The 3He(α, γ)7Be and 3He(α, γ)7Li reactions at astrophysical energies

The radiative capture cross sections for ³He(α, γ)⁷Be and ³He(α, γ)⁷Li at astrophysical energies have been studied microscopically in terms of the resonating group method. It was found that the astrophysical S-factors correlate strongly to the nuclear size and deformation of ⁷Be and ⁷Li. With the help of measured nuclear properties of these nuclei, a safety range of the absolute values of the S-factor was determined; the most recommended S(0)-values are 0.50 ± 0.03 keV · b for the ³He(α, γ)⁷Be reaction and 0.098 ± 0.006 keV · b for the ³H(α, γ)⁷Li reaction.     

Study of the 3He(4He,γ)7Be and 3H(4He,γ)7Li Reactions in an Extended Two-Cluster Model

 The ³He(⁴He, γ)⁷Be and ³H(⁴He, γ)⁷Li reactions are studied in an extended two-cluster model which contains α + h/t and ⁶Li + p/n clusterizations. We show that the inclusion of the ⁶Li + p/n channels can significantly change the zero-energy reaction cross sections, S(0), and other properties of the ⁷Be and ⁷Li nuclei, like the quadrupole moments Q. However, the results agree with the known correlation trend between S(0) and Q. Moreover, we demonstrate that the value of the zero-energy derivatives of the astrophysical S-factors are more uncertain than currently believed. Received June 17, 1999; revised February 22, 2000; accepted for publication April 17, 2000     

Study of the reaction 12C(γ, n 3He)2α

The possibility of separating, with the aid of photoemulsion, channels of the reaction ¹²C(γ, n ³He)2α that involve the formation of ⁷Be and ⁸Be intermediate nuclei in excited states is studied. The experimental energy distributions of these nuclei are obtained. The relative yields from these reaction channels are estimated.     

Nuclear structure studies of 125Te with (n,γ), (d,p) and (3He,α) reactions

Levels in ¹²⁵Te were investigated in the range up to 3.3 MeV excitation energy by the (n,γ), (d,p) and (³He,α) reactions. Over 160 levels and about 360 γ-transitions were established, most for the first time. The states below 2.3 MeV with the most complete spectroscopic information were interpreted in terms of the interacting boson-fermion model (IBFM). Unitary treatment of both positive- and negative-parity states is achieved with the same model parameter close to the intermediate case between O(6) and U(5) limits. Excitation energies, electromagnetic transition rates, γ-branchings and spectroscopic factors are discussed in connection with the possible structures. A family of low-spin negative-parity states has been identified and understood by the IBFM proving their antialigned origin.     

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.     

Energy levels in159Ho from159Tb(α, 4nγ)159Ho and159Tb(3He, 3nγ)159Ho reactions

The reactions¹⁵⁹Tb(, 4n)¹⁵⁹Ho and¹⁵⁹Tb(³He, 3n)¹⁵⁹Ho have been used to populate states in¹⁵⁹Ho. Gamma-ray spectra in single and coincidence modes have been studied. Assignments have been made for the bands built on the Nilsson states 7/2^–[523], l/2⁺ [411] and l/2^–[541]. The results are discussed in terms of rotational models.     

16O(α,γ)20Ne反应的实验研究

讨论了目前16O(α ,γ) 2 0 Ne反应的实验研究工作 ,并对2 0 Na β+—→2 0 N →16O +α的β+ 缓发衰变α能谱的相对强度值同文献进行了比较 ,讨论了低能激发能级、共振强度及其对共振截面的贡献、S因子的理论研究.The experimental investigations of 16 O(α,γ) 20 Ne reaction is reviewed. The energy spectrum of β + delay α decay were measured through the 20 Naβ +-→ 20 Ne *→ 16 O+α process, and the relative densities of α decays are compared with the reference s results. The low excitation energy levels, resonance strength and its contribution to the resonance crosses section are also discussed. Finally, we have calculated the reaction rate of the direct capture reaction.......     

РЕАКЦИЯ (γ, р) НА ИНДИИ

Иамеряется энергети ческое и угловое расп ределение φотопрото нов из индия, облучаемого γ-квантами с энергией E_γ=17,6 Мэв u 14,8 Мзв. При сравнении энерге тического и углового распределения было о бнару-жено, что значительная час ть протонов образует ся при эвапорации и лишь около 3% прямым φо тоэφφектом. Из энергетического р аспределения найден ы энергии возбуждени я E _β ^* ядра¹¹⁴Cd, 3,8; 4,9; 5,6; 6,3 и. 7,6 Мэв.     

Zur (γ,p)- und (γ,np)-Reaktion am Argon 40

Argon gas has been irradiated with 34 MeV bremsstrahlung. The yields of the reactions A⁴⁰(γ, p) Cl³⁹ and A⁴⁰ (γ, np) Cl³³ were determined relative to C¹²(γ, n) by β-counting. The resulting upper limits for the cross sections integrated to 28 MeV are 160 MeVmbarns for (γ, p), and 35 MeV mbarns for (γ, np). This does not confirm the anomalously high A⁴⁰ (γ, p)-cross section reported in the literature.     

РЕАКЦИЯ (γ, р) НА КОБАЛЬ ТЕ

- , Li(, ) ( =17,6. 14,8 MeV). , u . , gQ=0,74+-0,16 MeV ⁵⁸Fe E ^* : 6,76; 6,44; 5,90; 5,47; 4,98; 4,35; 3,50; 3,20 MeV. , .     

РЕАКЦИЯ (γ, р) НА КАДМИИ И ОЛОВЕ

, , , -. [3], . . , , ; . , . , . , . , , .

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(, p) Reaction on cadmium and tin

A study is made of the nuclear photoeffect on Sn and Cd where, in contrast to most of the experiments with this effect up to now, discrete rays were used. The paper complements paper [3], the experimental arrangement of which it has taken over. Several interesting results were obtained — particularly the discreteness of the energy spectrum and the unconventional form of the angular distribution. With tin, the top proton shell of which is completely occupied, the shape of the energy spectrum corresponds to the Wilkinson theory of gigant resonance; with cadmium the energy spectrum is similar to the evaporation spectrum. The angular distributions of the photoprotons of both elements do not satisfy the commonly used relations corresponding to existing theories of nuclear photoeffect. They can, however, be described quite well by empirical equations which contain associated Legendre polynomials of different orders. With both elements the results have features of both a direct and a collective process. The paper gives results, a satisfactory explanation of which would require a new theory including both types of processes.

     

方位角(α,β,γ)能确定刚性分子的自由度吗?

指出了大学物理教材中刚性双原子分子的转动自由度的个数不能用通常的方位角(α,β,γ)来确定,而用球坐标系可以准确地说明这一问题.     

8β-hydroxyeremophil-7(11)-ene-12,8α(4β,6α)-diolide分子的晶体结构

运用层析法、结晶法从狭苞橐吾全草中分离得到艾里莫芬烷型倍半萜8β-hydroxyeremophil-7(11)-ene-12,8α(4β,6α)-diolide化合物,并通过质谱、核磁共振氢谱和碳谱、氢核-氢核相关谱、异核多量子相干谱和异核多键相干谱进行结构鉴定．其单晶经X射线衍射测试表明,其晶体属正交晶系,空间群为P212121,晶胞参数为: a=6．8519(5),b=10．7191(8),c=18．5942(14)A,V=1365．67(18) A3,Z=4,Dc=1．354 mg／m3．F(000)=592,μ=0．101 mm-1     

低能d(d,γ)α反应s因子的理论研究

在唯象模型的基础上, 考虑到碰撞氘核的D态分量对跃迁矩阵元的贡献和⁴He基态D态成分,我们从理论上计算了低能d(d,γ)α反应的天体物理学S因子.由理论计算再现d-d系统的结合能和以及由共振群方法计算的d-d弹性散射相移,得到Woods-Saxon势参数. 并由此计算的S因子与实验数据在E_c.m.<3MeV范围符合得较好, 尤其在天体物理学感兴趣的几百keV以下能区, 理论计算结果很好地符合实验数据. 由理论计算结果外推,计算了目前还没有实验数据的使恒星核合成反应过程能够进行的恒星能区(约1—20keV)的S因子.     

(α,β,γ)-Nb5Si3电子结构和光学性质研究

基于第一性原理的密度泛函理论赝势平面波方法,采用局域密度近似,计算了不同结构的α-Nb₅Si₃,β-Nb₅Si₃和γ-Nb₅Si₃的电子结构、态密度以及光学性质.计算结果表明,Nb₅Si₃费米能级附近价带主要是由Nb的4d轨道及Si的3s和3p轨道贡献,导带主要由Nb的4d轨道贡献;Nb₅Si₃的光学性质具有各向异性的特征,其零频介电常数ε₁（0）=207,折射率n₀=13;在15 eV以上的高能区表现为无色透明.     

~(55)Mn(α,n)~(58m,g)Co,~(55)Mn(α,2n)~(57)Co和~(55)Mn(α,α′n)~(54)Mn反应的激发函数

用活化法和迭靶技术,在入射α粒子能量从10.4到26.5MeV范围内,测量了~(55)Mn(α,n)~(58m,g)Co、~(55)Mn(α,2n)~(57)Co和~(55)Mn(α,α′n)~(54)Mn反应的截面,并同激子模型理论计算作了比较,结果表明在上述反应中存在平衡前发射反应机制。     

Piezoelectric property of hot pressed electrospun poly(γ-benzyl-α, L-glutamate) fibers

Since the 1960s, the piezoelectricity in biopolymers (e.g. proteins and polynucleotides) has attracted considerable scientific attention. In particular, poly(glutamate)s have been one of the most popular targets for this research due to their well-defined helical structure and permanent polarity along the helical axis. To date, films of poly(glutamate)s have been shown to exhibit piezoelectricity only in shear mode (d₁₄), mainly due to the limitation in fabricating electrically poled polymer samples. This paper describes a combined electrospinning and hot press method that allows production of poled poly(??-benzyl-??,L-glutamate) (PBLG) films with piezoelectricity in all d₃₃, d₃₁ and d₁₄ modes for the first time. It is found that this PBLG film belongs to the matrix structure of C_??v group, which is the same as that of poled PVDF film. The moderately high piezoelectric coefficients in both d₃₃ and d₁₄ modes as well as their thermal stability make the poled PBLG film an excellent candidate for use in flexible transducers and small energy harvesting devices.     

Study of 113Cd by the 110Pd(α,nγ) reaction

The nuclear structure of ¹¹³Cd was studied using in-beam γ-ray spectroscopy. A level scheme, consisting of 65 levels and more than 100 transitions, was constructed on the basis of γγ coincidences using five compton-suppressed Ge detectors. Spins were assigned by means of excitation function slopes and angular distribution analysis. The resulting level scheme was interpreted in the framework of the interacting boson-fermion model.