Isotopic analysis of uranium by neutron activation and high resolution gamma ray spectrometry

A method is described for the non-destructive and accurate determination of the isotopic composition of uranium by activation analysis. The high resolving power of Ge(Li) detectors permits easy identification on a single gamma spectrum of the gamma peaks of²³⁹Np formed from²³⁸U by activation and those of fission products formed from²³⁵U. The ratio of the peak intensities is proportional to the²³⁸U/²³⁵U ratio in the sample. A precision of ±0.6% has been obtained.     

Fast neutron activation analysis using short-lived radionuclides

Fast neutron activation analysis experiments were performed to investigate the analytical possibilities and prospective utilization of short-lived activation products. A rapid pneumatic transfer system for use with neutron generators has been installed and applied for detecting radionuclides with a half-life from 300 ms to 20 s. The transport time for samples of total mass of 1–4 g is between 130 and 160 ms for pressurized air of 0.1–0.4 MPa. The reproducibility of transport times is less than 2%. The employed method of correcting time-dependent counting losses is based on the virtual pulse generator principle. The measuring equipment consists of CAMAC modules and a special gating circuit. Typical time distributions of counting losses are presented. The same 14 elements were studied by the conventional activation method (single irradiation and single counting) by both a typical pneumatic transport system (run time 3 s) and the fast pneumatic transport facility. Furthermore, the influence of the cyclic activation technique on the elemental sensitivities was investigated.     

Determination of 32 elements in rocks by neutron activation analysis and high resolution gamma-ray spectroscopy

Neutron activation analysis and Ge(Li) spectroscopy was used to determine 32 elements in seven U.S.G.S. standard rocks of a wide range of composition. Short half-life nuclides (10 sec-10 min) were used to measure Sc, Hf, Dy, Mg, Al, Ca, Ti, V (and Na) in an automated rabbit Ge(Li) detector system. The elements K, Cu, Zn, Ga, Sr, Ba, La, Eu, Sm (and Mn) were determined by dissolution of the irradiated sample followed by removal of²⁴Na on hydrated antimony pentoxide (HAP). Long-lived nuclides were used to measure Sc, Cr, Fe, Co, Zr, Rb, Sb, Cs, Ba, Ce, Eu, Yb, Tb, Lu, Hf, Ta and Th after decay of²⁴Na. The method involves little radiochemistry and the separation is selective for²⁴Na under the experimental conditions used. Elemental concentrations determined agree well with previously published data.     

Fast neutron activation analysis at Texas A&M University

Fast neutron generators are used at Texas A & M University to provide a supply of high energy neutrons for nuclear analytical measurements. A series of neutron activation analysis procedures have been developed for determining various major, minor and trace constituents in a variety of materials. These procedures are primarily developed to compliment our reactor based NAA program, thereby expanding the list of determinable elements to include those difficult or impossible to measure using thermal neutrons. A few typical methods are discussed. The unique implementation of the methodologies at Texas A & M are explained.     

Prompt gamma activation analysis using a chopped neutron beam

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.     

Fast neutron activation analysis of silicon in aluminum alloys

The silicon content in an aluminum-silicon alloy was measured by nondestructive fast neutron activation analysis with fission spectrum neutrons. A boron nitride irradiation container reduced the flux of thermal and epithermal neutrons at the sample position, enhancing the²⁹Si (n, p)²⁹Al reaction. A detection limit of 0.4% silicon in a 0.5 g alloy sample was obtained.     

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.     

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.     

Computer program for processing gamma spectra in neutron activation analysis

A program based on the method of least squares and written in the ALGOL-60 code was developed for data processing in the activation analysis of biological substances. The applicability of the program was checked on synthetic mixtures of the radioisotopes⁶⁴Cu,^69mZn and⁵⁶Mn measured with a scintillation γ-spectrometer.     

Prompt gamma cold neutron activation analysis applied to biological materials

Summary Cold neutrons at the external neutron guide laboratory (ELLA) of the KFA Jülich are used to demonstrate their profitable application for multielement characterization of biological materials. The set-up and experimental conditions of the Prompt Gamma Cold Neutron Activation Analysis (PGCNAA) device is described in detail. Results for C, H, N, S, K, B, and Cd using synthetic standards and the “ratio” technique for calculation are reported for several reference materials and prove the method to be reliable and complementary with respect to the elements being determined by INAA. IAEA fellow at the KFA from 6. 3. 91 to 2. 9. 91 on contract No. VIE/9016R.     

Short-time neutron activation gamma-ray spectroscopy

Short-time instrumental neutron activation analysis, with high throughput, sensitivity and accuracy without matrix interferences, can be achieved in spite of the initial high count rate from both short and long-lived nuclide activation, if the experimental conditions are optimized by the combination of techniques. Thus the initial usually high counting rate can be faced by a loss-free counting system to avoid blocking or distortion of the system. The rapid radioactive decay and the consequent low counting statistics of short lived nuclides can be compensated by source-detector distance variation during the counting period and by cyclic and cumulative activation. Matrix spectral interferences can be reduced by ion exchange before activation for selective element preseparation and by neutron spectrum optimization such as epithermal neutron activation for selective element peak enhancement.     

Short-time neutron activation gamma-ray spectroscopy

Short-time instrumental neutron activation analysis, with high throughput, sensitivity and accuracy without matrix interferences, can be achieved in spite of the initial high count rate from both short and long-lived nuclide activation, if the experimental conditions are optimized by the combination of techniques. Thus the initial usually high counting rate can be faced by a loss-free counting system to avoid blocking or distortion of the system. The rapid radioactive decay and the consequent low counting statistics of short lived nuclides can be compensated by source-detector distance variation during the counting period and by cyclic and cumulative activation. Matrix spectral interferences can be reduced by ion exchange before activation for selective element preseparation and by neutron spectrum optimization such as epithermal neutron activation for selective element peak enhancement.     

Prompt gamma neutron activation analysis (PGAA): recent developments and applications

Journal of Radioanalytical and Nuclear Chemistry - Prompt gamma neutron activation analysis has become an important part of the analytical toolkit, practiced at several research reactors worldwide....     

Fast determination of molybdenum and tellurium by neutron activation analysis

The utilization of 14.6-min ¹⁰¹Mo and 25-min ^101gTe for the determination of molybdenum and tellurium in biological materials by radiochemical neutron activation analysis is described for the first time. Radioisotopes were separated from the samples activated in a thermal neutron flux of about l0¹⁴n cm^-2 s^-1. The radiochemical procedure for molybdenum involves extraction of Mo⁺⁺ from 6 M HCl into diethylether, re-extraction into water, precipitation as oximate, and measurement of the gamma activity of ¹⁰¹Tc. The tellurium was separated by reduction to the element with SO₂ in 3 M HCl, dissolution in HNO₃, and reprecipitation as the element for the measurement of radioactivity. The sensitivity was estimated at ca. 10 ng at the level of confidence of 95%. The methods were tested by analyzing NBS- standard Bovine Liver and Orchard Leaves for molybdenum; the concentrations found were 3.2 ± 0.1 μg g^-1 and 300 ± 60 ng g^-1, respectively. The tellurium content of bovine liver was estimated at 90 ± 15 ng g^-1.     

Fast neutron activation analysis of Kalewa (Myanmar) coal

Aluminium, silicon, copper, iron, magnesium and sulfur in Kalewa (Myanmar) coal were determined by fast neutron activation analysis. For activation a KAMAN A-710 Neutron Generator was used. Kalewa coal was found to be low in sulfur and relatively rich in iron.     

Computer simulaion of gamma spectra in 14 MeV neutron activation analysis

The method of simulation of gamma-spectra based on the experimental library spectra of particular radioisotopes is described. The library spectra were obtained by activation of pure element sample with the use of a 14 MeV neutron generator, counting them with a NaI(T1) scintillation spectrometer and decomposing of mixed spectra to spectra of separate radioisotopes. The simulated and measured spectra of an artificial sample are compared.     

Coincidence and anti-coincidence measurements in prompt gamma neutron activation analysis with pulsed cold neutron beams

A novel approach is implemented to alleviate some persistent problems in neutron capture prompt gamma activation analysis (PGAA). Detection sensitivities of PGAA are often restricted by the following factors: poor signal to noise ratios, interferences from background signals, and, in some cases, overlapping energy lines from different origins, namely ultra short-lived decay lines interfering with prompt decay. Timing the gamma-ray acquisition with the actual capture events using a pulsed beam of cold neutrons allows discrimination between prompt and delayed emissions from a sample source as well as against background events. Coincidence gating selects the prompt gamma-ray emissions. Contributions of background capture gamma-rays are suppressed because of different flight times of neutrons to the sources of background radiation, providing a reduction in direct gamma-ray interferences. Anti-coincidence gating allows measurement of only decay radiation that originates from short-lived activated states of the nuclides after capture. Spectra of decaying nuclides are free of interfering prompt activities, as well as have lower continuum background from Compton scattering of high-energy prompt gamma-rays in the detector. The measurements provide the opportunity to use ultra-short half-life nuclides for analytical purposes, no sample transfer times are lost, and repetitive activation and counting cycles are achieved with the use of pulsed neutron beams.     

Fast neutron activation analysis of rare-earth elements in monazite from Korea

The relative ans single comparator methods have been applied to determine 7 rare-earth elements and U, Th in Korean Monazites by 14.5 MeV neutron activation analysis. The (n, 2n) nuclear reactions are used for all elements except La, for which (n, p) reaction is used. Al is used as a flux monitor for the relative method and as a singlle comparator for the single comparator method. The analytical results obtained by the two methods agree well within 3% deviation except for Sm and Gd. These results are also compared with the result obtained by a single comparator method using reactor neutron.