Prompt gamma ray neutron

Glascock, M.D., Spalding, T. G., Biers, J. C., and Corman, M.F. (1984). Analysis of copper-based metallic artefacts by prompt gamma-ray neutron activation analysis. Archaeometry 26 96-103. 

The safe and verifiable disposition, either by incineration or chemical neutralization of chemical warfare (CW) agents requires correct a priori identification of each munition or container to be processed. A variety of NDE techniques have been used or tested for the examination and characterization of munitions.[l,2] In the U.S., three widely used techniques are X-ray radiography, acoustic resonance spectroscopy (ARS), and prompt gamma ray neutron activation analysis (PINS). The technical bases, instrumental implementations, and applications of the U.S. versions of these methods are briefly discussed. 

Prompt gamma ray neutron activation methods such as PINS exhibit varying sensitivities for the detection of specific chemical elements, an important limitation. 

A conveiuent suite of NDE techniques is available for the characterization of muiution fill. Large numbers of similar stockpile munitions can be reliably and quickly classified using Acoustic Resonance Spectroscopy (ARS). Measurement times are about one minute per item. However, ARS measurements require a comparison template and are less usefiil for assay of old, rusted, and one of a kind munitions. For munitions of this type, x-ray radiography and assay by prompt gamma ray neutron activation analysis can reliably determine the munition fill, and ensure that the items are properly scheduled for destruction. 

With respect to the time of measurement, NAA falls into two categories (1) prompt gamma-ray neutron activation analysis (PGNAA), where measurements take place during irradiation, or (2) delayed gamma-ray neutron activation analysis (DGNAA), where the measurements follow radioactive decay. The latter operational mode is more common. 

PGNAA Prompt gamma-ray neutron activation analysis... 

Prompt gamma ray neutron activation analysis (PGNAA) is a proven method for the identification of chemical warfare agents, which is widely used as a nondestructive technique. 

This can result in a radioactive product from the A(n, t)A reaction where A is the stable element, n is a thermal neutron, A is the radioactive product of one atomic mass unit greater than A, and y is the prompt gamma ray resulting from the reaction. A is usually a beta and/or gamma emitter of reasonably long half-life. Where access to a nuclear reactor has been convenient, thermal neutron activation analysis has proven to be an extremely valuable nondestructive analytical tool and in many cases, the only method for performing specific analyses at high sensitivities... 

Ouri, Y., Shirari, N. and Ebihara, M. (2003) Chemical composition of Yamato (Y)980459 and Y000749 Neutron-induced prompt gamma-ray analysis study. Antarctic Meteorite Research, 16, 80—93. 

The prompt gamma-rays emitted following neutron or charged particle interactions with the target nuclide may be used as a basis for non-destructive analyses. The important advantage of this technique is that the determination does not depend in any manner on the half-life of a product radionuclide. In fact, using this technique, the product nuclide need not even be radioactive. Many conventional activation determinations are limited in their sensitivities by short half-life product radionuclides, or the fact that the most abundant or highest cross section isotope of the element to be determined leads to a stable product on irradiation. 

Figure 1. Histogram of detection limits for neutron activation analysis (NAA) and neutron-capture prompt gamma-ray activation analysis (PGAA). Data from Reference 15.

Neutron-capture prompt-gamma ray activation analysis (PGAA) is a recent addition to the nuclear analytical arsenal. In this technique the instantaneous gamma ray emission from a sample is measured as it is irradiated in a flux of reactor neutrons (33,3, 35). Because the sample must be several meters from either the core of the reactor or (less commonly) from the detector, the sensitivity of this technique is generally poorer than in conventional NAA. However, it is possible to measure small quantities of many elements which do not give radioactive neutron-capture products, notably 0.01 mg of H, 50 ng B, and 1 mg P in an electronics context. 

Andeeson DL (2000) Neutron capture prompt gamma-ray activation of meat homogenates. J Radioanal Nud Chem 244 225 - 229. 

Neutron activation analysts (NAA) can be accomplished by measurement of the prompt gamma rays during irradiation or by measurement of the delayed... 

FIGURE 32-6 Overview of the neutron activation process. The incident neutron is captured by the target nucleus to produce an excited compound nucleus, which de-excites with emission of a prompt gamma ray. The radioactive nucleus formed decays by emitting a beta particle. If an excited product nucleus is formed, a delayed gamma ray can be emitted. If decay is directly to the ground state of the product nucleus, no gamma ray is emitted. 

Two elemental analyzer systems have been developed, the "Continuous On-line Nuclear Assay of Coal", CONAC, (Science Application, Inc., Palo Alto, CA) and "The Elemental Analyzer" (MDH Industries, Inc., Monrovia, CA). Both of these units are based upon the measurement of prompt gamma rays that are emitted from a nucleus following the capture of a neutron. This technique is commonly known as prompt neutron activation analysis, PNAA. 

The very basis of PGAA, neutron capture followed by de-excitation of the compound nucleus through emission of characteristic gamma rays, provides information on the nuclear properties of the absorbing nuclide. Careful measurements permit determination of the prompt gamma-ray production cross section, which may be decoupled into the gamma yield, and neutron capture cross section. Quantitative PGAA maybe based on comparison with element standards... 

Yonezawa C, Wood AKH, Magara M, Sav ata S, Hoshi M, Ito Y, Tachikawa E (1993) Prompt gamma-ray analysis using JRR-3M cold and thermal neutron guide beams. In Proceedings of the 5th international symposium advanced nudear energy research (JAERI-M 93-228), Mito, Japan, vol 2. JAERI, Tokai, pp 854-861... 

The prompt gamma-ray cross sections were derived from a comparison of measurements with the neutron beam at the Budapest Reactor and other data from the literature (Molnar 2004 Choi et al. 2007). In some cases, these values were renormalized to better agree with the adopted total radiative cross section from all measurements. Delayed gamma-ray cross sections were derived from a comparison of Budapest Reactor measurements, corrected for activation and decay times, values derived from the ko database, and values adopted from total radiative cross sections and emission probability values from either the Table of Radionuclides (Be et al. 2004) or the ENSDF (2010) nuclear structure and decay database (O Table 36.3). 

CINDA (2003) The index to literature and computer files on microscopic neutron data. International Atomic Energy Agency, Vienna, http //www-nds.iaea.org Choi HD, Firestone RB, Lindstrom RM, Molnar GL, Mughabghab SF, Paviotti-Corcuera R, Revay Z, Trkov A, Zerkin V, Chunmei Z (2007) Database of prompt gamma rays from slow neutron capture for elemental analysis. International Atomic Energy Agency, Vienna... 

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