Norman, Lawrence Berkeley National Laboratory, and S.G. Prussin

Following the demonstration that delayed fission product gamma rays may be a robust signature for detecting fissionable materials embedded in thick cargos, an effort has been mounted to incorporate fission products and their gamma rays spectra directly into a Monte Carlo code for studies of system designs and sensitivity estimates. To provide a benchmark for the quality of such calculations, we are designing a well-characterized experimental scheme and will use it to measure the delayed gamma ray spectra from thermal fission of 235U and 239Pu under carefully controlled irradiation and decay conditions.

Supported by the Department of Homeland Security

In conjunction with senior scientists from the Lawrence Livermore and Lawrence Berkeley National Laboratories, we are assisting in a range of experimental and calculational activites designed to define the effectiveness of delayed fission gamma rays as a signature of the presence of fissionable materials embedded in thick cargos. The experimental measurements are designed to understand the practical issues of interferences, the characteristics of collimated neutron sources as the interrogating probe, etc. The calculational activities include support of system design and construction, the transport of the delayed gamma rays through various media, etc.

A five-year multidisciplinary program on the Berkeley campus called DoNuTS (Domestic Nuclear Threat Security) is directed at development of technology for detecting clandestine movements of fissionable material which might have fallen into the hands of terrorists. The program includes research in the Departments of Nuclear Engineering, Physics, Industrial Engineering and Operations Research as well as collaboration with national laboratories and industrial partners. The program has four primary thrust areas: (1) Advanced Materials for Radiation Detectors, (2) Data Mining, Pattern Recognition, and Machine Vision techniques for nuclear threat detection, (3) Nuclear Data, and (4) Signals and Networks for Detector Systems. The goal of this program is to develop a viable system for detecting Special Nuclear Material (SNM) in cargo containers and other modes of transport and to develop a workforce trained in this area for the future needs of government and industry.

As a part of the DoNuTS project, UCB has acquired a 3.5 MeV Pelletron accelerator from the Department of Homeland Security and is in the process of installing this device in the Nucleonics Laboratory on the Berkeley campus. This device will be used for fundamental measurements of nuclear properties of relevance to Homeland Security needs. Experiments to measure Nuclear Resonance Fluorescence (NRF) properties of SNM and the development of a photon source for SNM detection are planned.

This project aims at demonstrating Compton imaging based on the information provided by the measurement of the Compton-scatter induced electron. Being able to measure the scatter direction of the scattered electron will allow us to deduce the incident direction of the gamma ray on event-by-event basis increasing the sensitivity over conventional Compton imaging systems significantly. We have recently demonstrated – for the first time – electron-tracking based Compton imaging employing semiconductor detectors. This represents an important breakthrough in the development of a new generation of highly sensitive gamma-ray imaging instruments, particularly for energies above a few hundred keV.

Homeland Security, ranging from arrays of distributed small sensors (~ 10 cm3) to large-scale systems (~ 1 m3) mounted on trucks and more recently aerial platforms as well. Gamma-ray imaging is currently being evaluated for the detection, identification, and localization of nuclear materials for homeland security. In order to fully explore the potential of gamma-ray imaging in realistic environments, our efforts are divided into two aspects: (1) Evaluate and develop new and improved imaging technologies; (2) Obtain background data experimentally for a wide range of environments, time, and locations and develop models to predict these backgrounds based on complementary information. Our ultimate goal is the development and demonstration of a “Nuclear Street View” that enables users to “see” objects in three dimensions merged with a radiation map, also in three dimensions. The reconstruction of three-dimensional radiation maps is being developed in some of our other projects not only for homeland security but also for nuclear safeguards and nuclear physics applications. The reconstruction of three-dimensional objects based on (two-dimensional) video information has been developed previously by other groups, however, will be used here in connection with mapping to radiation fields for the first time.

We are developing technologies to reduce electronics noise in low background HPGe detector based systems to enable new physics research and applications, which have not been possible before. The underlying technology is based on very small (≤1mm2) so-called point contacts, which provides the potential to provide very low noise in medium-sized (~1 kg) HPGe detectors. We recently have demonstrated so-called p-type point contact (PPC) Ge detector operated with a noise resolution of 85 eV (FWHM). We believe that we can reduce this energy resolution value even further with a goal to realize an energy threshold of 100 eV or less. Such a low threshold combined with a ~kg scale Ge detector should allow us to observe – for the first time- the process of coherent neutrino scattering. Such an observation is not only important for our fundamental understanding of the world around us but will enable the detection of neutrinos with unprecedented sensitivity. For example, the antineutrinos emitted in the nuclear fission reactors could be measured indicating the power level and potentially the amount of nuclear materials used in the power plant as part of safeguards efforts to protect and monitor nuclear materials.