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.     

Neutron activation analysis of low level lithium in water samples

For determining low level lithium concentrations in water, a neutron activation method based on the measurement of tritium radioactivity produced by⁶Li(n,)³H reaction has been developed. This method is specific and free from interference by other chemical elements. Using a low background liquid scintillation counter for tritium measurement, the detection limit is approximately 0.3 ppm during irradiation at a thermal neutron flux density of 1.1·10⁷n·cm^–2·s^–1 for 6 hours by a small nuclear reactor and liquid scintillation counting for 2000 minutes     

Neutron scattering by hydrogen in cold neutron prompt gamma-activation analysis

The effects of neutron scattering by hydrogen within targets for cold neutron prompt -ray activation analysis (CNPGAA) have been characterized. For most targets studied, the probability for neutron absorption, and hence CNPGAA sensitivities (counts·s^–1·mg^–1), decrease with increasing H content and with target thickness. Comparisons with results from thermal neutron PGAA indicate that the effects of cold neutron scattering differ from those of thermal neutron scattering. CNPGAA sensitivities for l/v nuclides show similar sensitivity decreases, while Sm sensitivities show smaller decreases.     

Eine 3mg-252Cf-Bestrahlungsanordnung-Aufbau und Anwendungen

In the last years Cf-252 neutron sources will be incresingly used for nuclear analytical purposes. In the Central Institute of Isotope and Radiation Research, Leipzig, an irradiation equipment with a 3mg²⁵²Cf neutron source was constructed. It reaches thermal neutron fluxes of about 10⁷ n·cm^–2·s^–1. The construction of this equipment and the different moderation geometries are described. Possibilities of the application for neutron induced autoradiography, neutron radiography and neutron activation analysis are demonstrated on examples.     

Design Features of a Prompt Gamma Neutron Activation Analysis System at HANARO

The design features are described of a prompt gamma neutron activation analysis system at HANARO, a 30 MW research reactor in the Korea Atomic Energy Research Institute. The beam consists of polychromatic thermal neutrons diffracted by a set of pyrolytic graphite crystals at orders n in the range 1n6 at a Bragg angle of 45° on a horizontal beam line. A neutron flux of 1.0·10⁸ n·cm^–2·s^–1 is calculated at the sample position from the reflectivity of the crystal which has been confirmed in a measurement of a diffracted neutron spectrum using a time-of-flight spectrometer and gold-wire activation. The fast neutron and gamma backgrounds will be low due to the use of a diffracted beam and a tapered collimator. The detection system comprises a 30% n-type HPGe detector, signal electronics and a fast ADC. The first application of this system will be the analysis of boron concentration in biological samples for neutron capture therapy. Construction of the beam line and the arrangement of the detection system is proceeding.     

Neutron activation analysis for ultra low contents of uranium and thorium in aluminium and silica

Highly sensitive neutron activation analysis of uranium and thorium in high quality silica and aluminium has been investigated using the Japan Materials Testing Reactor (JMTR), having a thermal neutron flux higher than 10¹⁴ n/cm²/s. In order to determine ultra-low contents of uranium and thorium,²³⁹Np and²³³Pa as activation products were separated by using anion exchange and LaF₃ coprecipitation methods. As a result, a number of interfering radioactive isotopes containing double neutron capture product such as¹⁸³Ta were removed completely from the isolated²³⁹Np and²³³Pa fraction and the detection limits for uranium and thorium were found to be 2·10^–12 g and 4·10^–13 g, respectively.     

Intercomparison and determination of environmental standard samples by instrumental neutron activation analysis

To identify and improve the analytical technique for air pollution research, four kinds of environmental standard samples, i.e., airbome particulate matter, coal flyash, soil and pine needle supplied from the NIST and the IAEA were analyzed using thermal and epithermal neutron activation techniques. Sample irradiation was done at the irradiation facilities (neutron flux, 1 · 10¹³ n·cm^–2·s^–1) of the TRIGA MARK-III Research Reactor in the Korea Atomic Energy Research Institute. The accuracy and precision for the analysis of 40 trace and toxic elements in the samples were compared with the certified and reported values, respectively. In the analytical results of all standard reference materials, the relative standard deviation were within the 15% except for 11 elements and the relative error were agreed within the 10–20% except for 13 elements. The benefit of epithermal activation was investigated and the optimum analytical condition is reported.     

Prompt gamma neutron activation analysis of boron with a 241Am-Be neutron source

A prompt gamma neutron activation analysis (PGAA) setup installed at ANRTC has been used to analyze boron. It consists of a 22.6% REGe detector and a 740 GBq ²⁴¹Am-Be neutron source moderated with water and paraffin. At the sample irradiation position, the thermal neutron fluence rate measured was 2.36·10⁴ n·m^–2· s^–1 and the corresponding Cd-ratio was 22 for gold monitor. The absolute detection efficiency in the range of 120–1500 keV was determined using ¹⁵²Eu standard solution. The sensitivity and detection limit for standard boric acid samples has been determined. The boron content in boric acid prepared from Turkish borate ores is measured to be 15.91±0.46% wt.     

Prompt gamma neutron activation analysis of boron with a 241Am-Be neutron source

A prompt gamma neutron activation analysis (PGAA) setup installed at ANRTC has been used to analyze boron. It consists of a 22.6% REGe detector and a 740 GBq ²⁴¹Am-Be neutron source moderated with water and paraffin. At the sample irradiation position, the thermal neutron fluence rate measured was 2.36·10⁴ n·m^–2· s^–1 and the corresponding Cd-ratio was 22 for gold monitor. The absolute detection efficiency in the range of 120–1500 keV was determined using ¹⁵²Eu standard solution. The sensitivity and detection limit for standard boric acid samples has been determined. The boron content in boric acid prepared from Turkish borate ores is measured to be 15.91±0.46% wt.     

The feasibility of producing a99Mo:99mTc generator using the Miniature Neutron Source Reactor (MNSR)

A theoretical investigation of the feasibility of producing a molybdenum-99: technetium-99m generator from MoO₃ using a 30 kW Miniature Neutron Source Reactor (MNSR) has been made. At the rated thermal neutron flux of 10¹² n·cm^–2·s^–1 and irradiation time of 2.5 hours per day, for 8 consecutive days, activities of 7.1 mCi and 5.2 mCi were calculated for⁹⁹Mo and^99mTc, respectively. A 20 g sample of 99.5% chemically pure MoO₃ was used. The advantage for operating the reactor for 8 days instead of 6 days would be an increase of 11.4% and 15.5%, respectively, in the amount of⁹⁹Mo and^99mTc produced. it is calculated that an optimum irradiation scheme is achieved when the reactor is operated for an extended period of 5 hours a day for 5 days a week at a lower flux level of 7.5·10¹¹ n·cm^–2·s^–1. With this optimum operation scheme, there would be an increase in the weekly specific activity of 36% and 37.9% for⁹⁹Mo and^99mTc, respectively.     

Neutron activation determination of oxygen in ceramic materials on the basis of yttrium,barium and copper

A procedure of determining oxygen in superconducting materials on the basis of yttrium, barium and copper oxides with the application of 14 MeV-neutron activation has been developed. The method is based on determining the relation between oxygen and yttrium in the compounds investigated. Quantitative evaluation of this relation is performed with the aid of a comparator and two-component monitor. In order to minimize systematic errors, expressions accounting for spectrometer dead time under conditions of varying component activity are proposed. The procedure ensures determination of the relation between oxygen and yttrium with a relative error of 0.4%(10 parallel measurements) with NAA using a neutron generator with a neutron yield of (1–3)·10¹⁰ n·s^–1.     

Preliminary study of trace elements in human brain tumor tissues by instrumental neutron activation analysis

Elemental profiles of brain tumor tissues from 15 patients of astrocytomas (grade I–III) and normal human brain tissues of 23 male age matched autopsies as controls have been studied by instrumental neutron activation analysis. The SLOWPOKE reactor with a thermal neutron flux of 8·10¹¹n·cm^–2·s^–1 and swimming pool type reactor with a thermal neutron flux of 1·10¹³n·cm^–2·s^–1 were used for short and long irradiation of samples, respectively. Spectrophotometry was only used for analyzing phosphorus. A total of 18 elements Se, Na, K, Br, Cl, Mn, Mg, S, Ca, Cu, Hg, Cr, Fe, Rb, Zn, Co, Sc and P has been determined for this purpose. The reliability of methods has been checked by analyzing biological standard reference materials horse kidney (IAEA H-8) and bovine liver (NBS SRM 1577a). The analytical results showed that compared with the normal brain tissues, concentrations of Ca, Fe, Cu, Zn, Se, Mn, Br and Sc were significantly higher in tumor tissues (P<0.01) and concentrations of Rb, K and P were lower, while no differences for contents of Mg, S, Cr, Hg, Na and Cl were observed. A negative correlation between P and Ca in malignant and normal brain tissues was observed.     

Neutron activation analysis of major and trace elements in crude petroleum

We have determined the concentration of 25 trace elements in crude petroleum from seven Libyan oil fields by instrumental neutron activation analysis. Crude oil samples were irradiated with a thermal neutron dose rate of 10¹² and 10¹³ n·cm^–2·s^–1 in the Tajoura research reactor. The concentration of U, Br, Mg, Cu, Na, V, Cl, Al, Mn and Ca is in a range of 0.015 to 84 ppm and that of sulphur of 0.12 to 1.8%. The elements Sc, Cr, Ni, Fe, Co, Zn, Ag, Se, Sb, Ba, Cs, Yb, Hf and Hg have a concentration range of 0.009 to 8747 ppb. The coefficients of variation are within 10%. The elements V and Ni occur as both porphyrin and non-porphyrin and the ratio of these two forms varies over a wide range. The V/Ni ratios are located between 0.17 and 6.67, which are comparable to the reported values for the crude oils from other countries.     

Study on air pollution monitoring in Korea using instrumental neutron activation analysis

Trace elements in airborne particulate matter collected monthly at suburban and rural areas in Korea were analyzed by instrumental neutron activation analysis (INAA). Neutron irradiation of the samples was done at the irradiation hole (neutron flux 1·10¹³ n·cm^–2·s^–1) of the TRIGA Mark-III Research Reactor in the Korea Atomic Energy Research Institute. For the verification of the analytical technique, two reference materials, NIST SRM-1648 and NIES CRM-8, were chosen for analysis. The accuracy and precision of the determinations of the 40 elements were compared with the reference values. We used this method (1) to analyze 30 trace elements in airborne particulate matter collected monthly with the high volume air sampler (PM-10) at two different locations and (2) to confirm the possibility of using this method as a routine monitoring tool to find out environmental pollution sources.     

Study of the correlation of trace elments in human hair and internal organs by NAA

24 male autopsy cases aged 35–60 years have been collected from Shanghai China to study the relationships between human hair and internal tissues. Autopsy samples of hair, kidney-cortex, liver and lung were analyzed. A radiochemical neutron activation analysis (RNAA) based on a simple group extraction scheme was used for measuring the trace elements As, Cd, Hg, Cu and Zn. Zinc diethyldithiocarbamate Zn(DDC)₂ and methly isobutyl ketone-iodide have been chosen as reagent. Trace element of Se was determined by instrumental neutron activation analysis (INAA). A SLOWPOKE reactor with a thermal neutron flux of 8·10¹¹ n·cm^–2·s^–1 and a swimming pool type reactor with a thermal neutron flux of 1·10¹³ n·cm^–2·s^–1 were used for short and long irradiation of samples, respectively. The reliability of methods has been checked by analyzing biological standard reference materials Horse Kidney (IAEA H8), Tomato Leaves (NBS 1573) and Human Hair (NIES-5). The analytical results show that toxic elements As, Cd and Hg exist in a larger individual variability than the essential elements of Cu, Se and Zn for each tissue. A linear regression analysis related to the six elements of primary interest for the IAEA Coordinated Research Program (CRP) has been done by a computer program for each pair of hair-tissue. A positive correlation is found between concentration of As in hair and kidney-cortex, the correlation coefficient r is 0.751 (p<0.01). Positive correlations between concentration of Se in hair and liver, kidney-cortex and lung are also observed in this study. It shows that the elements As and Se in hair may be useful indicators for assessing certain internal tissues of normal persons. A comparison of Cd concentration in lung shows a significant difference between smokers and non-smokers. A significant correlation between element Cd and Zn in kidney-cortex is also presented in this paper.     

Determination of boron in glass by alpha-spectrometry

Alpha-spectrometric method has been used for the determination of boron in borosilicate glasses. For irradiation thermal neutrons with a flux of about 10⁵ n·cm^–2·s^–1, produced in a paraffin moderator surrounding a deuteron target of a small neutron generator, were used. Alpha-particles from the reaction¹⁰B(n, ) were detected by a Si solid state detector with a resolution of about 50 keV. The sensitivity of the method is 0.05 wt % boron in glass samples.This work was supported by the Hungarian Research Foundation (Contract No. 1734/91.).     

In vivo activation analysis of organ cadmium using the Tsing Hua Mobile Educational Reactor

This work describes a nuclear facility forin vivo prompt gamma activation analysis (IVPGAA) using a moderated neutron beam from a 0.1 W Tsing-Hua Mobile Educational Reactor (THMER). The IVPGAA measurement is a new technique for toxic cadmium determination in organs, which can efficiently be used in clinical diagnosis. The low-power nuclear reactor provides a total neutron flux of 3.3·10⁴ n·cm^–2·s^–1 on the surface of the central vertical neutron beam tube to which a liquid phantom is positioned. The capability of such partial-body irradiation facility is demonstrated. The detection limit of cadmium in the left kidney for a skin dose equivalent of 1.66 mSv (166 mrem) was 1.34 mg in a 500-s irradiation/counting period, and the sensitivity in the left kidney was 103 counts mg^–1·mSv^–1. The performance of IVPGAA system using the THMER nuclear facility therefore has the advantages of mobility and feasibility with high sensitivity under low neutron and gamma doses.     

Determination of trace concentration of boron in ADU by the nuclear track technique

A method for the determination of boron concentration in extracted (NH₄)₂ U₂O₇·H₂O (ADU) has been used. One ml of the aqueous solution is irradiated with thermal neutrons from a 10 Ci Am/Be neutron source with a flux of 0.2·10⁵ n·cm^–2·s^–1 and thermal column in the IRT-5000 with a flux of about 10⁷ n·cm^–2·s^–1. The alpha-activity due to the reaction¹⁰B(n, )⁷Li is recorded by a CR-39 alpha track detector. After the exposure, the alpha tracks are made visible in an optical microscope at magnification of 800X by etching the detector in 6N NaOH, and the track density is determined using calibration curves of known concentrations of boron. The boron concentration of the extracted ADU was found to be 5 ppm.     

Characterization of an epithermal irradiation facility

An epithermal energy neutron irradiation facility has been used to perform instrumental activation analysis for iodine, silicon, nickel, zirconium, uranium and thorium. The facility, which is adjacent to the fuel of the University of Virginia 2.0 MW pool reactor, consists of a dry sample region surrounded by a fixed cadmium shield. A boron nitride capsule can be used to hold the sample in the cadmium facility to further enhance the reduction of thermal neutron activation. The neutron fluence rate is 2.2×10¹⁶ n·m^–2·s^–1 for fission spectrum energy neutrons (measured with Ni(n,p)Co) and 8.2·10¹⁵ n·m^–2·s^–1 for resonance energy neutrons (measured with gold).Iodine has been measured at concentrations as low as 0.1 mg/kg with 3% counting statistics in powdered infant formula and 0.15 mg/kg with 5% statistics in liquid infant formula. Silicon has been measured at concentrations of 0.2% in biological samples with counting statistics between 5 and 10% and in coal and soil at concentrations greater than 4% with better than 1% statistics. Nickel has been measured in coal and soil at the 20 mg/kg level and higher with 6% statistics. Zirconium has been determined at 600 mg/kg and greater in ceramics with counting errors less than 3%. Uranium and thorium have been measured at the 10 mg/kg level with 3% counting statistics.     

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.