20Mgβ衰变谱学与15O(α,γ)19Ne反应(英文)

15O（α,γ）19Ne（p,γ）20Na反应链是高温CNO循环向快速质子俘获过程突破的一条关键路径,相关的反应率输入量可通过20Mg的β衰变可布居19Ne共振态并测量其衰变性质来获得。通过高效率高精度地测量20Mg β衰变中产生的质子与γ射线得到了20Mg衰变的详细信息,并构建了完整的衰变纲图,还进行了19Ne 4 033 keV共振态衰变性质的探索,获得了该态在20Mg β衰变中被布居的分支比上限。通过比20Mg和20O镜像能级跃迁的结果确认了同位旋非对称性,为检验相关理论模型提供了精确的实验数据。对于突破路径中有重要影响的19Ne 4 033 keV共振态的性质,有待更高统计的实验进一步研究。The breakout from the hot CNO cycle to the rapid proton capture process can occur via the 15O(α,γ)19Ne(p,γ)20Na reaction sequence, and the β decay of 20Mg can be used as an alternative method to characterize some specific resonances, which will provide detailed nuclear structure input for reaction rate calculations. The reliable information on the decay properties and structure of 20Mg was obtained by measuring the emitted particles and γ-rays in the β decay with high efficiency and high resolution. Attempt was also made to search for the decay channels associated with the 4 033 keV resonance in 19Ne. To test fundamental symmetries, the transitions in the mirror decays of 20Mg and 20O were compared. The precise experimental data presented here would be important to constrain the theoretical calculations. It is desirable to clarify the astrophysically relevant problem by further experiments with improved statistics on the basis of the present work.     

A Sensitivity Test of Extracting the Optical Potential Parameters for 6He＋209Bi from the Transfer Reaction 208pb（7Li,6He）209Bi

Recently, an indirect method has been proposed to study the optical model potential of exotic nuclear systems by fitting the transfer reaction angular distribution. The sensitivity test of this transfer method is performed with 2~8 pb（T Li,6 He）2~9 Bi as an example, by varying the potential parameters individually. The results indicate that, except for the ambiguity in the real potential depth V, other optical potential parameters of 6He＋209Bi as well as the structural information of the reactions can be extracted reliably, Moreover, the radius parameter of the bound state, rbound, is an extraordinarily sensitive parameter, which should be taken care of in the calculation procedure. The present work provides a theoretical reference for the application of the transfer method.     

sd壳层极丰质子核的β延迟衰变谱学

远离β稳定线原子核的结构是当前核物理领域的一个前沿热点。β衰变谱学是研究核结构的重要方法，尤其适用于低产额的滴线核。本文回顾了近年来在RIBLL1装置上开展的sd壳区极丰质子核β延迟衰变谱学的实验研究。该工作获得了15个原子核精确的半衰期、衰变子核的质量、β延迟的质子和双质子发射以及$\gamma $跃迁的能谱、分支比和比较半衰期等数据，并重建了衰变纲图，大大丰富了此区域内质子滴线附近原子核的衰变谱学信息。还介绍了探测器阵列和实验方法，概括了所研究核的衰变性质和半衰期等。特别地，对几个典型核，20Mg和22Si以及26P和27S的衰变性质进行了阐述。此外，对相关话题，如三体力、镜像核衰变不对称性、与银河系中26Al超丰问题相关的热核反应率等问题进行了探讨。     

替代反应法测量锕系核(n,f)和(n,xn)截面

对于某些中子反应截面,在直接测量上存在困难。为了获得那些对核能发展极其重要的核数据,人们提出替代反应法,即利用带电粒子代替中子进行反应,从而实现中子反应截面间接测量的方法。现有替代反应一般采用非弹激发、转移等周边反应,涉及的角动量远比中子反应的大,需要理论修正,这造成了一定的困难。有鉴于此,提出利用轻带电离子的俘获反应作为替代反应,其复合核自旋与中子反应的相当,有效避免了自旋修正的困难。根据这个思路,采用236U的（α,f）和（α,2n）反应作为替代反应,成功提取了239Pu的（n,f）和（n,2n）反应截面,与ENDFB7评价库数据在误差范围内符合较好,表明了替代反应法的优越性,可以在核数据测量中推广应用。There are always difficulties in the direct measurement of reactions induced by neutron, in order to obtain the neutron induced nuclear reaction data which are extremely important for nuclear power development, the surrogate reaction method, which uses charged particles instead of neutron, was proposed. The existing surrogate reaction method generally chooses peripheral reaction as the surrogate reaction, such as inelastic scattering excitation or transfer reaction. As a result, the angular momentum involved is always far larger than the neutron induced reaction, which causes difficulties in the theoretical calculation. Because of this, we proposed to use light-ion capture reaction as the surrogate reaction, the compound nuclei spin is similar with that of the neutron induced reaction, so that the difficulties in spin correction can be effectively avoided. Based on this idea, the 239Pu(n, f) and (n, 2n) reaction cross sections were successfully extracted using 236U(α,f) and (α,2n) reactions as the surrogate reaction. The results coincide well with the data of ENDFB7 within the error range, which shows that the surrogate reaction method has its own superiority, and it can be applied in the measurement of nuclear data.     

An Implantation and Detection System for Spectroscopy of 22,24Si

A new decay detection system with high detection efficiency and low detection threshold has been developed for charged-particle decay studies, including -delayed proton, decay or direct proton emission from proton-rich nuclei. The detection system was tested by using the -delayed proton emitter 24Si and was commissioned in the decay study of 22Si produced by projectile fragmentation at the First Radioactive Ion Beam Line in Lanzhou. Under a continuous-beam mode, the isotopes of interest were implanted into two double-sided silicon strip detectors, where the subsequent decays were measured and correlated to the preceding implantations by using position and time information. The system allows to measure protons with energies down to about 200 keV without obvious background in the proton spectrum. Further application of the detection system can be extended to the measurements of -delayed proton decay and the direct proton emission of other exotic proton-rich nuclei.     

近垒及垒下能区28Si+174Yb体系的裂变碎片质量分布

使用两块大面积平行板雪崩计数器,测量了近垒及垒下28Si+174Yb熔合裂变碎片质量-角度关联分布及质量分布。质量-角度二维图显示在该反应能量区间内并没有发现明显的准裂变成分。运用单高斯曲线拟合了裂变碎片的质量分布并抽取了质量宽度。结果表明:在库仑势垒以上,质量宽度随着反应能量的升高而增大;在库仑势垒以下能区,发现质量宽度随着反应能量的降低而呈现轻微增大的趋势。运用鞍点统计模型对本次实验数据拟合发现,需用比文献给出的更大的刚度系数才能重现实验结果,其物理原因还需要进一步研究。In order to study the fission mechanism, the mass distributions and mass-angle distributions of the fission fragments for 28Si+174Yb were measured near the Coulomb barrier. The mass-angle correlations do not indicate any possible quasi-fission events in this bombarding energy range. The mass distributions were fitted by the single Gaussian distribution and then the mass widths were extracted. At above-barrier energies, the mass widths were found to increase with the energy. However, the mass widths show slight increase with decreasing energy below the barrier. Additionally, the mass widths can not be reproduced in the framework of the saddle statistic model with the given parameter, so further study is still needed.     

Development of large-area quadrant silicon detector for charged particles

The quadrant silicon detector, a kind of passivated implanted planar silicon detector with quadrant structure on the junction side, gained its wide application in charged particle detection. In this paper, the manufacturing procedure, performance test and results of the quadrant silicon detector developed recently at the China Institute of Atomic Energy are presented. The detector is about 300 μm thick with a 48 mm×48 mm active area. The leakage current under the full depletion bias voltage of -16 V is about 2.5 nA, and the rise time is better than 160 ns. The energy resolution for a 5.157 MeV α-particle is around the level of 1%. Charge sharing effects between the neighboring quads, leading to complicated correlations between two quads, were observed when α particles illuminated on the junction side. It is explained as a result of distortion of the electric field of the inter-quad region. Such an event is only about 0.6% of all events and can be neglected in an actual application.     

近垒重离子熔合反应中的中子转移效应(英文)

近势垒及其以下能区重离子熔合反应中的中子转移耦合道效应是一个复杂且有争议的问题。简要介绍了近年来在中国原子能科学研究院的HI-13串列加速器上,基于静电偏转板装置完成的32S+90,94,96Zr,18O+74Ge和18O+58Ni等几个典型体系的熔合反应研究情况,并结合耦合道理论对实验数据进行了分析。选取反应体系时同时关注了正Q值的中子拾取和削裂道。另外,基于完全耦合道理论计算,提出了一种能够定量提取熔合反应中中子转移效应的自洽方法。这些研究进一步证实了垒下重离子熔合反应中的中子转移效应,同时指出了其复杂性。需要进一步的实验和理论研究来澄清相关核反应机制。The effect of neutron transfers on near-and sub-Coulomb-barrier fusion of heavy-ions is still a complicated and controversial problem. This paper reviews the recent experimental results of the fusion excitation functions of several typical systems, which have been measured by using an electrostatic deflector setup at the HI-13 tandem accelerator of CIAE. Both the neutron pickup and stripping effects were studied. Moreover, a self-consistent method to reliably isolate the transfer effect quantitatively based on the coupledchannels calculation is proposed. These studies give a further support for the neutron transfer effect on sub-barrier fusion of heavy-ions and its complexity. Further experimental and theoretical studies are needed for clarifying the relevant reaction mechanisms.     

7Li+11B 体系唯象光学势的研究

实验测量了7Li+11B 体系的弹性散射角分布,其中弹核7Li 的入射能量分别为9.85,13.3,18.3,23.3 和28.3 MeV,测量的角度范围为θc:m: ≈ 15◦ ∼ 80◦。通过对本次实验数据以及文献中34 MeV 的数据拟合,抽取了该体系的唯象光学势参数。结果表明,在固定作用势形状因子下,势深度与能量具有线性相依的关系:实部深度随着弹核能量的增加而线性减小,而虚部深度则在平均值10.35 MeV 附近变化。Angular distributions of 7Li+11B elastic scattering were measured at Elab(7Li)=9.85, 13.3, 18.3, 23.3 and 28.3 MeV within the angular range of θc:m: ≈ 15◦ s 80◦. The analyse of these angular distributions together with the data taken from literatures at Elab(7Li) = 34 MeV have been performed to extract the parameters of optical model potential. With the fixed geometrical shapes, the potential strengths show a concise relation to the reaction energy: the depths of real potential decrease linearly with energy increasing, whereas the depths of imaginary part just slightly vary around the average value of 10.35 MeV.     

Proton and Two-proton Emissions from Proton-rich Nuclei with 10≦Z≦20

Proton (p) and two-proton (2p) emissions from the proton-rich nuclei with 10≦Z≦20 have been explored by the in-fight decay and implantation decay methods, respectively, in a series of experiments at the HIRFL-RIBLL facility. The in-flight 2p emissions from the excited states of 28,29S /26,27P and 17;18Ne were studied by complete-kinematics measurements. Mechanisms of 2p decay and related p-p correlations have been explored. Obvious 2p correlated emissions have been observed in the cases of 28,29S but not in 27,28P, indicating the 2p halo plays an important role in the diproton emission. In the 17;18Ne cases, a small 2p opening angles were deduced by the HBT analyses, implying the BCS-BEC crossover may occur in the dilute nuclear matter. Moreover, 27S/26P/25Si, 22Si/20Mg, 23Si/22Al/21Mg, 24Si/23Al, and 36;37Ca were implanted in a thin double-sided-silicon-strip detector and their -delayed p and 2p decays have been measured by a surrounding silicon detector array under the continuous-beam mode. Important information on the nuclear spectroscopy, such as energy, lifetime, branching-ratio, and so on, has been extracted, which helps us to understand the nuclear structures of proton-rich exotic nuclei close to the drip-line.