A method for bulk hydrogen analysis based on transmission and back scattering of fast neutrons

A method was proposed for bulk hydrogen analysis. It is based on simultaneous detection of transmitted fast neutrons and back scattered thermal neutrons from the investigated samples by ³He detectors. The fast neutron beams were obtained from ²⁵²Cf and Pu–Be neutron sources. The experimental set-up as well as samples preparation were described. Incident thermal neutrons beams obtained from either ²⁵²Cf or Pu–Be sources, were used to investigate the samples by neutron backscattering. The results obtained from transmission and backscattering of fast neutrons were compared and discussed. The advantage and capabilities of the proposed method were presented. The results obtained using fast neutron beams are more sensitive than those obtained using thermal neutron beams. Validation procedures were proposed to credit the results.     

Characterization of prototype perforated semiconductor neutron detectors

Semiconductor detectors whose surfaces are coated with neutron-reactive material can be made to detect thermal neutrons, but with efficiencies only of a few percent. However, perforating the semiconductor material, filling the perforations with neutron-reactive material, and then coating the detector surface can lead to neutron detectors of much higher thermal neutron detection efficiencies, perhaps approaching or exceeding 50%. Several perforated semiconductor neutron detectors have been constructed, both for dosimetry and for position-sensitive neutron detection. The characterization of prototype devices based on these detectors is described.     

Determination of trace concentrations of transmuted stable nuclides in TMD detectors using PGAA

The capability of prompt gamma-ray activation analysis (PGAA) for neutron fluence dosimetry by means of transmutation detectors is reported. The metallic foils of Ni, Au, Cu and Nb and the small piece of Ge crystal, which were irradiated at the LVR-15 reactor at ?e? for several days, were selected for analysis by PGAA technique. Concentrations of transmuted stable nuclides in these foils were measured using the PGAA facility installed at the research reactor FRM II in Garching.     

Reactor neutrons irradiation effect on the photocatalytic activity of SnO<Subscript>2</Subscript> thin films

SnO₂ thin films synthesized by sol-gel are irradiated with reactor neutrons up to fast neutron fluence of 9.6 × 10¹⁷ neutrons cm^–2 at 40°C. The influence of defects generated by neutrons irradiation, through the properties modification, on the photo-catalytic activity of SnO₂ films is investigated. It is found that the photoactivity of the irradiated films is enhanced after reactor neutrons irradiation. An improvement of 41% is observed for the sample irradiated at a neutron fluence of 9.6 × 10¹⁷ neutrons cm^–2. This is attributed to several parameters modified by the reactor neutron irradiation principally the crystallite size and space charge region which are closely related to the photocatalytic performance.     

Property of TS-16N solid state nuclear track detectors as an imaging medium for macroautoradiography of alpha-emitters in biological specimens

Feasibility of TS-16N solid state nuclear track detectors for an imaging medium of rapid autoradiography of alpha-emitters is described. Though a little longer etching time was required, the contrast of autoradiographic image on this detector proved to be superior to CR-39 detectors whose property for macroautoradiography was previously reported by the authors. The resolutions of these two different type detectors were almost equivalent to each other. The autoradiography taken by way of trial proved that this detector could be used to study metabolism and dosimetry of internally deposited alpha-emitters. With further study, the inherent properties of this detector such as low background or high sensitivity should extend the field of track etch imaging technique such as fast neutron radiography.     

Recent developments of radioanalytical methods at the IBR-2 pulsed fast reactor

Experience in the application of radioanalytical methods, including NAA, at the IBR-2 pulsed fast reactor is reviewed. Details of the instruments dedicated to neutron activation analysis and radiography studies are reported. Applications of resonance neutrons to environmental monitoring, studying of water ecosystems, analysis of geological samples in oil extraction regions, and investigation of high-purity materials are exemplified.     

Inteferences in neutron and photon activation analysis

The effect of following interferences was quantitatively assessed in terms of interference factor by irradiating samples together with highly pure reagents at two reactor sites of diferent neutron spectra and fluxes for neutron activation analysis (NAA) and an electron LINAC for photon activation analysis (PAA). The interfering reactions studied are 91) fast neutron-induced reactions, (2) uranium fission (3) (n,γ) reactions of other target elements in NAA, and (4) reactions induced by secondary neutrons in PAA. Corrections for these interferences were successfully applied to the activation analysis of some geological reference rock samples and biological samples.     

Performance comparison of 2.8 MeV and <Superscript>241</Superscript>Am-Be neutrons based moisture measurement setups

Performance of a ²⁴¹Am-Be neutron source-based and 2.8 MeV neutrons-based moisture measurement setups have been compared using Monte Carlo simulation. In the setup fast neutrons transmitted through the sample were detected by a fast neutron detector, which was placed behind a massive long double truncated collimator. The setup geometry was optimized to detect maximum effect of 1–7 wt.% moisture on the neutron intensity transmitted through the sample. The yield of neutrons transmitted through concrete, coal, wood and soil samples containing 1–7 wt.% moisture was calculated for 2.8 MeV neutrons and neutrons from an ²⁴¹Am-Be source. The slopes of the fast neutron intensities transmitted through the samples vs. their moisture contents are very sensitive to the neutron energy and the sample composition. Higher slopes have been observed for the samples with larger bulk density. The slopes of fast neutron yield show dependence on the incident neutron energy. Larger slopes have been observed for neutrons with samller energy. Due to the overall large slopes of the transmitted intensity data of the samples for 2.8 MeV neutrons, it is expected to achieve better sensitivity in moisture measurements for a 2.8 MeV neutrons based moisture setup.     

Activation analysis opportunities using cold neutron beams

Guided beams of cold neutrons being installed at a number of research reactors may become increasingly available for analytical research. A guided cold beam will provide higher neutron fluence rates and lower background interferences than in present facilities. In an optimized facility, fluence rates of 10⁹ n·cm^–2·s^–1 are obtainable. Focusing a large area beam onto a small target will further increase the neutron intensity. In addition, the shift to lower neutron energy increases the effective cross sections. The absence of fast neutrons and gamma rays permits detectors to be placed near the sample without intolerable background, and thus the efficiency for counting prompt gamma rays can be much higher than in present systems. Measurements made at the hydrogen cold source of the FRJ-2 (DIDO) reactor at the KFA provide a numerical evaluation of the improvements in PGAA with respect to signal-to-background ratios of important elements and matrices.     

Determination of ko-factors of short-lived nuclides (T≧1 min) by thermal neutron activation technique

The k_o,Au-factors for 11 short-lived nuclides with T less than 1 min have been determined by irradiating the samples with thermal neutrons in the reactor thermal column using the pneumatic transfer system. The results obtained experimentally, without any error induced by the fast component of the reactor neutron spectrum and uncertainties of nuclear related characteristics, are in good agreement with the calculated data.     

Determination of cobalt in nickel in the sub-ppm level with cold neutrons

The determination of cobalt in nickel with neutron activation analysis (NAA) is hindered by an interfering nuclear reaction induced by fast neutrons. To overcome this obstacle cold neutron beam irradiation has been carried out. As a result, a cobalt concentration of 0.25±0.02 μg/g in nickel foil has been determined. This nickel foil is intended to become a reference material for neutron dosimetry.     

Determination of fluorine in geological samples using accelerator derived neutrons

A fast, neutron activation analysis technique is described for the determination of fluorine in geological samples. The method utilises the reaction¹⁹F(n,α)¹⁶N for the determination. However, it avoids the interference reaction from oxygen which produces the same radionuclide since the neutrons are derived from the bombardment of beryllium with 3 MeV deuterons. The maximum energy of the neutrons so produced is well below the threshold for the competing oxygen reaction. The results indicate that the method gives acceptable accuracy over the range of a few tens ppm to several percent fluorine content using suitable standards. Sample analysis time is only a few minutes allowing the analyses of large numbers of samples per day.     

Oxygen determination by fast neutron activation

A method for the determination of oxygen based on the reaction¹⁶O(n, p)¹⁶N is suggested. The samples are irradiated in stainless steel capsules with fast neutrons. The total neutron flux passing through the sample is proportional to the flux passing through the wall of the capsule. Therefore, the activity induced in the capsule according to the reaction⁵⁶Fe(n, p)⁵⁶Mn can be used to monitor the neutron flux through the sample. Thus, the necessity of maintaining the sample in an exact position during the irradiation is eliminated.     

Use of D–T-produced fast neutrons for in vivo body composition analysis: a reference method for nutritional assessment in the elderly

Body composition has become the main outcome of many nutritional intervention studies including osteoporosis, malnutrition, obesity, AIDS, and aging. Traditional indirect body composition methods developed with healthy young adults do not apply to the elderly or diseased. Fast neutron activation (for N and P) and neutron inelastic scattering (for C and O) are used to assess in vivo elements characteristic of specific body compartments. Non-bone phosphorus for muscle is measured by the ³¹P(n,)²⁸Al reaction, and nitrogen for protein via the ¹⁴N(n,2n)¹³N fast neutron reaction. Inelastic neutron scattering is used to measure total body carbon and oxygen. Body fat is derived from carbon after correcting for contributions from protein, bone, and glycogen. Carbon-to-oxygen ratio (C/O) is used to measure the distribution of fat and lean tissue in the body and to monitor small changes of lean mass. A sealed, D–T neutron generator is used for the production of fast neutrons. Carbon and oxygen mass and their ratio are measured in vivo at a radiation exposure of less than 0.06 mSv. Gamma-ray spectra are collected using large BGO detectors and analyzed for the 4.43 MeV state of carbon and 6.13 MeV state of oxygen, simultaneously with the irradiation. P and N analysis by delayed fast neutron activation is performed by transferring the patient to a shielded room equipped with an array of NaI(Tl) detectors. A combination of measurements makes possible the assessment of the quality of fat-free mass. The neutron generator system is used to evaluate the efficacy of new treatments, to study mechanisms of lean tissue depletion with aging, and to investigate methods for preserving function and quality of life in the elderly. It is also used as a reference method for the validation of portable instruments of nutritional assessment.     

Regent developments of radioanalytical methods at the IBR-2 pulsed fast reactor

Experience in application of radioanalytical methods, including NAA, at the IBR-2 pulsed fast reactor is reviewed. Details of the instruments dedicated to the neutron activation analysis and radiography studies are reported. Applications of resonance neutrons to environmental control, to analysis of geological samples in oil extraction regions, to testing the quality of food products, and to the investigation of high-purity materials to solve nuclear physics problems, are exemplified. Work to use isotopic neutron sources for an analysis for nitrogen in natural and synthetic materials is being carried out.     

Determination of rare earth elements in rice by INAA and ICP-MS

In order to improve the accuracy of reactor neutron activation analysis, flux gradients and spectrum changes in the irradiation capsule have been studied at the Kyoto University Reactor (KUR). The flux and spectrum monitoring samples of Fe, Co, Au, Sb, U and Ni were placed at several positions in a polyethylene irradiation capsule of 24 mm inner diameter and 98 mm length, and were irradiated in a pneumatic irradiation facility (Pn-2). The flux gradients were found to be rather negligible in the vertical (axial) direction while they were considerable in the radial one. The flux gradient was around 5%/cm for thermal neutrons and 10%/cm for epithermal and fast neutrons. The spectrum changes were dependent on the materials (polyethylene and silica) filled in the capsule. Based on these observations, the effect of the flux gradients and spectrum changes on the accuracy of reactor neutron activation analysis was discussed.     

Monoenergetic neutron sources below 100 MeV

Monoenergetic neutron sources are essential for fundamental studies in radiobiology and dosimetry, for measurement of cross sections and kerma coefficients, for calibration of detectors, for activation analysis and for fusion research. Monoenergetic neutrons below energies of 20 MeV are most conveniently produced by reactions between the hydrogen isotopes or between protons and ⁷Li. By proper choice of reaction type monoenergetic neutrons up to 20 MeV can be produced with negligible secondary background radiation. These reactions cannot provide monoenergetic beams between about 8 and 14 MeV and in this “gap” region inverse reactions are most favourable. The most practical way of producing quasi-monoenergetic neutron beams in the energy range from 20 to 100 MeV is by the bombardment of light elements with protons. Because of the relative simplicity of manufacturing suitable isotopically-pure targets and the large 0° cross section, the ⁷Li(p,n)⁷Be reaction is a convenient source of quasi-monoenergetic neutrons over this range of energies, although the ⁹Be(p,n)⁹B reaction is also used.     

Pulsed neutron-based on-line coal analysis

A neutron generator-based on-line coal analysis system is described, capable of measuring the content of the major and minor elements in coal. The system utilizes reactions produced from fast and themal neutrons, as well as from neutron activation with half lives of seconds or minutes. Characteristic γ-rays, detected with BGO detectors are used for the identification of the various chemical elements. The method for the analysis of the γ-ray spectra is presented, and the measurements of coal density, carbon and sulfur content are shown.     

U determination in environmental samples by delayed neutron activation analysis in Korea

A delayed neutron counting system has been implemented at the HANARO research reactor in 2007. Thermal neutron flux measured at the NAA #2 irradiation hole coupled to the delayed counting system, was higher than 3 × 10¹³ n cm⁻² s⁻¹. The delayed neutron counting system is composed of 18 ³He detectors which are divided into three groups with six detectors and the collected signals of each group are processed to a digital signal. The count numbers were measured with the uranium mass by using NIST SRMs under fixed analytical condition and their correlation could be determined. Finally, delayed neutron activation analysis has been carried out for the determination of uranium mass fraction in the collected environmental samples.     

Verwendung schneller Reaktorneutronen zur raschen und zerst?rungsfreien Spurenanalyse, insbesondere von Sauerstoff

Zusammenfassung Der intensive Fluß schneller Neutronen, wie er von Kernreaktoren geliefert wird, kann für eine rasche und zerstörungsfreie, aktivierungs-analytische Bestimmung einer Vielzahl von Elementen verwendet werden. Bei manchen Elementen läßt sich sogar bei der Aktivierung mit schnellen Reaktorneutronen eine im Vergleich zur Aktivierungsanalyse mit thermischen Neutronen tiefere Erfassungsgrenze erreichen. Werden die Proben in einem schnellen, halbautomatischen Rohrpostsystem zum Reaktorkern befördert, können auch sehr kurzlebige Radionuklide gemessen werden. Besonders Sauerstoff läßt sich über die Kernreaktion ¹⁶O(n, p)¹⁶N sehr empfindlich bestimmen, wobei die hochenergetischen -Quanten des 7,2 sec Stickstoff-16 gemessen werden. Es können so bis zu 10 ppm Sauerstoff in vielen Arten von Analysenproben erfaßt werden. Das halbautomatische Analysensystem, das mit Hilfe einer schnellen Rohrpost die Durchführung rascher und zerstörungsfreier Aktivierungs-analysen im Forschungsreaktor München erlaubt, wird beschrieben. Die Verwendung des Systems zur Sauerstoffanalyse und die damit zusammenhängenden Probleme werden genauer besprochen.

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Summary The intense fast-neutron fluxes, which are available in nuclear reactors, can be used for rapid and non-destructive activation analysis of many elements. Some elements have even superior detection limits for activation with fast reactor neutrons compared to reactor thermal-neutron activation. Short-lived radionuclides can also be measured using a fast pneumatic tube system. Oxygen can be determined by the nuclear reaction ¹⁶O(n, p)¹⁶N initiated by fast reactor neutrons counting the high-energy gamma rays of the 7.4 sec nitrogen-16. The method is suitable for determining as little as 10 ppm of oxygen in many types of analytical samples. The fast transfer system, which is used in the Munich research reactor for rapid and non-destructive activation analysis is described. The use of the transfer-system for oxygen activation analysis and problems associated with oxygen analysis are discussed.