Possible α decay chains from isotopes of superheavy element 120

We investigate the α decay half-lives of even-Z superheavy nuclei up to Z = 120 by the modified two-potential approach. Based on the density-dependent cluster model, the α daughter potential is obtained from the double folding integral, taking into account the effect of nuclear deformation. A reasonable formula related with the fissility parameter and the fission barrier height, is applied to evaluate the spontaneous fission half-lives of the studied nuclei. After the performance of the competition between α decay and spontaneous fission, possible α decay chains are proposed in pursuit of being useful for the future experiment.     

The cross-section investigation of (n, α) reaction on chromium isotopes

Cross-sections of the (n, α) reaction on chromium isotopes are of great importance for determining the radiation hardness of stainless steel, which is widely used in nuclear reactors. The EXFOR library contains a limited amount of the relevant experimental data, mainly for the reactions induced by neutrons with an energy around 14 MeV. There are no experimental data on the probability of the (n, α) reaction at the fission neutron energies. In this work we present results of investigating the ⁵⁰Cr(n, α) and ⁵²Cr(n, α) reactions. It is shown that the ENDF/B VII library evaluations for the ⁵⁰Cr(n, α) reaction are about 20 times as high as our experimental data. In addition, a structure that was predicted in none of the libraries is observed in the excitation function of the ⁵⁰Cr(n, α) reaction. The ⁵²Cr(n, α) reaction cross-sections at reactor neutron energies are obtained for the first time.     

Photofission of 238Pu, 240Pu, and 242Pu in the energy range 5–10 MeV

The cross sections for the photofission of plutonium isotopes ²³⁸Pu, ²⁴⁰Pu, and ²⁴²Pu in the energy range 5–10 MeV have been measured by using a beam of bremsstrahlung photons from the microtron installed at the Institute of Physics and Power Engineering (Obninsk). The energy regions below the fission barrier and above 6 MeV have been scanned with pitches of 0.05 and 0.1 MeV, respectively. In deriving the absolute cross section for ²³⁸Pu photofission, ²³⁸U photofission has been employed as a reference reaction. In measurements involving ²⁴⁰Pu and ²⁴²Pu nuclei, the neptunium isotope ²³⁷Np, which is characterized by a more regular dependence of the photofission cross section on excitation energy than ²³⁸U, has been chosen for the first time as a reference nucleus. The measured cross sections as functions of energy show resonance structures in the vicinity of the fission threshold that are consistent with those previously observed in the energy dependences of fissilities for corresponding direct reactions. The partial-wave cross sections for the J ^π K = 1^?0, 1^?1, and 2⁺0 photofission channels have been determined as functions of energy. At energies below some 5.5 MeV, the total cross section for photofission of each plutonium isotope being studied receives a significant contribution from quadrupole interaction. Within the one-dimensional model of a two-humped fission barrier, the parameters of the barriers for ²³⁸Pu, ²⁴⁰Pu, and ²⁴²Pu have been extracted from data and have then been compared with estimates based on previous measurements.     

Photo-neutron cross-section calculations of 142,143,144,145,146,150Nd rare-earth isotopes for (γ, n) reaction

The theoretical photo-neutron cross sections for (γ, n) reaction have been calculated on ^{142,143,144,145,146,150}Nd rare-earth isotopes at photon energies of 8–23 MeV using the PCROSS, TALYS 1.2, and EMPIRE 3.1 computer codes. TALYS 1.2 two-component exciton model and EMPIRE 3.1 exciton model has been used to calculate the pre-equilibrium photo-neutron cross sections. PCROSS Weisskopf-Ewing model has been used for the reaction equilibrium cross-section calculations. The obtained cross sections have been compared with each other and against the experimental values existing in the EXFOR database. Generally, pre-equilibrium model cross-section calculations are in good agreement with the experimental data for all reactions along the incident photon energy in this study.     

New data on (γ, n), (γ, 2n), and (γ, 3n) partial photoneutron reactions

Systematic discrepancies between the results of various experiments devoted to determining cross sections for total and partial photoneutron reactions are analyzed by using objective criteria of reliability of data in terms of the transitional photoneutron-multiplicity function F _i = σ(γ, in)/σ(γ, xn), whose values for i = 1, 2, 3, ... cannot exceed by definition 1.00, 0.50, 0.33, ..., respectively. It was found that the majority of experimental data on the cross sections obtained for (γ, n), (γ, 2n), and (γ, 3n) reactions with the aid of methods of photoneutron multiplicity sorting do not meet objective criteria (in particular, F ₂ > 0.50 for a vast body of data). New data on the cross sections for partial reactions on ¹⁸¹Ta and ²⁰⁸Pb nuclei were obtained within a new experimental-theoretical method that was proposed for the evaluation of cross sections for partial reactions and in which the experimental neutron yield cross section σ ^expt(γ, xn) = σ(γ, n) + 2σ(γ, 2n) + 3σ(γ, 3n) + ..., which is free from problems associated with determining neutron multiplicities, is used simultaneously with the functions F _i ^theor calculated within a combined model of photonuclear reactions.     

Structural,electronic and magnetic properties of gold cluster doped with calcium: Au n Ca (n = 1–8)

The geometrical structures, relative stabilities, electronic and magnetic properties of calcium-doped gold clusters Au _n Ca (n?=?1–8) have been systematically investigated by employing density functional method at the BP86 level. The optimised geometries show that the ground-state structures are planar structures for Au _n Ca (n?=?3–8) clusters. Ca-substituted Au _{n +1} clusters, as well as Au-capped Au _{n ?1}Ca clusters, are dominant growth patterns for the Au _n Ca clusters. The relative stabilities of Au _n Ca clusters for the ground-state structures are analysed based on the averaged binding energies, fragmentation energies and second-order difference of energies. The calculated results reveal that the Au₂Ca isomer is the most stable structure for small size Au _n Ca (n?=?1–8) clusters. The HOMO-LUMO energy gaps as a function of the cluster size exhibit a pronounced even–odd alternation phenomenon. Subsequently, charge transfers and magnetic moment of Au _n Ca (n?=?1–8) clusters have been analysed further.     

Paramagnetic center Cd+(2 S 1/2) in natural carbonate apatites Ca5(PO4)3 ? n (CO3) n (F,OH)

The stable paramagnetic center Cd⁺(² S _1/2) in natural sedimentary calcium phosphates containing a cadmium impurity has been studied using electron paramagnetic resonance. The parameters of the spectrum have been determined, and the influence of different radiation types on the paramagnetic center has been investigated.     

几个(n,d~*),(n,t)和(n,n′α)反应截面的测量

本文报告了En～14MeV中子以~(27)Al(n,a)~(24)Na或~(93)Nb(n,2n)~(92m)Nb反应截面为中子注量标准测得的~(92)Mo(n,d~*)~(91m)Nb,~(106)Cd(n,d~*)~(105)Ag;~(54)Fe(n,t)~(25m+g)Mn,~(58)Ni(n,t)~(56)Co;~(51)V(n,n'a)~(47)Sc和~(92)Mo(n,n'a)~(88)Zr的反应截面。文中还列举了能收集蓟的数据以作比较,中子能量是用铌锆截面比法测定的。     

In-plane London penetration depths near the critical temperature of Tl2Ba2Ca n−1Cu n O2n+4 and (Bi,Pb)2Sr2Ca n−1 Cu n O2n+4 (n=2,3)

From isothermalM(H) curves nearT _c , measured on polycrystalline Tl₂Ba₂Ca _n–1Cu _n O_2n +4 and (Bi, Pb)₂Sr₂Ca _n–1Cu _n O_2n+4 (n=2,3) samples, we deduce the in-plane penetration depths _ab as functions of temperature. An estimate according to the BCS weak-coupling clean-limit fit, which produces the data nearT _c very well, yields _ab(0)=3100 Å, 2320 Å 2210 Å, and 1960 Å for Bi₂Sr₂CaCu₂O₈, Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O₁₀, Tl₂Ba₂CaCu₂O₈, and Tl₂Ba₂Ca₂Cu₃O₁₀, respectively. A comparison between strong-coupling and weak coupling fitting curves clearly favours the weak-coupling temperature dependence of _ab nearT _c .     

Ca5(PO4)3F:Ce,Mn荧光粉的老化性能研究

通过对一系列Ca5(PO4)3F:Ce和Ca5(PO4)3F:Ce,Mn(以下简称FAP:Ce和FAP:Ce,Mn)样品在荧光灯中和在强紫外光(185nm+254nm)辐照下,发光效率衰减规律及样品漫反射光谱的变化的研究,并与普通卤粉((F,Cl)AP:Sb,Mn)进行对比,发现了该材料的老化速率与样品组分的关系,即随着材料中Ce浓度的增大和氧空位的增多,老化速率变快。并根据Ryan老化理论,对材料老化的物理机制进行了初步的推测。     

Single-phase Bi2+x(Ca,Sr) n+1 Cu n O2n+4+δ, n = 0, 1, 2, 3 AND ∞, and some substitutional DERIVATIVES

The preparation, structure and properties of five members of the homologous series Bi_2+x(Ca,Sr) _n+1 Cu _n O_2n+4+δ are discussed, namely for n = 0, 1, 2, 3 and ∞. The two end members are insulating phases with a fixed oxygen stoichiometry but the members n = 1, 2 and 3 are superconducting phases with T_c depending on the calcium to strontium ratio and on oxygen stoichiometry as determined by annealing temperature and oxygen partial pressure. Maximum zero resistance T_c 's obtained are n = 1: 76 K, n = 2: 91 K and n = 3: 106 K. The effects of Pb-substitution in n = 2 and n = 3 are discussed with particular reference to the stabilisation of the latter phase. Rare-earth substitution is shown to raise T_c for n = 2 to at least 101 K without the introduction of the n = 3 phase.     

闪烁体材料MBPO5:Ce(M=Ca,Sr,Ba)的制备及光谱性质

报道了Ce^3 掺杂的碱土金属硼磷酸盐的制备、结构和光谱性质。在助熔剂的作用下,用高温固相反应法制备了MBPO5(M=Ca,Sr,Ba)样品,并在还原气氛下成功地实现了Ce^3 的掺杂。用X射线衍射(XRD)和傅里叶红外吸收谱(FT-IR spectra)表征了样品的结构。X射线衍射结果表明,产物为六方相的菱硼硅铈矿(Stillwellite)结构。FT-IR spectra给出了BO4、PO4等基团的信息。测量并分析了材料在室温下的真空紫外一紫外(VUV-UV)激发光谱及相应的发射光谱。在紫外光的激发下,观察到Ce^3 的5d→FJ(J=7／2,5／2)的发射,分析了基质晶格对Ce^3 的激发和发射谱的影响,并测量了BaBPO5基质中Ce^3 的发光寿命。     

~(50,48,46)Ti的(n,p)(n,α)和~(58)Ni的(n,2n)(n,p)反应截面的测量

本文叙述了从13.50 MeV到14.81 MeV中子能区用活化法相对~(21)Al(n,α)~(24)Na的反应截面,对~(50)Ti(n,α)~(47)Ca、~(48)Ti(n,p)~(48)Sc、~(46)Ti(n,p)~(46)Sc、~(58)Ni(n,2n)~(57)Ni、~(58)Ni(n,p)~(58m+g)Co五个反应截面的测量。并将所得的结果和其他作者的结果进行了比较。     

(n,2n),(n,3n)反应激发函数的系统学研究

本文用包括平衡前发射在内的蒸发模型理论研究了(n,2n),(n,3n)反应的激发函数系统学.在对实验数据分析、拟合的基础上,得到一组较好的经验参数.利用这组参数计算得到的截面和实验结果符合较好.     

Cross section measurements for (n, 2n),(n, α)(n,p), and reactions on rhenium isotopes around 14 MeV neutrons and their theoretical calculations of excitation functions

Cross-section data of the ~(185)Re(n,2 n)~(184)mRe,~(185)Re(n,2 n)~(184)Re,~(185)Re(n,α)~(182 m14+m2+g)Ta,~(187)Re(n2 n)~(186 g,(m))Re,~(187)Re(n,α)~(184)Ta,and ~(187)Re(n,p)~(187)W reactions were measured at four neutron energies,namely 13.5,14.1,14.4,and 14.8 MeV,by means of the activation technique,relative to the reference cross-section values of the~(93)Nb(n,2 n)~(92 m)Nb reaction.The neutrons were generated from the T(d,n)~4 He reaction at the K-400 Neutron Generator at China Academy of Engineering Physics.The induced y activities were measured using a high-resolution γ-ray spectrometer equipped with a coaxial high-purity germanium detector.The excitation functions of the six abovementioned nuclear reactions at neutron energies from the threshold to 20 MeV were calculated by adopting the nuclear theoretical model program system Talys-1.9 with the relevant parameters properly adjusted.The measured cross sections were analyzed and compared with previous experiments conducted by other researchers,and with the evaluated data of BROND-3.1,ENDF/B-Ⅷ.0,JEFF-3.3,and the theoretical values based on Talys-1.9.The new measured results agree with those of previous experiments and the theoretical excitation curve at the corresponding energies.The theoretical excitation curves based on Talys-1.9 generally match mo st of experimental data well.     

几个(n,d),(n,t)和(n,n'α)反应截面的测量

本文报告了En～14MeV中子以²⁷Al(n,α)²⁴Na或⁹³Nb(n,2n)^92mNb反应截面为中子注量标准测得的⁹²Mo(n,d*)^91mNb,¹⁰⁶Cd(n,d*)¹⁰⁵Ag;⁵⁴Fe(n,t)^52m+gMn,⁵⁸Ni(n,t)⁵⁶Co;⁵¹V(n,n'α)⁴⁷Sc和⁹²Mo(n,n'α)⁸⁸Zr的反应截面.文中还列举了能收集到的数据以作比较,中子能量是用铌锆截面比法测定的.     

Cross Section Measurements for (n,d*)(n,t) and (n,n'α) Reactions

Cross sections for some (n,d*),(n,t) and (n,n'α)reactions have been measured by using the activation method relative to cross sections of ²⁷Al(n,α)²⁴Na or ⁹³Nb(n,2n)^92mNb reactions in neutron energies around 14MeV.In this paper some of the published cross section data have also been listed and compared with our results.The neutron energies were determined by the method of cross section ratios for the reactions of ⁹⁰Zr(n,2n) ^89m+gZr and ⁹³Nb(n,2n)^92mNb.     

(n,n)-(2n, 0)碳纳米管异质结的扭转力学特性

相近直径的锯齿型和扶手椅型碳纳米管可以共轴组合形成5-7碳环交替出现的柱形对称异质结. 本文利用分子动力学方法研究了直径相近且等长锯齿型和扶手椅型碳纳米管形成的(n, n)-(2n, 0)结在扭转过程中的扭矩和轴向应力随扭转角度的变化规律以及应力传递过程. 研究发现, (n, n)-(2n, 0)结扭转应变在达弹性限度内不会产生轴向应力, 该效应对基于碳纳米管扭转特性的纳米振荡器件的设计具有重要意义.     

Cr3+:GGG(Ca,Mg,Zr)和Nd3+,Cr3+:GGG(Ca,Mg,Zr)激光晶体的光谱特性

本文分析了Cr3+:GGG(Ca,Mg,Zr)的荧光谱和吸收谱,测算到Cr3+离子在4T2g-2Eg的能级间距为ΔE≈70cm-1,晶场强度Dq/B=2.50.说明由于GGGa(Ca,Mg,Zr)晶格扩大减弱了晶场,可望实现Cr3+:GGG(Ca,Mg,Zr)室温下的调谐及Nd3+:Cr3+:GGG(Ca,Mg,Zr)中Cr3+→Nd3+能量的转移.最后从理论上阐明了Cr3+在晶体GGG(Ca,Mg,Zr)中的能级结构.