The bulk irradiation of materials with 10-30 MeV protons promises to advance the study of radiation damage for fission and fusion power plants. Intermediate energy proton beams can now be dedicated ...to materials irradiation within university-scale laboratories. This paper describes the first such facility, with an Ionetix ION-12SC cyclotron producing 12 MeV proton beams. Samples are mm-scale tensile specimens with thicknesses up to 300 um, mounted to a cooled beam target with control over temperature. A specialized tensile tester for radioactive specimens at high temperature (500+ {\deg}C) and/or vacuum represents the conditions in fission and fusion systems, while a digital image correlation system remotely measures strain. Overall, the facility provides university-scale irradiation and testing capability with intermediate energy protons to complement traditional in-core fission reactor and micro-scale ion irradiation. This facility demonstrates that bulk proton irradiation is a scalable and effective approach for nuclear materials research, down-selection, and qualification.
The detection of special nuclear materials (SNM) in commercial cargoes is a major objective in the field of nuclear security. In this work we investigate the use of two-neutron time-correlations from ...photo-fission using the Prompt Neutrons from Photofission (PNPF) detectors in Passport Systems Inc.'s (PSI) Shielded Nuclear Alarm Resolution (SNAR) platform~\cite{pnpf} for the purpose of detecting \(\sim\)5~kg quantities of fissionable materials in seconds. The goal of this effort was to extend the secondary scan mode of this system to differentiate fissile materials, such as highly enriched uranium, from fissionable materials, such as low enriched and depleted uranium (LEU and DU). Experiments were performed using a variety of material samples, and data were analyzed using the variance-over-mean technique referred to as \(Y_{2F}\) or Feynman-\(\alpha\). Results were compared to computational models to improve our ability to predict system performance for distinguishing fissile materials. Simulations were then combined with empirical formulas to generate receiver operating characteristics (ROC) curves for a variety of shielding scenarios. We show that a 10 second screening with a 200~\(\mu\)A 9~MeV X-ray beam is sufficient to differentiate kilogram quantities of HEU from DU in various shielding scenarios in a standard cargo container.
Photofission is the process in which a nucleus disintegrates into two daughter products after absorbing a photon. Photofission near threshold in actinides is very similar to spontaneous fission in ...terms of the number of emitted decay neutrons and their energy distribution. Most of the neutrons are in the ~2 MeV energy range, and can be efficiently detected with liquid scintillator detectors. Thus, Prompt Neutrons from Photofission (PNPF) near threshold can be used as an excellent tool for the detection of actinides. Since the photofission cross section for most fissionable materials drops to near zero for incident photon energies of less than 6 MeV, a source of photons with a higher energy is needed, for example 9 MeV. At this energy interference from (γ, n) processes is minimal. Photon sources in this energy range are well suited for other non-intrusive inspection applications as well as searching for fissionable materials. Passport Systems, Inc. is currently operating a continuous wave (CW) 9 MeV electron accelerator and an array of liquid scintillator detectors to achieve this goal. Pulse shape discrimination (PSD) techniques are used determine the particle type. The remaining neutrons are also filtered through an in-house developed pileup rejection algorithm. The resulting neutron count is compared with the known background to determine the confidence level for possible shielded Special Nuclear Material identification. Initial testing of this system has been performed and the results will be presented. The results show the utility of a CW photon source as well as the ability to fuse the PNPF data with other data to reduce the dose to cargo, or scan times.
A lead-glass hodoscope calorimeter that was constructed for use in the Jefferson Lab Real Compton Scattering experiment is described. The detector provides a measurement of the coordinates and the ...energy of scattered photons in the GeV energy range with resolutions of 5 mm and 6%/\sqrt(E{\gamma} GeV). Features of both the detector design and its performance in the high luminosity environment during the experiment are presented.
Phys.Rev.Lett.98:152001,2007 Cross-section values for Compton scattering on the proton were measured at 25
kinematic settings over the range s = 5-11 and -t = 2-7 GeV2 with statistical
accuracy of a ...few percent. The scaling power for the s-dependence of the cross
section at fixed center of mass angle was found to be 8.0 +/ 0.2, strongly
inconsistent with the prediction of perturbative QCD. The observed
cross-section values are in fair agreement with the calculations using the
handbag mechanism, in which the external photons couple to a single quark.
Cross-section values for Compton scattering on the proton were measured at 25 kinematic settings over the range s = 5-11 and -t = 2-7 GeV2 with statistical accuracy of a few percent. The scaling ...power for the s-dependence of the cross section at fixed center of mass angle was found to be 8.0 +/ 0.2, strongly inconsistent with the prediction of perturbative QCD. The observed cross-section values are in fair agreement with the calculations using the handbag mechanism, in which the external photons couple to a single quark.
We have observed depolarization effects when high intensity cold neutron beams are incident on alkali-metal-spin-exchange polarized He-3 cells used as neutron spin filters. This was first observed as ...a reduction of the maximum attainable He-3 polarization and was attributed to a decrease of alkali-metal polarization, which led us to directly measure alkali-metal polarization and spin relaxation over a range of neutron fluxes at LANSCE and ILL. The data reveal a new alkali-metal spin-relaxation mechanism that approximately scales as the square root of the neutron capture-flux density incident on the cell. This is consistent with an effect proportional to the recombination-limited ion concentration, but is much larger than expected from earlier work.
Dual energy cargo inspection systems are sensitive to both the area density and the atomic number of an imaged container due to the Z dependence of photon attenuation. The ability to identify cargo ...contents by their atomic number enables improved detection capabilities of illicit materials. This work introduces a novel method for atomic number reconstruction by minimizing the chi-squared error between measured transparency values and a semiempirical transparency model. This method is tested using two Geant4 Monte Carlo simulated radiographic phantoms, demonstrating the ability to obtain accurate material predictions on noisy input images, even in the presence of shielding. Furthermore, we provide a simple procedure for porting this method to a commercial system, requiring an approximate model of the scanner’s beam spectra and detector response, along with only three calibration measurements.
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