多元素中子俘获瞬发γ射线分析方法的研究

进一步提出被测元素瞬发γ射线特征峰的面积与其含量的关系式。经实验证明对各常见元素的仪器分析回归值与化学分析值的均方根偏差皆小于０．５ｗｔ％。在铁矿石的分析实验中发现了慢化体的作用，它可明显地提高分析灵敏度。该套中子俘获瞬发谱仪对Ｈ瞬发γ峰（２．２２３ＭｅＶ）的ＦＷＨＭ为３ｋｅＶ。     

The optimization of gamma spectra processing in prompt gamma neutron activation analysis (PGNAA)

The uncertainty of the elemental analysis is one of the major factors governing the utility of on-line Prompt Gamma Neutron Activation Analysis (PGNAA) in the blending and sorting of bulk materials. In this paper, a general method applicable to Gamma spectra processing is presented and applied to PGNAA in mineral industry. Based on the Fourier transform of spectra and their de-correlation in the Fourier space (the improvement of the conditioning of the correlation matrix), processing of overlapping of characteristic peaks minimizes the propagation of random errors, which optimizes the accuracy and decreases the detection limits of elemental analyses. In comparison with classical methods based on the linear combinations of relevant regions of spectra the improvement may be considerable, especially when several elements are interfering. The method is applied to four case stories covering both borehole logging and on-line analysis on conveyor belt of raw materials.     

The characterization of legacy radioactive materials by gamma spectroscopy and prompt gamma activation analysis (PGAA)

To characterize legacy radioactive materials, it is necessary to determine both the radioactive and, in the case of carrier-based materials, the stable, non-radioactive chemical constituents. Reputable process knowledge may afford some insight but, absent such information, gamma spectroscopy and (non-destructive) prompt gamma activation analysis (PGAA) cover essentially all of the analytical needs, with the former addressing most radionuclides with the exception of the pure β⁻-emitters and the latter addressing the stable chemical constituents. This paper integrates both methods into a general analytical protocol based upon radioanalytical work performed at Lawrence Berkeley National Laboratory (LBNL) and PGAA work performed collaboratively by the various groups. A new LBNL-developed neutron generator is also discussed.     

Methodologies for hydrogen determination in metal oxides by prompt gamma activation analysis

Prompt gamma activation analysis (PGAA), available at The University of Texas at Austin (UT), has been employed for the direct determination of hydrogen content in a series of metal oxide materials typically used as cathodes in lithium ion battery systems. Special attention was given to the experimental setup including potential sources of error and system calibration for the detection of hydrogen. Spectral interference with hydrogen arising from cobalt was identified and corrected for. Limits of detection as a function of cobalt mass present in a given sample are also discussed. PGAA has proven to be a novel and precise technique for the determination of hydrogen in metal oxides. This type of investigation could provide valuable insight regarding the factors that limit the practical capacities of lithium ion oxide cathodes.     

An improved prompt gamma neutron activation analysis facility using a focused diffracted neutron beam

The performance of the prompt gamma neutron activation analysis (PGNAA) facility at the MIT Research Reactor has been improved by a series of modifications. These modifications have increased the flux by a factor of three at the sample position to 1.7 × 10⁷ n/cm² s, and have increased the sensitivity, on average, by a factor of 2.5. The background for many samples of interest is dominated by unavoidable neutron interactions that occur in or near the sample. Other background components comprise only 20% of the total background count rate. The implementation of fast electronics has helped to keep dead time reasonable, in spite of the increased count rates. The PGNAA facility at the MIT Research Reactor continues to serve as a major analytical tool for quantifying ¹⁰B in biological samples for Boron Neutron Capture Therapy (BNCT) research. The sensitivity for boron-10 in water is 18 750 cps/mg. The sensitivity for pure elements suitable for PGNAA analysis is reported. Possible further improvements are discussed.     

On the accuracy of protein determination in large biological samples by prompt gamma neutron activation analysis

A prompt gamma neutron activation analysis (PGNAA) facility has been developed for the determination of nitrogen and thus total protein in large volume biological samples or the whole body of small animals. In the present work, the accuracy of nitrogen determination by PGNAA in phantoms of known composition as well as in four raw ground meat samples of about 1 kg mass was examined. Dumas combustion and Kjeldahl techniques were also used for the assessment of nitrogen concentration in the meat samples. No statistically significant differences were found between the concentrations assessed by the three techniques. The results of this work demonstrate the applicability of PGNAA for the assessment of total protein in biological samples of 0.25-1.5 kg mass, such as a meat sample or the body of small animal even in vivo with an equivalent radiation dose of about 40 mSv.     

γ能谱解谱技术研究

在核弹头的辐射指纹比较研究中,发现现在流行的γ能谱解谱软件有很多缺点,这些缺点直接影响到辐射指纹比对的准确性。鉴于此,本文设计了新的解谱程序。并对一些典型的模拟核弹头γ能谱,分别使用本程序、ORTEC公司的GAMMAVISION软件、CANBERRA公司的GENNIE2000软件进行解谱比较,以说明本研究工作在γ能谱解谱方面的一些成果。研究结果不但可用于涉及核弹头的核裁军核查研究中,而且可用于涉及放射性测量分析的各个领域。     

APCP分析程序使中子活化实验条件最佳化

反应堆中子活化分析(NAA)是近年来迅速发展的核分析技术,由于该方法取样量少、快速、准确、灵敏度高、具有多元素同时分析等优点,适合于生物样品中微量元素的分析研究。实验中,如果感兴趣的元素很多,往往要全面考虑到各个待测元素的放射性核素,选用合适的中子通量和辐照时间、衰变时间、计数时间。在这种情况下,正确合理选择最佳化实验条件是十分重要的。传统的方法是通过反复实验尝试和误差方法来取得,这将变得非常费时费     

A benchmarked MCNP model of the in vivo detection of gadolinium by prompt gamma neutron activation analysis

Gadolinium (Gd)-based contrast agents are a valuable diagnostic aid for magnetic resonance imaging (MRI). The amount of free Gd deposited in tissues following contrast enhanced MRI is of toxicological concern. The McMaster University in vivo prompt gamma neutron activation analysis facility has been adapted for the detection of Gd in the kidney, liver, and the leg muscle. A simple model of the HPGe detector used for detection of the prompt γ-rays following Gd neutron capture has been created using Monte Carlo simulation. A separate simulation describing the neutron collimation and shielding apparatus has been modified to determine the neutron capture rate in the Gd phantoms. The MCNP simulation results have been confirmed by experimental measurement. The deviations between MCNP and the experiment were between 1% and 18%, with an average deviation of 3.8 ± 6.7%. The validated MCNP model is to be used to improve the Gd in vivo measurement sensitivity by determining the best neutron moderator/reflector arrangement.     

Phantom studies of Cd, Hg and Cl by prompt gamma neutron activation analysis using a Pu-Be neutron source

Prompt gamma neutron activation analysis is a means of non-invasive monitoring for occupational exposure to toxic heavy metals such as Cd and Hg. Preliminary kidney detection limits from previous phantom studies at McMaster were 13.6 ± 0.2 ppm for Cd (125 mL phantom) and 315 ± 24 ppm for Hg (125 mL phantom) using the ²³⁸Pu-Be neutron source and 0.88 ± 0.01 ppm for Cd (125 mL phantom) and 16.91 ± 0.05 ppm for Hg (30 mL phantom) using the thermal neutron beam port at the McMaster Nuclear Reactor. The detection limits vary greatly between the two methods due to differences in experimental set-up, neutron energy spectra and a difference in dose by more than a factor of 100. The Hg detection limit from preliminary data is much higher than expected for both neutron source types. In order to explain the apparent detection limit discrepancy, measurements of Hg and Cd phantoms were performed using the ²³⁸Pu-Be neutron source. The results were compared to phantom measurements of Cl, a well-known neutron activation element.     

Calculation of thermal neutron self-shielding correction factors for aqueous bulk sample prompt gamma neutron activation analysis using the MCNP code

In this work thermal neutron self-shielding in aqueous bulk samples containing neutron absorbing materials is studied using bulk sample prompt gamma neutron activation analysis (BSPGNAA) with the MCNP code. The code was used to perform three dimensional simulations of a neutron source, neutron detector and sample of various material compositions. The MCNP model was validated against experimental measurements of the neutron flux performed using a BF₃ detector. Simulations were performed to predict thermal neutron self-shielding in aqueous bulk samples containing neutron absorbing solutes. In practice, the MCNP calculations are combined with experimental measurements of the relative thermal neutron flux over the sample’s surface, with respect to a reference water sample, to derive the thermal neutron self-shielding within the sample. The proposed methodology can be used for the determination of the elemental concentration of unknown aqueous samples by BSPGNAA where knowledge of the average thermal neutron flux within the sample volume is required.     

分子活化分析

评述了可用于元素化学种态研究的分子活化分析技术的基本概念、实验方法、优缺点、以及在生物、环境和地学中的应用，并展望了分子活化分析的发展前景。     

Proton induced gamma ray emission analysis of nitrogen

The proton-capture reactions 14N(p,γ)15O and 15N(p,αγ)^12C have been studied to determine their applicabilities to the analysis of materials for 15N enrichment,It is true that precision of the measurement concerned in these techniques cannot compete with mass spectrometry,but their ease of application is of great advantage to the fast handling of very large batches of samples from stable nuclide tracer experiments.