Germanium Array For Neutron Induced Excitations Research Articles

Neutron inelastic scattering measurements on Xe136 at En=0.7 to 100 MeV

Experiments searching for neutrinoless double beta decay ($0\nu\beta\beta$) require precise energy calibration and extremely low backgrounds. One of the most popular isotopes for $0\nu\beta\beta$ experiments is $^{136}$Xe. In support of these experiments, the neutron inelastic scattering properties of this isotope have been measured at the GErmanium Array for Neutron Induced Excitations (GEANIE) at the Los Alamos Neutron Science Center. Time-of-flight techniques are utilized with high-purity germanium detectors to search for inelastic scattering $\gamma$ rays for neutron energies between 0.7 and 100 MeV. Limits are set on production of yet-unobserved $\gamma$ rays in the energy range critical for $0\nu\beta\beta$ studies, and measurements are made of multiple $\gamma$-ray production cross sections. In particular, we have measured the production of the 1313 keV $\gamma$ ray which comes from the transition of the first-excited to ground state of $^{136}$Xe. This neutron-induced $\gamma$ line may be useful for a novel energy calibration technique, described in this paper.

αand2p2nemission in fast neutron-induced reactions onNi60

Background: The cross sections for populating the residual nucleus in the reaction ${}_{Z}^{A}\text{X}{(n,x)}_{Z\ensuremath{-}2}^{A\ensuremath{-}4}\text{Y}$ exhibit peaks as a function of incident neutron energy corresponding to the ($n,{n}^{\ensuremath{'}}\ensuremath{\alpha}$) reaction and, at higher energy, to the ($n,2p3n$) reaction. The relative magnitudes of these peaks vary with the $Z$ of the target nucleus.Purpose: Study fast neutron-induced reactions on $^{60}\text{Ni}$. Locate experimentally the nuclear charge region along the line of stability where the cross sections for $\ensuremath{\alpha}$ emission and for $2p2n$ emission in fast neutron-induced reactions are comparable as a further test of reaction models.Methods: Data were taken by using the Germanium Array for Neutron-Induced Excitations. The broad-spectrum pulsed neutron beam of the Los Alamos Neutron Science Center's Weapons Neutron Research facility provided neutrons in the energy range from 1 to 250 MeV. The time-of-flight technique was used to determine the incident-neutron energies.Results: Absolute partial cross sections for production of seven discrete Fe $\ensuremath{\gamma}$ rays populated in $^{60}\text{Ni}(n,\ensuremath{\alpha}/2pxn\ensuremath{\gamma})$ reactions with $2\ensuremath{\le}x\ensuremath{\le}5$ were measured for neutron energies $1\phantom{\rule{4pt}{0ex}}\text{MeV}<{E}_{n}<250\phantom{\rule{4pt}{0ex}}\text{MeV}$. Hauser--Feshbach plus pre-equilibrium theoretical calculations are compared to the experimental results.Conclusions: There is good agreement between experimental results and theoretical predictions at lower neutron energies while discrepancies appear at higher neutron energies. The cross section for producing an isotope in fast neutron-induced reactions on stable targets via $\ensuremath{\alpha}$ emission at the peak of the ($n,\ensuremath{\alpha}$) and ($n,{n}^{\ensuremath{'}}\ensuremath{\alpha}$) reactions is comparable to that for $2p2n$ and $2p3n$ emission at higher incident energies in the nuclear charge region around Fe.

Neutron-inducedγ-ray production cross sections for the first excited-state transitions in20Ne and22Ne

Background: Neutron-induced reactions are a significant concern for experiments that require extremely low levels of radioactive backgrounds. Measurements of $\ensuremath{\gamma}$-ray production cross sections over a wide energy range help to predict and identify neutron backgrounds in these experiments.Purpose: The purpose of this experiment is to determine partial $\ensuremath{\gamma}$-ray production cross sections for neutron-induced reactions in natural neon.Methods: The broad spectrum neutron beam at the Los Alamos Neutron Science Center (LANSCE) was used for the measurement. Gamma rays from neutron-induced reactions were detected using the GErmanium Array for Neutron Induced Excitations (GEANIE).Results: Partial $\ensuremath{\gamma}$-ray cross sections were measured for the first excited-state transitions in ${}^{20}$Ne and ${}^{22}$Ne. The measured cross sections were compared to the talys and CoH${}_{3}$ nuclear reaction codes.Conclusions: These are the first experimental data for ($n,{n}^{\ensuremath{'}}$) reactions in neon. In addition to providing data to aid in the prediction and identification of neutron backgrounds in low-background experiments, these new measurements will help refine cross-section predictions in a mass region where models are not well constrained.

Partialγ-ray production cross sections for (n,xnγ) reactions in natural argon at 1–30 MeV

Background: Neutron-induced backgrounds are a significant concern for experiments that require extremely low levels of radioactive backgrounds such as direct dark matter searches and neutrinoless double-beta decay experiments. Unmeasured neutron scattering cross sections are often accounted for incorrectly in Monte Carlo simulations. Purpose: Determine partial gamma-ray production cross sections for (n,xng) reactions in natural argon for incident neutron energies between 1 and 30 MeV. Methods: The broad spectrum neutron beam at the Los Alamos Neutron Science Center (LANSCE) was used used for the measurement. Neutron energies were determined using time-of-flight and resulting gamma rays from neutron-induced reactions were detected using the GErmanium Array for Neutron Induced Excitations (GEANIE). Results: Partial gamma-ray cross sections were measured for six excited states in Ar-40 and two excited states in Ar-39. Measured (n,xng) cross sections were compared to the TALYS and CoH3 nuclear reaction codes. Conclusions: These new measurements will help to identify potential backgrounds in neutrinoless double-beta decay and dark matter experiments that use argon as a detection medium or shielding. The measurements will also aid in the identification of neutron interactions in these experiments through the detection of gamma rays produced by (n,xng) reactions.

( n,2 n) and ( n,3 n) cross-sections of neutron-induced reactions on 150Sm for [formula omitted] MeV

Cross-section measurements were made of prompt discrete γ -ray production as a function of incident neutron energy ( E n = 1 – 135 MeV ) on a 150Sm sample of 1550 mg / cm 2 of Sm 2 O 3 enriched to 95.6% in 150Sm. Results are compared with enhanced Hauser–Feshbach model calculations including the pre-equilibrium reactions. Energetic neutrons were delivered by the Los Alamos Neutron Science Center facility. The prompt-reaction γ -rays were detected with the compton-suppressed germanium array for neutron-induced excitations (GEANIE). Incident neutron energies were determined by the time-of-flight technique. Excitation functions for thirteen individual γ -rays up to E x = 0.8 MeV in 149Sm and one γ -ray transition between the first excited and ground state in 148Sm were measured. Partial γ -ray cross-sections were calculated using GNASH, an enhanced Hauser–Feshbach statistical nuclear reaction model code, and compared with the experimental results. The particle transmission coefficients were calculated with new systematic “global” optical model potential parameters. A coupled-channels optical model based on a soft rotor model was employed to calculate the particle transmission coefficients. The pre-equilibrium part of the spin-distribution in 150Sm was calculated using the quantum mechanical theory of Feshbach, Kerman, and Koonin (FKK) and incorporated into the GNASH reaction model code. The partial cross-sections for discrete γ -ray cascade paths leading to the ground state in 149Sm and 148Sm have been summed (without double counting) to estimate lower limits for reaction cross-sections. These lower limits are combined with Hauser–Feshbach model calculations to deduce the reaction channel cross-sections. These reaction channel cross-sections agree with previously measured experimental and ENDF/B-VII evaluations.

Gamma-Ray Production Cross Sections in Multiple Channels for Neutron-Induced Reaction on 48Ti for En = 1 to 200 MeV

Prompt γ-ray production cross sections were measured on a 48Ti sample for incident neutron energies from 1 to 200 MeV. Partial γ-ray cross sections for transitions in 45-48Ti, 45-48Sc, and 43-45Ca were determined. The observation of about 130 transitions from 11 different isotopes in the present work provides a demanding test of reaction model calculations, and is the first study in this mass region to extract partial γ-ray cross sections for many different reaction channels over a wide range of incident neutron energies. The neutrons were produced by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center/Weapons Neutron Research facility. The prompt-reaction γ rays were detected with the large-scale Compton-suppressed GErmanium Array for Neutron Induced Excitations (GEANIE). Event neutron energies were determined by the time-of-flight technique. The γ-ray excitation functions were converted to partial γ-ray cross sections and then compared with model calculations using the enhanced GNASH reaction code. Compound nuclear, preequilibrium emission, and direct reaction mechanisms are included. Overall, the model calculations of the partial γ-ray cross sections are in good agreement with measured values.

Effect of preequilibrium spin distribution onTi48+ncross sections

Nuclear model calculations of discrete \ensuremath{\gamma}-ray production cross sections produced in $^{48}\mathrm{Ti}$($n,{n}^{'}{\ensuremath{\gamma}}_{i}$)$^{48}\mathrm{Ti}$ and $^{48}\mathrm{Ti}$($n,2n{\ensuremath{\gamma}}_{i}$)$^{47}\mathrm{Ti}$ reactions were made as a function of incident neutron energy from ${E}_{n}=1$ MeV to 35 MeV and compared with new experimental results using the large-scale Compton-suppressed germanium array for neutron induced excitations (GEANIE) at LANSCE. The Hauser-Feshbach reaction code GNASH, incorporating the spin distribution for the preequilibrium process calculated with the Feshbach-Kerman-Koonin (FKK) quantum-mechanical preequilibrium theory, was used to calculate partial \ensuremath{\gamma}-ray transition cross sections. The comparisons of calculated and experimental data demonstrate that, the FKK model for preequilibrium leads a better overall reproduction of the experimental data above ${E}_{n}=10$ MeV, where preequilibrium processes are important. The FKK calculation predicts a strong reduction in the high-spin state population in $^{48}\mathrm{Ti}$ by inelastic scattering. Population of low-spin states was also affected, however the change in the low-lying 983.5-keV (${2}^{+}$) state production is small because almost all \ensuremath{\gamma}-ray decay cascades feed this transition. In addition, the FKK calculation has a significant impact on the partial \ensuremath{\gamma}-ray transition cross sections for the ($n,2n$) reaction above ${E}_{n}=15$ MeV. The calculated cross sections for high-spin states in $^{47}\mathrm{Ti}$ are reduced, and those from the low-spin states are enhanced, in agreement with the experimental cross section data.

Neutron induced inelastic cross-sections of 150Sm for En = 1–35 MeV

Cross-section measurements were made of prompt γ-ray production as a function of incident neutron energy (En=1–35MeV) on an enriched (95.6%) l50Sm sample. Energetic neutrons were delivered by the Los Alamos National Laboratory spallation neutron source located at the Los Alamos Neutron Science Center (LANSCE) facility. The prompt-reaction γ-rays were detected with the large-scale Compton-suppressed germanium array for neutron induced excitations (GEANIE). Neutron energies were determined by the time-of-flight technique. The γ-ray excitation functions were converted to partial γ-ray cross-sections taking into account the dead-time correction, target thickness, detector efficiency and neutron flux (monitored with an in-line fission chamber). Partial γ-ray cross-sections were predicted using the Hauser–Feshbach statistical reaction code GNASH. Above En∼8MeV, the pre-equilibrium reaction process dominates the inelastic reaction. The spin-distribution transferred in pre-equilibrium neutron induced reactions was calculated using the quantum mechanical theory of Feshbach, Kerman and Koonin (FKK). These pre-equilibrium spin distributions were incorporated into a new version of GNASH and the γ-ray production cross-sections were calculated and compared with experimental data. The difference in the partial γ-ray cross-sections using spin-distributions with and without pre-equilibrium effects is discussed.