New gamma-ray intensities for the <Superscript>14</Superscript>N(n,γ)<Superscript>15</Superscript>N high energy standard and its influence on PGAA and on nuclear quantities

The ¹⁴N(n,γ)¹⁵N reaction is a primary γ-ray source for high energy calibration of detectors. The relative γ-ray-intensities of ¹⁵N and the relative γ-ray detection efficiency function have been simultaneously determined up to 10 MeV from γ-peak areas alone. Absolute γ-ray-intensities were obtained with proper renormalization to known absolute intensity. The influence of these new intensity values are assessed for use in PGAA. Any consistently used set of calibration intensities applied in the creation of library values and for analysis do not influence the concentrations. Contrary to this, quantities based on sums of γ-ray cross sections may provide different answers with the new ¹⁵N intensities and they give means to validate them.     

Pulsed neutron-based on-line coal analysis

A neutron generator-based on-line coal analysis system is described, capable of measuring the content of the major and minor elements in coal. The system utilizes reactions produced from fast and themal neutrons, as well as from neutron activation with half lives of seconds or minutes. Characteristic γ-rays, detected with BGO detectors are used for the identification of the various chemical elements. The method for the analysis of the γ-ray spectra is presented, and the measurements of coal density, carbon and sulfur content are shown.     

Quantitative analysis of phosphorus by (p, γ) reactions

Measured values of the intensities of characteristic γ-rays emitted under the bombardment of protons on a thick target of phosphorus are tabulated. The intensity of each characteristic γ-ray is measured and used for quantitative analysis of phosphorus in any sample with a sensitivity of 50 to 1000 ppm.     

Low level Pu and Am estimation in liquid waste from nuclear reactor

Estimation of very low amount up to pico-gram of Am and Pu in the liquid waste of U–Pu fuel cycle of the irradiated U fuel from the nuclear reactor has been carried out using combined method of α- and γ-ray spectrometric techniques. ²⁴¹Am was estimated by γ-ray spectrometry from a plancheted source. In spite of the same α energy of 5.49 MeV for ²⁴¹Am and ²³⁸Pu, the amount ²³⁸Pu was estimated by α spectrometry from the same plancheted source after subtracting amount of the ²⁴¹Am obtained from γ-ray spectrometry. The amount of Am and Pu obtained by this technique is found to be superior compared to other techniques even in the presence of Th, U and fission products.     

Neutron activation determination of noble metals using a selective group separation scheme

A rapid and comprehensive method has been developed for the determination of ppm to sub-ppb amounts of Ru, Pd, Ag, Os, Ir, Pt and Au, based on thermal neutron irradiation, dissolution of samples, selective absorption on Srafion NMRR ion exchange resin and high resolution γ-ray spectrometry. Two noble metals “specific” resins were tested for their absorption behaviour. The method has been used for analysis of standard rocks, ores, minerals, lunar samples, coal, coal fly ash, and several biological materials.     

Analytical performance of some methods for the determination of trace elements in lichens used as air quality assessment

In this study, the validity of the effective (virtual) point-detector concept for the CdZnTe (CZT) detector for disc-shaped radioisotope sources has been investigated in the photon energy range of 50–662 keV. It has been found that the virtual point-detector model is valid for conventional CZT detectors. The photon energy dependence of the virtual interaction depth (VID) in the CZT detector does not seem to fit to a good trend. However, in general, the measured VID values are increasing with increasing γ-ray energy in the range of 50–662 keV, but the VID values always remain within the physical thickness of the CZT detector. For instance, the VID value was measured to be about 4.4±0.5 mm in the 5 mm thick CZT detector at 662 keV γ-ray energy. In application, the VID values for photons can be used for efficiency calculation models by scaling the measured detection efficiency as a function of energy and source-to-detector distance.     

The use of non-destructive high energy gamma photon activation for trace element survey analysis

An empirical study has been made of the potential of high energy γ photon activation and high resolution γ-ray spectrometry for the survey analysis of trace elements in a variety of materials. Human blood, urine, bone ash, standard glass (NBS, SRM 612) and air particulates, along with synthetic multi-element standards, have been studied following irradiation with γ photons of maximum energy 17–45 MeV. Elements found to be suited to determination by γ activation include Sb, As, Bi, Cd, Cs, Ca, Ce, Cr, Fe, Au, Pb, Mg, Mo, Ni, Nb, Rb, Sr, Tl, Ti, Tm, Zn and Zr. γ spectra, elemental concentrations measured, and/or limits of detection observed, for the matrices studied are given.     

Gamma-ray yield dependence on bulk density and moisture content of a sample of a PGNAA setup: A Monte Carlo study

Monte Carlo calculations were carried out to study the dependence of γ-ray yield on the bulk density and moisture content of a sample in a thermal-neutron capture-based prompt gamma neutron activation analysis (PGNAA) setup. The results of the study showed a strong dependence of the γ-ray yield upon the sample bulk density. An order of magnitude increase in yield of 1.94 and 6.42 MeV prompt γ-rays from calcium in a Portland cement sample was observed for a corresponding order of magnitude increase in the sample bulk density. On the contrary the γ-ray yield has a weak dependence on sample moisture content and an increase of only 20% in yield of 1.94 and 6.42 MeV prompt γ-rays from calcium in the Portland cement sample was observed for an order of magnitude increase in the moisture content of the Portland cement sample. A similar effect of moisture content has been observed on the yield of 1.167 MeV prompt γ-rays from chlorine contaminants in Portland cement samples. For an order of magnitude increase in the moisture content of the sample, a 7 to 12% increase in the yield of the 1.167 MeV chlorine γ-ray was observed for the Portland cement samples containing 1 to 5 wt.% chlorine contaminants. This study has shown that effects of sample moisture content on prompt γ-ray yield from constituents of a Portland cement sample are insignificant in a thermal-neutrons capture-based PGNAA setup.     

Prompt gamma-ray yields from proton bombardment of transition elements (Ti to Zn)

Gamma-ray yields from bombardment with protons of thick targets of Ti, V, Mn, Cr, Fe, Co, Ni, Cu and Zn are tabulated for proton energies ranging between 0.6 and 3.2 MeV. The applications of these reactions for quantitative analysis of these chemical elements are discussed. The sensitivity of this technique of analysis is poorer than the PIXE method for these transition elements, but is sufficient for rapid and accurate quantitative analysis of alloys when elements are present in concentrations down to 1%. The knowledge of the γ-ray energies and intensities produced by the bombardment of these elements with protons is also necessary for solving interferences with several γ-rays induced in light elements, for which the proton induced γ-ray technique is sensitive, without any correction for photon attenuation.     

On-line and bulk analysis of coal and metalliferous ores

Coal and mineral processing operations can be controlled more economically if information on process variables is obtained continuously. Much of this information can be provided by nuclear techniques. Recent Australian developments in on-line nuclear gauges are reviewed. Techniques have been developed, field tested and commercialised for the on-line analysis of ash and moisture in coal and for the in-stream determination of solids weight fraction and ash in coal slurries. Techniques are being developed for the on-line analysis of moisture in coke and sulphur in lead sinter feed. As well, techniques are being developed for the bulk analysis of silver, lead and zinc in drill cores.     

A compilation of X- and gamma-ray sensitivities from isotopes produced by the (n, γ) reaction for utilization in instrumental neutron activation analysis

A comprehensive compilation of X- and γ-ray emitting isotopes produced by the (n, γ) reaction is reported in this paper for application to instrumental neutron activation analysis (INAA). The X- and γ-ray sensitivities are computed theoretically by a computer code. Interfering photons from isotopes of neighbouring elements are identified by the code and the percentage interference is computed. Additionally an advantage factor (X-ray: γ-ray sensitivity) is computed, which is a figure of merit for X-ray spectroscopy in INAA. Further, mathematical representation of background continua for typical matrices encountered in INAA allow the calculation of elemental detection limits for the X-ray and γ-ray photons.     

Quantitative analysis of aluminium by prompt nuclear reactions

A new physical method of analysis of samples containing small quantities of aluminium is described. The sample is bombarded with fast protons and the resulting γ-rays are analysed by the Ge(Li) technique. The high selectivity of these detectors allows identification of the nuclei responsible for the γ-ray emission. A careful analysis has been made of the different nuclear reactions involved in the production of γ-rays in the bombardment of aluminium. Four γ-rays have been observed with sufficient intensities for rapid determination: 843 keV, 1013 keV, 1368 keV and 1778 keV. Thick-target excitation yields are presented and discussed in view of their use in analysis. A complete tabulation of these reactions is also presented. The method allows the determination of the aluminium concentration in every solid matrix in the 100 ppm range. In some cases concentrations as low as 10 ppm can be observed. All these determinations are quantitative. Lower concentrations can be detected qualitatively. Examples of the application of the method to different substances are the following: stainless steel, inorganic compounds, crystals, evaporated layers, etc. The resonance pattern observed in the intensity curves can be used to measure the homogeneity and the thickness of thin layers containing aluminium (0.2 to 4 μm). In most cases the method can be considered non-destructive and there is no residual radioactivity. Analysis of a sample of a total weight not exceeding 0.1 mg can be achieved.     

Stopping power effects in the determination of14N by a resonance reaction

The applicability of the¹⁴N(p,p’ γ₁)¹⁴N nuclear reaction in the determination of the absolute abundance of¹⁴N, with a 2% uncertainty, was demonstrated at 4.3 MeV bombarding energy. The fact that almost all of the thick target γ-ray yield resulted from a resonance at Ep=4.0 MeV allowed to consider the necessary stopping-power corrections only at the energy of that resonance. Alternatively, the method was used to obtain the stopping power of 4.0 MeV protons in complex biological materials. Supported in part by the International Atomic Energy Agency, Vienna, Austria.     

Quantitative analysis by (p,X) and (p, γ) reactions at low energies

Production of atomic X-rays and nuclear γ-rays by bombardment with 0–3 MeV protons of thick targets is described. In the case of low-Z atomic X-rays, the absorption in the target is very large, while in the case ofK X-rays from high-Z atoms or for γ-rays, this phenomenon is negligible. Both of these reactions can be used for analysis of elements from F to U, and the sensitivities and the accuracies of the determinations are discussed. A table is given showing the γ-ray energies observed in 11 substances and the limits of sensitivity.     

Photo-neutron cross-section of 100Mo

The ¹⁰⁰Mo(γ, n) reaction cross-section was experimentally determined at end point bremsstrahlung energy of 10 and 12.5 MeV using off-line γ-ray spectrometric technique. It was also found that ¹⁰⁰Mo(γ, n) reaction cross-section increases sharply from the end point bremsstrahlung energy of 10 MeV to 12.5 MeV, which may be because of GDR around the energy region of 12–16 MeV. The ¹⁰⁰Mo(γ, n) reaction cross-section as a function of photon energy was calculated theoretically using TALYS 1.2 computer code. The flux-weighted average values of ¹⁰⁰Mo(γ, n) reaction cross-section for bremsstrahlung having end point energy of 10 and 12.5 MeV were also calculated using the experimental and theoretical data of mono-energetic photon. The present experimental ¹⁰⁰Mo(γ, n) reaction cross-sections were compared with the bremsstrahlung flux-weighted average values of experimental and theoretical data and found to be in the lower side for 10 MeV and in the higher side for 12.5 MeV.     

Fast neutron activation analysis: High resolution gamma spectroscopy

The purpose of this study was to demonstrate the versatility of combining the use of high resolution, Ge(Li) γ-detectors with the techniques of fast neutron activation analysis. A compilation of γ-ray spectra are presented for irradiation of 30 elements with 14.8 MeV neutrons under standard conditions and the origin of all major photopeaks is determined.     

The stability of biological specimens during charged particle bombardment

Consecutive short bombardment of thick biological specimens with proton beams demonstrated that the yield from oxygen decreases with increasing amounts of total deposited beam; those from carbon and sulfur appear not to be affected, while significant yield increases are observed with respect to the γ-ray yields of all the other investigated isotopic nuclear reactions. The yield alterations were investigated in freeze-dried plant and animal specimens as well as in targets prepared by air drying at several temperatures. Only in ashed specimens do the γ-ray yields remain constant as a function of increasing amounts of deposited beam. The yield alterations induced by the beam on non-ashed biological specimens depend on (I) the total dissipated beam charge, (II) energy of the beam, (III) chemical element, (IV) origin of the biological specimen, and (V) method of preparation of the target. The underlying mechanism and implications of the yield alterations in the elemental analysis of non-ashed biological specimens are investigated and discussed.     

Reinvestigation of low-lying levels of231Th

Low-lying excited levels of²³¹Th fed through α-decay of²³⁵U were investigated by using α-γ and γ-γ coincidence technique. From the analyses for co-relating energy levels and transition intensities, we found that the most favorable transition from 205.3 keV ([631]7/2) level that is fed by the most dominant α transition from²³⁵U is 19.6 keV transition (205.3 keV [631]7/2⁻→185.7 keV [631]5/2⁻). We also found that the transition probability of 109.2 keV, 205.3 keV [631]7/2⁻→96.1 keV [633]9/2⁺, was corrected to be weak. These findings can explain why the 185.7 keV γ-ray is so strongly observed, 0.57 photons/ga, in the γ-spectrum associated with the α-decay of²³⁵U. The decay scheme of²³¹Th levels previously reported has been modified according to the present analysis.     

Computer-assisted qualitative analysis of gamma-ray spectra

A computer program is described to perform the identification of isotopes in neutron activated samples. The γ-ray energies as obtained from a Ge(Li) γ-ray spectrum are compared with those of a library, containing data for about 250 isotopes. Isotopes whose γ-ray energies match closely with the unknowns are selected as possible constituents. Unlikely attributions are then eliminated by a careful inspection of the γ-rays found. Further exploitation of half-life, the way of production and the sensitivity for the given irradiation and measurement conditions, allow the selection of the most likely constituents in the source. The results of the automated identification agree closely to those obtained by an experienced investigator. The program is written in FORTRAN IV for a PDP-9 computer with a 16 K word memory.     

An analytical representation of the response of the NaI(T1) detector for the gamma-ray spectrum analysis

An analytical function for describing the response function of γ-rays from the NaI(Ti) detector was constructed with the purpose of establishing the method of automatic γ-ray spectrum analysis. The response was found to be divided into six portions; the function of each portion joins smoothly to the one representing the adjacent part. Empirical equations for the parameters specifying the response function were found as functions of the γ-ray energy in relation to the detector dimension. The obtained response function was fitted to the observed spectrum by the least squares method. The calculated spectrum agreed well with the observed one.