Thermal Neutron Capture Gamma Rays Research Articles

Investigation the Effects of Neutron Source Number and Arrangement in Landmines Detection by Thermal Neutron Capture Gamma Ray Analysis

Thermal neutron capture can be used as a successful technique for detection of non-metallic landmines via the detection of their constituent like nitrogen. Recently, it has been shown that the detection of 10.829 MeV photons from the 14N(n,γ)15N reaction can be used for finding the landmines. In this method a high-energy neutron source like 241Am-Be inside water as a moderator is used to have thermal neutron. In this paper we have investigated the effects of the number of neutron sources and their orientation on the gamma ray spectrum by using MCNP4C code. The best case for number of sources and their positions and orientations have been achieved corresponding to maximum flux of 10.829 MeV photons.

Absolute efficiency calibration of high-purity germanium detector in the range 120–8500 keV

This article reports the efficiency response curve of the high-purity germanium detector over the wide energy range, covering from 120 to 8500 keV. The efficiencies were measured for different counting geometries by using point radionuclide standards (mono-energetic as well as multi-gamma emitters) supplied by IAEA and the capture gamma-ray facility installed at PINSTECH nuclear reactor PARR-1. The measured efficiencies were required to fit with a suitable fitting function for interpolation within the energy range of interest. Several fitting functions were proposed in the literature covering different energy ranges. The functions giving the best fit to experimental data are presented. The work has successfully extended the response curve beyond 1500–8500 keV, which is the region where the standard calibration radionuclides are not available. The thermal neutron capture gamma-ray facility provided the collimated neutron beam, extracted from the core of the reactor and made to react with ammonium chloride target to produce the capture gamma rays for determining the efficiencies in the extended region. It was found that the capture gamma-ray provides a satisfactory solution to extend the absolute efficiency calibration in the MeV range. It was also found that the fitting function that is linear in its parameter was highly satisfactory up to 1500 keV but proved insufficient upto 8500 keV. The exponential function giving the good fit over the range has been presented. Good agreement has been found between the experimentally measured absolute efficiencies and the predicted result.

Monte Carlo assessment of soil moisture effect on high-energy thermal neutron capture gamma-ray by 14N

Among many conventional techniques, nuclear techniques have shown to be faster, more reliable, and more effective in detecting explosives. In the present work, neutrons from a 5 Ci Am–Be neutron source being in water tank are captured by elements of soil and landmine (TNT), namely 14N, H, C, and O. The prompt capture gamma-ray spectrum taken by a NaI (Tl) scintillation detector indicates the characteristic photo peaks of the elements in soil and landmine. In the high-energy region of the gamma-ray spectrum, besides 10.829 MeV of 15N, single escape (SE) and double escape (DE) peaks are unmistakable photo peaks, which make the detection of concealed explosive possible. The soil has the property of moderating neutrons as well as diffusing the thermal neutron flux. Among many elements in soil, silicon is more abundant and 29Si emits 10.607 MeV prompt capture gamma-ray, which makes 10.829 MeV detection difficult. The Monte Carlo simulation was used to adjust source–target–detector distances and soil moisture content to yield the best result. Therefore, we applied MCNP4C for configuration very close to reality of a hidden landmine in soil.

Possibilities of Using Sources of Neutron Radiation for Radiation Testing of Dikes of Trunk Pipelines

Methodical aspects of in-tube testing of the media surrounding a trunk pipeline are considered. The method is based on radiating media with a source of fast neutrons and the subsequent measurement of the albedo of thermal neutrons and neutron-capture gamma rays. On the basis of a laboratory model of a pipeline segment, a set of model experiments was conducted to assess the information content of radiation signals for different types of media surrounding pipes.

New Catalog of Neutron Capture γ Rays for Prompt Gamma Activation Analysis

Thermal neutron capture gamma rays were remeasured for all stable elements, except helium, at the guided neutron beam facility in Budapest. Energies, relative intensities and partial production cross-sections were determined with high precision for about 14, 000 gamma rays of 82 elements. The new experimental data were supplemented with isotopie data from ENSDF and the original papers and were evaluated. The resulting accurate new level and decay schemes comprise 35, 000 gamma-ray transitions. The new database is practically complete for light nuclei, hence capture cross-sections could be inferred from the measured partial gamma-ray production cross-sections. Precise neutron separation energies were also deduced from the fits to level schemes. The new elemental datasets will be the basic input to a new IAEA database for prompt gamma activation analysis, a chemical method of elemental analysis. The new isotopie sets will be provided for updating the thermal neutron capture datasets of ENSDF.

CdWO 4 scintillator as a compact gamma ray spectrometer for planetary lander missions

The objective of this work is to develop a gamma ray spectrometer (GRS) suitable for use on planetary rover missions. The main characteristics of this detector are low weight, small volume low power and resistance to cosmic ray radiation over a long period of time. We describe a 3 cm diameter by 3 cm thick CdWO 4 cylindrical scintillator coupled to a PMT as a GRS for the energy region 0.662–7.64 MeV. Its spectral performance and efficiency are compared to that of a CsI(Tl) scintillator 2.5 cm diameter by 6 cm thick coupled to a 28 mm×28 mm PIN photodiode. The comparison is made experimentally using 137Cs, 60Co, 6.13 MeV gamma rays from a 13C(α,γn)O 16* source, 7.64 MeV thermal neutron capture gamma rays emitted from iron bars using a 252Cf neutron source, and natural radioactivity 1.46 MeV 40K and 2.61 MeV 232Th gamma rays. We use a Monte Carlo method to calculate the total peak efficiency of these detectors and the full energy, first and second escape peak efficiencies. The experimental and calculated results agree well. We investigated the usefulness of these detectors for a GRS on a Mars lander mission. Although both detectors meet desired specifications, it was found that CdWO 4 has advantages over CsI(Tl) being a more compact detector of higher efficiency. Using a shaping amplifier of 24 ms, CdWO 4 spectrometer exhibited a 6.8% FWHM at 662 keV. At 6.13 MeV, CdWO 4 detector possesses an intrinsic total and full energy peak efficiencies of 16.7% and 6.3%, respectively. These efficiencies are nearly a factor of 1.6 and 4 greater than the corresponding efficiencies of the CsI(Tl) detector. A proposed gamma ray spectroscopy system to be placed on a rover, consists of a central detector surrounded by a Compton suppressor shield. The central detector is a cylindrical CdWO 4 detector and the Compton suppressor shield is made of segmented CdWO 4, coupled to PIN photodiodes. The shield also prevents thermal neutron activation of the central detector.

On-Belt Analysis of Ash in Coal

A new neutron and gamma-ray analysis system has been developed for the direct on-conveyor belt analysis of ash in coal. This analysis system incorporates a method for ash measurements that is relatively independent of changes in segregation, belt loading, and ash composition. Consequently, the analysis system provides greater accuracy than on-belt dual energy gamma-ray transmission (DUET) gauges but at a much lower cost than by-line prompt gamma-ray neutron activation analysis (PGNAA) analyzers and samplers. The NITA (Neutron Inelastic scatter and Thermal capture Analysis) method simultaneously measures prompt neutron inelastic scatter and thermal neutron capture gamma rays from bulk coal samples using a 241 Am-Be fast neutron source and bismuth germanate (BGO) detectors in transmission and backscatter geometries. The NITA method has been tested in both laboratory feasibility studies and, more recently, under simulated industrial conditions using a prototype analyzer. Measurements have been carried out on coal samples of ash contents from 6.7 to 49.4 wt% (dry basis (d.b.)) with variable ash composition and at thicknesses between 100 and 300 mm. The results show that accuracies of ∼0.5 wt% ash are achievable over a wide range of ash values, compositions, and thicknesses.

Photonuclear cross-sections of233U using neutron capture gamma-rays, near threshold

The photofission and photoneutron cross-sections of233U have been measured by using monochromatic and discrete photons produced by thermal neutron capture gamma-rays in several targets placed at the core of the IEA-R1 reactor in the energy interval from 5.43 MeV to 9.72 MeV. The evaluation of the total photoabsorption cross-sections and the parameters: single fission barrier, relative fissionability, fission probability, neutron emission/fission competition, nuclear temperature are also presented.

Photonuclear cross sections of Pu-239 using neutron capture gamma rays, near threshold

The photofission and photoneutron cross sections of Pu-239 have been measured by using monochromatic and discrete photons produced by thermal neutron capture gamma rays in several targets placed at the core of the IEA-R1 reactor in the energy interval from 5.43 MeV to 9.72 MeV. Analysing the photofission and photoneutron data we have observed similarities between the cross sections obtained for Pu-239 in comparison with the data obtained by other authors. From the photofission cross sections obtained and according to the liquid drop model, the height of the simple fission barrier was determined: F.B. = (5.7 ± 0.2) MeV. The relative fissionability to U-238 was also determined and shown to be energy independent: F.R. = (3.32 ± 0.41). For the competition between the photoneutron and the photofission emission (Γn/Γf) a constant value was found: (0.44 ± 0.05). By using this result the following nuclear temperature for Pu-239 was determined on basis of Nuclear Constant Temperature model of level density: T = (0.49 ± 0.05) MeV. The total photoabsorption cross sections were calculated as well as the photofission branching ratio (Γf/ΓA), or fission probability Pf. A constant value was also found: Pf = (0.70 ± 0.06).

Measurements of protein in limbs by IVNAA

A method for the determination of protein in human limbs by in vivo neutron activation analysis of their nitrogen content is described. The neutron flux is provided by a collimated 740 GBq (20 Ci) Pu−Be source. The 10.83 MeV thermal neutron capture gamma-rays from14N are detected by a 12.7 cm by 10.2 cm NaI(T1) detector. The nitrogen and hydrogen in an arm, the lower and the upper legs of two volunteers were measured with a statistical error around 3.6%–18% and 0.26%–0.56%, respectively. Also, the ratio of nitrogen to hydrogen in the limbs was compared. For a 1.000 s irradiation the dose equivalent was 0.3 mSv (30 mrem).

Angular distribution of Pu-239 photofission fragments near threshold, using neutron capture gamma rays

The angular distribution of Pu-239 photofission fragments produced by thermal neutron capture gamma rays in two targets placed in the IEA-R1 (Instituto de Energia Atomica-Reator 1) research reactor were measured. Angular distributions of the form W(θ) = A + B sin2θ were observed for discrete excitation energies of 5.43 MeV (sulphur target) and 7.35 MeV (lead target). An anisotropy that corresponds to (B/A = −0.122 ± 0.036) was recorded for E = 5.43 MeV. The angular distribution for E = 7.35 MeV was practically isotropic: (B/A = −0.01 ± 0.02).

Transport calculations of depth-dose distributions for gadolinium neutron capture therapy

Depth-dose distributions were calculated for thermal and epithermal neutron fluence and capture gamma ray dose rates using a two-dimensional neutron-coupled gamma-ray transport code (DOT 3.5) for gadolinium neutron capture therapy. The results show that (i) a capture gamma-ray dose rate of 10 Gy h-1 was obtained with a thermal neutron fluence rate of 1.5*109 cm-2 s-1 in a simulated tumour containing 5000 PPM gadolinium placed near the surface of a water phantom. (ii) deep-seated tumours may be treated with epithermal neutrons, and (iii) gadolinium neutron capture therapy appears to achieve comparable dose distributions to those of boron neutron capture therapy.

Radiative strength functions of germanium from thermal neutron capture.

Thermal neutron capture gamma rays from germanium have been studied using an internal irradiation facility and a pair spectrometer. Energy and intensity of transitions in four germanium isotopes were determined and their level and separation energies inferred. The separation energies are ${\mathit{S}}_{\mathit{n}}$ ${(}^{71}$Ge)=7415.95\ifmmode\pm\else\textpm\fi{}0.05 keV, ${\mathit{S}}_{\mathit{n}}$ ${(}^{73}$Ge)=6782.94\ifmmode\pm\else\textpm\fi{}0.05 keV, ${\mathit{S}}_{\mathit{n}}$ ${(}^{74}$Ge)=10 196.31\ifmmode\pm\else\textpm\fi{}0.07 keV, and ${\mathit{S}}_{\mathit{n}}$ ${(}^{75}$Ge)=6505.26\ifmmode\pm\else\textpm\fi{}0.08 keV. The E1 reduced strength function, 〈${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}\mathit{i}}$${\mathit{D}}^{\mathrm{\ensuremath{-}}1}$${\mathit{E}}_{\mathit{i}}^{\mathrm{\ensuremath{-}}3}$${\mathit{A}}^{\mathrm{\ensuremath{-}}2/3}$〉, of these germanium isotopes was found to be (1.8\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}9}$ ${\mathrm{MeV}}^{\mathrm{\ensuremath{-}}3}$, a value lower than the global average. The M1 strength function 〈${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}\mathit{i}}$${\mathit{D}}^{\mathrm{\ensuremath{-}}1}$${\mathit{E}}_{\mathit{i}}^{\mathrm{\ensuremath{-}}3}$〉 of $^{74}\mathrm{Ge}$ was estimated to be (20\ifmmode\pm\else\textpm\fi{}9)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}9}$ ${\mathrm{MeV}}^{\mathrm{\ensuremath{-}}3}$ which agrees with the global average. The average B(E2)\ensuremath{\downarrow}\ifmmode\bar\else\textasciimacron\fi{} of $^{74}\mathrm{Ge}$ using the present thermal data and the previous resonance data from literature was found to be 18\ifmmode\pm\else\textpm\fi{}10${\mathit{e}}^{2}$ ${\mathrm{fm}}^{4}$ MeV $^{\mathrm{\ensuremath{-}}1}$ which agrees with the value predicted by the Axel-Brink hypothesis.

Thermal neutron capture γ-ray spectrum of lanthanum

The thermal neutron capture gamma rays from the reaction 139La(n, γ)140La were investigated using a pair spectrometer and the tangential facility at the McMaster University Nuclear Reactor. A large number of previously unreported transitions have been observed from which details of the 140La structure are inferred. The level density is found to be consistent with a statistical model encompassing nuclear temperature. The reduced E1 strength function of 140La was found to be (1.4 ± 0.4) × 10−9 MeV−3. The giant dipole resonance model seems to overestimate the E1 strength in this nucleus. The separation energy of 140La is found to be 5161.00 ± 0.05 keV.

Transport calculations of the influence of physical factors on depth-dose distributions in boron neutron capture therapy

Distributions of thermal neutron fluence and capture gamma ray absorbed dose rates were evaluated, taking into consideration various physical factors relevant to boron neutron capture therapy. The use of a larger neutron irradiation aperture was associated with an increase in thermal neutron fluence and capture gamma ray absorbed dose rates. Radiation leakage was more significant with smaller phantoms. Attenuation of thermal neutron fluence rates by 10B suggested that there was an optimal 10B concentration (<100 PPM) for a given tumour. Deuteration of water allowed better penetration of thermal neutrons with less capture gamma rays and is potentially applicable for the treatment of deep-seated brain tumours.

53Cr(n, γ); Transition energies and levels excited in thermal neutron capture

The nuclear level structure of 54Cr was studied by thermal-neutron capture gamma-ray spectroscopy of an enriched sample of 53Cr and compared with a natural chromium sample by means of a Ge(Li) spectrometer, using an external beam at the SAFARI-1 reactor. Eighty of the ninety observed transitions allocated to 54Cr (as compared with the previously observed total of 42) could be placed in a level and decay scheme, representing more than 99% of the total observed intensity. The energy precision of several levels observed in other reactions was improved and limits were imposed on their spins. The sensitivity of the experiment allowed the observation of low-lying levels up to spin 4. A new level is proposed at 3925.5 keV, close to the known level of 3927.6 keV. Improved gamma branching ratios were obtained for a number of levels. The neutron binding energy was found to be in agreement with previous determinations.

Thermal neutron capture gamma-rays from natural cerium and osmium

A revised table of energy and intensity of prompt gamma-rays from thermal neutron capture in natural cerium and osmium is recommended for use in high resolution analytical prompt gamma-ray spectroscopy.

Thermal neutron capture gamma rays from sulfur isotopes: Experiment and theory.

We have carried out a systematic investigation of $\ensuremath{\gamma}$ rays after thermal neutron capture by all stable sulfur isotopes ($^{32}\mathrm{S}$, $^{33}\mathrm{S}$, $^{34}\mathrm{S}$, and $^{36}\mathrm{S}$). The measurements were made at the internal target facility at the Los Alamos Omega West Reactor. We detected a larger number of $\ensuremath{\gamma}$ rays: \ensuremath{\sim}100 in $^{33}\mathrm{S}$, \ensuremath{\sim}270 in $^{34}\mathrm{S}$, \ensuremath{\sim}60 in $^{35}\mathrm{S}$, and \ensuremath{\sim}15 in $^{37}\mathrm{S}$. Before developing detailed level schemes, we culled and then consolidated the existing information on energies and ${J}^{\ensuremath{\pi}}$ values for levels of these nuclides. Based on the current data, we have constructed detailed decay schemes, which imply that there are significant populations of 26 excited states in $^{33}\mathrm{S}$, 70 states in $^{34}\mathrm{S}$, 20 states in $^{35}\mathrm{S}$, and 7 states in $^{37}\mathrm{S}$. By checking the intensity balance for these levels and by comparing the total intensity of primary transitions with the total intensity of secondary $\ensuremath{\gamma}$ rays feeding the ground state, we have demonstrated the relative completeness of these decay schemes. For strongly populated levels, the branching ratios based on the current measurements are generally better than those available from previous measurements. In all four cases, a few primary electric dipole ($E1$) transitions account for a large fraction of the capture cross section for that particular nuclide. To understand and explain these transitions, we have recapitulated and further developed the theory of potential capture. Toward this end, we reviewed the theory relating off-resonance neutron capture to the optical-model capture. We studied a range of model-dependent effects (nature and magnitude of imaginary potential, surface diffuseness, etc.) on the potential capture cross section, and we have shown how experimental data may be analyzed using the expression for channel capture suitably modified by a factor that takes into account the model-dependent effects. The calculations of cross sections for most of the primary transitions in the sulfur isotopes are in good agreement with the data. Some discrepancies for weaker transitions can be explained well by an interfering compound-nucleus contribution to capture. This contribution is of the magnitude expected from statistical surveys of resonance capture data. Estimates of the cross section due to the valencecapture mechanism in $s$-wave resonances show that this cross section should dominate the more complicated compound-nucleus contributions.

In-Situ Elemental Analysis of Coal and Strategic Metals by Neutron Activation: ABSTRACT

Starting in 1969, the U.S. Geological Survey (USGS) developed neutron techniques for borehole measurement of the elemental composition of ores, and it successfully made a borehole ultimate analysis of coal in 1977. Borehole measurements permit real-time evaluation of ore quality without the expense of coring or the delays and expense associated with laboratory analyses. Two technological innovations have made such measurements possible: the availability of small californium-252 fission neutron sources from the Savannah River Operations Office of the Department of Energy, and the development, by USGS and Princeton Gamma-Tech, of the melting-cryogen-cooled high-purity germanium borehole gamma-ray detector. A technique of relating mass fractions to measured gamma-ray intensi ies, which eliminates the need for detailed knowledge of the geometry of the neutron distribution, was used to calculate elemental compositions without using test pits or computer borehole modeling. Most of the common elements in the earth's crust can be detected by neutron techniques. In coal all of the major constituents except oxygen (C, H, N, S, Si, Al, Fe, Ti) can be determined quantitatively by thermal neutron capture gamma-ray spectroscopy. The latest innovation in this field is the replacement of the 252Cf neutron source with a neutron generator, a type of ion accelerator. These generators, used for many years by the petroleum logging industry, produce neutrons having an energy of 14 MeV. The neutron generator is a safer tool than californium, because no radiation is e itted by the device until it is turned on in the borehole. Coupling a neutron generator with a high-resolution detector to form a borehole measuring system was pioneered by workers at Sandia National Laboratories. USGS has built and put into service one neutron generator based on the Sandia design, and now is building a second. This new device enables the experimenter to use higher energy (n,n^prime), (n,p), (n,2n), and (n,^agr) reactions as well as the (n,^ggr) thermal neutron capture reaction. Both the (n,n^prime) and the (n,p) reactions on 16O permit quantitative measurement of oxygen, and the inelastic scattering excitation of carbon in coal provides increased sensitivity over that of the (n,^ggr) reaction. Reactions caused by 14 MeV-neutron irradiation that are used in ex loration for strategic metals such as Cr, Ni, Mn, V, Co, Ti, and W are tabulated. End_of_Article - Last_Page 1442------------

The application of thermal neutron capture gamma rays to matrix identification in a transuranic waste assay system based on an electron accelerator

A Ge(Li) detector with a preamplifier modified to handle high count rates was used on-line with an electron linear accelerator for thermal neutron capture gamma-ray spectroscopy. The measurements identified seven potential matrix constituents in bulk containers of transuranic waste. This information is needed to make necessary corrections for matrix attenuation and absorption effects on neutron and photon assay results.