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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

A portable and monoenergetic 24 keV neutron source based on 124Sb-9Be photoneutrons and an iron filter

A portable monoenergetic 24 keV neutron source based on the 124Sb-9Be photoneutron reaction and an iron filter has been constructed and characterized. The coincidence of the neutron energy from SbBe and the low interaction cross-section with iron (mean free path up to 29 cm) makes pure iron specially suited to shield against gamma rays from 124Sb decays while letting through the neutrons. To increase the 124Sb activity and thus the neutron flux, a >1 GBq 124Sb source was produced by irradiating a natural Sb metal pellet with a high flux of thermal neutrons in a nuclear reactor. The design of the source shielding structure makes for easy transportation and deployment. A hydrogen gas proportional counter is used to characterize the neutrons emitted by the source and a NaI detector is used for gamma background characterization. At the exit opening of the neutron beam, the characterization determined the neutron flux in the energy range 20–25 keV to be 6.00±0.30 neutrons per cm2 per second and the total gamma flux to be 245±8 gammas per cm2 per second (numbers scaled to 1 GBq activity of the 124Sb source). A liquid scintillator detector is demonstrated to be sensitive to neutrons with incident kinetic energies from 8 to 17 keV, so it can be paired with the source as a backing detector for neutron scattering calibration experiments. This photoneutron source provides a good tool for in-situ low energy nuclear recoil calibration for dark matter experiments and coherent elastic neutrino-nucleus scattering experiments.

Dark Matter detectors (WIMPs, axions, etc.)↗
DOE OSTI2015

Monte Carlo simulations of photoneutron activation in a medical LINAC

The first step of the present study was to simulate the γ-radioactivity produced by photoneutrons in the treatment head of a decommissioned medical LINAC. These results, obtained with MCNPX and CINDER'90, are then compared with γ-ray spectrometric measurements of parts of the treatment head. Our ultimate objective is to simulate the associated production by photonuclear reactions of pure β-emitters, which are more difficult to access experimentally than the γ-ray emitters. (authors)

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Short-Pulse Photoneutron Production on Beryllium Using the Mercury Pulsed Power X-ray Source

An x-ray beam can produce neutrons using beryllium as a photoneutron converter because of the relatively low 9 Be(ɤ,n) reaction energy threshold. Previous photoneutron production simulations have focused on using a linear accelerator and heavy water to generate photoneutrons for potential medical therapies. This experimental work focused on creating a short, intense neutron pulse using the Mercury pulsed power machine at the U.S. Naval Research Laboratory, which fired a Bremsstrahlung photon beam with an energy endpoint of 4.8 MeV. Several independent detector systems were included in the experiment to measure both the characteristics of the x-ray pulse and resulting photoneutrons. We discovered the neutron pulse follows the time history of the x-ray pulse, enabling neutron pulses as short as 30 ns with less than 10% shot-to-shot variation. The approach offers a high-flux of neutrons with a higher end-point energy than using a heavy water converter. Previous experiments at Mercury have generated fission neutrons using a higher x-ray endpoint and 238 U(n,f). Results indicate that with an optimized diode and beryllium converter target design, neutron production could be further increased.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

Measurement of Photoneutrons from Depleted Uranium and Comparison Study Using MCNPX-PoliMi

High-energy photon interrogation is a nondestructive technique that is used to detect special nuclear materials and characterize nuclear waste. The development of such systems is complex and requires Monte Carlo simulations to optimize system performance. Monte Carlo simulations rely on various scattering, absorption, and photonuclear cross-section data. While the scattering and absorption cross-section data have been extensively studied and validated with experiments, the results obtained from photonuclear simulations are often found to underpredict measured results, indicating uncertainties in the photonuclear cross sections themselves. Thus, there is a need for new measured results that can be used to quantify underpredictions in simulations using photonuclear cross-section data. In the present work, we interrogated depleted uranium with a 9-MV electron linac and detected photoneutrons with trans-stilbene organic scintillators. The measurement of photoneutrons with organic scintillators is challenging due to the presence of the intense photon flux, which causes issues such as pulse pile-up, detector saturation, and poor signal-to-background ratio. To mitigate these challenges, we used iron and polyethylene shielding of varying thicknesses around the depleted uranium target and a neural network–based digital pulse processing algorithm to recover neutron and photon information from piled-up events. Our goal was to compare the measured photoneutron count rate with the simulated rate obtained using the MCNPX-PoliMi transport code. For a light output window of 0.28 to 2.67 MeVee (1.66- to 6.85-MeV proton recoil energy), we found that the simulated count rate obtained using the ENDF/B-VII photonuclear cross-section library underpredicts the measured rate by 32.8% 3.2%. Additionally, we compared the simulated and measured photoneutron light output distributions. For the least thicknesses of shielding, the simulation was found to underpredict measurements in the 0.70- to 2.67-MeVee light output window. For the greatest thicknesses of shielding, the simulation was found to underpredict the measurement across the entire light output window of 0.28 to 2.67 MeVee.

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
DOE OSTI2019

Photoneutron reaction cross section measurements on Mo 94 and Zr 90 relevant to the p -process nucleosynthesis

The photodisintegration cross sections for the 94 Mo(γ,n) and 90 Zr(γ,n) reactions have been experimentally investigated with quasi-monochromatic photon beams at the High Intensity γ-ray Source (HIγS) facility of the Triangle Universities Nuclear Laboratory (TUNL). The energy dependence of the photoneutron reaction cross sections was measured with high precision from the respective neutron emission thresholds up to 13.5 MeV. Here, these measurements contribute to a broader investigation of nuclear reactions relevant to the understanding of the p-process nucleosynthesis. The results are compared with the predictions of Hauser-Feshbach statistical model calculations using two different models for the dipole γ-ray strength function. Lastly, the resulting 94 Mo(γ,n) and 90 Zr(γ,n) photoneutron stellar reaction rates as a function of temperature in the typical range of interest for the p-process nucleosynthesis show how sensitive the photoneutron stellar reaction rate can be to the experimental data in the vicinity of the neutron threshold.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Photoneutron reactions in astrophysics

Among key problems in nuclear astrophysics, that of obtaining deeper insight into the mechanism of synthesis of chemical elements is of paramount importance. The majority of heavy elements existing in nature are produced in stars via radiative neutron capture in so-called s- and r processes, which are, respectively, slow and fast, in relation to competing β{sup −}-decay processes. At the same time, we know 35 neutron-deficient so-called bypassed p-nuclei that lie between {sup 74}Se and {sup 196}Hg and which cannot originate from the aforementioned s- and r-processes. Their production is possible in (γ, n), (γ, p), or (γ, α) photonuclear reactions. In view of this, data on photoneutron reactions play an important role in predicting and describing processes leading to the production of p-nuclei. Interest in determining cross sections for photoneutron reactions in the threshold energy region, which is of particular importance for astrophysics, has grown substantially in recent years. The use of modern sources of quasimonoenergetic photons obtained in processes of inverse Compton laser-radiation scattering on relativistic electronsmakes it possible to reveal rather interesting special features of respective cross sections, manifestations of pygmy E1 and M1 resonances, or the production of nuclei in isomeric states, on one hand, and to revisit the problem of systematic discrepancies between data on reaction cross sections from experiments of different types, on the other hand. Data obtained on the basis of our new experimental-theoretical approach to evaluating cross sections for partial photoneutron reactions are invoked in considering these problems.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Photoneutron reactions in the range of giant dipole resonance

The well-known significant systematic disagreements between data on partial photoneutron reaction cross sections obtained in experiments using quasimonoenergetic annihilation photons and bremsstrahlung were investigated using objective physical criteria of data reliability. It was shown that many data are not reliable because of significant systematic uncertainties of the photoneutron multiplicity sorting methods used. The experimental-theoretical method for evaluation of reliable partial reaction cross sections was proposed and many new data were obtained.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Study of the Thermal Neutron Spectrum of the W-Be Photoneutron Source of the INR RAS

The possibility of reconstructing the neutron flux density of a W-Be photoneutron source using neutron activation analysis of Ag, Mn, Fe, Mn, and Ti samples is considered. The use of simple functions as AE{sup –B}, describing particular regions of the spectrum, as a reconstruction option is discussed. The dependence of the deviation of the measured reaction rates on those calculated in this study on the parameters of approximating functions is investigated. The convergence of the reconstruction results is obtained by increasing the amount of experimental data. This reconstruction method can be used for the operational measurement of the thermal neutron flux density of the photoneutron source and for the optimization of the source parameters.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Computational study of tungsten and depleted uranium photoneutron targets for a 20 MeV electron linear accelerator

Neutron production can be realized with a high energy electron linear accelerator by using Bremsstrahlung and photoneutron converters. In this study, Monte Carlo N-Particle Code (MCNP) was used to evaluate potential photonuclear target designs for a high energy electron linear accelerator for applications such as neutron radiography and neutron resonance spectroscopy. A computational model was developed to inform a target design that would yield a high number of neutrons. It consists of a 20 MeV electron beam incident on a Bremsstrahlung target and a photonuclear target to generate neutrons. This computational model showed that a thickness of 0.75 inches for both tungsten and depleted uranium yields the most neutrons from photoneutron reactions. Saturation in the total number of generated neutrons was observed at over 0.75-inch thickness for both evaluated materials. Depleted uranium yielded approximately twice the number of neutrons overall compared to tungsten. The highest neutron surface flux for Depleted Uranium was 1.06 × 10-4 neutrons/cm2/source electron, and for Tungsten it was 5.12 × 10-5 neutrons/cm2/source electron. The optimal target design for this study’s application would consist of a 0.75 inch-thick block of depleted uranium with the length, width, and/or diameter varying dependent on application.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Photoneutron Production Using an Electron Linear Accelerator for Applications in Neutron Imaging

Photoneutron production is possible using an electron linear accelerator and a target capable of generating photonuclear reactions. A short pulse neutron source can be useful for neutron imaging dynamic experiments. This study is aimed at the feasibility of photoneutron production using a 20 MeV electron linear accelerator and tungsten and depleted uranium targets of various thicknesses. MCNP6 (Monte Carlo N-Particle) code will be used to develop a computational model to estimate total neutron yield, and this will be verified at the Idaho State University’s Accelerator Center. After verification of the neutron yield and energy spectra, an additional MCNP6 model will be developed to analyze the neutron imaging processes. This study will potentially prove it is possible to conduct multi-mode imaging experiments on the anticipated Scorpius electron linear accelerator at the Nevada National Security Sites.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Absolute photoneutron cross sections of Sm isotopes

Photoneutron cross sections for seven samarium isotopes, {sup 144}Sm, {sup 147}Sm, {sup 148}Sm, {sup 149}Sm, {sup 150}Sm, {sup 152}Sm and {sup 154}Sm, have been investigated near neutron emission threshold using quasimonochromatic laser-Compton scattering γ-rays produced at the synchrotron radiation facility NewSUBARU. The results are important for nuclear astrophysics calculations and also for probing γ-ray strength functions in the vicinity of neutron threshold. Here we describe the neutron detection system and we discuss the related data analysis and the necessary method improvements for adapting the current experimental method to the working parameters of the future Gamma Beam System of Extreme Light Infrastructure - Nuclear Physics facility.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

SU-F-T-655: Evaluation of Neutron Dose Equivalent Inside of Treatment Vault of Radiotherapy by Photoneutron Production in the Primary Barriers

Purpose: Photon beams with energy higher than 10 MV interact with metal material in the primary barriers, where lead or steel have been widely used, neutrons can be generated. Monte Carlo simulations were performed to simulate the production of photoneutrons and the neutron shielding effect. Methods: For two photon beam energies, 15 MV and 18 MV, we simulated to strike metal sheets (steel and lead), and the ambient dose equivalents were calculated at the isocenter (in the patient plane) while delivering 1 Gy to the patient. For these cases, the thickness of the neutron shielding materials (Borated polyethylene (BPE) and concrete) were simulated to reduce the patient exposure by neutron doses. Results: When 18 MV photons interact with the metal sheets in the primary barrier, the evaluated neutron doses at the isocenter inside the treatment vault were 48.7 µSv and 7.3 µSv for lead and steel, respectively. In case of 15 MV photons, the calculated neutron doses were 18.6 µSv and 0.6 µSv for lead and steel, respectively. The neutron dose delivered to the patient can be reduced to negligible levels by including a 10 cm thick sheet of BPE or 22 cm thick sheet of concrete. Conclusion: When bunker shielding is designed with a primary barrier including a metal sheet inside the wall for a high energy machine, proper neutron shielding should be constructed to avoid undesirable extra dose.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Data on photoneutron reactions from various experiments for {sup 133}Cs, {sup 138}Ba and {sup 209}Bi nuclei

Basic methods for determining cross sections for photoneutron partial reactions are examined. They are obtained directly in experiments with quasimonoeneregetic annihilation photons or from the cross section for the (γ, xn) = (γ, 1n) + 2(γ, 2n) + 3(γ, 3n) +... neutron-yield reaction in experiments with bremsstrahlung photons by introducing corrections based on statistical nuclear-reaction theory. The difference in the conditions of these experiments, which leads to discrepancies between their results because of sizable systematic errors, is analyzed. Physical criteria are used to study the reliability of data on the photodisintegration of {sup 133}Cs, {sup 138}Ba, and {sup 209}Bi nuclei. The cross sections for partial and total reactions satisfying the reliability criteria are evaluated within the experimental–theoretical method (σ{sup eval}(γ, in) = F{sub i}{sup theor} × σ{sup expt}(γ, xn)) on the basis of the experimental cross sections σ{sup expt}(γ, xn) and the results of the calculations within the combined model of photonuclear reactions.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Evaluated Cross Sections of Photoneutron Reactions on the Isotope {sup 116}Sn and Spectra of Neutrons Originating from These Reactions

With the aid of the results obtained by evaluating cross sections of partial photoneutron reactions on the isotope {sup 116}Sn and the energy spectra of neutrons originating from these reactions, the possible reasons for the well-known discrepancies between the results of different photonuclear experiments were studied on the basis of a combinedmodel of photonuclear reactions. On the basis of physical criteria of data reliability and an experimental–theoretical method for evaluating cross sections of partial reactions, it was found that these discrepancies were due to unreliably redistributing neutrons between (γ, 1n), (γ, 2n), and (γ, 3n) reactions because of nontrivial correlations between the experimentally measured energy of neutrons and their multiplicity.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Direct + Semidirect E1 Photoneutron Reactions: Semimicroscopic Description

The particle-hole dispersive optical model is implemented to describe together E1 photo-absorption and direct + semidirect photoneutron reactions accompanied by excitation of the giant dipole resonance. Being based on this description, a quantitative estimation of the partial and total branching ratios for direct one-neutron decay of the mentioned giant resonance in a few medium-heavy neutron-closed-shell nuclei is obtained. Calculation results are compared with corresponding experimental data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Study of Extracted Beam Characteristics of the Photoneutron Source at the Institute for Nuclear Research of the Russian Academy of Sciences

The characteristics of the extracted beam of thermal neutrons at the IN-LUE photoneutron source are investigated. A collimator with a cross-section diameter of 30 mm, located at an angle of 67° relative to the electron beam direction, was used to extract neutrons from the source. The neutron flux density as a function of the distance from the source center and the distribution of flux density over the distance from the collimator axis (beam profile) are obtained.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Using time of flight separation to observe photoneutron production by X-rays incident on beryllium - 25592

The neutron time-of-flight (nTOF) component of the Brazos experiment conducted at the Naval Research Laboratory using the Mercury accelerator observed the production of photoneutrons in a beryllium target bombarded by an approximate 5 MeV endpoint Bremsstrahlung x-ray source. Properly spaced and shielded plastic scintillators and quartz and sapphire radiators were able to measure time-separated scattered x-ray and neutron signals. Validated with simulations, the measured neutron signal is consistent with greater than 3x10{sup 9} total neutrons off the beryllium target. (authors)

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

A tabletop, ultrashort pulse photoneutron source driven by electrons from laser wakefield acceleration

Relativistic electron beams driven by laser wakefield acceleration were utilized to produce ultrashort neutron sources. The experiment was carried out on the 38 fs, ∼0.5 J, 800 nm Ti:Sapphire laser in the 10 TW UT3 laser lab at University of Texas at Austin. The target gas was a high density pulsed gas jet composed of 90% He and 10% N2. The laser pulse with a peak intensity of 1.5 × 1018 W/cm2 interacted with the target to create a cylindrical plasma channel of 60 μm radius (FWHM) and 1.5 mm length (FWHM). Electron beams of ∼80 pC with the Gaussian energy distribution centered at 37 MeV and a width of 30 MeV (FWHM) were produced via laser wakefield acceleration. Neutron fluences of ∼2.4 × 106 per shot with hundreds of ps temporal length were generated through bremsstrahlung and subsequent photoneutron reactions in a 26.6 mm thick tungsten converter. Results were compared with those of simulations using EPOCH and GEANT4, showing agreement in electron spectrum, neutron fluence, neutron angular distribution and conversion rate.

Jiao, X. J.↗