New insights into the 243Am + 48Ca reaction products previously observed in the experiments on elements 113, 115, and 117

Results of a new series of experiments on the study of production cross sections and decay properties of the isotopes of element 115 in the reaction (243)Am+(48)Ca are presented. Twenty-one new decay chains originating from (288)115 were established as the product of the 3n-evaporation channel by measuring the excitation function at three excitation energies of the compound nucleus (291)115. The decay properties of all newly observed nuclei are in full agreement with those we measured in 2003. At the lowest excitation energy E*=33 MeV, for the first time we registered the product of the 2n-evaporation channel, (289)115, which was also observed previously in the reaction (249)Bk+(48)Ca as the daughter nucleus of the decay of (293)117. The maximum cross section for the production of (288)115 is found to be 8.5 pb at E*≈36 MeV.     

Gammasphere上裂变丰中子核核结构若干前沿领域的新进展(Ⅰ:第一和第二部分)(英文)

(第一和第二部分):使用Gammasphere多探测器系统对252Cf裂变源瞬发γ射线进行γ-γ-γ和γ-γ(θ)符合测量,裂变丰中子原子核核结构若干前沿领域的深入研究获得了新的进展。高达5.7×1011以上的三重和更高重符合事件的数据统计,以及更少压缩的三维数据为宽广未知丰中子核区的寻找和研究提供了有利的条件。在具有重要物理意义的若干丰中子核区首次建立,或显著扩展了一批包括转晕态和转晕附近能态的高自旋能级纲图。在偶-偶丰中子核110,112Ru和108Mo中鉴别出了手征对称破缺结构。丰中子110,112Ru附近核的三轴形变基态具有最低的能量,在它们之中已确认了接近最大值的三轴形变。在这些Ru和Mo同位素中观察到的手征双线能带展示出手征破缺的一切特征,特别是其理想的能量简并,表明它们在迄今已报道的手征破缺结构中,具有最好的手征特性。研究了手征结构从具有γ软度的108Ru到具有大三轴形变的110,112Ru的过渡。斜轴推转(TAC)和随机相近似(RPA)理论计算成功地拟合了在这些偶-偶丰中子核中观察到的手征双线能带的特性,并指定其为软手征振动态。在这些偶-偶核中观察到的手征破缺不可能归纳为奇-奇核中那样的简化的几何图像。前者来自闭壳外所有中子的相互作用。对双幻核132Sn附近N=83同中素链的系统研究为这个极富吸引力的核区提供了大量新的谱学信息。N=83同中素135Te(Z=52),136I(Z=53),137Xe(Z=54),138Cs(Z=55)和139Ba(Z=56)的最新能级信息,特别是首次建立的138Cs高自旋能级纲图和壳模型理论计算表明,Z=50质子闭壳外少数g7/2价质子激发同N=82中子闭壳外之唯一f7/2价中子的耦合对该核区能级结构具有关键作用。观察到了132Sn和208Pb附近核区谱学信息的相似性和相对应的三粒子和五粒子态。在135Te中观察到了磁转动,这是在双幻核132Sn附近观察到的首例磁转动。     

Magnetic properties of 166Er and the collective model

The E2/M1 admixtures for nine γ-ground band transitions in ¹⁶⁶Er were measured. Mixing ratios, δ(E2/M1), were calculated based on a general treatment of magnetic properties in the framework of the collective model. The agreement with the experimental values is generally good.     

New insights into neutron-rich nuclei at high spin

With new high statistic data, new isotopes and new high-spin structures are observed in neutron-rich nuclei populated in the spontaneous fission of ²⁵²Cf. The ¹³⁵Te levels are extended, and many new levels in ^139,141Ba observed. The coexistence of collective and single particle-hole states is found in ¹³⁵Te. The N = 83 ¹³⁵Te and ¹³⁹Ba show marked differences associated with differences in their particle and hole states. New levels in ¹⁴¹Ba complete evidence for two opposite-parity doublets characteristic of stable octupole deformation. In ^114,116Pd a second backbend is observed for the first time in this mass region and the backbend in ¹¹⁸Pd occurs earlier than in ^112-116Pd because of a reduction in pairing. Gamma-type vibrational bands are seen up to 13⁺ to 15⁺ in ^104,106Mo, ^108-112Ru, and ^112-116Pd. Their behavior reflects prolate to triaxial shapes in these nuclei. The levels of ^162,164Gd are observed for the first time. As N increases toward mid-shell at 104, the moments of inertia in N = 100 ¹⁶⁴Gd show an unexpected decrease compared to N = 98 ¹⁶²Gd. The levels in ^162,164Gd form remarkable shifted identical bands with nuclei separated by 2n, 2p, α, and 2α. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: j.h.hamilton@vanderbilt.edu     

Collective Band Structures in Neutron-Rich ^108Mo Nucleus

High spin states in the neutron-rich ^108Mo nucleus are studied by measuring prompt γ-rays following the spontaneous fission of 252Cf with a Gammasphere detector array. The ground-state band is confirmed, and the one-phonon γ-vibrational band is updated with spin up to 12h. A new collective band with the band head level at 1422.4keV is suggested as a two-phonon γ-vibrational band. Another new band is proposed as a two-quasi- proton excitation band. Systematic characteristics of the collective bands are discussed.     

Observation of α-decay in thallium nuclei,including the new isotopes 184Tl and 185Tl

With the use of an on-line isototpe separator α-decay was observed for the first time in thallium nuclides, including the new isotopes ¹⁸⁴Tl and ¹⁸⁵Tl. Their identification has led to the observation of the 0⁺ deformed band head in ¹⁸⁴Hg and allows for the possibility of determining whether ¹⁸⁵Hg is deformed in its ground state.     

丰中子核145,147La的八极形变

通过对²⁵²Cf自发裂变产生的瞬发γ谱的实验研究,建立与扩展了丰中子核^145,147La的高自旋态能级图,最高自旋态达到(41/2⁺)与(43/2^－).测得的交叉相联的相反宇称带及带间的强化E1跃迁说明在^145,147La中形成强的八极形变.对¹⁴⁵La的研究表明,具有轴对称形状的四极形变与具有反演不对称形状的八极形变在同一核中产生共存与竞争.在πh_11/2带中观测到的带交叉位于ω≈0.26—0.30MeV附近,由推转壳模型计算表明,它是由一对i_13/2中子的顺排所引起的.     

Reinvestigation of Collective Bands in 107Tc

The high spin states of a neutron-rich ^107 Tc nucleus are reinvestigated by observing prompt γ-rays from the spontaneous fission of ^252 Cf. The previous level scheme is updated. A collective band based on the π5/2- [303] orbital is confirmed and extended. Inconsistencies in the configuration assignments for a type of positive parity bands of odd-A 105,107,109 Tc in the previous reports are clarified according to the g factor calculations. A new band based on the 1499.5 keV level in ^107Tc is proposed as a two-phonon γ-vibrational band.     

Extended collective bands in neutron-rich 109Ru

Levels in the neutron-rich 109Ru have been studied by observing the prompt γ-rays following the spontaneous fission fragments of 252Cf. The ground state band and the negative parity bands have been confirmed and extended. A positive parity band with the band head level at 332.5 keV is newly identified and suggested as a single-neutron excitation band built on the 7/2+ [404] Nilsson orbital. Some structural characteristics of these bands are discussed.