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.     

Performance of the University of Texas cold-neutron prompt gamma activation analysis facility

The University of Texas cold-neutron prompt gamma-activation analysis (PGAA) facility is operational at the 1-MW UT TRIGA research reactor. The UT-PGAA facility utilizes a guided cold neutron beam produced by the Texas Cold Neutron Source. The cold neutrons are transported to the PGAA chamber via a 6-m long curved neutron guide followed by an 80-cm long converging neutron guide. A program of testing, optimizing, and calibrating the UT-PGAA facility is currently underway. Preliminary results for the sensitivities and detection limits of boron, hydrogen, and silicon in semiconductor materials are given.     

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.     

Capillary neutron optics for prompt-gamma activation analysis

A neutron lens has been constructed to focus cold neutrons from the exit of a⁵⁸Ni neutron guide, which delivers a beam to the Prompt-Gamma Activation Analysis (PGAA) station at the NIST Cold Neutron Research Facility. The lens compresses a neutron beam of cross section 50 mm× 45 mm onto a focal spot of diameter 0.53 mm (fwhm) wich an average gain of 80 in neutron current density. PGAA measurements have been performed to demonstrate the enhanced sensitivity and detection limits for various elements and the spatial resolution in one transverse dimension. For the two test particles (a gadolinium glass bead and cadmium metal of sizes less than 0.5 mm), the gain in the -count rate with the lens is a factor of 60, and the detection limit is improved by a factor of 20. The system can be used for two-dimensional mapping of samples on a sub-millimeter scale to complement other analytical techniques such as neutron depth profiling (NDP).     

On the construction of a new instrument for cold-neutron prompt gamma-ray activation analysis at the FRM-II

Summary A new flexible prompt gamma-ray activation analysis (PGAA) station will be installed and operated at the FRM-II reactor in Garching at the beginning of the year 2006. The PGAA station has been moved from the Paul Scherrer Institute (PSI), Villigen, Switzerland and is now being re-designed for three different experimental applications: PGAA instrument, cold neutron tomography setup and a compact Ge-array. Simulations of the beam guide have been carried out in order to yield the best conditions for each of the instruments, and are discussed here. A number of the PGAA applications are listed here. A new project dealing with a systematic measurement of bulky composition of small amount of meteorites (~100 mg) is proposed. Results of a test measurement of the Dhurmasala meteorite composition at the PGAA station at the Budapest Research Reactor are presented. Expected parameters of the PGAA facility at FRM-II are compared both with those at PSI and with the Budapest facility.     

Cold neutron facility for prompt gamma-neutron activation analysis

The restart of the recently upgraded research reactor in Budapest is foreseen at the end of this year. A number of fast, thermal and cold neutron beams will serve for research, industrial and educational activities. One of the cold neutron guide end positions will be utilized for neutron capture prompt gamma-ray activation analysis (PGAA). Further development of the PGAA method as well as new applications in environmental research, biology and medicine are planned.     

Cold neutron prompt gamma-ray activation analysis at NIST — Recent developments

The cold neutron capture prompt -ray activation analysis (CNPGAA) spectrometer located in the Cold Neutron Research Facility (CNRF) at NIST has proven useful for the analysis of hydrogen and other elements in a wide variety of materials. Modifications of the instrument and the CNRF have resulted in improved measurement capabilities for PGAA. The addition of an atmosphere-controlled sample chamber and Compton suppression have reduced -ray background and increased signal-to-noise ratio. More recent revisions are expected to yield still further improvement in analytical capabilities. Replacement of the D₂O ice cold source with a liquid H₂ moderator is expected to yield a 5–10 fold increase in neutron capture rate, and improved neutron and -ray shielding will result in further reduction of the background. Other modifications to the instrument allow easier sample mounting and more precise positioning of samples in the neutron beam. Significant improvements in detection limits and analytical accuracy are expected.     

Optimization of HANARO cold neutron induced prompt gamma activation analysis system by using Monte Carlo code

Prompt gamma activation analysis (PGAA) is a nuclear analytical technique for non-destructive determination of elemental and isotopic compositions. The principle of PGAA technique is based on detection of captured gamma-ray emitted from an analytical sample while being irradiated with neutrons. Use of a cold neutron beam guide greatly reduces the gamma-ray background at the analytical sample while maintaining a neutron capture rate is comparable to that of standard thermal neutron PGAA. A new cold neutron induced prompt gamma activation analysis (CN-PGAA) system has been under construction since April of 2009 at the HANARO Cold Neutron Building (KAERI, Republic of KOREA). In this study, the Compton suppression factor of the CN-PGAA system was estimated to be 5.5 using a ⁶⁰Co radioactive source in conjunction with the MCNPX simulations. Several parameters of the CN-PGAA system were studied to estimate and optimize the performance of the system: scintillation material in the guarded detector of a Compton suppression spectrometer (CSS); the relative positions of the HPGe detector and annular detector; and the distance between the HPGe detector and back catcher BGO detectors of the CSS. In addition, the neutron ray-trace simulation package, McStas, was adopted to predict the neutron flux and wavelength distribution at the end of the cold neutron beam guide. These results served as input for the MCNPX simulation of the CN-PGAA system.     

Measuring hydrogen by cold-neutron prompt-gamma activation analysis

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.Contributions of the National Institute of Standards and Technology are not subject to copyright.     

Use of INAA,PGAA, and RNAA to determine 30 elements for certification of an SRM: Tomato Leaves, 157a

Analyses for certification have been made for the determination of 30 elements in the National Institute of Standards and Technology (NIST) Tomato Leaves renewal reference material, SRM 1573a. Three of the analytical techniques used were instrumental neutron activation analysis (INAA), radiochemical neutron activation analysis (RNAA), and prompt gamma activation analysis (PGAA). These techniques provided data on 19 elements by INAA, 10 elements by PGAA, and 7 elements by RNAA, with some overlap between techniques. For example, INAA was able to obtain overall analytical uncerainties (at the 95% confidence level) averaging ±2.2% for major and minor constituents (Ca, Mg, K), ±3.3% for constituents from 1 to 1000 g/g (Na, Fe, Al, Mn, Ba, Zn, Rb, La, Cr), and ±6.4% for elements between 10 and 1000 ng/g (Co, V, Se, Th, Sc, Sb), using sample dry weights of approximately 150 mg. These analyses represent the most extensive use to date of nuclear analytical techniques in the certification of a trace element SRM at NIST.     

Cold neutron prompt gamma activation analysis at NIST: A progress report

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.     

Fitting the boron peak and resolving interferences in the 450–490 keV region of PGAA spectra

Prompt gamma activation analysis (PGAA) is one of the most powerful analytical methods for the determination of boron because of its very large neutron capture cross section. The peak of boron in the PGAA spectra is highly broadened due to the Doppler-effect. An improved method is presented to fit the boron peak, and to resolve interference with the gamma-rays of sodium and other matrix components. The method has been checked on test samples and on geological samples as well.     

Prompt Gamma Activation Analysis with the Texas Cold Neutron Source

A Prompt Gamma Activation Analysis (PGAA) facility is being developed at The University of Texas at Austin (UT). The UT-PGAA facility will utilize a focused cold-neutron beam from the Texas Cold Neutron Source (TCNS). the TCNS consists of a cold source cryostat and a curved neutron guide. the use of a guided focused cold-neutron beam will provide a high capture reaction rate and low background. The UT-PGAA facility will be used in the nondestructive determination of B, Cd, Gd and S in biological and environmental samples.     

The new cold neutron depth profiling instrument at NIST

The Cold Neutron Depth Profiling (CNDP) instrument at the NIST Cold Neutron Research Facility (CNRF) is now operational. The neutron beam originates from a 16 liter D₂O-ice cold source and passes through a filter of 13.5 cm of single crystal sapphire. The neutron energy spectrum may be described by a 65 K Maxwellian distribution. The sample chamber configuration allows for remote controlled scanning of 15 cm×15 cm samples and varying of both sample and detector angle. The improved sensitivity over the current thermal depth profiling instrument has permitted the first nondestructive measurements of¹⁷O profiles. Results of some of the first sample measurements are presented.     

Prompt gamma-ray neutron activation analysis methodology for determination of boron from trace to major contents

Prompt gamma ray neutron activation analysis methodologies were standardized using a reflected neutron beam and Compton suppressed γ-ray spectrometer to quantify boron from trace to major concentrations. Neutron self-shielding correction factors for higher boron contents (0.2–10 mg) in samples were obtained from the sensitivity of chlorine by irradiating KCl with and without boron. This method was validated by determining boron concentrations in six boron compounds and applied to three borosilicate glass samples with boron contents in the range of 1–10 mg. Low concentrations of boron (10–58 mg kg⁻¹) were also determined in two samples and five reference materials from NIST and IAEA.     

反应堆瞬发γ活化成像技术研究进展

瞬发γ活化成像技术(Prompt Gamma Activation Imaging,PGAI)是基于瞬发γ中子活化分析技术(Prompt Gamma Neutron Activation Analysis,PGAA)的一种新型元素成像技术,具有PGAA非破坏性、高灵敏度的多元素分析特点,同时可研究大体积样品内元素含量的三维分布情况。与移动中子源(如同位素中子源、加速器中子源)相比,反应堆中子源具有高通量的冷/热中子,因此,基于反应堆中子源的PGAI装置具有更加广阔的应用前景。鉴于PGAI技术的重要性,主要介绍了PGAI技术原理和测量方法、列举了国内外具有代表性的PGAI装置及特点,并指出当前PGAI技术研究现状与应用进展。其中,与中子层析成像(Neutron tomography,NT)结合的PGAI是目前研究的重点。随着国内高通量中子反应堆的持续稳定运行以及PGAI装置的建立和技术发展,相信未来PGAI技术能在我国更多领域得到广泛和深入应用。     

Determination of carbon,nitrogen and phosphorus in cattail using cold neutron prompt-gamma activation analysis

Summary A method for the determination of carbon, nitrogen, and phosphorus in cattail using cold neutron prompt-gamma activation analysis (CNPGAA) has been developed and evaluated through the analysis of standard reference materials (SRM). After extensive preparation, approximately 400 mg cattail samples from the lower Apalachicola River floodplain were irradiated in the CNPGAA facility at the National Institute of Standards and Technology (NIST). The results of numerous field samples and two standard reference materials using the nuclear method show favorable comparison to results obtained by a CHNS/O analyzer.     

Quantitative Prompt Gamma Analysis Using a Focused Cold Neutron Beam

We report the first quantitative results using a focused cold neutron beam for prompt gamma activation analysis (PGAA). We have measured the prompt gamma signal from known Fe, Cr, Ti, B, and Cd specimens in the focusing geometry, from which we determine the sensitivities for these elements by the method of standard addition. Furthermore, we show results of measurements for homogeneous standard reference materials (boron in SRM 611 glass, and iron and chromium in a steel alloy SRM 160b) to verify the sensitivities determined. Finally, we present a position-dependent study of the Cr to Fe mass ratio in an industrial material, taking advantage of the narrowly focused beam. Existing problems for achieving routine quantitative analysis using the focused beam and suggestions for future directions are discussed.