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.     

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).     

Instrumental neutron activation analysis of tungsten in various steel samples

The instrumental neutron activation analysis /INAA/ of tungsten in various steel samples has been done with a 2 Ci²⁵²Cf fission neutron source having an integrated neutron flux of 10¹⁰ ns^–1 and measuring the -activity of¹⁸⁷W on a 4 K multi-channel analyzer /MCA/ coupled to a high purity germanium /HPGe/ detector. The tungsten content of various steel samples was between 0.017 and 0.024%.     

Measurement of thermal neutron capture cross sections of 237Np and 242Pu using prompt gamma neutron activation

Several samples of ²³⁷Np and ²⁴²Pu were irradiated in the guided cold neutron beam of the prompt gamma activation analysis facility at the Budapest Research Reactor. The thermal neutron capture cross sections of ²³⁷ Np and ²⁴²Pu were evaluated from the obtained prompt and delayed gamma ray data. The thermal neutron capture cross sections for ²³⁷Np(n,γ)²³⁸Np was found to be $ \sigma_{0} ({}^{237}{\text{Np}}) = 170.4 \pm 7.4\,{\text{b}} $ and for ²⁴²Pu(n,γ)²⁴³Pu to be $ \sigma_{0} ({}^{242}{\text{Pu}}) = 19.6 \pm 3.9\,{\text{b}} $ .     

Determination of tungsten in ores by X-ray fluorescence technique and X-rays in neutron activation analysis

Two distinct analytical methods have been described for analysis of W in tungsten ores. For the proposed study, thick and thin samples were analyzed by using X-ray fluorescence technique with great accuracy. Standard comparison method is based on the measurement of K line for tungsten. Also, W has been determined in similar ore samples by neutron activation analysis followed by X-ray spectrometry employing a²³⁸Pu-Be neutron source. The measured Re K-X rays are emitted in internal conversion of¹³⁷W produced during thermal neutron activation.     

Large-sample neutron activation analysis: Present status and prospects

Neutron activation analysis is attractive for trace-element determinations in large samples. Facilities for reactor irradiation and -ray spectrometry of kilogram-size cylindrical samples are described. The thermal neutron flux is ca. 5·10¹²m^–2·s^–1 with a _th/ _epi>10⁴, so neutron self-thermalization can be neglected. The correction for the neutron attenuation within the sample is derived from measurement of the neutron flux depression just outside the sample. Correction for -attenuation in the sample is performed via linear attenuation coefficients derived via transmission measurements. Also the natural radioactivity in the sample is taken into account. Examples are given of materials to which large sample INAA has been applied successfully, and further lines of development and exploration are indicated.     

Determination of the ratio of the hydrogen and manganese absorption cross sections by the manganese bath technique

The ratio of the hydrogen and manganese neutron absorption cross sections, _H/_Mn, is a most important parameter in the determination of radioactive neutron source strength by the manganese bath technique. The ratio is well measured by observing the change in⁵⁶Mn activity induced in the manganese bath by a fixed neutron source as the manganese concentration of the bath is changed. In the present study, the neutron source was a Maxwellian beam from²⁵²Cf. Concentrations were determined by the two methods: volumetric and gravimetric. The cross section ratio has turned out to be _H/_Mn=0.02506.     

Corrections for carbon and oxygen interference in the 14-MeV neutron activation determination of nitrogen

Reactions in the carbon and oxygen atoms of sample matrix can lead to errors in the 14 MeV neutron activation determination of nitrogen based on the¹⁴N(n, 2n) reaction, particularly as a consequence of proton-induced reactions leading to¹³N formation in samples of an organic nature. In this study, the extent of such interferences have been evaluated by measuring the apparent N contribution when a series of alcohols and a water sample were irradiated with 14 MeV neutrons from a Texas-Nuclear neutron generator under the same conditions used for trace N determination and contributions amounting to from 0.1 to 1% apparent N content observed (and corrected for). Owing to neutron flux in stabilities and assymetries, flux monitoring was done with aluminum foils on either side of the samples for N analysis, and which were counted for²⁴Na. Two samples of foodstuff were analyzed correction for C and O interference, agreed with conventional analysis within ±10%.     

Determination of phosphorus in biological samples by thermal neutron activation followed by β--counting

Phosphorus has been determined using the ^- emitter³²P by instrumental neutron activation analysis (INAA) in several NBS and IAEA standards and samples of biological origin such as human and animal blood, cancerous tissue, edible plant leaves, diets, milk samples, etc. The method involves thermal neutron irradiation for 2–10 h in a reactor followed by ^--counting on an end-window gas flow proportional counter using an aluminium filter. The results are within ±10% of the certified values in most cases.     

A system for the determination of silicon in the human lung using neutrons from A 2MV Van de Graaff generator

Neutron activation analysis, using inelastic scattering, provides a quantitative, non-invasive technique of studying silica burdens and is potentially useful as a screening procedure for occupationally exposed workers. In this method, silicon is measured using the fast neutron inelastic scattering reaction²⁸Si(n,n )²⁸Si which emits 1779 keV -rays. The method requires a source of fast neutrons (> 2MeV). A 2MV Van de Graaff generator has been developed to produce a pulsed beam of 5.2 MeV neutrons. The pulsed beam has the advantage of improving measurement sensitivity by separating in Bone the inelastic scattering -rays from those due to thermal-neutron capture reactions. The incident neutron energy was chosen to maximise the silicon -ray count rate, while keeping the signal from the competing reaction³¹P(n,)²⁸Al negligible.     

Boron content of the Freetown drinking water

A method is described for the analyses of water samples in the Freetown area of Sierra Leone /West Africa/, for their boron concentrations. The method involves alpha counting during thermal neutron irradiation of the samples utilising the¹⁰Ba/n,/⁷Li reaction. The alpha counting is via a liquid scintillator which also incorporates the water samples. A detailed outline of the experimental setup is given and the results obtained from measurement on water samples presented.     

Determination of arsenic in some Myanmar indigenous medicines by neutron activation analysis

Am(Be) neutron source was used for activation of samples and⁷⁶As radioactivity measured by both ^– and -counting techniques. The samples analyzed were raw materials traditionally used in formulating Myanmar indigenous medicines. The results were compared with those obtained by volumetric analysis and those reported in the literature.     

Multielement analysis of archaic Chinese bronze and antique coins by fast neutron activation analysis

Samples of archaic bronze have been investigated by fast neutron activation analysis using both the absolute and relative method. The components Cu, Zn, Sn and Pb have been determined quantitatively. For the detection of lead via the short-lived isomeric state^207mPb, cyclic activation and measurement technique was used with pneumatic sample transfer between detector and central irradiation position of the neutron tube. For nondestructive analysis of antique Chinese coins the samples had to be irradiated outside the neutron generator KORONA. The activation reactions, the evaluation of the elemental concentrations and the accuracy of the results are discussed. The data were corrected for -ray self-absorption in the samples and summing of coincident -rays in the detector. According to reported typical compositions of Chinese bronze from different dynasties, the age of the samples has been derived from the results obtained.     

Instrumental neutron activation analysis of Na in biological materials

Sodium contents in seven mixtures of biological materials from varying aliquants of wheat flour and oyster tissue were analyzed using the INAA (instrumental neutron activation analysis) method. The samples were activated in the thermal column (TC) of the 1 MW TRIGA reactor at our laboratory. To analyze and compare the measured results, the ratioa of the epithermal neutron flux to the thermal neutron flux was determined in the TC, the rotating rack (RR) and the pneumatic terminal (PT). Due to the negligible interferences of²⁴Mg(n, p)²⁴Na and²⁷Al(n, )²⁴Na to²³Na(n, )²⁴Na, the Na results were obtained with 97% accuracy and 99% precision. It is shown that the method is suited for accurately determining Na contents in 12 various biological materials, especially for the samples that are low in Na content. From the cadmium ratio measurements of Au (4.9 eV resonance of¹⁹⁸Au) and Sm (8 eV resonance of¹⁵³Sm), ratios ofa_e/₀ were determined at 0.0011, 0.052 and 0.053 in the TC, RR and PT activation positions, respectively.     

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.     

Thermal neutron activation analysis of Cu in its ores by using an241Am−Be neutron source

A thermal neutron activation method has been developed for the determination of Cu in Cu–Pb–Zn ores and chalcopyrite ore concentrates using the reaction⁶³Cu(N, )⁶⁴Cu. The samples were irradiated with thermal neutrons from an²⁴¹Am–Be neutron source and the annihilation -radiations of 0.511 MeV were counted on 3×3 NaI(T1) detector coupled with single channel pulse height analyzer. The method is nondestructive, economical and ideal for bulk analysis of ores with 1–16% Cu.     

Preconcentration of trace elements for neutron activation analysis using activable tracers

Use of an enriched isotope as an activable tracer is proposed for the preconcentration of trace elements in neutron activation analysis. As a test of this method, contents of cadmium in various biological standard samples were determined by addition of an enriched¹¹⁶Cd tracer in the preconcentration step followed by neutron irradiation and -ray spectrometry. The principle, advantage, and limitations of the method are also discussed.     

Small sample in-vivo neutron activation analysis using californium sources

This work describes an in vivo neutron activation analysis facility for small samples, such as rats or human hand, using two 100 g²⁵²Cf neutron sources. The irradiation area is a cylindrical space, of 12 cm diameter and about 15 cm length, with fairly uniform neutron flux distribution. Experimental data on the reproducibility, effects of volume and other conditions for in vivo measurements are given. Comparative atomic absorption data on calcium measurements on rats are reported. The facility is now used for animal experiments as well as human hand irradiations in clinical investigations involving calcium metabolism and bone diseases.     

Activation analysis of selenium in organic samples,through selenium-77m,on a pre-separation basis

A method is described to separate trace amounts of selenium in organic samples without using a carrier, based on the adsorption on active carbon filters of the complex formed with APDC at pH 1.5. The separation is made prior to the neutron irradiation and the correction for selenium in the reagents performed by the irradiation of a blank. The method has been successfully used in fodder samples as well as some other organic reference materials, using a fast pneumatic transfersystem, which takes the samples from the irradiation position to the counting position in 3s, with the only limitation of the thermal neutron flux available, 4.7·10¹¹ cm^–2·s^–1. Detection limits of 0.1 g are obtained under these experimental conditions.     

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.