Session H12: Mini-Symposium: Applied Low Energy Nuclear Physics

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The efficient and accurate detection of fast neutrons and gamma rays is essential in many instruments developed for nuclear nonproliferation and safeguards applications. Recent advances in silicon photomultiplier (SiPM) technology and new organic scintillator materials have enabled new capabilities for neutron and gamma ray detection with the potential to improve the current systems used in the field. Areas of application include multiplicity counters for fast neutrons emitted by spontaneous and induced fission of actinides, and imaging systems used for detecting, locating, and characterizing fission sources. Our group has demonstrated pulse shape discrimination (i.e., the ability to distinguish neutron-induced pulses from gamma ray-induced pulses) with stilbene detectors at low neutron energies (a few hundred keV). We also developed arrays of organic fast neutron and gamma ray detectors (up to 40 detectors) operated in time-coincidence. In this work, we show the application of these arrays for multiplicity, imaging, and nuclear fission studies.   

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Radioisotopes for targeted alpha therapy are of increased interest of late at the Cyclotron Institute at Texas A{\&}M University. Astatine-211 shows great promise for cancer treatment, and its chemistry is not very well understood. Current efforts focus on the development of bismuth targets for astatine-211 production via the Bi-209($\alpha $,2n)At-211 nuclear reaction, followed by a chemical separation of the astatine-211 from the bulk bismuth. Other alpha-emitting radionuclides may also be produced using heavy ion beams. The state of the program will be discussed.   

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The properties of astatine-211 make it a great candidate for targeted alpha therapy for cancer due to its short half-life (7.2 h) and non-toxic decay pathway. However, its natural occurrence is miniscule, and is produced in useful quantities via the $^{\mathrm{209}}$Bi($\alpha $,2n)$^{\mathrm{211}}$At using a 28.5 MeV alpha beam. The Texas A{\&}M Cyclotron Institute has recently joined this effort to produce astatine-211 in a location proximal to major cancer research centers. It is useful to have an accurate procedure to determine the total activity of the astatine produced prior to removing the target from the irradiation chamber. Data from a high-purity germanium (HPGe) detector, a dose calibrator, and a cadmium-telluride (CdTe) detector are being cross-calibrated to determine the total astatine activity in the target chamber using the CdTe detector prior to extraction. This information allows for rapid determination of the quantity of astatine produced.   

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$^{40}$K is a ubiquitous background for many low-energy physics experiments and for many low-energy exotic physics searches. But $^{40}$K has positive uses too, it forms the basis of K-Ar geochronological dating techniques and it allows study of a third-forbidden unique $\beta$-decay. The precision of $^{40}$K $\beta$-decay information is an important uncertainty in low energy exotic physics searches and is one of the limits on the K-Ar geochronology dating technique accuracy and precison. The $^{40}$K $\beta$-decay information uncertainty is dominated by one branch of the \textsuperscript{40}K decay that has never been experimentally measured, the electron capture decay directly to the ground state of $^{40}$Ar. This unknown decay path impacts the estimated amount of $^{40}$K based on the number of measured 1461 keV $\gamma$ rays at the few percent level and it affects the K-Ar geochronology dating technique at the same level. With data taken at Oak Ridge National Laboratory, this small decay branch was measured by the KDK (potassium decay) collaboration by integrating an X-ray detector into the Modular Total Absorption Spectrometer (MTAS). We report details of the technique used to measure this decay branch, the expected sensitivity, and the status of the analysis.   

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The National Ignition Facility at Lawrence Livermore National Laboratory uses $^{86}$Kr as a diagnostic tool to measure the neutron flux produced by fusion reactions. As krypton is chemically inert, it can be implanted directly into the fuel capsule, and the reaction products can be measured to determine the flux of fusion neutrons. $^{86}$Kr cross sections are also a valuable tool for studying both the $^{85}$Kr branching point in the s-process and determining the neutron flux in stars. In this work, experimental data on the neutron production, radiative capture, inelastic scattering and total cross sections of $^{86}$Kr were used in conjunction with the fast region nuclear reaction code EMPIRE and a new resonance region evaluation to produce a new evaluation of neutron-induced reactions on $^{86}$Kr. We adopted a slightly deformed Koning-Delaroche optical model potential to provide a rigid-rotor coupling scheme, along with corrections to fill missing experimental information on the structure and decay of $^{86}$Kr. The evaluated cross sections are in good agreement with the available experimental data.   

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With the discovery of the pandemonium effect, the necessity of total absorption measurements of beta decay quickly became apparent. Of particular interest in the field of nuclear energy are accurate measurements of the beta feeding intensities of fission products. To this end, the beta feeding intensities of 104Mo were measured using the Modular Total Absorption Spectrometer (MTAS) at Argonne National Laboratory (ANL). Due to a complicated level scheme of the daughter nucleus, 104Tc, this isotope reveals a unique need to study low lying states populated by beta decay. This presentation will present the difference between existing high precision measurements and our total absorption measurements. Additional attention will be given to the gamma spectrum at low lying levels including a discussion of the challenges of disentangling multi-gamma cascades with individual gamma energies less than 150 keV and the presence of conversion electrons.   

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In an extensive data mining effort we retrieved experimental data for $^{\mathrm{238}}$U neutron-induced fission product yields (FYs) spanning over 60 years. In the majority of the experiments FYs were measured with the activation technique, and - as a consequence of its experimental limitations - more than 75\% of the data points report cumulative FYs. In this work, we studied these experimental data to identify how the incoming neutron energy affects the competition of fission modes in $^{\mathrm{238}}$U, especially around symmetric fission, and we compared experiments with the prediction from the GEF model (one of the leading phenomenological fission models, developed by K.H.~Schimdt, B.~Jurado \emph{et al.}). The independent FYs from GEF were complemented with isomeric yield ratios, and converted to cumulative FYs using information from the ENDF/B-VIII.0 decay data sub-library, in order to allow a direct comparison with experimental cumulative FYs. The agreement between the model and experiments is excellent around symmetric fission. As part of this work, the energy dependence of the isomeric yield ratios was also studied, and it was compared with values in the latest evaluated FY library, and with theory.