Measurements and model calculations of activation cross sections for 232Th(n,2n)231Th reaction between 13.57 and 14.83 MeV neutrons

In this study, activation cross sections were measured for the reaction of ²³²Th(n,2n)²³¹Th (T_1/2 = 25.5 h) by using neutron activation technique at six different neutron energies from 13.57 and 14.83 MeV. Neutrons were produced via the ³H(²H,n)⁴He reaction using SAMES T-400 neutron generator. Irradiated and activated high purity Thorium foils were measured by a high-resolution γ-ray spectrometer with a high-purity Germanium (HpGe) detector. In cross section measurements, the corrections were made for the effects of γ-ray self-absorption in the foils, dead-time, coincidence summing, fluctuation of neutron flux, low energy neutrons. For this reaction, statistical model calculation, which the pre-equilibrium emission effects were taken into consideration, were also performed between 13.57 and 14.83 MeV energy range. The cross sections were compared with previous works in literature, with model calculation results, and with evaluation data bases (ENDF/B-VII, ENDF/B-VI, JEFF-3.1, JENDL-4.0, JENDL-3.3, and ROSFOND-2010).     

Measurements and statistical model calculations of activation cross-sections for 26Mg(n,α)23Ne reaction between 13.6 and 14.9 MeV neutron energies

Activation cross-sections were measured at neutron energies from 13.6 to 14.9 MeV for the reaction ²⁶Mg(n,α)²³Ne. The production of relatively short-lived activity and the spectra accumulation have been carried out by the cyclic activation method. Corrections were made for the effects of gamma-ray attenuation, random coincidence summing (pulse pile-up), dead time, and scattered low energy neutron contribution. Statistical model calculations for which the pre-equilibrium emission effects are taken into consideration were also performed. Results were compared with the previous investigations.     

Isomeric cross-sections of In and Rh at neutron energies of a few MeV

Neutron capture cross-sections are measured at five different neutron energies (1.07 ± 0.20, 1.48 ± 0.18, 1.89 ± 0.17, 2.30 ± 0.16 and 2.85 ± 0.15 MeV) for the isomeric states of In and Rh. The comparative γ-activation technique has been used. The present results are compared with previous data wherever available.     

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.     

The 63Cu(n,2n)62Cu and 65Cu(n,2n)64Cu cross sections at 14.8 MeV

Measurements have been made of the ⁶³Cu(n,2n)⁶²Cu and ⁶⁵Cu(n,2n)⁶⁴Cu cross sections. Separated isotope targets were irradiated with 14.8 MeV neutrons and the resulting ⁶²Cu and ⁶⁴Cu activities were measured using both 4πβ-γ coincidence counting and by counting in coincidence the annihilation radiation produced following the β⁺-decay of ⁶²Cu and ⁶⁴Cu. The variation in the neutron flux and the neutron energy were measured during each single irradiation. Good agreement was obtained for the cross-section values using the two methods. However, the standard deviation of the mean of the ⁶⁵Cu(n,2n)⁶⁴Cu cross-section measurements was significantly greater when the 4πβ-γ coincidence method was used. The measurements were made relative to the ⁵⁶Fe(n,p)⁵⁶Mn cross section. Values of 549 ± 11 and 968 ± 20 mbarn were obtained using a value of 108.5 mbarn for the Fe cross section at 14.8 MeV.     

14.8 MeV中子诱发78Kr(n,2n)77Kr反应截面的测量

快中子诱发(n,2n)反应截面的测量在核反应机制研究和核技术应用等方面有着广泛的应用价值。本文在中国原子能科学研究院的高压倍加器上,基于活化法实验测量了78Kr(n,2n)77Kr在148 MeV能点的反应截面。样品靶为高纯78Kr气体样品,用十万分之一天平称重得到78Kr的质量,将两片高纯93Nb薄片分别固定在样品靶两侧以监测中子注量率。利用T(d,n)4He反应产生148 MeV中子,轰击距中子源约10 cm的样品靶大于4 h后,用准确刻度过效率的HPGe探测器测量活化产物 77Kr和92Nbm的活度。利用蒙特卡罗程序计算中子注量率修正、样品自吸收修正、样品几何修正等因子,得到了78Kr(n,2n)77Kr的反应截面,并将结果与文献值和评价数据库进行了比较。研究结果有助于提高78Kr(n, 2n)77Kr反应截面测量和评价的水平。     

Measurement of activation cross-sections for (n,2n) reactions producing short-lived nuclei in the energy range between 13.4 and 14.9 MeV

Activation cross-sections for 18 (n,2n) reactions producing short-lived nuclei with half-lives between 20 s and 38 min were measured in the energy range between 13.4 and 14.9 MeV by an activation method. The measured target isotopes were ¹⁴N, ³¹P, ⁵⁴Fe, ⁶³Cu, ⁷⁹Br, ⁸⁷Rb, ⁹²Mo, ¹⁰⁸Pd, ¹¹³In, ¹³²Ba, ¹³⁸Ba, ¹⁴⁰Ce, ¹⁴¹Pr, ¹⁴⁴Sm and ¹⁶⁵Ho. Four cross-sections for ¹⁰⁸Pd, ¹³²Ba, ¹⁴⁴Sm and ¹⁶⁵Ho were obtained at six-point energies for the first time. The intense 14 MeV neutron source facility (OKTAVIAN) at Osaka University was used for irradiation. All cross-section values were relatively obtained on the basis of the standard cross-section of ²⁷Al(n, α) ²⁴Na reaction (ENDF/B-VI). To obtain reliable neutron activation cross-sections, careful attention was paid to neutron irradiation and induced activities measurement. The present results were compared with previous data and the evaluated data in JENDL-3.2, JENDL-Activation File and ENDF/B-VI. The previous data measured at multi-point energies show reasonable agreement with the present results in comparison with those at one-point energy. There are overestimations of the cross-section for ³¹P in JENDL-3.2 and ENDF/B-VI, and for ¹³²Ba and ¹⁶⁵Ho in JENDL-Activation File.     

Measurements of double-differential neutron emission cross-sections of 238U and 232Th for 2.6, 3.6 and 11.8 MeV neutrons

Double-differential neutron emission cross-sections (DDXs) of ²³⁸U and ²³²Th were measured for 2.6, 3.6 and 11.8 MeV incident neutrons using a time-of-flight (TOF) method at the Tohoku University 4.5 MV Dynamitron accelerator facility. In DDXs for En=2.6 MeV, discrete structures by vibrational level groups are visible clearly around excitation energy (Ex) around 0.75 and 1.15 MeV, while inelastic scattering to continuum-levels become dominant at En=3.6 MeV for both nuclei. For En=11.8 MeV, continuum structures with strong forward peaking are dominant with some discrete structures at around 0.7–4.0 MeV excitation energy for both of ²³⁸U and ²³²Th. Partial cross-sections for the elastic and inelastic scattering processes were also derived from the DDX data.     

Cross-section measurements for the Mo (n,p) Nb reaction at the neutron energies from 13.6 to 14.9 MeV

Cross sections were measured at neutron energies from 13.6 to 14.9 MeV for the reaction ⁹⁷Mo(n,p)^97mNb leading to isomer of Niobium-97 isotope. The production of relatively short-lived isomer activity and the spectra accumulation have been carried out by cyclic activation method. Corrections were made for the effects of gamma ray attenuation, random coincidence summing (pulse pileup), dead time, neutron flux fluctuations and scattered low energy neutron contribution. Statistical model calculations for which the pre-equilibrium emission effects are taken into consideration were also performed for the investigated reaction between 13.0 and 15.0 MeV neutron energy range.     

Direct neutron spectrum measurement to validate Zr(n,2n) reaction cross-section at 14 MeV

Lithium zirconate, Li₂ZrO₃, is known as a candidate blanket material in a fusion reactor. Various neutronics benchmark experiments for zirconium have thus been carried out so far. According to the independent benchmark studies by two parties, the neutron spectrum calculations show fairly large overestimation for most evaluated nuclear data libraries. However, the reason has not yet been made clear up to now. The author's group expects it would be due to a problem of evaluation for the ^natZr(n,2n) reaction cross-section, because the cross-section measurement is basically not possible with the foil activation method for zirconium isotopes except for ⁹⁰Zr.In the present study, two neutrons emitted from ^natZr(n,2n) reaction have been measured directly to investigate the reason for the above overestimation. The measurement was done with our own special technique of detecting angle-correlated neutrons by the coincidence detection technique and the pencil-beam DT neutron source of FNS, JAEA. Angle-correlated energy differential cross-sections for ^natZr(n,2n) reaction were successfully measured. The obtained total cross-section above the emitted neutron energy of 800 keV was fairly larger than the one evaluated in JENDL-3.3. The total cross-section of ^natZr(n,2n) reaction was estimated by extrapolating the spectrum down to zero energy taking into account the nuclear temperature. The estimated cross-section value with the nuclear temperature of 1 MeV, which is larger than the one adopted in JENDL-3.3, was in acceptable agreement with JENDL-3.3. It is suggested from the result that the disagreement pointed out in the previous benchmark studies may be due to inappropriate nuclear temperature used in the evaluation. Further investigation of the nuclear temperature employed in the nuclear data evaluation should thus be carried out once again.     

Product yields for the photofission of ~(232)Th,~(234,238)U,~(237)Np,and ~(239,240,242)Pu actinides at various incident photon energies

Photofission fragments mass yield for~(232)Th,~(234;238) U,~(237) Np, and~(239;240;242) Pu isotopes are investigated.The calculations are done using a developed approach based on Gorodisskiy's phenomenological formalism. The Gorodisskiy's method is developed to be applied for the neutron-induced fission. Here we revised it for application to photofission. The effect of emitted neutron prior to fission on the fission fragment mass yields has also been studied. The peak-to-valley ratio is extracted for the240 Pu isotope as a function of energy. Obtained results of the present formalism are compared with the available experimental data. Satisfactory agreement is achieved between the results of present approach and the experimental data.     

人骨骼中~(228)Th、~(230)Th和~(232)Th含量的同时测定

本文介绍了用α谱仪同时测定人骨骼中~(228)Th、~(230)Th和~(232)Th含量的方法。样品用浓 HNO_3和 H_2O_3湿灰化,草酸钙共沉淀载带、CL-5208萃淋树脂和743阳离子交换树脂联合分离后,电沉积制源,在低温半导体α谱仪上测量。该方法对~(234)Th的全程回收率为95.0±1.7%,对铀和镭的去污系数分别为6.3×10~4和1.5×10~3,对~(228)Th、~(230)Th、~(232)Th 的探测下限分别为0.432、0.135和0.108Bq/kg(鲜重)。     

Measurement of the cross sections for the reactions Cr(n,2n)Cr, Zn(n,2n)Zn, Y(n,2n)Y and Zr(n,2n)Zr from 13.5 to 14.8 MeV

Cross section measurements for the reactions ⁵²Cr(n,2n)⁵¹Cr, ⁶⁶Zn(n,2n)⁶⁵Zn, ⁸⁹Y(n,2n)⁸⁸Y and ⁹⁶Zr(n,2n)⁹⁵Zr were carried out in the neutron energy range 13.47–14.79 MeV applying the activation technique. Neutrons were produced via the T(d,n)⁴He reaction, making use of the variation of neutron energy with the emission angle. The neutron fluences incident on the samples were determined relative to the well-evaluated cross section for the reaction ⁹³Nb(n,2n)^92mNb.

The induced γ-ray activities of the irradiated Zn, Zr and Y₂O₃ samples and their monitor foils were measured by means of a calibrated Ge(Li) γ-ray detector at the KFI, Debrecen. At the IRK, Vienna, relative γ-ray measurements using a high-purity Ge detector were combined with integral γ-ray counting by means of a NaI(TI) well-type detector on the Cr, Zn and Zr foils of highest activity and on some Nb monitor foils; integral γ-ray counting only was applied in the case of the Y₂O₃ samples. All necessary corrections were taken into account.

The results are compared to the corresponding results of cross section measurements published in the literature. The uncertainties obtained in this work are considerably smaller in most cases than the uncertainties given by other authors.     

Measurement of activation cross-sections of (n,np+d) reactions producing short-lived nuclei in the energy range between 13.4 and 14.9 MeV using an intense neutron source OKTAVIAN

Activation cross-sections for 17 (n, np+d) reactions producing short-lived nuclei with half-lives between 42 s and 23 min, were measured in the energy range between 13.4 and 14.9 MeV by an activation method. The measured target isotopes were ²⁶Mg, ^{29, 30}Si, ^{53, 54}Cr, ⁶⁷Zn, ⁸⁷Sr, ^{98, 100}Mo, ¹⁰²Ru, ^{105, 106, 108}Pd, ¹²³Te, ¹⁶³Dy, ¹⁷⁹Hf and ¹⁸⁹Os. Eleven cross-sections for ²⁶Mg, ³⁰Si, ⁸⁷Sr, ¹⁰⁰Mo, ¹⁰²Ru, ^{105, 106}Pd, ¹²³Te, ¹⁶³Dy, ¹⁷⁹Hf and ¹⁸⁹Os were obtained for the first time, and four cross-sections for ^{53, 54}Cr, ⁶⁷Zn and ¹⁰⁸Pd were obtained at six-point energies for the first time. An intense 14 MeV neutron source, OKTAVIAN at Osaka University was used for irradiation. All cross-section values were relatively obtained on the basis of the standard cross-section of ²⁷Al(n, α)²⁴Na reaction (ENDF/B-VI). To obtain reliable neutron activation cross-sections, careful attention was paid to neutron irradiation and induced activity measurement. The present results were compared with the evaluated data in JENDL-3.2, JENDL-Activation File and ENDF/B-VI. The cross-sections are underestimated for ¹⁰²Ru and ¹⁰⁸Pd in JENDL-3.2.