Capture Gamma Research Articles

A potential alternative/complement to the traditional thermal neutron based counting in Nuclear Safeguards and Security

A new concept for thermal neutron based correlation and multiplicity measurements is proposed in this paper. The main idea of the concept consists of using 2.223MeV gammas (or 1.201MeV, DE) originating in the 1 H (n,γ)2D-reaction instead of using traditional thermal neutron counting. Results of investigations presented in this paper indicate that gammas from thermal neutron capture reactions preserve the information about the correlation characteristics of thermal (fast) neutrons in the same time scale. Therefore, instead of thermal neutron detectors (or as a complement) one may use traditional and inexpensive gamma detectors, such as NaI, BGO, CdZnTe or any other gamma detector. In this work we used D8×8cm2 NaI scintillator to test the concept. Thus, the new approach helps to address the problem of replacement of 3He-counters and problems related to the specific measurements of spent nuclear fuel directly in the spent fuel pool. It has a particular importance for Nuclear Safeguards and Security. Overall, this work represents the proof of concept study and reports on the experimental and numerical evidence that thermal neutron capture gammas may be used in the context of correlation and multiplicity measurements. Investigations were performed using a 252Cf-correlated neutron source and an 241Am-Be-random neutron source. The related idea of the Gamma Differential Die-Away approach is investigated numerically in this paper as well, and will be tested experimentally in future work.

Capture and fission with DANCE and NEUANCE

A summary of the current and future experimental program at DANCE is presented. Measurements of neutron capture cross sections are planned for many actinide isotopes with the goal to reduce the present uncertainties in nuclear data libraries. Detailed studies of capture gamma rays in the neutron resonance region will be performed in order to derive correlated data on the de-excitation of the compound nucleus. New approaches on how to remove the DANCE detector response from experimental data and retain the correlations between the cascade gamma rays are presented. Studies on 235U are focused on quantifying the population of short-lived isomeric states in 236U after neutron capture. For this purpose, a new neutron detector array NEUANCE is under construction. It will be installed in the central cavity of the DANCE array and enable the highly efficient tagging of fission and capture events. In addition, developments of fission fragment detectors are also underway to expand DANCE capabilities to measurements of fully correlated data on fission observables.

A method to evaluate hydraulic fracture using proppant detection

Accurate determination of the proppant placement and propped fracture height are important for evaluating and optimizing stimulation strategies. A technology using non-radioactive proppant and a pulsed neutron gamma energy spectra logging tool to determine the placement and height of propped fractures is proposed. Gd2O3 was incorporated into ceramic proppant and a Monte Carlo method was utilized to build the logging tools and formation models. Characteristic responses of the recorded information of different logging tools to fracture widths, proppant concentrations and influencing factors were studied. The results show that Gd capture gamma rays can be used to evaluate propped fractures and it has higher sensitivity to the change of fracture width and traceable proppant content compared with the exiting non-radioactive proppant evaluation techniques and only an after-fracture measurement is needed for the new method; The changes in gas saturation and borehole size have a great impact on determining propped fractures when compensated neutron and pulsed neutron capture tool are used. A field example is presented to validate the application of the new technique.

Monte Carlo 시물레이션에 기초한 포획모드 중성자-감마 스펙트럼 존데 설계 및 반응 분석

본 연구에서는 중성자-감마 스펙트럼검층 존데 설계를 목적으로 Monte Carlo 시물레이션을 이용하여 열중성자 반응의 우세한 영역 파악 및 포획감마 스펙트럼의 에너지피크 값에 기초한 지층 구성 원소 구분을 수행하였다. 14 MeV 에너지준위의 중성자를 방출하는 중성자발생장치를 선원으로 이용하여 선원으로부터 10 cm 간격으로 12개의 중성자 검출기들을 배열함으로써 거리에 따른 열중성자 양을 측정하였다. 시추공 영향 저감을 위해 존데모형에 차폐재를 적용하여 보다 정확한 열중성자 측정을 수행하여 열중성자 반응이 우세한 위치를 분석한 뒤, 이 위치에서 검출된 포획감마 에너지 스펙트럼을 분석하여 지층을 구성하는 주요 원소 및 그 양을 확인하였다. 본 연구 결과는 중성자-감마 스펙트럼검층 존데의 신호대잡음 비 향상과 포획감마 검출기 최적 위치 선정에 도움이 될 것으로 판단된다. For efficiently designing neutron induced gamma spectroscopy sonde, Monte Carlo simulation is employed to understand a dominant location of thermal neutron and classify the formation elements from the energy peak of capture gamma spectrum. A pulsed neutron generator emitting 14 MeV neutron particles was used as a source, and flux of thermal neutron was calculated from the twelve detectors arranged at each 10 cm intervals from the source. Design for reducing borehole effects using shielding materials was also applied to numerical sonde model. Moreover, principal elements and quantities of numerical earth models were verified through the energy spectrum analysis of capture gamma detected from a gamma detector. These results can help to enhance the signal-to-noise ratio, and determine an optimal placement of capture gamma detectors of neutron induced gamma spectroscopy sonde.

The effect of replacing sand by iron slag on physical, mechanical and radiological properties of cement mortar

In the present study, the effects of replacing sand by high percentages of basic-oxygen furnace slag on the compressive strength, bulk density and gamma ray radiation shielding properties of mortar have been investigated. Cement mortar of mix proportion 1:3 including various percentages of iron slag was designed. The percentages of replacement were 0%, 40%, 80% and 100% by weight of fine aggregate. Mortar mixes were prepared with water cement ratio of 0.44 and cured in potable water for 90days. The attenuation measurements were performed using gamma spectrometer of NaI (Tl) detector. The utilized radiation sources comprised 137Cs and 60Co radioactive elements with photon energies of 0.662MeV for 137Cs and two energy levels of 1.17 and 1.33MeV for the 60Co. Likewise, half value layer (HVL), tenth value layer (TVL) and the mean free path (mfp) for the tested samples were measured. Results of this investigation indicated that the strength properties of mortars increased significantly upon replacing sand partially by iron slag. It was also observed that the inclusion of iron slag as partial replacement with fine aggregate enhances the bulk density of mortar. On the other hand, full sand replacement by iron slag has significant effects on shielding efficiency in thick shields, as it reduces the capture gamma rays better than normal mortar incorporating sand.

Capability of self-organizing map neural network in geophysical log data classification: Case study from the CCSD-MH

Well log interpretation is one of the prime sources of information for deep lithology in drilling research. Because of the complex geological features of the crystalline metamorphic rocks, more complex nonlinear functional behaviors exist for well log interpretation purposes. Hence, establishing a prediction technology that can accurately interpret/classify well log data in terms of lithology is of major significance. This study, for the first time, explores the application of self-organizing map neural network (SOM) in the classification of metamorphic rocks from Chinese Continental Scientific Drilling Main Hole (CCSD-MH) log data. For this purpose, a total of 33,326 data points derived from resistivity, P-wave velocity, bulk density, photoelectric absorption capture cross section, gamma ray, potassium content and neutron logs were used as an input pattern to a SOM to classify lithology in five categories: orthogneiss, paragneiss, eclogite, amphibolite and ultramafic rocks. Comparison of SOM results to those of feed-forward neural network (FFNN) was also carried out. The cross-validation method was used to investigate the robustness of the two neural networks in terms of classification accuracy in the context of lithology clustering tasks by sampling rotation. Statistical tests such as student paired samples t-test was carried out to guide in classification decision of the CCSD-MH data. The results of this study have proven that SOM appears to be comparable to FFNN in classifying lithology using geophysical log data from crystalline rocks. This proposed SOM approach can serve as practical alternative technology to be used in drilling research.

Uncertainty Quantification of Concrete Utilized in Dry Cask Storage

The objective of this paper is to analyze the uncertainty in radiation dose rate estimates outside of a used nuclear fuel (UNF) dry cask storage unit due to the parametric variability of concrete compositions and densities. This requires the selection of a limited number of concrete compositions from a standardized database and the development of a reference dry cask model, which can be used to estimate dose rate from neutrons and gamma rays. The model was developed for use in calculations with MCNP, with reference data from a UNF assembly source and geometry details based on the Holtec HI-STORM 100S UNF dry cask storage system, both provided by the Comanche Peak nuclear power plant. A number of cases have been developed and analyzed to compare the effects of variations in concrete compositions considering nominal densities, variations from nominal densities, fixed densities regardless of the specific composition, and variations in the decay source. The analysis confirmed that the parametric variability of concrete compositions is a major source of uncertainty in evaluations of dry cask dose rates. While precise results depend on the compositions compared, general trends can be identified. The largest fraction of the dose value in all cases, typically 70%, is due to gamma rays produced by the fission products. Density variation had a dominant effect on the dose rate. Composition variations, while density was held fixed, indicated that the specific composition data significantly impact the dose rates produced by neutrons and associated capture gamma rays. The impact due to composition variation on neutron dose rate was found to be on the order of 70% or higher for these test cases. The analysis indicates that uncertainties in concrete characteristics at the time of on-site pour procedures impact the actual shielding efficiency and, therefore, must be evaluated.

Neutron Capture Cross Section Measurement on91Zr at J-PARC/MLF/ANNRI

The neutron capture cross section measurement on 91Zr was performed at neutron TOF beam line ANNRI installed at J-PARC/MLF. Prompt capture gamma rays from the sample were detected with an array of large Ge detectors at a distance of 21.5 m from the spallation neutron source by the time-of-fligh (TOF) method. The neutron capture gamma-ray pulse-height spectra from the 182-eV p-wave resonance and the 292-eV s-wave resonance were obtained by gating on the TOF regions, respectively. Though the decay patterns of primary transitions from the capture state were quite different between resonances, the prominent characteristics common to both resonances was the very strong ground-state transition from the 935-keV state. Therefore, a ground-state transition method was applied to obtain the capture yield, so that the background components due to impurities were successfully eliminated. The preliminary result of the neutron capture cross section for 91Zr up to 5 keV is presented.

Numerical study on determining formation porosity using a boron capture gamma ray technique and MCNP

Formation porosity can be determined using the boron capture gamma ray counting ratio with a near to far detector in a pulsed neutron-gamma element logging tool. The thermal neutron distribution, boron capture gamma spectroscopy and porosity response for formations with different water salinity and wellbore diameter characteristics were simulated using the Monte Carlo method. We found that a boron lining improves the signal-to-noise ratio and that the boron capture gamma ray counting ratio has a higher sensitivity for determining porosity than total capture gamma.

Neutron Capture Cross Sections and Gamma Emission Spectra from Neutron Capture on 234,236,238U Measured with DANCE

A new measurement of the 238U(n, γ) cross section using a thin 48 mg/cm2 target was made using the DANCE detector at LANSCE over the energy range from 10 eV to 500 keV. The results confirm earlier measurements. Measurements of the gamma-ray emission spectra were also made for 238U(n, γ) as well as 234,236U(n, γ). These measurements help to constrain the radiative strength function used in the cross-section calculations.

Measurements of Capture Gamma Rays from the Neutron Resonances of 74Se and 77Se at the J-PARC/MLF/ANNRI

Neutron resonance capture γ-ray measurements on 74Se and 77Se were performed with a 4π Ge spectrometer in the Accurate Neutron–Nucleus Reaction measurement Instrument (ANNRI) at the Japan Proton Accelerator Research Complex (J-PARC). The relative intensities of primary transitions were derived for the 27-eV resonance of 74Se and the 113-, 212-, 291-, 342-, 690- and 864-eV resonances of 77Se, respectively. For the 27-eV resonance of 74Se, a strong transition to the 293-keV state was observed. Moreover, new resonances of 74Se were found at 6, 123, 436 and 640 eV. It was confirmed that those resonances had originated in the neutron capture reaction of 74Se by obtaining the TOF spectrum corresponding to the strong 287-keV ground-state transition γ ray. As for 77Se, differences of the decay pattern were found between the resonances.

Measurement of Capture Gamma Rays from 99Tc Neutron Resonances at the J-PARC/ANNRI

Primary gamma rays from the neutron capture resonances for 99Tc were measured at the J-PARC/ANNRI. The transition pattern from the first resonance is similar to that from the capture reaction of thermal neutrons. On the other hand, transition patterns from the higher energy resonances are completely different, and there is no clear dependence on the spin-parities of the resonances.

Measurements of keV-neutron capture cross sections and capture gamma-ray spectra of 105Pd

The neutron capture cross sections and capture gamma-ray spectra of 105Pd were measured in the region from 15 to 100 keV and at 585 keV. A neutron time-of-flight method was utilised with an anti-Compton NaI(Tl) spectrometer and a 1.5-ns pulsed neutron source by the 7Li(p,n)7Be reaction. The capture yields were obtained by applying a pulse-height weighting technique to the observed net capture gamma-ray pulse-height spectra. The capture cross sections of 105Pd were derived with errors less than 5%, using the standard capture cross sections of 197Au. The evaluated capture cross sections of JENDL-4.0 and ENDF/B-VII.1 were compared with the present results. The evaluations of JENDL-4.0 and ENDF/B-VII.1 were larger than the present results by 3%–15% in the region from 15 to 100 keV and at 585 keV. The capture gamma-ray spectra of 105Pd were also derived by unfolding the observed net capture gamma-ray pulse-height spectra. The multiplicities of capture gamma rays of 105Pd were obtained from the capture gamma-ray spectra.

Spherical shields perturbed to ellipsoids in transport theory

One-dimensional spheres are perturbed to ellipsoids, and perturbation theory for inhomogeneous transport problems is applied to estimate the leakage of an uncollided decay gamma ray, a neutron thermal capture gamma ray, and a neutron inelastic scatter gamma ray. Only the shielding is perturbed, not the source. The surface transformation function for the sphere-to-ellipsoid change-of-shape perturbation is derived. Schwinger, Roussopolos, and combined perturbation estimates are applied. The perturbation estimates are defined to estimate the total (4π) flux at an external spherical surface detector, and they were accurate for point-detector fluxes when the leakage estimated from a point detector was similar to the total external surface flux. For uncollided line fluxes, the Schwinger estimate worked very well when the response of interest was the total external surface flux, but perturbation theory did not work well when the response of interest was the flux measured at a single external point (unless extra care was taken to account for geometric effects). For thermal capture line fluxes, the Roussopolos estimate was extremely accurate for one point detector location but its accuracy depended on the detector location. For inelastic scatter line fluxes, the detector fluxes were relatively insensitive to the detector location and the perturbation estimates were fairly accurate.

Gamma Cascade Transition of <sup>51</sup>V(n<sub>th</sub>, <i>g </i>)<sup>52</sup>V Reaction

The thermal neutron capture gamma radiations for 51V(n, g)52V reaction have been studied at Dalat Nuclear Research Reactor (DNRR). The gamma two-step cascade transition was measured by event-event coincidence spectrometer. The added-neutron binding energy in 52V was measured as 7.31 MeV. Energy and the intensity transition of cascades were consistent with prediction of single particle model. Furthermore, the spin and the parity of levels were confined.

Pulsed neutron gamma-ray logging in archaeological site survey

An archaeological survey method based on neutron gamma-ray logging is described. The method relies on the measurement of capture gamma radiation induced by neutron irradiation from a pulsed generator. This technique provides elemental information on the irradiated zone by spectroscopic analysis of the gamma-ray data. This approach has been studied with Geant4 Monte Carlo simulations. In particular, irradiation volume for a deuterium–deuterium and deuterium–tritium (D-T) neutron generator and sampling volume for the D-T source were estimated. In addition, a neutron log response, which illustrates the capability of the neutron tool to localize artifacts lying beneath the surface, is shown.

Monte Carlo characterizations mapping of the (γ,n) and (n,γ) photonuclear reactions in the high energy X-ray radiation therapy

AimThe aim of this work was to map the characteristics of (n,γ) and (γ,n) reactions in a high energy photon radiation therapy. BackgroundPhotoneutrons produced in the high energy X-Ray radiation therapy may damage patients and staff. It is due to high RBE of the produced neutrons according to their energy and isotropic emission. Characterization of the photoneutrons can help us in appropriate shielding. Materials and methodsThis study focused on the photoneutron and capture gamma ray phenomena. Characteristics such as dose value, fluence and spectra of both the neutrons and the by produced prompt gamma ray were described. Results and discussionNeutron and prompt gamma spectra in different points showed the neutrons to be thermalized when increasing the distance from the linac. Energy of the neutrons changed from about 0.6MeV at the isocentre to around 10−08MeV at the outer door position. Although the neutrons were found as fast neutrons, their spectra showed they were thermal neutrons at the outer door position. Additionally, it was seen that the energy of the gamma rays is higher than the scattered X-ray energy. The energy of gamma rays was seen to be up to 10MeV while the linac photons had energy lower than 1MeV. Neutron source strength obtained in this work was in good agreement with the published data, which may be a confirmation of our simulation accuracy. ConclusionThe study showed that the Monte Carlo simulation can be applied in the radiotherapy and industrial radiation works as a useful and precise estimator. We also concluded that the dose from the prompt gamma ray at the outer door location is higher than the scattered radiation from the linac and should be considered in the shielding.

Sample dependent response of a LaCl3:Ce detector in prompt gamma neutron activation analysis of bulk hydrocarbon samples

The response of a LaCl3:Ce detector has been found to depend upon the hydrogen content of bulk samples in prompt gamma analysis using 14MeV neutron inelastic scattering. The moderation of 14MeV neutrons from hydrogen in the bulk sample produces thermal neutrons around the sample which ultimately excite chlorine capture gamma rays in the LaCl3:Ce detector material. Interference of 6.11MeV chlorine gamma rays from the detector itself with 6.13MeV oxygen gamma rays from the bulk samples makes the intensity of the 6.13MeV oxygen gamma ray peak relatively insensitive to variations in oxygen concentration. The strong dependence of the 1.95MeV doublet chlorine gamma ray yield on hydrogen content of the bulk samples confirms fast neutron moderation from hydrogen in the bulk samples as a major source of production of thermal neutrons and chlorine gamma rays in the LaCl3:Ce detector material.Despite their poor oxygen detection capabilities, these detectors have nonetheless excellent detection capabilities for hydrogen and carbon in benzene, butyl alcohol, propanol, propanic acid, and formic acid bulk samples using 14MeV neutron inelastic scattering.

Standard spectrum measurement and simulation of elemental capture spectroscopy log

We have established a set of laboratory measurements which is used for capturing element gammma spectrum. Standard captured gamma ray spectra for ten elements, including Si, Ca, Fe, are obtained using the measurements for the first time in China. We also simulated the capture gamma ray spectra of the ten elements using Monte Carlo methodology with the same parameters of our experimental measurements. Comparing the experiment and simulation results with the data from the International Atomic Energy Agency’s Nuclear Data Center, we obtained the standard captured gamma ray spectra of the ten elements, which, as calibration spectra, are used to calibrate the raw spectrum in data processing. This method solved the key problem during the conversion from the original measuring spectrum to the yield of each element in the data processing. The method can effectively improve the accuracy of the element yield calculation.

Measurement of gamma attenuation for ANR end shield model using CaSO4:Dy phosphor

In the present study, gamma attenuation factors were measured for End shield model of Advanced Nuclear Reactor (ANR). The model is of the size 700×700×1250mm3 and made of steel ball and water mixture with 2×2 lattice locations at the centre of the model. The measurements were carried out using CaSO4:Dy TL phosphor. The streaming of gamma rays (includes core gamma, fission product gamma, activation gamma and capture gamma) was found to be attenuated by a factor of about 1500–4000 at a distance of 1125mm from the incident face of the model, when it is filled with the mixture of water and steel ball. The corresponding exposure rate of streaming gamma rays was found to be about 1.2–2R/h. The attenuation factors derived from the study was used for the designing of actual End shield for ANR.