Measurement of the 93Nb(n,n')93mNb Reaction Cross Section at 14.5 and 14.9MeV

Abstract

Cross sections at 14.5 and 14.9 MeV for the low threshold energy reaction of ⁹³Nb(n, n')^93mNb were measured by the activation method at the FNS (Fusion Neutronics Source) of JAERI. Although there are multiple experimental data for this reaction cross section from the threshold to 9 MeV, only one data at 14.3 MeV has been reported by Ryves et at. The correction for low energy neutron contribution was found very sensitive on the reaction rate determination. Careful treatments were performed to arrive at final error evaluation considering neutron spectrum calculated with a Monte Carlo Code and cross section curves available. The cross sections measured in the present work are larger by more than 30% than those in both IRDF-90 and JENDL Dosimetry File, which are based on the data of Ryves et al. On the other hand, the present data are lower by 10-15% than the evaluation by Odano et al. It is highly recommended to re-evaluate the cross section by taking the present data into account.     

Evaluation Methods of Resonance Absorption for System with Pellet Surrounded by Fuel Solution

Abstract

The reaction cross sections of ²⁷Al(n, p)²⁷Mg, ²⁷Al(n, a)²⁴Na, ⁵⁶Fe(n, p)⁵⁶Mn, ⁹⁰Zr(n, 2n)^89m+gZr and ⁹³Nb(n, 2n)^92mNb have been measured by the activation method in an energy range of 13.3–14.9 MeV using the intense D-T neutron source, FNS. Absolute flux was determined by the associated α-particle counting method incorporated with neutron spectra obtained from both a Monte Carlo calculation and a time-of-flight measurement. Corrections were extensively performed not only for the neutron flux determination, but also for the low energy neutron contribution to the reaction rates. The present data were compared with comprehensive evaluations as well as recent experimental data. The measured cross sections of ²⁷Al(n, a)²⁴Na, ⁵⁶Fe(n, p)⁵⁶Mn and ⁹⁰Zr(n, 2n)^89m+gZr are generally in good agreement within experimental errors with the values in both the JENDL Dosimetry File and IRDF-90. It is also shown that there are the overestimation of the cross sections for ⁹³Nb(n, 2n)^92mNb in the JENDL Dosimetry File, and the over- estimation and underestimation of the cross section for ²⁷Al(n, p)²⁷Mg in the JENDL Dosimetry File and IRDF-90, respectively.     

Cross-section measurements for (n, 2n), (n,p) and (n, α) reactions on strontium isotopes at the neutron energy about 14 MeV

Cross-sections for ⁸⁴Sr(n, 2n)⁸³Sr, ⁸⁶Sr(n, 2n)^85mSr, ⁸⁶Sr(n, 2n)⁸⁵Sr, ⁸⁸Sr(n, 2n)^87mSr, ⁸⁴Sr(n, p)⁸⁴Rb, ⁸⁶Sr(n, p)⁸⁶Rb, ⁸⁸Sr(n, p)⁸⁸Rb and ⁸⁸Sr(n, α)^85mKr reactions have been measured at neutron energies from 13.5 to 14.6 MeV using activation technique and by means of γ-ray spectrometry. The neutron flux was determined using the monitor reaction ⁹³Nb(n, 2n)^92mNb and the neutron energies were measured by the method of cross-section ratios for ⁹⁰Zr(n, 2n)⁸⁹Zr to ⁹³Nb (n, 2n)^92mNb reactions. The results of present work are compared with data published previously.     

Measurements of the Y(n,γ)Y cross-section in the neutron energy range of 13.5-14.6 MeV

The ⁸⁹Y(n,γ)^90mY cross-section has been measured at three neutron energy points between 13.5 and 14.6 MeV using the activation technique and a coaxial HPGe γ-ray detector. The data for the ⁸⁹Y(n,γ)^90mY cross-sections are reported to be 0.39 ± 0.02, 0.43 ± 0.02, and 0.38 ± 0.02 mb at 13.5 ± 0.2, 14.1 ± 0.1, and 14.6 ± 0.2 MeV incident neutron energies, respectively. The first data for the ⁸⁹Y(n,γ)^90mY reaction at neutron energy points of 13.5 and 14.1 MeV are presented. The natural high-purity Y₂O₃ powder was used as target material. The fast neutrons were produced by the T(d,n)⁴He reaction. Neutron energies were determined by the method of making cross-section ratios of ⁹⁰Zr(n,2n)^89m+gZr and ⁹³Nb(n,2n)^92mNb reactions, and the neutron fluencies were determined using the monitor reaction ⁹³Nb(n,2n)^92mNb. The results obtained are compared with existing data.     

Measurement of the activation cross section for the (p,xn) reactions in niobium with potential applications as monitor reactions

Excitation functions of the ⁹³Nb(p,n)^93mMo, ⁹³Nb(p,pn)^92mNb and ⁹³Nb(p,αn)⁸⁹Zr nuclear reactions were measured up to 17.4 MeV by the conventional activation method using the stacked-foil technique. Stacks were irradiated at different incident energies on the TR19/9 cyclotron at the Edmonton PET Centre. The potential of the measured excitation functions for use as monitor reactions was evaluated and tested by measuring activity ratios at a different facility. Single Nb foils were irradiated at incident energies in the range from 12 to 19 MeV on the TR19/9 cyclotron at Brookhaven National Laboratory. Results are compared with the published data and with theoretical values as determined by the nuclear reaction model code EMPIRE.     

Activation cross sections for (n, p) reactions on nickel isotopes induced by neutrons around 14 MeV

The cross sections of ⁵⁸Ni(n, p)^58(m+g)Co,⁶⁰Ni(n, p)^60mCo,⁶¹Ni(n, p)⁶¹Co and ⁶²Ni(n, p)^62mCo reactions induced by neutrons around 14 MeV were measured using activation technique and a coaxial HPGe γ-ray detector. The natural nickel foils of 99.9% purity were used as target materials. Fast neutrons were produced by the T(d, n)⁴He reaction. The neutron flux was determined using the monitor reaction ²⁷Al(n, α)²⁴Na and the neutron energies were measured with the method of cross-section ratios for ⁹⁰Zr(n, 2n)⁸⁹Zr to ⁹³Nb(n, 2n)^92mNb reactions. The results of this work are compared with the collected partial recent data published previously and the estimations obtained from the published empirical formula based on the statistical model with dependence on the Q-value and odd-even effect taken into consideration.     

Measurements of activation cross sections for Lu(n, α)Tm,Lu(n, α)Tm and Lu(n, p)Yb reactions induced by neutrons around 14 MeV

The cross sections for the ¹⁷⁵Lu(n, α)¹⁷²Tm, ¹⁷⁶Lu(n, α)¹⁷³Tm and ¹⁷⁵Lu(n, p)^175m+gYb reactions have been measured in the neutron energy range of 13.5–14.8 MeV using the activation technique. The first data for ¹⁷⁵Lu(n, α)¹⁷²Tm reaction cross sections are presented. In our experiment, the fast neutrons were produced via the ³H(d, n)⁴He reaction on K-400 Neutron Generator at Chinese Academy of Engineering Physics (CAEP). Induced gamma activities were measured by a high-resolution (1.69 keV at 1332 keV for ⁶⁰Co) gamma-ray spectrometer with high-purity germanium (HPGe) detector. Measurements were corrected for gamma-ray attenuations, random coincidence (pile-up), dead time and fluctuation of neutron flux. The neutron fluences were determined by the cross section of ⁹³Nb(n, 2n)^92mNb or ²⁷Al(n, α)²⁴Na reactions. The neutron energy in the measurement was by the cross section ratios of ⁹⁰Zr(n, 2n)^89m+gZr and ⁹³Nb(n, 2n)^92mNb reactions. The results were discussed and compared with experimental data found in the literature and with results of published empirical formulae.     

Measurement of (n, n′) reaction cross-sections of 79Br, 90Zr, 197Au and 207Pb with pulsed d-D neutrons

Activation cross-sections for the (n, n′) reaction were measured by means of the activation method at neutron energies of 3.1 and 2.54 MeV using a pulsed neutron beam. The target nuclei were ⁷⁹Br, ⁹⁰Zr, ¹⁹⁷Au, and ²⁰⁷Pb whose half-lives were between 0.8 and 8 s. The value of the ⁹⁰Zr(n, n′) ^90mZr reaction was obtained for the first time. In order to confirm the pulsed neutron beam measuring method, the cross-section data of ⁷⁹Br and ¹⁹⁷Au were compared with previous data obtained using a pneumatic sample transport system. The results of this comparison were in agreement within the range of experimental error. The d-D neutrons were generated by bombarding a deuterated titanium target with a 350-keV d⁺-beam at the 80° beam line of the Fusion Neutronics Source (FNS) at the Japan Atomic Energy Research Institute. In order to obtain reliable activation cross-sections, careful attention was paid to correct the efficiency for a volume source, and the self-absorption of gamma rays in irradiated samples. The systematics of the (n, n′) reaction at a neutron energy of 3.0 MeV, which can predict cross-section of (n, n′) reaction with an accuracy of 50%, was proposed for the first time on the basis of our data.     

~(176)Hf(n,2n)~(175)Hf反应截面测量

采用相对测量技术,以活化法对13.4～14.8MeV范围内的176Hf(n,2n)175Hf反应截面进行了测量。样品固定在距离D-T中子源20cm处的圆环的不同位置上进行中子辐照,采用93Nb(n,2n)92Nbm作为监测反应,活化产物采用高纯锗探测器进行了测量,所得14MeV附近的176Hf(n,2n)175Hf反应截面实验值为(2100±85)mb,对实验结果与公开文献值和ENDF/B6.8评价库数据进行了比对。     

Neutron sputtering yields from Nb,Au and Co

Employing a neutron source based on the ⁹Be (d, n) reaction, high energy neutron sputtering yields have been determined for Nb, Au and Co. Two experiments have been conducted. In the first, graphite catcher foils were used and in the second, polished Si wafers. From data collected in the first experiment the neutron sputtering yields of Nb, Au and Co were determined to be in the range of 10^?5 to 10^?4 particles per incident neutron. Examination of the collector foils from the second experiment did not show any evidence of large particle (> 1 μm) ejection from the Nb targets.     

Activation cross-section for reactions induced by 14 MeV neutrons on natural silver

Cross-sections for (n, 2n), (n, p), and (n, α) reactions have been measured on silver isotopes at the neutron energies from 13.5 to 14.8 MeV using the activation technique in combination with high-resolution γ-ray spectroscopy. Corrections were made for the literature cross-sections of ¹⁰⁹Ag(n, 2n) ^108mAg reaction with incorrect half-life of product ^108mAg. Neutrons were produced via the ³H(d, n)⁴He reaction using solid TiT. The neutron fluences were determined using the monitor reaction ²⁷Al(n, α)²⁴Na. The neutron energy in this measurement was determined by cross-section ratios for the ⁹⁰Zr(n, 2n) ^89m+gZr and ⁹³Nb(n, 2n)^92mNb reactions. Data are reported for the following reactions: ¹⁰⁹Ag(n, 2n)^108mAg, ¹⁰⁷Ag(n, 2n)^106mAg, ¹⁰⁹Ag(n, p)^109m+gPd, and ¹⁰⁹Ag(n, α)^106mRh. The cross-sections were discussed and compared with experimental data found in the literature, and with the comprehensive evaluation data in ENDF/B-VII, JENDL-3.3, and JEFF-3.1/A libraries.     

Activation cross sections for Os(n,p)Re, Os(n,p)Re and Os(n,n′)Os reactions from 13.5 to 14.8 MeV

Cross sections for (n,p) and (n,n′) reactions have been measured on osmium isotopes at the neutron energies from 13.5 to 14.8 MeV using the activation technique in combination with high-resolution gamma-ray spectroscopy. Neutrons were produced via the ³H(d,n)⁴He reaction using solid TiT. The neutron fluences were determined using the monitor reaction ⁹³Nb(n,2n)^92mNb. Data are reported for the following reactions: ¹⁹⁰Os(n,p)^190mRe, ¹⁹⁰Os(n,p)^190gRe, ¹⁹⁰Os(n,p)¹⁹⁰Re, ¹⁸⁸Os(n,p)¹⁸⁸Re and ¹⁹⁰Os(n,n′)^190mOs. Nuclear model calculations using the code HFTT, which employs the Hauser-Feshbach (statistical model) and exciton model (precompound effects) formalisms, were undertaken to describe the formation of the products. The cross sections were discussed and compared with experimental data found in the literature, with values of model calculations including the pre-equilibrium contribution, and with evaluation data of JEFF-3.1/A.     

Enrichment of 87mSr by Recoil Effect of (n, 2n) Reaction

A method has been developed to enrich ^87mSr by (n, 2n) reaction, as a preliminary study for the enrichment of ⁴⁷Ca. The method is based on capturing the recoils from a scattered target into a solidified phase of several percent by weight of gelatine in water. A fine strontium carbonate powder is suspended uniformly in gelatine phase, and irradiated with neutrons of 14 MeV. The results show that 4~23% of the induced ^87mSr activities were separated into the gelatine phase, with an enrichment factor of 4–16.     

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.     

Shielding performance of newly developed boron-loaded concrete for DT neutrons

In order to enhance the neutron-shielding performance of concrete in neutron-generation facilities from the viewpoint of reduction of effective dose rates in operation and radioactive wastes in decommission, we developed concrete with boron of more than 10 wt%. We performed a neutron-shielding experiment using the mockup of the newly developed boron-loaded concrete and Deuterium Tritium (DT)neutrons at the Fusion Neutronics Source in the Japan Atomic Energy Agency, and measured the reaction rates of ⁹³Nb(n,2n)^92mNb and ¹⁹⁷Au(n,γ)¹⁹⁸Au reactions in the mockup. The calculations were conducted using MCNP-5.14 and FENDL-2.1. The calculation results agreed well with the measured ones, and we confirmed that the accuracy was very good on the atomic composition data of boron-loaded concrete and their nuclear data. In addition, we calculated the neutron and photon effective dose rates and reaction rates of ⁵⁹Co(n,γ)⁶⁰Co and ¹⁵¹Eu(n,γ)¹⁵²Eu reactions, which produce critical radioisotopes in decommission, in boron-loaded concrete and other concretes with DT neutrons, and the experimental condition presently used. The dose rates and reaction rates were drastically reduced by using boron-loaded concrete and it was concluded that boron-loaded concrete had very good shielding performance for DT neutrons.     

Neutron excitation functions for Sc, Nb, and Ni in the energy range 13–19 MeV

Activation techniques have been used to measure the excitation functions for ⁴⁵Sc(n, 2n)^{44m + g}Sc and Nb(n,2n)^92mNb in the energy range 13–19 MeV and ⁵⁸Ni(n,p)^{58m + g}Co and ⁵⁸Ni(n,2n)⁵⁷Ni in the energy range 13–17 MeV. The neutrons were produced by the ³H(d,n)⁴He reaction with the Auburn University 3 MV Dynamitron accelerator. Absolute cross-sections were measured using the mixed powder method with ²⁷Al(n,α)²⁴Na as the monitor reaction. The experimental isomeric-yield ratios were determined by measuring the ground state gamma activity resulting from the reaction and making a least squares fit to the time behavior of the activity in which the cross-section ratio was treated as a variable parameter. Cross-sections calculated from the semi-empirical relation due to Pearlstein are given for qualitative comparisons with the present results.     

Recoil range of 2.7 MeV tritons produced by the 6Li(n, α) 3H reaction in Li2O single crystals

The tritium release from Li₂O single crystals due to a recoil process during neutron irradiation was investigated. The linear relationship between the number of tritium atoms ejected from Li₂O and the ⁶Li(n, α) ³H reaction density was observed up to about 1 × 10²⁴ reactions/m³ and the linearity was deviated above this reaction density. From this linear relationship, the recoil range of 2.7 MeV tritons in Li₂O single crystals was determined and discussed in terms of the calculated value.     

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.     

New integral experiments for large angle scattering cross section data benchmarking with DT neutron beam at JAEA/FNS

A new integral experiment with a deuteron–triton fusion (DT) neutron beam started in order to validate scattering cross section data. First the DT neutron beam was constructed with a collimator. The performance of the collimator system and the characteristics of the DT neutron beam were measured. Second a new integral experiment for type 316 stainless steel (SS316) was carried out with this DT neutron beam. The DT neutron beam of 3.5 cm in diameter was injected to the front surface center of an SS316 cylindrical assembly. Reaction rates of the ⁹³Nb(n,2n)^92mNb reaction in the assembly were measured with the activation foil method and were calculated with the Monte Carlo transport calculation code. The measurement points were located at three positions, on the center of the beam axis and at 15 cm and 30 cm apart from the axis. The ratio of calculation to experiment of the ⁹³Nb(n,2n)^92mNb reaction rate became smaller than 1 with the distance from the beam axis. Then, the dependency of each reaction rate on scattering angle was calculated. It was proved that at off-axis positions, where C/E is smaller than 1, 90° scattering contribute relatively larger than at on-axis positions and backward scattering made little contribution to the results in this experiment. The reasons of the discrepancy between the measured and calculated data will be investigated.     

Evaluation of reactivity bonus due to (n, 2n) multiplication in Be/BeO-reflected 233U uranyl nitrate solution systems

Beryllium experiences (n, 2n) multiplication reaction for neutrons having energy above the threshold of ≈ 1.8 MeV. In the case of beryllium-reflected/moderated reactor assemblies these (n, 2n) neutrons contribute additional reactivity. This paper evaluates the reactivity contribution due to (n, 2n) reactions in the Be and BeO reflector of reflected ²³³U uranyl nitrate solution systems in spherical geometry in the light of the latest ⁹Be cross-section data. The results shows that the (n, 2n) reactions in a given thickness of reflector are directly proportional to the core leakage and thus very much a function of core radius. In the core radius range of 4–15 cm the reactivity bonus due to (n, 2n) reactions in a 30-cm thick Be reflector varies from 6.2 to 3.0%, which corresponds to a critical mass saving of ≈18–9%. The corresponding reactivity contributions for BeO reflected systems are ≈25% lower.