Resonance Neutron Capture Research Articles

The Threshold of Detection of Fission Materials by ZnWO4 and Bi4Ge3O12 Scintillation Detectors

In the present work we found the maximum discovery distance for 239Pu-Be source using the detectors based on ZWO (ZnWO4) and BGO (Bi4Ge3O12) oxide scintillators. Detection distance was defined by using the radiation monitoring system ”PORTAL”. This research gives us data for estimation of the contribution of low-energy cascade gamma quanta CGQ. The CGQ emitted by excited scintillator nuclei defined the effective discovery distance of the fast neutrons source. The maximum detection distance was obtained with PMT in a single-photon counting mode. The maximum discovery distance for a BGO scintillator of size Ø40×40 mm – 38 cm, ZWO scintillator of size Ø52×40 mm – 54 cm, with reliability about 0.001. The results of the experiment on the ZWO scintillator can be explained by the registration of additional gamma quanta from the inelastic scattering reaction and the CGQ arising from resonant neutron capture region. This two mechanisms further lead to increase the sensitivity of the detector and increase the detection distance of the monitoring system. The key features of the monitoring system are: ZWO oxide scintillator, wide band measuring path, utilize PMT in single photon mode. The obtained detection distance was about 1.4 times higher in comparison with the spectrometric recording mode and 1.9 times higher in values of efficiency. Our results demonstrate the advantages of the ZWO scintillator compared to the BGO and demonstrate the possibility of using the resonant capture mechanism by ZWO detector nuclei to increase the fast neutrons sensitivity. The resonance capture mechanism increase sensitivity and maximum detection distance of the monitoring system. The low-energy gamma-quanta, which discharge of compound nuclei, are substantially suppressed in comparison with the classic spectrometric recording mode.

Reactor production of promethium-147

In this paper, we describe the 147Pm production yields and level of impurities from several targets that consisted of milligram quantities of highly enriched 146Nd oxide irradiated at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory for durations ranging from 24 to 180 h. A comparison between theoretical and experimental data are also presented, and attempts were made to empirically evaluate the neutron capture cross-sections of 41.3-d 148mPm and 5.4-d 148gPm. For a one-cycle irradiation (~24 days), 147Pm yield reaches a maximum value of 101.8 MBq/mg (2.75 mCi/mg) at 60 days after the end of bombardment. Because of large neutron capture cross-sections of 147Pm, the yield of 147Pm does not significantly increase with longer irradiation. Our estimates of the thermal neutron capture cross-section and resonance integral for 146Nd at 1.48 ± 0.05 b and 2.56 ± 0.25 b, respectively, were consistent with the reported values. The effective neutron capture cross-section of 147Pm to 148mPm was 53.3 ± 2.7 b–a factor of 2 lower than the 98.7 ± 6.5 b calculated from reported cross-sections. The measured σeff to the ground state (5.37-d 148gPm) was 82.0 ± 4.1 b; ~34% lower than the value of 139 ± 10 b calculated from reported cross-sections. In this work, we also describe the development of a chemical process based on extraction and ion-exchange chromatography for separation of 147Pm from milligram quantities of 146Nd and other impurities. Sequential separation of Pm from the Nd target and from other radioisotopic impurities (153Gd and 154&155Eu, 192Ir, and 60Co) was achieved using a LN extraction resin in HCl media followed by further purification of Pm from 60Co and 192Ir using a low cross-linking cation exchange resin. Based on these data, we estimated that two rounds of purification under our experimental conditions can provide a mass separation factor of >104 between Pm and Nd. Our data indicate that curie quantities of 147Pm with suitable chemical and radioisotopic purity for applications in beta voltaic batteries can be produced by irradiating gram quantities of highly enriched 146Nd in the flux trap of HFIR for one cycle.

Neutron resonance capture analysis and chemometric tools: an integrated approach

A joint approach based on the Neutron Resonance Capture Analysis (NRCA) integrated by chemometric tools namely Principal Component Analysis (PCA) is used to determine the semi-quantitative isotopic composition of a large set of Sumerian pottery. Here, we present NRCA results from the experimental campaign carried out on the INES beamline at the ISIS pulsed neutron and muon source (Rutherford Appleton Laboratory, UK). The potteries come from the archaeological site still under excavation of Abu Tbeirah, a 3rd millennium BCE site located in Southern Iraq, in the S-E periphery of the city of Nasiriyah. NRCA allows to determine the presence and the relative isotopic amounts, while the Principal Component Analysis distinguishes the elements/isotopes linked to the raw materials from the decay products due to contaminants that affect the potteries under investigation.

Neutron-resonance capture analysis on the VESUVIO spectrometer: Towards high-throughput material characterisation

We discuss the possibility to characterise nuclear quantum effects on the dynamics of heavy nuclei by means of neutron-resonance capture analysis on the VESUVIO spectrometer at ISIS. VESUVIO is equipped with yttrium-aluminium-perovskite gamma-sensitive detectors that can be used to record the Doppler-broadened line shape from a neutron-induced resonance in the neutron-energy range between 1 and 100 eV. The measurement of nuclear momentum distributions for heavy atoms using deep inelastic neutron scattering, the traditional technique for light-weight nuclei from hydrogen to fluorine, is currently severely limited by the resolution of the instrument. On the other hand, gamma-Dopplerimetry studies as the one presented here on gold allow for exquisite precision and short data-collection measurements, of the order of one hour, for the measurements, rendering the technique ideal for high-throughput investigations.

Measurements of the thermal neutron cross-section and resonance integral for the 108 Pd(n,γ) 109 Pd reaction

Abstract The thermal neutron capture cross-section (σ0) and resonance integral (I0) of the 108Pd(n,γ)109Pd reaction have been measured relative to that of the monitor reaction 197Au(n,γ)198Au. The measurements were carried out using the neutron activation with the cadmium ratio method. Both the samples and monitors were irradiated with and without cadmium cover of 0.5 mm thickness. The induced activities of the reaction products were measured with a well calibrated HPGe γ-ray detector. In order to improve the accuracy of the results, the necessary corrections for the counting losses were made. The thermal neutron capture cross-section and resonance integral of the 108Pd(n,γ)109Pd reaction were determined to be σ0,Pd = 8.68 ± 0.41 barn and I0,Pd = 245.6 ± 24.8 barn, respectively. The obtained results are compared with literature values and discussed.

Erratum to: Neutron capture measurements and resonance parameters of dysprosium

After publication of the paper, the authors realized that the acknowledgements were not correct. Their correct version appears in this erratum.

Examination of photon strength functions for Dy162,164 from radiative capture of resonance neutrons

Examination of photon strength functions for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi mathvariant="bold">Dy</mml:mi><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>162</mml:mn><mml:mo>,</mml:mo><mml:mn>164</mml:mn></mml:mrow></mml:mmultiscripts></mml:math> from radiative capture of resonance neutrons

Rhenium resonance parameters from neutron capture and transmission measurements in the energy range 0.01 eV to 1 keV

Rhenium is a refractory metal with potential uses in nuclear reactor applications, particularly those at very high temperatures. Measurements have been made using natural samples. Natural rhenium consists of two isotopes: 185Re (37.40%) and 187Re (62.60%). The electron linear accelerator (LINAC) at the Rensselaer Polytechnic Institute (RPI) Gaerttner LINAC Center was used to explore neutron interactions with rhenium in the energy region from 0.01 eV to 1 keV. Neutron capture and transmission measurements were performed by the time-of-flight technique. Two transmission measurements were performed at flight paths of 15 m and 25 m with 6Li glass scintillation detectors. The neutron capture measurements were performed at a flight path of 25 m with a 16-segment sodium iodide multiplicity detector. Resonance parameters were extracted from the data using the multilevel R-matrix Bayesian code SAMMY. A table of resonance parameters and their uncertainties is presented. The uncertainties in resonance parameters were propagated from a number of experimental quantities using a Bayesian analysis. Uncertainties were also estimated from fitting each Re sample measurement individually. The measured neutron capture resonance integral for 185Re is (4 ± 1)% larger than ENDF/B-VII.1. The capture resonance integral for 187Re is (3 ± 1)% larger than ENDF/B-VII.1. Other findings from these measurements include: a decrease in the thermal capture cross section for 185Re of (2 ± 2)% from ENDF/B-VII.1; a decrease in the thermal capture cross section for 187Re of (3 ± 4)% from ENDF/B-VII.1; a decrease in the thermal total cross section for 185Re of (2 ± 2)% from ENDF/B-VII.1; and a decrease in the thermal total cross section for 187Re of (6 ± 5)% from ENDF/B-VII.1. Considering the uncertainties, none of the indicated changes in thermal cross sections represents a statistically significant change from ENDF/B-VII.1.

Thermal neutron capture cross-section and resonance integral measurements of 139La(n, $ \gamma$ γ )140La and 140Ce(n, $ \gamma$ γ )141Ce using a Am-Be neutron source

Thermal neutron capture cross-sections and resonance integrals of 139La(n,\( \gamma\))140La and 140Ce (n,\( \gamma\))141Ce are measured with respect to reference reactions 197Au(n,\( \gamma\))198Au and 55Mn(n,\( \gamma\))56Mn using the neutron activation technique. Measurements are carried out using neutrons from an Am-Be source located inside a concrete bunker. Two different methods are used for determining self-shielding factors of activation foils as well as for finding the epithermal neutron spectrum shape factor. For 139 La with reference to 197 Au and 55 Mn the measured thermal cross sections are \( 9.24 \pm 0.25\) b and \( 9.28 \pm 0.37\) b, respectively, while the measured resonance integrals are \( 12.18 \pm 0.67\) b and \( 11.81 \pm 0.94\) b, respectively. For 140 Ce with reference to 197 Au and 55 Mn the measured thermal cross sections are \( 0.44 \pm 0.01\) b and \( 0.44 \pm 0.02\) b, respectively, while the measured resonance integrals are \( 0.55 \pm 0.03\) b and \( 0.54 \pm 0.04\) b, respectively. The present measurements are compared with earlier measurements and evaluations. Presently estimated values confirm the established 139La(n,\( \gamma\))140La cross-sections. The presently measured thermal capture cross-section 140Ce(n,\( \gamma\))141Ce , though lower than the evaluated data, is having higher accuracy compared to previous measurements with large uncertainties. The resonance integral measured is higher (like most previous measurements) than most evaluations requiring a revision of the evaluated data.

Interference effect between neutron direct and resonance capture reactions for neutron-rich nuclei

Interference effect of neutron capture cross section between the compound and direct processes is investigated. The compound process is calculated by resonance parameters and the direct process by the potential mode. The interference effect is tested for neutron-rich $^{82}$Ge and $^{134}$Sn nuclei relevant to $r$-process and light nucleus $^{13}$C which is neutron poison in the $s$-process and produces long-lived radioactive nucleus $^{14}$C ($T_{1/2}=5700$ y). The interference effects in those nuclei are significant around resonances, and low energy region if $s$-wave neutron direct capture is possible. Maxwellian averaged cross sections at $kT=30$ and $300$ keV are also calculated, and the interference effect changes the Maxwellian averaged capture cross section largely depending on resonance position.

Orthodontic archwire composition and phase analyses by neutron spectroscopy.

Quantitative metallurgical and phase analyses employing neutron diffraction technique were conducted on two as-received commercial rectangular austenitic stainless steel orthodontic archwires, G&H and Azdent, 0.43×0.64 mm (0.017×0.025 inch). Results showed a bi-phase structure containing martensitic phase (45.67% for G&H and 6.62% for Azdent) in addition to the expected metastable austenite. The former may be a strain-induced phase-transformation arising during the cold working process of wire fabrication. Further neutron resonance capture analysis determinations provided atomic and isotopic compositions, including alloying elements in each sample, complementary to the results of traditional energy dispersive X-ray spectroscopy. Together, these results assist in relating commercial alloying recipes and processing histories with mechanical performance, strength and ductility in particular.

Influence of the neutron transport tube on neutron resonance densitometry

Neutron Resonance Densitometry (NRD) is a non-destructive assay technique of nuclear materials in particle-like debris that contains various materials. An aim of NRD is to quantify nuclear materials in a melting fuel of Fukusima Daiichi plant, spent nuclear fuel and annihilation disposal fuel etc. NRD consists of two techniques of Neutron Resonance Transmission Analysis (NRTA) and Neutron Resonance Capture Analysis (NRCA) or Prompt Gamma-ray Analysis (PGA). A density of nuclear material isotopes is decided with NRTA. The materials absorbing a neutron in a wide energy range such as boron in a sample are identified by NRCA/PGA. The information of NRCA/PGA is used in NRTA analysis to quantify nuclear material isotopes. A neutron time of flight (TOF) method is used in NRD measurements. A facility, consisting of a neutron source, a neutron flight path, and a detector is required. A short flight path and a strong neutron source are needed to downsize such a facility and put NRD into practical use. A neutron transport tube covers a flight path to prevent noises. In order to investigate the effect of neutron transport tube and pulse width of a neutron source, we carried out NRTA experiments with a 2-m short neutron transport tube constructed at Kyoto University Research Reactor Institute - Linear Accelerator (KURRI-LINAC), and impacts of shield of neutron transport tube and influence of pulse width of a neutron source were examined. A shield of the neutron transport tube reduced a background and had a good influence on the measurement. The resonance dips of 183 W at 27 eV was successfully observed with a pulse width of a neutron source less than 2 μs.

Neutron resonance analysis for nuclear safeguards and security applications

Neutron-induced reactions can be used to study the properties of nuclear materials of interest in the fields of nuclear safeguards and security. The elemental and isotopic composition of these materials can be determined by using the presence of resonance structures. This idea is the basis of two non-destructive analysis techniques which have been developed at the GELINA neutron time-of-flight facility at JRC-Geel: Neutron Resonance Capture Analysis (NRCA) and Neutron Resonance Transmission Analysis (NRTA). A combination of NRTA and NRCA has been proposed for the characterisation of particle-like debris of melted fuel formed in severe nuclear accidents. In this work, we present a quantitative validation of the NRTA technique which was used to determine the areal densities of Pu enriched reference samples used for safeguards applications. Less than 2% bias has been obtained for the fissile isotopes, with well-known total cross sections.

Measurement of the neutron capture resonances for platinum using the Ge spectrometer and pulsed neutron beam at the J-PARC/MLF/ANNRI

The neutron capture cross-section for platinum was measured at J-PARC/MLF/ANNRI. The intense pulsed neutron beam was impinging on a natural platinum foil sample and the emitted prompt γ-rays were detected by a Ge spectrometer. The peak energies of the low energy resonances for natural platinum are consistent with those of the JEFF-3.1.2, RUSFOND2010 and next-JENDL data libraries except for the 20-eV resonance. The resonance cross-sections of the next-JENDL library do not contradict the present measurements within the uncertainty of the absolute value of the present work. We analysed the prompt γ-ray spectrum and found a clear 7921.93 keV peak that originates from the transition from the 196 Pt compound state to its ground state. The neutron capture cross-section for 195 Pt was obtained by choosing events of this peak. The peak energies of most of the low energy resonances are almost consistent with those of the RUSFOND2010 and next-JENDL libraries. However, there was a disagreement for the 20-eV resonance.

Time-of-flight and activation experiments on147Pm and171Tm for astrophysics

The neutron capture cross section of several key unstable isotopes acting as branching points in the s-process are crucial for stellar nucleosynthesis studies, but they are very challenging to measure due to the difficult production of sufficient sample material, the high activity of the resulting samples, and the actual (n,γ) measurement, for which high neutron fluxes and effective background rejection capabilities are required. As part of a new program to measure some of these important branching points, radioactive targets of 147 Pm and 171 Tm have been produced by irradiation of stable isotopes at the ILL high flux reactor. Neutron capture on 146 Nd and 170 Er at the reactor was followed by beta decay and the resulting matrix was purified via radiochemical separation at PSI. The radioactive targets have been used for time-of-flight measurements at the CERN n_TOF facility using the 19 and 185 m beam lines during 2014 and 2015. The capture cascades were detected using a set of four C6 D6 scintillators, allowing to observe the associated neutron capture resonances. The results presented in this work are the first ever determination of the resonance capture cross section of 147 Pm and 171 Tm. Activation experiments on the same 147 Pm and 171 Tm targets with a high-intensity 30 keV quasi-Maxwellian flux of neutrons will be performed using the SARAF accelerator and the Liquid-Lithium Target (LiLiT) in order to extract the corresponding Maxwellian Average Cross Section (MACS). The status of these experiments and preliminary results will be presented and discussed as well.

Resonance region measurements of dysprosium and rhenium

Neutron capture and transmission measurements have been performed, and resonance parameter analysis has been completed for dysprosium, Dy, and rhenium, Re. The 60 MeV electron accelerator at RPI Gaerttner LINAC Center produced neutrons in the thermal and epithermal energy regions for these measurements. Transmission measurements were made using 6 Li glass scintillation detectors. The neutron capture measurements were made with a 16-segment NaI multiplicity detector. The detectors for all experiments were located at ≈25 m except for thermal transmission, which was done at ≈15 m. The dysprosium samples included one highly enriched 164 Dy metal, 6 liquid solutions of enriched 164 Dy, two natural Dy metals. The Re samples were natural metals. Their capture yield normalizations were corrected for their high gamma attenuation. The multi-level R-matrix Bayesian computer code SAMMY was used to extract the resonance parameters from the data. 164 Dy resonance data were analyzed up to 550 eV, other Dy isotopes up to 17 eV, and Re resonance data up to 1 keV. Uncertainties due to resolution function, flight path, burst width, sample thickness, normalization, background, and zero time were estimated and propagated using SAMMY. An additional check of sample-to-sample consistency is presented as an estimate of uncertainty. The thermal total cross sections and neutron capture resonance integrals of 164 Dy and Re were determined from the resonance parameters. The NJOY and INTER codes were used to process and integrate the cross sections. Plots of the data, fits, and calculations using ENDF/B-VII.1 resonance parameters are presented.

Physical particularities of nuclear reactors using heavy moderators of neutrons

In nuclear reactors, thermal neutron spectra are formed using moderators with small atomic weights. For fast reactors, inserting such moderators in the core may create problems since they efficiently decelerate the neutrons. In order to form an intermediate neutron spectrum, it is preferable to employ neutron moderators with sufficiently large atomic weights, using 233U as a fissile nuclide and 232Th and 231Pa as fertile ones. The aim of the work is to investigate the properties of heavy neutron moderators and to assess their advantages. The analysis employs the JENDL-4.0 nuclear data library and the SCALE program package for simulating the variation of fuel composition caused by irradiation in the reactor. The following main results are obtained. By using heavy moderators with small neutron moderation steps, one is able to (1) increase the rate of resonance capture, so that the amount of fertile material in the fuel may be reduced while maintaining the breeding factor of the core; (2) use the vacant space for improving the fuel-element properties by adding inert, strong, and thermally conductive materials and by implementing dispersive fuel elements in which the fissile material is self-replenished and neutron multiplication remains stable during the process of fuel burnup; and (3) employ mixtures of different fertile materials with resonance capture cross sections in order to increase the resonance-lattice density and the probability of resonance neutron capture leading to formation of fissile material. The general conclusion is that, by forming an intermediate neutron spectrum with heavy neutron moderators, one can use the fuel more efficiently and improve nuclear safety.

Measurement of the isomer production ratio for the Cd112(n,γ)Cd113 reaction using neutron beams at J-PARC

The astrophysical origin of a rare isotope $^{115}\mathrm{Sn}$ remains an open question. An isomer (${T}_{1/2}=14.1\phantom{\rule{4pt}{0ex}}\mathrm{y}$) in $^{113}\mathrm{Cd}$ is an $s$-process branching point from which a nucleosynthesis flow reaches $^{115}\mathrm{Sn}$. The $s$-process abundance of $^{115}\mathrm{Sn}$ depends on the isomer production ratio in the $^{112}\mathrm{Cd}(n,\ensuremath{\gamma})^{113}\mathrm{Cd}$ reaction. However, the ratio has not been measured in an energy region higher than the thermal energy. We have measured $\ensuremath{\gamma}$ rays following neutron capture reactions on $^{112}\mathrm{Cd}$ using two cluster high-purity germanium (HPGe) detectors in conjunction with a time-of-flight method at J-PARC. We have obtained the result that the relative $\ensuremath{\gamma}$-ray intensity ratio of the isomer is almost constant in an energy region of up to 5 keV. This result suggests that the $s$-process contribution to the solar abundance of $^{115}\mathrm{Sn}$ is minor. We have found that the ratio of a resonance at 737 eV is about 1.5 times higher than other ratios. This enhancement can be explained by a $p$-wave neutron capture. This result suggests measurements of decay $\ensuremath{\gamma}$ rays to isomers are effective to assign the spin and parity for neutron capture resonances.

Measurement of neutron capture onXe136

$^{136}$Xe is a 0{\nu}{\beta}{\beta} decay candidate isotope, and is used in multiple experiments searching for this hypothetical decay mode. These experiments require precise information about neutron capture for their background characterization and minimization. Thermal and resonant neutron capture on $^{136}$Xe have been measured at the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos Neutron Science Center. A neutron beam ranging from thermal energy to greater than 100 keV was incident on a gas cell filled with isotopically pure $^{136}$Xe. The relative neutron capture cross sections for neutrons at thermal energies and the first resonance at 2.154 keV have been measured. Additionally, the {\gamma} cascades for these captures have been measured, and cascade models have been developed which may be used by 0{\nu}{\beta}{\beta} experiments using $^{136}$Xe.

LaBr3γ-ray spectrometer for detecting 10B in debris of melted nuclear fuel

Neutron resonance densitometry has been proposed as a nondestructive analytical method for quantifying special nuclear material (SNM) in the rock- and particle-like debris that is to be removed from the Fukushima Daiichi nuclear power plant. The method is based on neutron resonance transmission analysis (NRTA) and neutron resonance capture analysis combined with prompt-γ-ray analysis (NRCA/PGA). Although quantification of SNM will predominantly rely on NRTA, this will be hampered by the presence of strong neutron-absorbing matrix materials, in particular 10B. Results obtained with NRCA/PGA are used to improve the interpretation of NRTA data. Prompt γ rays originating from the 10B(n, αγ) reaction are used to assess the amount of 10B. The 478keV γ rays from 10B, however, need to be measured under a high-radiation environment, especially because of 137Cs. To meet this requirement, we developed a well-shaped γ-ray spectrometer consisting of one cylindrical and four rectangular-cuboid LaBr3 scintillators combined with a fast data-acquisition system. Furthermore, to improve the gain stability of the main detector, a special high-voltage divider was developed. Because of the reduction in gain shift, a 3.8% resolution at 662keV was obtained for long-term measurements. By using the data-acquisition system, which consists of eight 250MHz digitizers, input signals of over 500kHz per channel were recorded. The work reported herein demonstrates that, with such a spectrometer, the impact of the Compton edge of 662keV γ rays from 137Cs is significantly reduced, which allows the 10B amount to be determined with greater sensitivity.