Spectroscopic Measurement in 9He and 12Be

Spectroscopy for neutron-rich nuclei ⁹He and ¹²Be has been performed by means of heavy-ion double charge exchange (HIDCX) (¹⁸O, ¹⁸Ne) reaction on stable target nuclei ⁹Be and ¹²C, respectively. Several clear peaks in ¹²Be at low excitation energy region even above neutron separation energy have been observed in one-shot measurement, whereas no prominent signals of ⁹He have been observed owing to the small cross section. It is shown that the HIDCX reaction is a new powerful spectroscopic tool for study of unstable neutron-rich nuclei.     

Production of 6He and 9Be by radiative capture and four-body recombination

In this work we estimate the production rates for the three-body radiative capture processes α + n + n → ⁶He + γ and α + α + n → ⁹Be + γ, as well as the four-body recombination reactions α + α + n + n → ⁶He + α, ^α + n + n + n → ⁶He + n, α + α + n + n → ⁹Be + n and α + α + α + n → ^BeBe + α. These processes compete as a source of ⁶He and ⁹Be. The hyperspherical adiabatic expansion method is used. With this method no assumption is made about the capture mechanism. Both sequential and direct capture are included. The production rates for the radiative and the four-body recombination processes are found to be comparable for a mass density of about 10⁷g/cm³ ( ～ 10³⁰ neutrons/cm³) and temperatures of a few GK.     

9Be + 12C, 9Be + 16O,9Be + 19F reactions at energies below the barrier

The ¹⁶O + ⁹Be reactions have been studied from E_c.m. = 2.0 MeV to 5.1 MeV, an energy near the top of the Coulomb barrier. The cross section for the neutron transfer reaction ⁹Be(¹⁶O,¹⁷O¹ (0.87 MeV))⁸Be has been measured over this range by detecting the prompt 0.87 MeV γ-rays. The total fusion cross section has been determined from E_c.m. = 2.8 to 5.1 MeV by observing individual γ-ray transitions in the evaporation residues with a Ge(Li) detector, and then summing the separate yields. Direct processes are found to dominate the reaction yield below E_c.m. = 4 MeV. A comparison of the energy dependence of the fusion cross section for this reaction and the ¹²C + ¹³C reaction, which proceeds via the formation of the same compound nucleus, ²⁵Mg, reveals differences at sub-barrier energies. Optical model and incoming-wave boundary condition calculations are presented. Data have also been obtained for the near optimum Q-value neutron-transfer reactions ⁹Be(¹²C, ¹³C¹)⁸Be and ⁹Be(¹⁹F, ²⁰F)⁸Be, and these are discussed in terms of a simple model of sub-barrier direct reactions.     

Spectroscopy of9He with the (13C,13O)-reaction on9Be

First results of the double-charge-exchange reaction⁹Be(¹³C,¹³O)⁹He, E_Lab=380 MeV, are presented. The ground state and an excited state at 3.8 MeV are clearly seen. A preliminary value of the⁹He mass excess is obtained: 41.5±0.6 MeV. Spectra of of the⁹Be(¹³C,¹⁴O) He-reaction have been measured with high resolution. The ground state transition appears as a pronounced sharp peak, but no other narrow peaks are observed.     

晕核6He（25 MeV/u）在9Be上的破裂反应

25 MeV/u 6He+9Be反应的实验中利用多个探测器望远镜对反应产物进行了测量, 对实验中各个角度测量到的4He进行观察, 将其中两个有高能峰成分的探测器划分成三部分, 得到不同角度4He的单举能谱和破裂产生4He的微分截面. Different products of 6He nuclei from 9Be target has been measured with a 6He beam at energy of 25 MeV/u. The energy spectra at different angles for 4He isotope were analyzed and the experiment differential cross sections for the direct breakup reaction were obtained.     

晕核6He(25 MeV/u)在9Be上的弹性散射研究

分析了北京大学核物理实验小组在日本RIKEN实验室完成的25 MeV/u 6He和9Be的弹性散射实验数据，得到了弹性散射微分截面角分布. 利用双折叠模型，并通过拟合弹性散射微分截面得到了此弹靶体系在此能量下的弹性散射光学势. We analyzed the 6He elastic scattering from 9Be target at 25 MeV/u. A Center of Beam (CB) method was used to calibrate the particle tracking detectors and set the reference system of the detection system. The double folding model approach was used to calculate the real part of the optical model potential. The preliminary optical model potential parameters were extracted by fitting the experimental differential elastic scattering cross sections.     

25MeV/u 6He在9Be靶上的弹性转移反应研究

报告了25MeV/u ⁶He在⁹Be靶上的弹性散射和弹性转移的实验结果. 用光学模型和一阶DWBA的方法计算了弹性散射和³He集团转移的截面, 计算结果和实验测量基本一致. 计算表明³He在⁹Be中的谱幅度应该明显大于壳模型的理论计算值0.70.     

25MeV/u 6He+9Be破裂反应的α碎片发射

测量了在25MeV/u 6 He轰击9Be靶的破裂反应产生的α碎片双微分截面及角分布,并在Serber模型的框架下计算了在破裂反应中衍射破裂与擦去过程的贡献,并对结果进行了讨论. 结果表明基于包含衍射破裂和擦去过程的Serber模型可以对6He的直接反应进行较好地描述,擦去过程的贡献远大于衍射破裂的贡献. 相对于6Li而言,6He较大的去2n微分截面源于它的弱束缚特性.     

Proton decay of spin isospin modes excited by the12C(6Li,6He)12N reaction

First investigations of the reaction¹²C(⁶Li,⁶He)-¹²N(p)¹¹C were used to study spin-isospin strength in the nucleus¹²N at E_Li=156 MeV. While the⁶He ejectiles were detected at _He=0° using a magnetic spectrograph, the decay protons were analysed in a wide range of backward angles (100°_p<170°) with=" an=" arrangement=" of=" semiconductor=" strip=" detectors.=" singles=" spectra=" were=" extracted=" as=" well=" as=" coincident=" excitation=" strength=" for=" the=" decay=" to=" low=" lying=" levels=">¹¹C. For the decay to the¹¹C ground state angular correlations were evaluated for six different energy regions in¹²N^*.The authors wish to thank the staff of the Karlsruhe Cyclotron Laboratory for their cooperation. This work has been funded by the German Federal Minister for Research and Technology (BMFT) under contract no. 06ER262I and by the Kernforschungs-zentrum Karlsruhe.     

Electroproduction of low energy charged pions on9Be,12C and16O

Measurements of electroproduced pions with an energy of 10MeV are presented. The results of a calculation based on the PWIA are compared with the presented data as well as with data at higher pion energies.     

Reactions induced by 35 MeV 6He beam on 12C and 14C

The ⁶He+^12,14C scattering and reactions have been studied using a 35 MeV ⁶He radioactive beam and preliminary results are presented. The three-body reaction ⁶He+¹²C ↦ ¹⁰Be+2 α has been clearly identified and sequential decay of intermediate states in ¹⁴C has been studied. Search for an analog reaction on ¹⁴C, ⁶He+¹⁴C ↦ ¹²Be+2 α, has not given conclusive results yet. Other interesting reactions with this entrance channel are discussed.     

Three-body decays of light nuclei: 6Be, 8Li, 9Be, 12O, 16Ne, and 17Ne

The theoretical approach to the two-proton radioactivity and three-body decays developed in (L.V. Grigorenko, R.C. Johnson, I.G. Mukha, I.J. Thompson, M.V. Zhukov, Phys. Rev. Lett. 85, 22 (2000) and to be published in Phys. Rev. C) is applied to the range of light nuclear systems. We study nuclear structures, widths, and momentum correlations for the decay fragments. Strong contradictions with experiment, as well as effects of special interest, are found in ¹²O and ¹⁶Ne nuclei. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: l.grigorenko@surrey.ac.uk     

Influence of spin-orbit coupling in (3He, 7Be) α-pickup on 12C and 16O

The (³He, ⁷Be) reaction on ¹²C and ¹⁶O at 41 MeV is analyzed in terms of α-pickup finite range DWBA including spin-orbit coupling. Angular distributions for the ground state ($\text{3}\text{2}{}^{\mathrm{?}}$) and first excited state ($\text{0.429}\text{MeV}\text{,}\text{1}\text{2}{}^{\mathrm{?}}$) of ⁷Be, significantly differing in shape, are simultaneously described by the calculations.     

On spectral temperatures of negative pions produced in d 12C, 4He12C, and 12C12C collisions at 4.2 A GeV/c

The experimental transverse momentum distributions of negative pions produced in d ¹²C, ⁴He¹²C, and ¹²C¹²C collisions at 4.2 A GeV/c were analyzed in the framework of Hagedorn Thermodynamic Model. The spectral temperatures of π ^? mesons as well as their relative contributions to the total multiplicity of π ^? mesons were extracted from fitting the p _t spectra by two-temperature Hagedorn function. The results were compared systematically with the earlier results obtained from analysis of non-invariant center-of-mass energy spectra of negative pions produced in the analyzed collisions.     

Measurement of the147Gd mass excess by the (12C,9Be) reaction

The mass excess of the¹⁴⁷Gd nucleus was measured from the¹⁴⁴Sm(¹²C,⁹Be)¹⁴⁷Gd reaction using the 72 MeV¹²C beam of the Orsay MP Tandem and the “Bacchus” magnetic spectrometer. The measurement is auto-calibrated by the¹⁰Be spectrum from the¹⁴⁴Sm(¹²C,¹⁰Be) reaction. The derived value of the mass excess of¹⁴⁷Gd is ?75.401±0.025 MeV. It is compared with other recent results and with calculated values.     

9Be(3He,n)11C and 11B(3He,n)13N Reactions at Energies below Coulomb Barrier

Angular distributions have been measured for ⁹Be(³He, n)¹¹C and ¹¹B(³He, n)¹³N reactions for the neutron group leading to the ground state at E_3He = 0.90, 1.00, 1.20, 1.40 MeV and 1.70, 1.90 MeV respectively. To fit the experimental data, the theory of two nucleon stripping reactions below the Coulomb barrier has been considered. Taking Coulomb distorted wave functions for the interacting particles in the initial channel, a closed analytical form for the differential cross-section has been obtained. The other two cases using the plane wave Born approximation and the distorted wave Born approximation are also applied to the experimental data. The agreement between the Coulomb distorted wave calculations and the experimental data is better than with the PWBA and DWBA. The spectroscopic factors are extracted by fitting the experimental data with the theoretical calculations.