In vivo analysis for nitrogen using a252Cf source

A set up forin vivo determination of nitrogen has been built. Phantoms containing different amounts of nitrogen have been measured as well as a volunteer in a pilot study. A total body protein content of 18.8 kg was calculated, to be compared with 17.0 kg estimated from potassium measurements.     

Study of a neutron radiography system using Cf neutron source

This paper presents a study about moderation and collimation of a neutron radiography system using ²⁵²Cf. A Monte Carlo Code, MCNP4B, has been used to obtain a maximum and more homogeneous thermal neutron flux in the collimator outlet next to the image plane. Among the various moderator materials investigated, high density polyethylene proved to be the most efficient, with a thermalization factor of 56 cm². Using a collimator design assembly it was possible to obtain a normalized thermal neutron flux, at the image plane of 6×10⁻⁶ n cm⁻² s⁻¹ at an effective collimator ratio of 7.5, or 3.2×10⁻⁷ n cm⁻² s⁻¹ at an effective collimator ratio of 50.     

Neutron activation analysis with PE moderated252Cf neutron source

The 1.369 MeV -rays emitted from²⁴Na²⁴Mg+^–+ after²³Na(n,)²⁴Na reaction were counted by high purity germanium (HPGe) detector and the half-life of²⁴Na was derived. This process was simulated by Monte Carlo Neutron and Photon Transport Code (MCNP-4A).²⁵²Cf neutron source was moderated by a polyethylene (PE) cylinder to increase the cross section of neutron absorption reaction and to decrease the biological hazard. NaCl powder of 20 cm³ and 40 cm³ volume in cylindrical polypropylene capsules were irradiated by the neutrons passed through the moderator. MCNP-4A was used to determine the optimum size of PE moderator, to assume the realistic geometry of the HPGe detector, and to assume the absolute efficiencies of the detector. The count rates for 1.369 MeV -rays in the HPGe detector were calculated by MCNP-4A for 20 cm³ and 40 cm³ NaCl. The accumulated counts calculated tumed out to be higher than those actually measured by 31% with a relative error of 3%. The half-life of²⁴Na measured within 4% and 1% for 20 cm³ and 40cm³ NaCl agrees with that of the reference. So, we can say that the result of MCNP-4A has about 30% of accuracy and 3% of precision in simulating the neutron activation analysis.     

Elemental concentrations in geochemical reference samples by neutron capture prompt gamma-ray spectroscopy

A facility for neutron capture prompt gamma-ray activation analysis, installed on a curved thermal neutron guide at the ILL High Flux Reactor, is described. Elemental sensitivities for B, Sm and Gd have been measured. The performance of the facility has been assessed by the measurement of these trace elements in eleven USGS geochemical reference samples and comparison of the results with existing values. Preliminary concentrations of B, Sm and Gd are also reported for twelve French GRS.     

Multi-element analysis of environmental samples by cold and thermal guided neutron induced prompt gamma-ray measurement

Non-destructive multi-element determination in environmental samples by neutron-induced prompt -ray analysis (PGA) has been investigated. Comparative standardization for the elements including H, B, C, N, Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Mn, Fe, Co, Cd, Sm, Gd, Hg by PGA has been carried out using the cold and thermal guided neutron beams of JRR-3M reactor and then several environmental reference materials have been analyzed. Accuracy and precision of better than 20% were found for these elemental analyses except for H, C, N and Cl in biological samples. Detection limits in various environmental matrices were 25 to 820 ng/g for B, Cd, Sm and Gd, 1.1 to 820 g/g for H, Na, S, Cl, K, Ti, Mn, Co and Hg, and 0.031 to 10% for C, N, Mg, Al, Si, P, Ca and Fe. The present method is being applied to environmental studies of post war Persian Gulf together with INAA and ICP-MS.     

The neutron flux of a252Cf neutron activation analysis device using the MCNP code

This report presents results from the application of the Monte Carlo N-Particle (MCNP) computer code to the²⁵²Cf neutron activation analysis (NAA) Device in the Technical Physics Institute of the Heilongjiang Science Academy of the People's Republic of China. The thermal and epithermal neutron flux at the sample positions and the neutron and photon fluxes on the surfaces of the device were calculated. A comparison between the calculated and experimental thermal and epithermal neutron fluxes at sample positions yield relative errors of less than 10% for the thermal neutron flux.     

Development of a neutron beam line and detector system for multiple prompt gamma-ray analysis

A neutron beam line for multiple prompt gamma-ray analysis was constructed at the Japan Atomic Energy Agency. A detector system for the MPGA was constructed at the C2-3-2 beam line in January 2005. It comprised eight (upgraded in March 2007) clover Ge detectors with a BGO Compton suppressor. High efficiency detector system provides an advantage in terms of the detection limit of MPGA when compared to the result of PGA. The supermirror neutron bender was improved and a supermirror neutron guide was installed upstream of the sample position.     

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.     

Activation analysis of halogens in photographic emulsions using a252Cf neutron multiplier

A nondestructive neutron activation technique for the simultaneous direct determination of chlorine, bromine, and iodine in silver halide mixtures is described using a²⁵²Cf neutron multiplier (CFX). About 5–50 mg of sample are used. The analysis is semiroutine, without the need for a monitor included with each sample since the flux stability and reproducibility are within ±1%, decaying only with the 2.65 year half-life of²⁵²Cf. The precision and accuracy are counting-statistics controlled and are generally ±1% RSD or better. The method offers an attractive alternative to existing chemical and instrumental methods for these determinations in silver halide mixtures because it has the potential for providing reasonably rapid analyses with good precision and accuracy.     

The application of a252Cf neutron multiplier for routine instrumental neutron activation analysis

The successful application of instrumental neutron activation analysis for routine determinations depends on the ability to produce accurate and precise analytical results in a relatively short time. An important factor in obtaining the desired speed has been the availability of a low-cost, moderate-flux neutron source for on-site use. The²⁵²Cf neutron multiplier (CFX), designed and constructed by Intelcom Rad Tech Corporation of San Diego, California, is a subcritical assembly capable of continuous, stable operation and has provided us with the ability to determine more than 35 elements as major and minor components. The CFX produces a thermal neutron flux of ∼2×10³ n/cm²-sec by a 100-fold multiplication of the neutrons emitted from a 1 mg²⁵²Cf source. Of particular importance in its application at Kodak has been the determination of the halogens Cl, Br, and I, both singly and simultaneously, in various matrices including photographic materials.     

Instrumental neutron activation analysis of Al,V and Ti employing252Cf as a thermal neutron source

A rapid method for the determination of Al, V and Ti has been developed and is used for the analysis of these elements in different ores and alloys. An isotopic neutron source²⁵²Cf having a thermal neutron flux of the order of 8.5×10⁷ n·cm^–2 sec^–1 has been used for thermal neutron bombardment. Activity measurements were performed on a HPGe detector coupled to a PC based MCA unit. Depending on the half-life of the (n, ) product, different irradiation and cooling times were employed and thus the elements of interest were analyzed sequentially.     

A low cost neutron capture prompt gamma-ray analysis facility at a research reactor

A low cost neutron capture prompt gamma activation analysis facility has been constructed at The University of Michigan's Pheonix Memorial Laboratory. Although the neutron beam used has a fairly large epithermal component (Cd ratio 7.1), background levels are low enough to result in satisfactory measurement of over 16 different elements. For the elements of greatest sensitivity (samarium, boron, gadolinium, and cadmium) minimum detectable levels of 3.6·10⁻⁵ to 1.4·10⁻⁵ gram for a one hour measurement are possible. The fast neutrons incident to the detector were found to be minimal. Estimates of up to 3 years of continuous operation before measurable damage is expected.     

2D elemental analysis approach in focused neutron beam induced prompt gamma-ray analysis at JAEA

We have constructed a new system which could analyze a position distribution of several elements in a sample with 2 dimensional prompt γ-ray analysis (2D PGA) system using focused neutron beam at JAEA. We aimed that the system could analyze local information in a sample with a good signal γ-ray from interested elements to noise of background γ-ray ratio. As a result, this system could determine the position resolution and spatial resolution within 1 mm.     

Determination of some macro and micro nutrients in soils of Maharashtra State by instrumental neutron activation analysis using 252Cf as a thermal neutron source

Some macro and micronutrients in soils from some districts of Maharashtra State have been determined by instrumental neutron activation analysis. Neutrons from ²⁵²Cf have been used for irradiation. The activity induced was measured by a HPGe detector coupled to a MCA unit. The statistical evaluation of the method has been explained. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mercury and cadmium determination in water by prompt (n, γ) method—252Cf as the neutron source

An evaluation of the sensitivity of mercury and cadmium determinations in large volumes of water is presented. A 10-μg²⁵²Cf source immersed in the water sample served as a neutron source. The (n, γ) reaction on hydrogen and the inelastic scattering from oxygen produced a background count rate that limited sensitivity. A lower limit of 20 ppm for both mercury and cadmium was found. The procedures described here can be applied to most of the other heavy metals. Research sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation.     

Development of a procedure for measuring nitrogen by cold neutron prompt gamma-ray activation analysis

An instrument for cold neutron prompt gamma-ray activation analysis (CNPGAA) has been used for the nondestructive determination of nitrogen. The samples were analyzed in an evacuated box to minimize background from neutron capture by atmospheric nitrogen. The system features lower background and lower detection limits than obtainable with the University of Maryland-National Institute of Standards and Technology (NIST) thermal neutron PGAA instrument. CNPGAA has been used to measure nitrogen in standard reference materials which included biological materials and soils; the results are in agreement with certified values. The detection limit for nitrogen in most biological and geological samples is near 1000 mg kg-1.     

Design of a new instrument for cold neutron prompt gamma-ray activation analysis at NIST

A new instrument for cold neutron prompt gamma-ray activation analysis (CNPGAA) is being designed and constructed at the NIST Center for Neutron Research (NCNR). The new instrument is expected to have lower gamma-ray and neutron background and better detection limits for most elements than the current cold neutron PGAA instrument. Other advantages over the current facility will include the ability to analyze larger samples and greater overall measurement capability due to the addition of scanning stages, cryostats, and sample changers.     

Non-destructive elemental analysis of large meteorite samples by prompt gamma-ray neutron activation analysis with the internal mono-standard method

Prompt gamma-ray neutron activation analysis (PGNAA) using the internal mono-standard method was tested for its applicability to analyzing large solid samples including irregularly shaped meteorite samples. For evaluating the accuracy and precision of the method, large quantities of the Geological Survey of Japan standardized rock powders (JB-1a, JG-1a, and JP-1) were analyzed and 12 elements (B, Na, Mg, Al, Cl, K, Ca, Ti, Mn, Fe, Sm, and Gd) were determined by using Si as an internal standard element. Analytical results were mostly in agreement with literature values within 10 %. The precision of the method was also shown to be within 10 % (1σ) for most of these elements. The analytical procedure was then applied to four stony meteorites (Allende, Kimble County, Leedey, Lake Labyrinth) and four iron meteorites (Canyon Diablo, Toluca (Mexico), Toluca (Xiquipilco), Squaw Creek) consisting of large chunks or single slabs. For stony meteorites, major elements (Mg, Al, Si, S, Ca, and Ni), minor elements (Na and Mn) and trace element (B, Cl, K, Ti, Co, and Sm) were determined with adequate accuracy. For iron meteorites, results for the Co and Ni mass fractions determined are all consistent with corresponding literature values. After the analysis, it was confirmed that the residual radioactivity remaining in the sample after PGNAA was very low and decreased down to the background level. This study shows that PGNAA with the internal mono-standard method is highly practical for determining the elemental composition of large, irregularly shaped solid samples including meteorites.     

A miniature planar magnetron glow discharge source for analysis of submicroliter volume aqueous samples using atomic emission spectroscopy

A miniature planar magnetron glow discharge source with a chamber volume of 60 ml has been designed and evaluated for the analysis of less than 1 μl of aqueous samples by atomic emission spectroscopy. Limits of detection for magnesium, silver, boron, europium and copper in the presence of a magnetic field are observed to be 3 to 40 times lower than for the source without a magnetic field when the measurements are made under the compromised discharge conditions for each type of source. Emission intensity in the presence of the magnetic field is found to increase as a square function of the discharge current. The improved detection limits for the magnetically enhanced glow discharge source are attributed to the increased current density of the discharge in the presence of the magnetic field which formed a plasma ring localized above the cathode surface. An RSD in the range 15–25% is observed for these measurements.