Session FH: Mini-Symposium on Applications of Nuclear Physics II

Opportunities for applied measurements using the PROSPECT antineutrino detector: reactor physics and safeguards

Disagreement of reactor antineutrino spectrum and flux measurements with updated predictions indicates that we have much to learn about the complicated processes underlying antineutrino production in reactors, as well as hinting at new physics. A number of new efforts seek to address these questions, including the PROSPECT experiment planned at the HFIR research reactor. In addition to greatly advancing our understanding of reactor antineutrino emissions, PROSPECT can support a rich applied physics program. The detection technology developed for PROSPECT will enable precision antineutrino spectrum measurements close to essentially any reactor type. Here we describe how such measurements provide opportunities to probe fissile isotope and fission daughter distributions, and their potential use for reactor physics and safeguards applications.   

New Decay Data Sub-library for Calculation of Nuclear Reactors Antineutrino Spectra

The ENDF/B-VII.1 decay data sub-library contains up-to-date decay properties for all known nuclides and can be used in a wide variety of applications such as decay heat, delayed nu-bar and astrophysics. We have recently completed an upgrade to the ENDF/B-VII.1 decay data sub-library in order to better calculate antineutrino spectra from fission of actinide nuclides. This sub-library has been used to identify the main contributors to the antineutrino spectra as well as to derive a systematic behavior of the energy integrated spectra similar to that of the beta-delayed neutron multiplicities. The main improvements have been the use of the TAGS data from Algora et al and Greenwood et al, as well as some of the single beta spectrum data from Rudstam et al to obtain beta minus level feedings. Additionally, we have calculated the antineutrino spectra for neutron energies higher than thermal, needed for highly-enriched uranium cores, such as the HFIR in ORNL that will be used in the PROSPECT experiment. These calculations are relevant since the high precision beta spectra which are used in many antineutrino calculations were measured at thermal energies. The impact of the fission yield data on these calculations will be discussed.   

Long Distance Reactor Antineutrino Flux Monitoring

The feasibility of antineutrino detection as an unambiguous and unshieldable way to detect the presence of distant nuclear reactors has been studied. While KamLAND provided a proof of concept for long distance antineutrino detection, the feasibility of detecting single reactors at distances greater than 100km has not yet been established. Even larger detectors than KamLAND would be required for such a project. Considerations such as light attenuation, environmental impact and cost, which favor water as a detection medium, become more important as detectors get larger. We have studied both the sensitivity of water based detection media as a monitoring tool, and the scientific impact such detectors might provide. A next generation water based detector may be able to contribute to important questions in neutrino physics, such as supernova neutrinos, sterile neutrino oscillations, and non standard electroweak interactions (using a nearby compact accelerator source), while also providing a highly sensitive, and inherently unshieldable reactor monitoring tool to the non proliferation community. In this talk I will present the predicted performance of an experimental non proliferation and high-energy physics program.   

Detection of special nuclear material by observation of delayed neutrons with a novel fast neutron composite detector

Detection of shielded special nuclear material is crucial to countering nuclear terrorism and proliferation, but its detection is challenging. By observing the emission of delayed neutrons, which is a unique signature of nuclear fission, the presence of nuclear material can be inferred. We report on the observation of delayed neutrons from natural uranium by using monoenergetic photons and neutrons to induce fission. An interrogating beam of 4.4 MeV and 15.1 MeV gamma-rays and neutrons was produced using the $^{11}$B(d,n-$\gamma)^{12}$C reaction and used to probe different targets. Neutron detectors with complementary Cherenkov detectors then discriminate material undergoing fission. A Li-doped glass-polymer composite neutron detector was used, which displays excellent n/$\gamma$ discrimination even at low energies, to observe delayed neutrons from uranium fission. Delayed neutrons have relatively low energies ($\sim $0.5 MeV) compared to prompt neutrons, which makes them difficult to detect using recoil-based detectors. Neutrons were counted and timed after the beam was turned off to observe the characteristic decaying time profile of delayed neutrons. The expected decay of neutron emission rate is in agreement with the common parametrization into six delayed neutron groups.   

Detection of Shielded Special Nuclear Material With a Cherenkov-Based Transmission Imaging System

Detection of shielded special nuclear material, SSNM, while in transit, offers a unique challenge. Typical cargo imaging systems are Bremsstrahlung-based and cause an abundance of unnecessary signal in the detectors and doses to the cargo contents and surroundings. Active interrogation with dual monoenergetic photons can unveil the illicit material when coupled with a high-contrast imaging system while imparting significantly less dose to the contents. Cherenkov detectors offer speed, resilience, inherent energy threshold rejection, directionality and scalability beyond the capability of most scintillators. High energy resolution is not a priority when using two well separated gamma rays, 4.4 and 15.1 MeV, generated from low energy nuclear reactions such as $^{11}$B(d,n-$\gamma$)$^{12}$C. These gamma rays offer a measure of the effective atomic number, Z, of the cargo by taking advantage of the large difference in photon interaction cross sections, Compton scattering and pair production. This imaging system will be coupled to neutron detectors to provide unique signature of SNM by monitoring delayed neutrons. Our experiments confirm that the Cherenkov imaging system can be used with the monoenergetic source to relate transmission and atomic number of the scanned material.   

Verification of Minimum Detectable Activity for Radiological Threat Source Search

The Department of Homeland Security's Domestic Nuclear Detection Office is working to develop advanced technologies that will improve the ability to detect, localize, and identify radiological and nuclear sources from airborne platforms. The Airborne Radiological Enhanced-sensor System (ARES) program is developing advanced data fusion algorithms for analyzing data from a helicopter-mounted radiation detector. This detector platform provides a rapid, wide-area assessment of radiological conditions at ground level. The NSCRAD (Nuisance-rejection Spectral Comparison Ratios for Anomaly Detection) algorithm was developed to distinguish low-count sources of interest from benign naturally occurring radiation and irrelevant nuisance sources. It uses a number of broad, overlapping regions of interest to statistically compare each newly measured spectrum with the current estimate for the background to identify anomalies. We recently developed a method to estimate the minimum detectable activity (MDA) of NSCRAD in real time. We present this method here and report on the MDA verification using both laboratory measurements and simulated injects on measured backgrounds at or near the detection limits.   

Precise Nuclear Data Measurements Possible with the NIFFTE fissionTPC for Advanced Reactor Designs

The Neutron Induced Fission Fragment Tracking Experiment (NIFFTE) Collaboration has applied the proven technology of Time Projection Chambers (TPC) to the task of precisely measuring fission cross sections. With the NIFFTE fission TPC, precise measurements have been made during the last year at the Los Alamos Neutron Science Center from both U-235 and Pu-239 targets. The exquisite tracking capabilities of this device allow the full reconstruction of charged particles produced by neutron beam induced fissions from a thin central target. The wealth of information gained from this approach will allow systematics to be controlled at the level of 1\%. The fissionTPC performance will be presented. These results are critical to the development of advanced uranium-fueled reactors. However, there are clear advantages to developing thorium-fueled reactors such as Liquid Fluoride Thorium Reactors over uranium-fueled reactors. These advantages include improved reactor safety, minimizing radioactive waste, improved reactor efficiency, and enhanced proliferation resistance. The potential for using the fissionTPC to measure needed cross sections important to the development of thorium-fueled reactors will also be discussed.   

Feasibility of Colliding-beam fast-fission reactor via $^{238}$U$^{80+}+^{238}$U$^{80+}\to $4 FF$+$ 5n $+$ 430 MeV beam with suppressed plutonium and direct conversion of fission fragment (FF) energy into electricity and/or Rocket propellant with high specific impulse

Uranium-uranium colliding beam experiment$^{1}$, used fully ionized $^{238}$U$^{92+}$ at energy 100GeV$\to \leftarrow $100 GeV, has measured total $\sigma = $ 487 b. Reaction rate of colliding beams is proportional to neutron flux-\textit{squared}. First functional Auto-Collider$^{3-6}$, a compact Migma IV, 1 m in diameter, had self-colliding deuterons, D$^{+}$, of 725 KeV$\to \leftarrow $725 KeV, resulting in copious production of T and $^{3}$He. U$+$U Autocollider\textit{ ``EXYDER}'' will use strong-focusing magnet$^{7}$, which would increase reaction rate by 10$^{4}$. 80 times ionized U ions accelerated through 3 MV accelerator, will collide beam 240 MeV$\to \leftarrow $240 MeV. Reaction is: $^{238}$U$^{80+\, }+ \quad^{238}$U$^{80+\, }\to $ 4 FF$+$ 5n $+$ 430 MeV. Using a simple model$^{1}$ fission $\sigma_{f}$ $\sim$ 100 b. Suppression of Pu by a factor of 10$^{6}$ will be achieved because NO thermal neutron fission can take place; only fast, 1 -3 MeV, where $\sigma_{abs}$ is negligible. Direct conversion of 95{\%} of 430 MeV produced is carried by electrically charged FFs which are magnetically funneled for direct conversion of energy of FFs \textit{via} electrostatic decelerators$^{4,\, 11}$. 90{\%} of 930 MeV is electrically recoverable. Depending on the assumptions, we project \underline {electric} power density production of 20 to 200 MW$_{e}$ m$^{-3}$, equivalent to Thermal 1.3 -- 13 GW$_{th}$m$^{-3}$. If one-half of unburned U is used for propulsion while rest powers system, heavy FF ion mass provides specific impulse Isp$=$10$^{6}$ sec., 10$^{3}$ times higher than current rocket engines.