利用镜像核转移反应研究短寿命不稳定核(p,γ)反应

介绍利用中子转移反应和镜像核的电荷对称性来间接研究丰质子核的(p,γ)反应。该方法有助于更充分地利用北京HI-13串列加速器次级束流线(GIRAFFE)上现有次级束流，拓宽其实验研究范围，间接得出质子辐射俘获截面（或反应率）且减小其不确定性（相对于已有数据）。在GIRAFFE上利用逆运动学测量了⁸Li(d,p)⁹Li反应的角分布，通过该方法间接确定了天体物理重要反应⁸B(p,γ)⁹C的直接俘获贡献。作为不同于以往的方法，给⁸B(p,γ)⁹C反应的现有研究结果提供了一独立的交叉检验。分析²⁶Mg(d,p)²⁷Mg反应基态、第一、第二激发态的角分布，间接确定²⁶Si(p,γ)²⁷P反应的直接和共振俘获贡献，首次从实验上导出²⁶Si(p,γ)²⁷P反应的直接俘获贡献。此方法也可以用于其它一系列重要的天体物理反应的研究。     

Neutron yield of the reactions Li6(t,n) and Li7(t,n)

The differential cross section is determined for the formation of neutrons at an angle of 0 ° in the reactions Li⁶(t,n) and Li⁷(t, n) in the 0.175–2.4 Mev triton energy range. In the reaction Li⁶(t,n) resonance in the neutron yield is observed at E_t = 1.875 Mev, corresponding to a Be⁹ excitation level of 18.936 Mev.Two resonances are detected in the neutron yield of the reaction Li⁷(t, n): at E_t = 0.765 Mev and E_t = 1.735 Mev, which indicates the presence of Be¹⁰ nucleus excitation levels of 17.78 and 18.46 Mev, respectively. The cross section of the reaction Li⁶(t, n) in resonance is d/d(0 °)_res = 37.2 mb/sr; for the reaction Li⁷ (t, n) the cross section at the first resonance is d/d(0 °)_res = 95 mb/sr; at the second resonance d/d(0 °)_res = 159 mb/sr.The angular distributions of neutrons are given for the interval of angles 0–135 ° (every 15 °) for triton energies of 0.358, 0.559, 1.006, 1.218, 1.370, 1.572, 2.123 Mev.The total cross section for the formation of neutrons at E_t = 2.123 Mev in the reaction Li⁶ (t,n) is equal to 324±32.3 mb in the reaction Li⁷ (t, n) to 1332±83.3 mb.     

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.     

Investigation of the reactions Li6(t,n), Li7(t,n), Li7(He3, n), Be9(t,n)B11, and Be9(He3, n)C11

Neutron yields have been measured in the bombardment of thin targets containing Li⁶, Li⁷, and Be⁹, by tritium and He³ ions, the energies of the accelerated particles ranging as high as 1.4 Mev. The neutron yield from the reactions Li⁶(t, n) and Be⁹(t, n) is proportional to the penetrability of the Coulomb barrier. In the reactions Li⁷(t, n) and Li⁷(He³, n), when the kinetic energies of the accelerated particles are small resonances are detected, corresponding to levels of the component nuclei near the threshold of these reactions. The thresholds for formation of slow neutrons have been investigated in the interaction of tritons with Li⁶, Li⁷, and Be⁹ nuclei. In the reactions Li⁶(t, n)Be⁸ and Li⁷(t, n)Be⁹ slow neutrons are detected, corresponding to the formation of the Be⁸ nucleus in excited states with energies of 16.08, 16.66, and 16.94 Mev and the Be⁹ nucleus in a state with energy 10.50 Mev. In the reaction Be⁹(t, n)B¹¹ no slow neutron thresholds were observed.The nuclear photoemulsion method was used to measure the neutron spectra in all of the investigated reactions at zero angle of incidence. The neutron spectra are in agreement with the established data [1] on the energy levels of the Be⁸, Be⁹, Be⁹, B¹¹, and C¹¹ nuclei.The authors are grateful to all these comrades for their contribution.     

Determination of (n,2n) Reaction Cross Sections for Some Nuclei with Asymmetry Parameter

The (n,2n) reaction cross sections for targets of ^203,205Tl, ^{204,206,207,208}Pb, ²⁰⁹Bi, ²³²Th and ²³⁸U were calculated both theoretically and semi-empirically. Theoretical calculations were done using two different computer codes: PCROSS computer code for the full exciton model and ALICE/ASH-2006 computer code for the geometry dependent hybrid (GDH) model with the incident neutron energy up to 25 MeV. Semi-empirical calculations were done using formulas derived by several researchers. The obtained results have been discussed and compared with the available experimental data taken from the literature. The different nuclear reaction program codes used in the present study show considerable differences depending upon the selected energy range. Especially PCROSS calculation results show a disagreement above the incident energy of about 16 MeV for all the studied nuclei. Moreover, even though the graphs qualitatively agree in shape, they differ in magnitude below 15 MeV.     

Activation Cross Section Measurements for ~(93)Nb(n,2n)~(92g)Nb Reaction Induced by 14 MeV Neutron

The cross section for the ~(93)Nb(n,2n)~(92g)Nb reaction is measured by activation method. The experimental result is 1355±149 mb at the neutron energy of 14.6±0.3 MeV. And the excitation curve of ~(93)Nb(n,2n)~(92g)Nb reaction is calculated by using HFTT program in neutron energy range from 9 MeV to 16 MeV.     

Effect of alloying elements (Cu, Fe, and Nb) on the creep properties of Zr alloys

The thermal creep behaviors of Zr-based alloys containing Cu, Fe and Nb were investigated under constant load stress at temperatures of 280 and 330 °C, and a stress range of 100-140 MPa. To evaluate an alloying effect on a creep, Zr-based alloys were selected as the binary and ternary systems of Zr-0.3Cu, Zr-0.3Fe, Zr-0.5Nb-0.3Cu and Zr-0.5Nb-0.3Fe. The final annealing of these alloys was performed at 510 °C for 8 h to obtain a recrystallization structure for all the tested alloys. A microstructure characterization test was carried out for the samples before and after the creep test by using TEM, and the results were used to understand the creep mechanism. Creep tests were performed for up to 70 h, which showed a steady-state secondary creep rate in all the alloys. The value of the stress exponent was about 5.5 in all the alloys. The dislocation density was increased by increasing the applied stress, regardless of the alloy system. From the results of this study, it was revealed that the Nb as an alloying element showed the strongest effect on the creep resistance among the added alloying elements, and Fe was more effective than Cu from the viewpoint of creep resistance.     

Ratio tests of dosimetry cross-sections for Nb(n,2n)Nb and Au(n,2n)Au to Al(n,α)Na reactions

Cross-section ratios of reaction ⁹³Nb(n,2n)^92mNb and ¹⁹⁷Au(n,2n)¹⁹⁶Au to the standard reaction ²⁷Al(n,α)²⁴Na have been measured in order to test the recently compiled dosimetry files: JENDL Dosimetry File and International Reactor Dosimetry File 1990 (IRDF-90). The experimental results for both reactions were consistent with the calculated ones based on IRDF-90 except for the ⁹³Nb(n,2n)^92mNb above 19 MeV.Both reactions, especially ⁹³Nb(n,2n)^92mNb, were recommended as new neutron monitors above 12 MeV because of their favorable characteristics from the decay-property and cross-section viewpoints.     

Excitation Functions of Some Neutron Production Targets on (d,2n) Reactions

Deuterons are weakly bound nuclei which easily undergo break up reactions. This is well known at low energies, around 10 MeV, where deuteron beams have been used to produce neutrons very efficiently. These neutrons have a widely application field such as fission energy production and hybrid reactor systems. In this study, neutron emission cross sections produced by (d,2n) reactions for spallation neutron targets such as ⁵²Cr, ⁵⁶Fe, ^60,62,64Ni, ^63,65Cu, ^{182,183,184,186}W, ²³²Th, ²³⁵U and ²³⁸U have been investigated. Hybrid model and geometry dependent hybrid model were used to calculate the pre-equilibrium neutron-emission cross sections. For the reaction equilibrium process, Weisskopf–Ewing model calculations were selected. The obtained results have been discussed and compared with the available experimental data and found agreement with each other.     

(n,2n)和(n,3n)激发函数的计算

本文从入射中子能量为E=14MeV的σ_(n,2n)实验值出发,应用复合核模型,计算了十三种无分支比复合核衰变的非裂变重核(A>169)的(n,2n)、(n,3n)激发函数。与实验激发曲线比较,讨论了计算的合理性和可靠性。     

Helium irradiation of Ni-(Zr or Nb) metallic glasses: Blistering,flaking and bubble formation

NiZr and NiNb are potential metallic glasses for nuclear applications. We have studied blistering, flaking and bubble formation in Ni₆₄Zr₃₆, Ni₃₃Zr₆₇ and Ni₆₀Nb₄₀ glasses under helium ion bombardment at room temperature. The effect of projectile energy (50–150 keV), total dose (0.01–10 × 10¹⁸ ions/cm²), dose rate (10–100 μA/cm²) and thermal crystallization on critical dose for blistering and/or flaking, average blister diameter and development of surface topography was examined. The surface damage effects in metallic glasses were in general similar to those for crystalline materials with the notable exception that the critical dose values are higher by about 50–100% for metallic glasses. TEM investigations revealed irradiation induced partial crystallization of Ni₃₃Zr₆₇ glass. Metallic glasses Ni₆₄Zr₃₆ and Ni₆₀Nb₄₀ were stable under helium irradiation and have also shown very high resistance against blistering and/or flaking. The possible mechanisms of helium trapping in metallic glasses are also discussed.     

~(238)U,~(235)U和~(93)Nb的次级中子能谱和双微分截面计算

一、引言自1966年Griffin提出激子模型以来,经过人们多年的工作,激子模型在计算次级中子能谱方面取得了一定的成功,用于角分布计算也有所进展。但迄今预平衡计算和平衡(蒸发)计算不能统一,计算结果不能定量地符合实验。其一个主要的原因是激子态     

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.     

6Li(n,t)4He反应微分截面的实验测量

用屏栅电离室对1．85和2．67MeV中子^6Li(n,t)^4He反应的微分截面及截面进行了测量。使用氚固体靶通过T(p,n)^3He反应产生中子,利用BF3长中子管进行相对中子通量监测,绝对中子通量则用^238U(n,f)反应来刻度。测量结果与已有数据进行了比较。