Measurement of ke V-Neutron Capture Cross Sections and Capture Gamma-Ray Spectra of 147,148,149,150,152,154Sm

The neutron capture cross sections and capture γ-ray spectra of ^{147,148,149,150,152,154}Sm were measured in the neutron energy region of 10 to 90 keV and at 550 keV. A neutron time-of-flight method was adopted with a 1.5-ns pulsed neutron source by the ⁷Li(p, n)⁷Be reaction and with a large anti-Compton NaI(Tl) γ-ray spectrometer. A pulse-height weighting technique was applied to observed capture γ-ray pulse-height spectra to derive capture yields. The capture cross sections were obtained with the error of about 5% by using the standard capture cross sections of ¹⁹⁷Au. The present results were compared with the evaluated values of JENDL-3.2 and previous measurements. The capture γ-ray spectra were obtained by unfolding the observed capture γ-ray pulse-height spectra. An anomalous shoulder was clearly observed around 3 MeV in the γ-ray spectra of ^150,152,154Sm, and the energy position of the shoulder was consistent with the systematics obtained in our previous work.     

Measurement of keV-Neutron Capture Cross Sections and Capture Gamma-Ray Spectra of 167 Er

The neutron capture cross sections and capture γ-ray spectra of ¹⁶⁷Er were measured in the neutron energy region of 10 to 90keV and at 550 keV. Using a neutron time-of-flight method with a 1.5-ns pulsed neutron source by the ⁷Li(p, n)⁷Be reaction, the measurement was performed by detecting prompt γ rays from an enriched capture sample with a large anti-Compton Nal(Tl) spectrometer. A pulse-height weighting technique was applied to observed capture γ-ray pulse-height spectra to extract capture yields. The capture cross sections were derived with the error of about 5% by using the standard capture cross sections of ¹⁹⁷Au. The present results were compared with the evaluated values of ENDF/B-VI and the previous measurement. The present measurement at 550 keV was the first one. The capture γ-ray spectra were obtained by unfolding the observed capture γ-ray pulse-height spectra. An anomalous shoulder was clearly observed around 3 MeV in the γ-ray spectra and the energy position of the shoulder was consistent with the systematics obtained in our previous work. The multiplicities of the observed γ rays were derived from the γ-ray spectra.     

Method of Measuring Boron-10 Depletion in Control Blade

The neutron capture cross sections and capture γ-ray spectra of ^143,145,146Nd were measured in the neutron energy region of 10 to 90 keV and at 550 keV. A neutron time-of-flight method was adopted with a 1.5-ns pulsed neutron source by the ⁷Li(p, n)⁷Be reaction and with a large anti-Compton NaI(Tl) γ-ray spectrometer. A pulse-height weighting technique was applied to observed capture γ-ray pulse-height spectra to derive capture yields. The capture cross sections were obtained with the error of about 5% by using the standard capture cross sections of ¹⁹⁷Au. The evaluated values of JENDL-3.2 and previous measurements were compared with the present results. The capture γ-ray spectra were obtained by unfolding the observed capture γ-ray pulse-height spectra. An anomalous shoulder was observed around 2 MeV in the γ-ray spectra of ^145,146Nd, and the energy position of the shoulder was consistent with the systematics obtained in our previous work.     

Measurement of keV-neutron capture cross-sections and capture γ-ray spectra of Fe and Fe

The neutron capture cross-sections and the capture γ-ray spectra of ⁵⁶Fe and ⁵⁷Fe have been measured in the neutron energy range from 10 to 90 keV. Pulsed keV-neutrons were produced from the ⁷Li(p,n)⁷Be reaction by bombarding a lithium target with a 1.5-ns bunched proton beam from a 3 MV Pelletron accelerator. The incident neutron spectrum on the capture sample was measured using a time-of-flight method with a ⁶Li-glass detector. The capture γ-rays emitted from an iron or standard gold sample were detected with a large anti-Compton NaI(Tl) spectrometer. The capture yield of the iron or gold sample was obtained by applying a pulse-height weighting technique to the corresponding capture γ-ray pulse-height spectrum. The capture cross-sections of ^56,57Fe were derived with errors less than 5% using the standard capture cross-sections of ¹⁹⁷Au. The capture γ-ray spectra were obtained by unfolding the observed capture γ-ray pulse-height spectra. The present results for the capture cross-sections were compared with the previous measurements and the evaluated values of ENDF/B-VII.0 and JENDL-3.3. The Maxwellian-averaged capture cross-sections of ⁵⁶Fe and ⁵⁷Fe at 30 keV are derived as 12.22 ± 2.06 mb and 44.48 ± 7.56 mb, respectively.     

Measurement of keV-Neutron Capture Cross Sections and Capture Gamma-Ray Spectra of 209Bi

The capture cross sections and capture γ-ray spectra of ²⁰⁹Bi were measured in a neutron energy region from 5 to 80keV and at 520 keV, using pulsed keV neutrons from the ⁷Li(p, n)⁷Be reaction and a time-of-flight method. The capture γrays from a bismuth or standard gold sample were detected with a large anti-Compton NaI(Tl) spectrometer. The capture yield of the bismuth or gold sample was obtained by applying a pulse-height weighting technique to the corresponding capture y-ray pulse-height spectrum. The derived capture cross sections from 5 to 80 keV were in good agreement with recent measurements, but that at 520 keV was about half of previous measurements. This large discrepancy at 520 keV was ascribed to the incorrect background-subtraction in the previous measurements from a comparison between the present and previous capture γray spectra. Strong transitions from the capture states to low lying states of ²¹⁰Bi were observed in the present γray spectra. The multiplicities of observed y rays were obtained from the γray spectra.     

Evaluation of neutron nuclear data on tantalum isotopes

Neutron nuclear data on four isotopes of tantalum have been evaluated for the next version of Japanese Evaluated Nuclear Data Library general-purpose file in the energy region from 10^?5 eV to 20 MeV. Unresolved resonance parameters were obtained by fitting to the total and capture cross sections calculated from nuclear models, while resolved resonance parameters were selected from experimental data. A statistical model code was applied to evaluate cross sections above the resolved resonance region. Compound, pre-equilibrium and direct-reaction processes were considered for cross-section calculation. Coupled-channel optical-model parameters were employed for the interaction between neutrons and nuclei. Giant-dipole and pygmy resonance parameters for E1 γ-ray transition from tantalum isotopes were determined so as to reproduce measured γ-ray spectrum for ¹⁸¹Ta. The present results reproduce experimental data very well. The evaluated data are compiled into Evaluated Nuclear Data File (ENDF) formatted data files.     

Measurement of keV-neutron capture cross-sections for 164Dy

The neutron capture cross-sections of ¹⁶⁴Dy were measured in the neutron energy region of 10 to 90 keV using the 3-MV Pelletron accelerator of the Research Laboratory for Nuclear Reactors at the Tokyo Institute of Technology. Pulsed keV neutrons were produced from the ⁷Li(p,n)⁷Be reaction by bombarding a lithium target with the 1.5-ns bunched proton beam from the Pelletron accelerator. The incident neutron spectrum on a capture sample was measured by means of a TOF method with a ⁶Li-glass detector. Capture γ-rays were detected with a large anti-Compton NaI(Tl) spectrometer, employing a TOF method. A pulse-height weighting technique was applied to observed capture γ-ray pulse-height spectra to derive capture yields. The capture cross-sections were obtained by using the standard capture cross-sections of ¹⁹⁷Au. The present results were compared with the previous measurements and the evaluated values of ENDF/B-VI.     

Emission Probabilities of Gamma Rays from the Decay of 233Pa and 238Np,and the Thermal Neutron Capture Cross Section of 237Np

In order to determine the thermal neutron capture cross section of ²³⁷Np, the relevant γ emission probabilities of the 312-keV γ-ray from the decay of ²³³Pa and the 984-keV γ-ray from the decay of ²³⁸Np are deduced from the ratio of the emission rate to the activity. The emission rate and activity are measured with a Ge detector and a Si detector, respectively. The measured emission probability for 312-keV γ-ray is 41.6±0.9% and that for 984-keV γ-ray is 25.2±0.5%. The emission probabilities are used to correct the thermal neutron capture cross section of ²³⁷Np reported previously, and gives 168±6b. The neutron capture cross section is also determined as 169±6b by α-ray spectroscopic method. The measured emission probabilities and capture cross section are compared with others from references. By averaging these values deduced by different methods, the value of 169±4b is recommended as the thermal neutron capture cross section of ²³⁷Np for 2,200 m/s neutrons.     

Comparison of Nuclear Waste Glass Leached in Natural Groundwater at 14°C with That in Synthesized Groundwater at 70°C

The influence of fast neutron irradiation was studied for CdTe radiation detectors in the range of fluence 1.0 × 10⁸-1.8 × 10¹¹ n/cm². The effect of γ-ray heavy irradiation toward the detector was also investigated for the comparison. Americium-241 and ¹³⁷Cs γ-ray spectra measured before and after irradiation were compared to examine the change of the detector performance. A pulse height and a rise time of a radiation signal were simultaneously measured in order to evaluate the transport property of both elections and holes. Peak shift toward lower energies was observed in the ²⁴¹Am γ-ray spectrum after fast neutron irradiation. Electron μτ product showed large decrease with increasing the neutron fluence, while the one for holes remained unchanged. For the γ-ray irradiation, the spectrum shape of ¹³⁷Cs changed due to the influence of carrier detrapping. Experimental results support that the electron-trapping center generated by fast neutrons degrades the detector performance of the CdTe detector.     

Calculation of Gamma-Ray Production Cross Sections at Neutron Energies of 1–20 MeV

In order to prepare the p-ray data library requested in a design of fission and fusion reactors, γ-ray production cross sections and spectra of Al, Si, Ca, Fe, Ni, Cu, Nb, Ta, Au and Pb have been obtained at the neutron energies of 1–20 MeV, using a spin-dependent multi-step evaporation model. Calculations include dipole and quadrupole transition without the distinction between electric and magnetic process, and take explicit account of the role of yrast levels. The effects of the yrast levels and γ-ray strength function upon γ-ray production are also investigated in relation to particle emission. At the incident neutron energies where (n,n^γ ) and/or (n,2^nγ ) reactions are dominant, the present model is shown to be able to predict the production of secondary γ-rays (<9.0 MeV) from medium-heavy to heavy nuclei with reasonable accuracy.     

Calculation of Response Function of NE-213 Organic Liquid Scintillator for Gamma-Rays

A Monte Carlo code was newly developed to examine response functions of a 2 in. dia. by 2 in. long NE-213 liquid scintillator for γ-ray. This code included the electron transport and the electron-photon cascade calculation to handle the wall and end effect induced by high energy electrons. Results of the Monte Carlo calculation were compared with measured values for standard sources, reaction γ-ray and thermal neutron capture γ-ray, and fairly good agreement was obtained.

Response functions for monoenergetic γ-ray of energies 1~10 MeV were calculated at 1 MeV intervals. The calculations were made in parallel incident geometry without the peripheral material components surrounding the scintillator. The results are tabulated in this paper. A response matrix calculated from the above data was applied to the unfolding of NE-213 pulse height spectra using the FERDO code and fairly good results were obtained in absolute values.     

Production of the Isomeric State of 138Cs in the Thermal Neutron Capture Reaction 137Cs(n, γ)138Cs

In order to obtain precise data of the neutron capture cross section of the reaction ¹³⁷Cs(n, γ)¹³⁸Cs, the production probability of isomer state ^138mCs was measured in this work. Targets of about 0.37MBq ¹³⁷Cs were irradiated for 3 min in. the pneumatic tube facility (Pn-3) of Kyoto University Reactor (KUR). The 1,436 keV gamma;-ray emitted from both of ^138gCs and ^138mCs was measured. A ratio of the production probability between ^138gCs and ^138mCs was deduced from time dependence of peak counts of 1,436 keV γ-ray by making use of difference of half-lives of ^138gCs (33.41 min) and ^138mCs (2.91 min). The production probability of ^138mCs was obtained as 0.75plusmn;0.18 and this value revised the effective cross section upwards by 9plusmn;2percnt;. The effective cross section ô and the thermal neutron capture cross section σo were obtained as ô=0.29±0.02 b and σ=0.27±0.03b with taking into account the production of ^138mCs.     

计算机模拟γ测量谱

一个建立在微机DOS环境下的计算机模拟γ射线测量谱系统以一个实测的^135Cs谱作为模板,对活化测量谱和同位素源的γ射线谱进行了成形模拟。谱中包含了对全能峰、康普顿沿、康普顿坪和反散射峰的模拟。模拟系统具有谱峰面积计算、谱成形、谱显示、谱处理、谱存盘等功能。利用该模拟程序对^137Cs源、^152Eu源、^60Co源的γ射线谱以及锆样品和岩石样品的中子活化测量谱进行了模拟,模拟谱与实际测量谱非常接近。     

Gamma-Ray Spectra of Fission Products Observed with Lithium Drifted Germanium Detectors

The γ-ray spectra of fission products from thermal neutron irradiation of natural U were observed with an encapsulated Ii-drift-Ge γ-ray spectrometer. The spectra were recorded at various periods after irradiation—1, 2, 5, 12, 30, 250 days and 3 years. The γ-ray spectra of eight individual fission products including ²³⁹Np were also studied. Due to the high resolution obtained with the detector, many nuclides were identified which would have been undetectable without resorting to chemical separation.     

Radiochemical Determination of Neutron Capture Cross Sections of 241Am

The thermal neutron capture cross sections and the neutron capture resonance integrals of ²⁴¹Am leading to the production of the isomer ²⁴²Am and the ground-state ^242gAm were measured radiochemically by the Cd-ratio technique with neutron flux monitors of Co/Al and Au/Al alloy. Highly-purified ²⁴¹Am targets were irradiated in an aluminum capsule by using JMTR. The neutron fluxes and their epithermal neutron fractions were determined by measuring γ-rays of ⁶⁰Co and ¹⁹⁸Au. The yields of ^242mAm and ^242gAm were decided by analyzing growth and decay curves of the α-ray activity ratios ²⁴²Cm/²⁴¹Am. The resultant thermal neutron capture cross sections are 85.7 ± 6.3 b and 768 ± 58 b for ^242mAm and ^242gAm, and the resonance integrals 114±7 b and 1,694±146 b, respectively. The differences between the present results and the evaluated values by Mughabghab are 38–59%. The isomeric ratios, g/(m+g), of 0.90±0.09 for thermal neutrons and 0.94±0.11 for epithermal neutrons are, however, almost consistent with evaluated values.     

KeV-Neutron Capture in Cesium-133, Gold-197 and Tantalum-181

The keV-neutron capture in ¹³³Cs, ¹⁹⁷Au and ¹⁸¹Ta was studied by measuring the cross section and the emitted gamma-ray spectrum. The neutron was produced with the KUR linear accelerator and a photoneutron target, and the samples were placed at 11.7 m from the neutron source. The gamma-rays following the keV-neutron capture were detected with a pair of C₆D₆ scintillators. The relative capture cross section between 3.2 and 270 keV was normalized to the absolute cross section at 24 keV obtained with an iron-filtered neutron beam. The results of ¹³³Cs and ¹⁹⁷Au are in good agreement with the recently measured and evaluated capture cross sections.

The capture gamma-ray spectrum was obtained by unfolding the observed spectrum with the response functions of the detector. The gamma-ray strength function, which represents the average gamma-ray transition probability, was derived with the spectrum fitting method. The level density distributions used in the calculation of spectrum fitting were investigated and it is found that the constant temperature level density is preferable. The gamma-ray strength functions for ¹⁹⁸Au and ¹³⁴Cs show the 5.5-MeV bump and the deficiency of strength compared with the tail of giant dipole resonance, and that for ¹⁸²Ta does not give the bump but shows the similarity to the tail of giant resonance. The results were compared with other data.     

Studies of Ceramic Fuels with the Use of Fission Gas Release Loop, (II)

The γ-ray spectra of fission gases released from UO₂-graphite pellets under neutron irradiation were measured. With and without separating fission gases into xenon and krypton, 25 kinds of γ-ray were observed and assigned to nine nuclides, ^85mKr, ⁸⁷Kr, ⁸⁸Kr(⁸⁸Rb), ¹³³Xe, ¹³⁵Xe, ^135mXe and ¹³⁸Xe (¹³⁸Cs). A value of 15 min is proposed for the half-life of ¹³⁸Xe, based on analysis of the decay curves. Discussion is given on problems related to determination of the release rate of each fission product through measurement of the height of each peak in the γ-ray spectrum.     

Measurement of Gamma-Ray Production Cross Sections of Iron for Incident Neutron Energies between 6 and 33 MeV

Measurement of differential γ-ray production cross sections, i.e. (n, x γ) cross sections, of Fe was made for neutron energies from 6 to 33 MeV. Neutrons used in the experiment were white neutrons produced with (p, n) reactions by 35 MeV protons using a thick Be target. The neutron energy was analyzed by the time-of-flight method and bunched into 3 MeV wide energy bins, for each of which the spectrum of secondary γ-rays produced in an Fe sample was measured by a BGO scintillator at an angle of 144° to the neutron beam direction.

The obtained (n, xγ) cross sections agreed well with other data and the evaluated data file of ENDF/B-IV at neutron energies below 15 MeV where data were existing. The JENDL-3 file overestimated the γ-ray spectra at γ-ray energies of 3 to 7 MeV. The present work newly provided the data in the neutron energy range above 20 MeV. The GNASH calculation made by Young reproduced the measured data fairly well even at these higher energies.     

Measurements of Average Cross Section for 232Th(n, 2n)231Th Reaction to Neutrons with Fission-Type Reactor Spectrum and of Gamma-Ray Intensities of 231Th

The average cross section for the ²³²Th(n, 2n)²³¹Th reaction to neutrons with the energy spectrum close to that of fission neutrons was obtained in the core of the Kyoto University Reactor, KUR. The value obtained was 12.5±0.84 mb. This value agrees satisfactorily with Phillips' and with the calculated value obtained with the cross section in the U-K library and the Maxwellian fission neutron spectrum given by Leachman. A somewhat poorer agreement is seen with the calculated value obtained from Butler & Santry's cross section and Leachman's spectrum. The discrepancy amounts to 24 and to 39% respectively, for the average cross sections calculated with these two excitation functions and the fission neutron spectrum given by McElroy.

By making use of a Ge(Li) counter whose photopeak efficiency had been carefully calibrated, the absolute intensities were determined for eleven photopeaks observed on the γ-ray spectrum emitted by ²³¹Th.     

Measurement of Thermal Neutron Capture Cross Section and Resonance Integral of the Reaction 133Cs(n, γ)134m,134gCs

The measurements of the thermal neutron (2,200 m/s neutron) cross section (σ₀) and the resonance integral (I ₀) of the ¹³³Cs(n, γ;) reaction were performed by an activation method to obtain fundamental data for research on the transmutation of nuclear wastes. The cross sections for the formations of the isomeric state ^134mCs and the ground state ^134mCs were measured respectively by following the behavior of the γ-ray counting rate after the irradiation.

The thermal neutron capture cross sections and the resonance integrals of the ¹³³Cs(n, γ) reaction were determined to be 2.70±0.13 b and 23.2±1.8 b for the formation of the isomeric state ^134mCs, and 26.3±1.0 b and 275±16 b for the formation of the ground state of ^134gCs. The results for the reaction ¹³³Cs(n, γ)^134m+gCs were 29.0±l.0 b and 298±16 b, respectively. As for the thermal neutron capture cross section for the formation of ^134m+gCs, the evaluated value (29.00 b) of JENDL-3.2 agreed with the present result. The reported value by Baerg et al. was in good agreement with the present result within the limits of error on the thermal neutron capture cross section for ^134mCs. On the other hand, the resonance integral for ^134m+g Cs was 32% smaller than the experimental value by Steinnes et al.