Measuremets of presolar grain in meteorite using neutron activation analysis with multi-parameter coincidence method

Neutron activation analysis with multi-parameter coincidence method was developed at the Japan Atomic Energy Agency (JAEA) and a non-destructive, ultra-high sensitive multi-elemental determination has been realized. The multi-parameter coincidence method is carried out with an array of 19 germanium detectors, GEMINI-II. Using this system, very weak γ-rays emitted from trace amounts of elements can be detected. The presolar grains were extracted from the Allende meteorite. Trace elements in the presolar diamonds were measured by neutron activation analysis with multi-parameter coincidence method.     

Determination of trace elements using multi-parameter coincidence spectrometry

In this study, sensitive trace element analyses were carried out without chemical separation by the combination of neutron activation analysis and multi-parameter coincidence spectroscopy. A long-lived radioisotope ¹²⁹I in algae samples and iridium in geological samples were analyzed.     

Multiple gamma-ray detection method and its application to nuclear chemistry

A new radionuclide quantification method is proposed on the basis of multiple gamma-ray detection, which is two or higher fold gamma-ray coincidence method. The coincidence method has so far been used for nuclear structure study. We apply this method for quantification of radioactive nuclei. The advantage of this method consists of high energy resolution and high sensitivity. It is successfully applied to nuclear waste analysis, neutron activation analysis and prompt gamma-ray analysis. The principle of the multiple gamma-ray detection method and future perspectives for an innovative pulsed neutron source and a new detector system will be presented.     

New technique for the determination of trace elements using multiparameter coincidence spectrometry

Multiparameter coincidence g-ray spectrometry based on g-g coincidence is widely used in the field of nuclear structure studies, and has produced many succesful results. In this paper, feasibility of the method for neutron activation analysis of trace elements was studied. Particularly, a long-lived radioisotope ¹²⁹I (T_1/2 = 1.57^.10⁷ y) in algae samples and iridium in geological samples has been determined.     

Multiparameter Coincidence Spectrometry Applied to the Non-Destructive Neutron Activation Analysis of Meteorites

Abstract

A non-destructive method for the neutron activation analysis of chondritic meteorites by multiparameter coincidence spectrometry is described. Results for sodium, cobalt, nickel and iridium are presented, and agree with single coincidence spectrometry measurements. Scandium photopeaks are prominent in the multiparameter spectrum and this element could also be determined. The advantages of multiparameter spectrometry over single coincidence counting are outlined.     

Multiple prompt gamma-ray analysis and construction of its beam line

By combining neutron activation analysis with multiple gamma-ray detection (gamma-gamma coincidence), we have proved better sensitivity and resolution for the trace element analysis than the ordinary single gamma-ray detection method. We now try to apply the multiple gamma-ray detection method to the prompt gamma ray analysis (PGA). We have established a new cold neutron beam line for PGA in Japan Research Reactor, JRR-3M, at Tokai establishment of Japan Atomic Energy Research Institute (JAERI). It consists of a beam shutter, a beam attenuator, a gamma-ray detector array, a sample changer, and a beam stopper. We construct a high-efficiency gamma-ray detector array specially designed for this purpose. Its performance has been evaluated with the Monte Carlo simulation code, GEANT 4.5.0.     

Simultaneous determination of Ir and Se in K-T boundary clays and volcanic sublimates

Our instrumental analytical method for an ultra-sensitive determination of Ir and Se in sediments and volcanic emission products is based on epithermal neutron activation analysis (ENAA) coupled with multiparameter coincidence spectrometry. An adequate setting of the energy paths and of the multiparameter coincidence spectrometry. An adequate setting of the energy paths and of the multiparameter analyzer allows a simultaneous counting of⁷⁵Se and¹⁹²Ir coincidences. This tool has been used to analyse different sediments sampled at the Cretaceous-Tertiary boundary (KTB) and volcanic samples in order to discuss the extra-terrestrial or volcanic origin of the Ir anomaly.     

Coincidence counting for PGNAA applications: Is it the optimum method?

Summary One of the main advantages of γ-γ coincidence counting is the reduction of the background spectrum, pulse pile-up, and summing effects (for simple schemes). For prompt gamma-ray neutron activation analysis (PGNAA), the sources of background include the gamma-rays from the natural background, from surrounding materials, from the neutron source, and from detector neutron activation. While this counting approach effectively increases the signal-to-noise (S/N) ratio, it also decreases the signal counting rate. This adds some practical limitations to using this approach. In this work, two examples are presented for the efficient use of the coincidence counting approach.     

Dating of some Romanian fossil bones by combined nuclear methods

A set of fossil bones from Romania has been analysed by accelerator mass spectrometry and by neutron activation analysis in order to estimate their age. The temporal attributing of Malu Rosu archaeological settlement has been extensively analyzed. The radiocarbon age, determined by accelerator mass spectrometry, for this site is 5510±200 BP. This is in agreement with the age of 6000±2000 BP, obtained by the dating method based on fluorine content, determined by neutron activation analysis.     

Determination of copper in geological material by neutron activation and gamma-gamma coincidence spectrometry

The copper content of some geological samples has been determined by thermal neutron activation and subsequent coincidence gamma-spectrometry, taking advantage of the 180 degrees annihilation quanta of (64)Cu. By this means the interference of (24)Na, which is often the major gamma-activity induced in geological materials, is greatly reduced. The method is precise to about +/- 5 %, and the error is of the same order. The method should be especially attractive for application to samples with a copper content of 100-1000 ppm.     

The correct and incorrect way to calibrate a Compton suppression counting system for gamma-ray efficiency

Gamma-ray efficiency calculations for a germanium detector have been made for a Compton suppression system. Results have shown that for radionuclides that have gamma rays in coincidence the photopeaks can be severely depressed leading to erroneous results. While this can be overcome in routine neutron activation analysis using a comparator method, special consideration must be given to determine the suppression for coincident gamma rays when calculating the efficiency curve and for radionuclide activities. This is especially important for users of the k ₀ method and for fission product identification using Compton suppression methods.     

Metrological role of neutron activation analysis. IB. Inherent characteristics of relative INAA as a primary ratio method of measurement

This is the second part of a paper which deals with the advantages and disadvantages of relative instrumental neutron activation analysis concerning traceability and uncertainty, and the current scope and possible future extensions of neutron activation analysis as a primary ratio method. The first part of this paper has been published in this Journal [1]. Received: 19 March 2001 Accepted: 2 October 2001     

Monte Carlo calculations and neutron spectrometry in quantitative prompt gamma neutron activation analysis (PGNAA) of bulk samples using an isotopic neutron source

An activation analysis facility based on an isotopic neutron source (185 GBq ²⁴¹Am/Be) which can perform both prompt and cyclic activation analysis on bulk samples, has been used for more than 20 years in many applications including 'in vivo' activation analysis and the determination of the composition of bio-environmental samples, such as, landfill waste and coal. Although the comparator method is often employed, because of the variety in shape, size and elemental composition of these bulk samples, it is often difficult and time consuming to construct appropriate comparator samples for reference. One of the obvious problems is the distribution and energy of the neutron flux in these bulk and comparator samples. In recent years, we have attempted to adopt the absolute method based on a monostandard and to make calculations using a Monte Carlo code (MCNP4C2) to explore this further. In particular, a model of the irradiation facility has been made using the MCNP4C2 code in order to investigate the factors contributing to the quantitative determination of the elemental concentrations through prompt gamma neutron activation analysis (PGNAA) and most importantly, to estimate how the neutron energy spectrum and neutron dose vary with penetration depth into the sample. This simulation is compared against the scattered and transmitted neutron energy spectra that are experimentally and empirically determined using a portable neutron spectrometry system. This revised version was published online in August 2006 with corrections to the Cover Date.     

Monte Carlo source simulation technique for solution of interference reactions in INAA experiments: a preliminary report

A new method using Monte Carlo source simulation of interference reactions in neutron activation analysis experiments has been developed. The neutron spectrum at the sample location has been simulated using the Monte Carlo code MCNP and the contributions of different elements to produce a specified gamma line have been determined. The produced response matrix has been used to measure peak areas and the sample masses of the elements of interest. A number of benchmark experiments have been performed and the calculated results verified against known values. The good agreement obtained between the calculated and known values suggests that this technique may be useful for the elimination of interference reactions in neutron activation analysis.     

Determination of yttrium in rare earths by photon activation analysis

The determination of yttrium in the presence of large amounts of the rare earths by the thermal neutron reaction (89)Y(n, gamma)(90)Y is complicated because of frequent problems of sample self-shielding from major constituents of the sample, and the difficulty of separating (90)Y, a pure beta-emitter, from other elements which are very similar chemically. A non-destructive photon activation analysis method has been developed for this determination. Bremsstrahlung from a 35-muA beam of 35-MeV electrons induces the photonuclear reaction (89)Y(gamma, n)(88)Y. Optimum sensitivity is obtained by coincidence counting of the 0.90 and 1.84 MeV gamma-rays associated with the decay of (88)Y. The detection limit is less than 1 mug of yttrium.     

Practical aspects of neutron activation determination of the platinum metals

Triple gamma coincidence counting of¹⁹²Ir allowed the determination of Ir by instrumental neutron activation analysis down to 1 ppb in ultrabasic rocks and down to ca. 20 ppb in some high-furnace slags; the limiting factor for the latter matrix was the presence of¹²⁴Sb. Radiochemical neutron activation analysis of the USGS standard rocks revealed that the Ir contents are up to three orders of magnitude lower than previously reported, except for the ultrabasic rocks. The factor of merit of several scintillation and semiconductor, gamma-ray detectors was determined for the neutron activation determination of Pd, Pt and Os. In the case of radiochemically pure sources, a NaI(Tl) wafer was preferred; in the presence of high-energy gamma-emitters, a Ge(Li) low-energy photon detector was superior.     

Characterization of InxGa1−xAs crystals by 14 MeV neutron activation analysis

Indium doped GaAs crystals are analyzed quantitatively for indium by non-destructive 14 MeV neutron activation analysis. Experimental conditions are optimized to provide a precision of ±5% and a practical sensitivity of 50 ppm, by weight. The accuracy of the neutron activation method is established by comparison with the results obtained by atomic absorption and Rutherford back-scattering techniques. The method has been applied for determining the homogeneity of indium distribution of wafers by sectional analysis and is demonstrated as a reference method for calibrating the low temperature photoluminescence technique.     

Design and construction of a facility for neutron activation analysis using the 14 MeV neutron generator at HMS Sultan

The potential for using a small, sealed tube, DT neutron generator for neutron activation analysis has been well documented but not well demonstrated, except for 14 MeV activation analysis. This paper describes the design, construction and characterization of a neutron irradiation facility incorporating a small sealed tube DT neutron generator producing 14 MeV neutrons with fluence rates of 2·10⁸ s⁻¹ in 4π (steady state) and 10¹¹ s⁻¹ in 4π (pulsed). Monte Carlo modeling using MCNP4c and McBend9 has been used to optimize the design of this facility, including the location of a thermal irradiation facility for conventional neutron activation analysis. A significant factor in designing the facility has been the requirement to conform with Ionising Radiation Regulations and the design has been optimized to keep potential radiation doses to less that 1 μSv/h at the external walls of the facility. Activation of gold foils has been used for flux characterization and the experimental results agree well with the modeling.     

A rapid radiochemical procedure for uranium determination in natural waters

A neutron activation analysis method for the determination of uranium in natural fresh waters is described. The method is based on a preconcentration step by precipitation of the metal oxinate on a phenolphtalein bed followed by instrumental neutron activation analysis. Preliminary investigations with²³⁹U radiotracer were carried cut to set up the best working conditions and to evaluate the chemical yield. The whole procedure has been applied to the determination of uranium in river water.     

Neutron activation analysis by combined capture and decay gamma-spectrum method

The usual method of the neutron activation analysis is performed by the measurement of the characteristic nuclear radiations of the produced radioactive isotope by neutron irradiation. An advance in this field has recently been proposed in which the prompt capture γ-rays are observed in addition to the nuclear radiation of the produced nucleus. The characteristic energy spectra of these two kinds of γ-radiations are the main basis for the combined activation analysis method. The experimental setup consists of a γ-radiation pulse height energy spectrum system which is synchronized with a pulsing neutron generator of ‘D—T’ or ‘D—D’ reaction. The present results indicate that a qualitative and semi-quantitative determination of a number of elements is feasible, with an overall error of 10–15%.