Fast neutron induced fission neutron spectra below the incident energy

A fast pneumatic transfer system for an instrumental neutron activation analysis and delayed neutron counting system were reconstructed with new designs of a functional improvement at the HANARO research reactor in 2006. The design, conception, operation and control of these systems are described. Also the experimental characteristic parameters by a functional operation test and an irradiation test of these systems, such as the transfer time, the neutron flux, the temperature of the irradiation position with an irradiation time, the radiation dose rate when the rabbit is returned, etc., are reported to provide a user information as well as for the management and safety of the reactor.     

Energy-dependent characteristics of prompt neutron anisotropic emission by 244Cm and 240Pu according to Monte Carlo simulations

Journal of Radioanalytical and Nuclear Chemistry - It is well known that prompt neutrons from nuclear fissions show anisotropic emission properties that have been studied for nuclear safeguards...     

Determination of pre-scission kinetic energy in low energy fission using isotonic charge distribution model

The spectral lines of the 478 keV prompt -ray from^7*Li produced in the¹⁰B(n, )^7*Li reaction were measured for a silicon wafer coated with a thin boron layer using neutron beams. The shapes of the Doppler broadened lines were found to depend greatly on the angle between the measurement axis and the boron layer surface. The angular dependence was interpreted according to whether the energetic^7*Li ions are ejected into air or into the substance in the forward or backward recoil of^7*Li to the -ray detector.     

Fine structure of mass and charge distribution in low energy fission

Studies of finer details in mass and charge distribution fission leads to a better understanding of the fission process. Experimental determination of independent and cumulative yields using radiochemical techniques as well as mass spectrometers and fission product recoil separators form the basis of such studies. It has been established that closed shells as well as an even number of nucleons influence both mass and charge distributions. The magnitudes of these effects may be estimated from existing experimental yield data and various fission models. Using our measurements of several fission yields and those existing in the literature we have calculated even-odd proton and neutron effects for various low energy fissioning systems. Where enough data existed, direct calculations were made, whereas for other cases the Z_p-model of WAHL has been used. It is found that the even-odd proton effect is well established and pronounced in thermal neutron fission of²³⁵U and²³³U. Lesser effects were found for reactor neutron induced fission of²³²Th, thermal neutron fission of²³⁹Pu and spontaneous fission of²⁴⁵Cm and²⁴⁹Cf. No effect seems to exist in the thermal neutron fission of²⁴¹Pu and the spontaneous fission of²⁵²Cf. The even-odd neutron effect is found to be much lower than the corresponding proton effect in²³⁵U and²³³U fissions and is nonexistent in the rest of the fissioning systems.     

The history of the discovery of nuclear fission

Following with the discovery of the electron by J. J. Thomson at the end of the nineteenth century a steady elucidation of the structure of the atom occurred over the next 40 years culminating in the discovery of nuclear fission in 1938–1939. The significant steps after the electron discovery were: discovery of the nuclear atom by Rutherford (Philos Mag 6th Ser 21:669–688, 1911), the transformation of elements by Rutherford (Philos Mag 37:578–587, 1919), discovery of artificial radioactivity by Joliot-Curie and Joliot-Curie (Comptes Rendus Acad Sci Paris 198:254–256, 1934), and the discovery of the neutron by Chadwick (Nature 129:312, 1932a, Proc R Soc Ser A 136:692–708, 1932b; Proc R Soc Lond Ser A 136:744–748, 1932c). The neutron furnished scientists with a particle able to penetrate atomic nuclei without expenditure of large amounts of energy. From 1934 until 1938–1939 investigations of the reaction between a neutron and uranium were carried out by E. Fermi in Rome, O. Hahn, L. Meitner and F. Strassmann in Berlin and I. Curie and P. Savitch in Paris. Results were interpreted as the formation of transuranic elements. After sorting out complex radio-chemistry and radio-physics O. Hahn and F. Strassmann came to the conclusion, beyond their belief, that the uranium nucleus split into smaller fragments, that is nuclear fission. This was soon followed in 1939 by its theoretical interpretation by L. Mietner and O. Frisch.     

The recommended k0-factors for neutron-induced prompt gamma-ray analysis and the prompt gamma-ray emission probabilities

Recommended k ₀-factors for gamma-lines of 24 elements useful for neutron-induced prompt gamma-ray analysis (PGA) and which are not influenced by neutron spectrum differences were obtained from the k ₀-factors measured with the cold and thermal neutron guided beams of JRR-3M, by statistical calculation. The prompt gamma-ray emission probabilities were derived from the recommended k ₀-factors using atomic weight, isotopic abundance and thermal neutron capture cross section all related to the k ₀-factors, for which one can obtain accurate data. The derived gamma-ray emission probabilities for the light elements (H to Ca) agreed well within ±10% with those of the ENSDF values, which reflect recent data while the agreement for heavy elements (Ti to Pb) was ±40% with those of the ENSDF, which are still composed of old data. This revised version was published online in July 2006 with corrections to the Cover Date.     

Measurement of proton-induced prompt low energy photons by high resolution spectrometry: The analysis of lanthanides

Photons below 200 keV excited by protons from 1.8 to 5.4 MeV were measured from the lanthanides. The K X-rays were sufficiently resolved for analysis, and the sensitivity attainable was or the order of 100 g.g^–1. Apart from La and Ce, all the rare earths also yielded low energy gamma-rays suitable for qualitative analysis and for the determination of minor components at concentrations above mg.g^–1. Some excitation functions are reported and results are given for test analyses of geological materials.     

The emission of X-rays by fission fragments

Approximately 5% of the -ray transitions in fission fragments are internally converted, giving rise to X-rays. X-ray energies are characteristic of Z, but yields depend strongly and not smoothly on Z and A of the fragments and on time. If these biases can be accepted, X-rays can be used to identify the atomic number of fission fragments. More generally, internal conversion and X-ray emission must be interpreted in the context of detailed knowledge of -ray transitions.     

The use of element ratios to eliminate analytical bias in cold neutron prompt gamma-ray activation analysis

Analytical bias due to neutron scattering and absorption in cold neutron prompt gamma-ray activation analysis (CNPGAA) is largely eliminated for homogeneous samples when element ratios are measured. Application of sensitivity ratios (measured relative to titanium) to the multielement analysis of the Allende meteorite increases both the speed and accuracy of the measurement. Greater measurement accuracy is achieved for some samples when ratios of element concentrations are reported. Problems are encountered when applying the ratio method to measurement of elements which deviate from 1/v behavior, and when gamma-ray attenuation or sample heterogeneity are significant.     

The influence of the solvent on the conformational energy differences due to the anomeric effect

The solvation free energy ΔG^sol of molecules exhibiting the anomeric effect is computed in an approach that considers a continuous distribution for the solvent. A partition of ΔG^sol into separately evaluated contributions confirms that changes in the energy of the systems due to changes in conformation of the solute are ruled by the electrostatic contribution. A comparison with the “exact” values indicates that the approximate expression for the electrostatic contribution to ΔG^sol are not accurate enough to permit a proper modeling of the solvent influence on the anomeric effect. The systems are composed of methanediol, methoxymethanol, dimethoxymethane, and 2-methoxytetrahydropyran in carbon tetrachloride, chloroform, acetone, and water. The calculations have been performed at the SCF level with the STO -3G and 4–31G basis sets.     

The epithermal neutron flux distribution in a nuclear reactor and its effect on epithermal neutron activation analysis

The shape of the epithermal neutron energy distribution has been determined in two irradiation positions of the University of London CONSORT II reactor. The method applied involves cadmium ratio measurements using a series of resonance detectors. Principles of the method and some considerations relative to epithermal neutron activation analysis in connection with the deviation of the epithermal neutron flux distribution from the 1/E law are given.     

Sulphur determination by proton-induced prompt gamma emission: The effect of the matrix and its importance in coal analysis

The determination of sulphur through -ray spectrometry induced by 5 MeV protons was chosen to study the effect of dilution and spike addition on the stopping power of the matrix and applied to the determination of sulphur in coal. Changes in the matrix cannot be ignored even for the spiking technique.     

Measurement of proton-induced prompt low energy photons by high resolution spectrometry: The analysis of noble metals

Using HPGe detectors, the K X-rays and prompt gamma-rays below 200 keV from Ru, Rh, Pd, Ag, Re, Os, Ir, Pt and Au were measured under bombardment with protons from 1.8 to 5.4 MeV. Excitation functions for analytically important gamma-rays were determined. Interference-free sensitivities were calculated and the method was tested by the analysis of standard dental alloys.     

The determination of boron in biological materials by neutron irradiation and prompt gamma-ray spectrometry

A prompt-gamma neutron activation technique has been developed using the (n, ) apparatus situated at the O degree through-tube of the Imperial College CONSORT II Reactor with a thermal neutron flux at the target position of approximately 2×10⁶ n cm^–2 sec^–1, and a Compton-suppression system involving a lithium-drifted germanium (Ge(Li)) detector and a sodium iodide anti-Compton shield. Boron levels of 1–5 g g^–1 (detection limit 0.05 g B for 10,000 sec period of measurement) can be attained using the Compton-suppression system with graphical inter-polation correction for the 472 keV sodium-ray peak contribution to the Doppler-broadened 478 keV boron gamma-ray peak resulting from the¹⁰B(n, )⁷Li reaction. Very good agreement is reached for boron levels compared using this system for various Standard Reference Materials and other published values. Measurement of the boron content of bone and tooth samples from rheumatoid arthritis individuals shows lower levels, (p<0.05); 16.13±7.53 g g^–1, when compared with a control population; 19.79±4.18 g g^–1. A positive correlation existed between the boron content of bone and tooth material for each study group. Results indicate that boron availability may be associated with rheumatoid arthritis.     

Absolute yields of the fission products in the neutron induced fission of 232Th and 233U

Absolute yields of 10 fission products in the reactor neutron induced fission of ²³²Th and 17 fission products in the thermal neutron induced fission of ²³³U have been determined using track etch-cum γ-ray spectrometric technique. The number of fissions occurring in the target is obtained by recording the fission events in a mica track detector. The fission product atoms are determined by the direct counting of the irradiated target on a 60 cm³ Ge(Li) detector coupled to a 4096 channel analyser. A one step radiochemical separation was done, before gamma ray counting, for few fission products in the reactor neutron induced fission of ²³²Th. The measured yield values are compared with the available literature data and an analysis of the possible errors are done. The overall uncertainty in the measurements is estimated to be 4–5%.     

Application of prompt gamma neutron activation analysis in the aluminium industry of Egypt

Prompt gamma-ray energy spectrum following the capture of thermal neutrons by the atomic nuclei in an alumina ore sample was measured using a HPGe detector in a borehole environment. Based on the in formation obtained from the spectrum and nuclear data the nuclear ratio that compares the content of an unknown element with an estimate of aluminium in the ore can be determined. The work aimed to explore the applicability of this technique for quality control measurements in the aluminium industry of Egypt.     

Evaluation of some X-rays and low energy gamma-rays in instrumental neutron activation analysis

The dependence of self-absorption of X-rays and low energy -rays on energy and sample matrix has been studied for^94mNb,¹²⁸I,^104mRh,²³⁹U and²³³Th. Experimentally determined attenuation factors have been compared to calculated values. The use of these nuclides in the instrumental neutron activation of practical samples has been evaluated.     

The determination of boron in sedimentary rocks by neutron irradiation and prompt γ-ray spectrometry

Prompt γ-rays following the (n_th, α) reaction on¹⁰B have been measured to determine the boron content of sedimentary rocks. Employing an external reactor neutron beam with only modest flux, it is possible to assay boron at concentrations typically encountered in this material (>5 μg/g). The technique relies on the use of chemical standards and the values obtained for 9 North American shales are compared with measurements performed by emission spectrography. Detection limits and statistical errors as a function of beam time are also discussed. Department of Geology, Mcmaster University, Hamilton, Ontario (Canada)