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Abstract  

By irradiating with cold neutrons and avoiding hydrogenous materials of construction, we have developed a PGAA instrument at the Cold Neutron Research Facility at NIST with hydrogen detection limits in the microgram range in many materials. Quantities of 5–10 g H/g are presently measurable in gram-sized samples of silicon or quartz, and of order 0.01 wt % can be quantitatively measured in complex silicate rocks.

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Summary  

A beam chopper has been developed at the cold neutron PGAA facility of the Budapest Research Reactor. In the open phase of the chopper the usual prompt gamma-spectrum is recorded, while in the decay phase short-lived decay lines can be collected with good counting statistics on an extremely low baseline. A series of elements has been measured with the chopped beam technique to assess the capabilities of the new technique. An archaeological sample was also examined, to demonstrate how spectral interferences can be resolved.

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Abstract  

Silver and gold were analysed in coins and medals by inelastic gamma-scattering reaction. The irradiation was performed with a 740 TBq (20 kCi)60Co source. After irradiation the isomer activities were measured with a well type NaI(Tl) scintillation counter and evaluated by means of a software program.

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Summary  

The new PGAA facility using diffracted neutron beam was developed in Korea. The basic characteristics of the facility were studied in detail. A general formalism of the k 0 factor as extended to non-1/v absorber and arbitrary neutron spectrum was discussed and the actual data for Cd, Sm, Eu, Gd have been measured and determined successfully owing to the simple nature of the diffracted neutron spectrum. The k 0 factors for B, N, Si, P, S and Cl were also determined and showed consistent results with previously reported ones. At an early stage, feasibility of boron concentration analysis and measurement of thermal neutron capture cross sections has been studied. The PGAA facility is now open to users. A considerable amount of beam time is already dedicated to studies on the elemental analysis.

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Abstract  

The PGAA facility at the Budapest Research Reactor has been continually upgraded and developed since its start-up in 1996, as a result of which its performance has improved considerably. The installation of the cold neutron source, the partial change to supermirror neutron guides and their realignment increased the flux by almost two orders of magnitude. The data acquisition has been modernized as well; digital spectrometers were tested and implemented in novel forms of gamma-ray spectrum collection. This year a higher-efficiency HPGe detector and a new data acquisition module were put into operation. Most recently all the neutron guides were changed to supermirror-coated ones to further increase the neutron flux. The improved evaluation software makes possible a more reliable elemental analysis of the samples. In this progress report these developments are critically reviewed. The characteristics of the latest system are also described. It is the first time that a set of new partial gamma-ray production cross sections are presented, which are based on the new intensity values of 14N(n,γ)15N calibration standard.

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Abstract  

Tables of nuclear data were compiled for the purpose of routine gamma (photon) activation analysis. The tables are arranged in two parts. The first one lists the readionuclides in order of their atomic number. In the second one, the emitted gamma-ray photons are tabulated in order of increasing energy. Tables contain the gamma emitters produced by the following photonuclear reactions: (γ, γ), (γ, n), (γ, p), (γ, p+n), (γ, 2n), (γ, 3n), (γ, 4n), (γ, 2p), (γ, α), (γ, α+n), (γ, α+p). This set corresponds to the maximum energy of the bremsstrahlung of roughly 45 MeV. The program for output of the tabulated data is made such that it is possible to reduce the data as required for specific irradiation and measuring conditions (reaction thresholds, energy and intensity of gamma-rays, half-lives and target elements).

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Summary  

{\rtf1\ansi\ansicpg1250\deff0\deflang1038\deflangfe1038\deftab708{\fonttbl{\f0\froman\fprq2\fcharset238{\*\fname Times New Roman;}Times New Roman CE;}{\f1\froman\fprq2\fcharset2 Symbol;}} {\colortbl ;\red0\green0\blue0;} \viewkind4\uc1\pard\f0\fs24 Tests of three different digital spectrum analyzers have been performed at the prompt-gamma activation analysis (PGAA) facility of the Budapest Research Reactor to characterize their applicability in PGAA. In a series of measurements with radioactive and (n,\f1 g\f0 ) sources we focused on the special demands, of broad energy range.\cf1 \cf0 Peak widths have been studied at different energies and gains, the time stability and the noise sensitivity have also been examined.\cf1 \cf0 The results have been compared to the performance of the analog system routinely used in our analysis. \par }

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Abstract  

The activating field of microtron bremsstrahlung is characterized by sharp recession of intensity in lateral and longitudinal directions. Therefore, the irradiation of several samples simultaneously results in their different activation which is a source of systematic error. Evaluation of correction coefficients needed for quantitative analysis by measurement of thin copper disks placed between the samples does not result in acceptable data. For these purposes a method for 3D-activating field monitoring and Monte-Carlo simulation for computation of the needed correction coefficients has been developed. The monitor represents the copper foil wrapped round the sample assembly. The autoradiogram of the irradiated monitor is used for characterization of the activating field. The Monte-Carlo simulation model involves both the field characteristics and the results obtained while making single training analysis.

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Abstract  

An instrument for prompt gamma-ray activation analysis is now in operation at the NIST Cold Neutron Research Facility (CNRF). The cold neutron beam is relatively free of contamination by fast neutrons and reactor gamma rays, and the neutron fluence rate is 1.5·108 cm–2·s–1 (thermal equivalent). As a result of a compact target-detector geometry the sensitivity is better by a factor of as much as seven than that obtained with an existing thermal instrument, and hydrogen background is a factor of 50 lower. We have applied this instrument to multielement analysis of the Allende meteorite and other materials.

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