New Neutron-Rich Isotope 208Hg

The new neutron-rich isotope ²⁰⁸Hg has been identified for the first time from the reaction products in fully-stopping thick ^nat.Pb target bombarded by 30MeV/u ¹²C beam provided by the Heavy Ion Research Facility in Lanzhou.Assignment of the nuclide ²⁰⁸Hg was based on the measurements of the deacy γ energy and halflife of its daughter ²⁰⁸Ti,which was grown up with ²⁰⁸Hg β-deacy.The half-life of ²⁰⁸Hg β-deacy was determined to be 42+23－12 min.The average production cross section of ²⁰⁸Hg over the incident energy region from Coulomb barrier to 30MeV/u is found to be 1.1±0.5μb.     

Searching Triaxial Superdeformation in 175Hf

A two-dimensional Total Routhian Surface(TRS) calculation is carried out in order to ascertain if there is triaxial superdeformation in ¹⁷⁵Hf. A five quasi-particle configuration is chosen in the calculation. Unfortunately, the TRS minimum does not show up in the total potential energy surface.     

HIRFL上合成的第一个新核素—208Hg

本文简述在中科院近物所HIRFL上发现的第一个新核素208Hg的合成和鉴别,兼论利用HIRFL提供的中能重离子束开展远离β稳定线核素合成和衰变研究的优势、困难以及拟采用的物理和技术路线。 The synthesis and identification of the first discovered new nuclide 208Hg on HIRFL(Heavy Ion Research Facility of Lanzhou) were described. In this paper the superiorities, difficultiesas well as the physical and technical line about the synthesis and decay study for the nuclides far fromβ-stability line to be made at HIRFL were discussed.     

New Gamma Rays from the Neutron-Rich Isotope 189W Decay

The natural Osmium powder was irradiated with fast neutrons.After the chemical separation,the characteristic gamma ray spectra and the time-sequential spectra in the W fraction were measured.11 new gamma lines os ¹⁸⁹W unknown previously were found.     

Collective Bands in Neutron-Rich 107Ru Nucleus

Through measuring prompt γ-rays emitted in the spontaneous fission of ²⁵²Cf with higher statistic data,level structures in the neutron rich,odd A¹⁰⁷Ru nucleus have been re investigated. New level scheme of ¹⁰⁷Ru has been established. The ground state band was extended with spin up to 27 2h. The νh_11/2 band structure observed in our previous publication has been confirmed and extended. These results clear up the inconsistence between our earlier work and results from another experiment published recently. A collective band built on (9/2^－) level has been observed for the first time. Some important features of the level scheme have been discussed.     

New Nuclide 129Pm Near the Proton Drip Line

The very neutron-deficient nuclide ¹²⁹Pm was produced via the ⁹²Mo(⁴⁰Ca, p2n) reaction and identified for the first time by using the X-γ coincidence in combination with a He-jet tape transport system. From the decay of a 99keV γ ray which corresponds to the 5/2^－→1/2^－ transition in the daughter nucleus ¹²⁹Nd following the (EC+β⁺) decay of ¹²⁹Pm, the half-life of ¹²⁹Pm was determined to be 2.4(6)s.     

Langevin study of neutron emission in the reactions 16O+181Ta and 19F+178Hf

The pre-scission neutrons measured in the reactions ¹⁶O+¹⁸¹Ta and ¹⁹F+¹⁷⁸Hf are studied via a Langevin equation coupled with a statistical decay model. We find that because of the mass asymmetry of different entrance channels, the spin distributions of compound nuclei would be different, consequently, the measured neutrons in these two reactions would also different. This means that the entrance channel will affect the particle emission in the fission process of hot nuclei.     

First Experimental Determination of Half-Life for New Nuclide 65Se

By using experimental data obtained from the measurement of beta-delayed proton decay of ⁶⁵Se produced in ⁴⁰Ca(²⁸Si,3n)reaction,the absolute detection efficiency of particle telescope for rotating radioactive source was imitatively calcu-lated.The half-life of ⁶⁵Se was thus accurately determined to be 9.6_-4.1^+5.3 ms.The β-delayed proton energy of ⁶⁵Se was 3.70±0.08MeV.The partial decay scheme of ⁶⁵Se β-delayed proton decay was revised and proposed.     

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.     

Collective Band Structures in Neutron-Rich Odd-A 145,147Ce Nuclei

Through study of the prompt r-rays emitted in the spontaneous fission of ²⁵²Cf, high spin states of neutron-rich odd-A ^145,147Ce nuclei have been investigated. The levels in ¹⁴⁷Ce have been extended. A collective band in ¹⁴⁵Ce have been identified for the first time. The results from the particle rotor model calculations indicate that the yrast bands in ¹⁴⁵Ce and ¹⁴⁷Ce originate from vi_13/2 orbital coupling and the ground states of ¹⁴⁵Ce and ¹⁴⁷Ce originate from (vh_9/2,vf_7/2) and vh_9/2 configiration, respectively. No obvious octupole deformation was observed in these two isotopes, but a side band obtained in ¹⁴⁷Ce may show some octupole correlations.     

Identification of Collective Bands in Neutron-Rich 113Ru Nucleus

Through measuring high-fold prompt γ- ray coincidence events following the spontaneous fission of 252 Cf with the Gammasphere detector array, new level scheme in the very neutron-rich odd-A 113Ru nucleus has been established. An intruder collective band based on 11/2^－ level has been identified with spin up to 31/2 k and excitation energy 3.6 MeV. This band most probably originates from vh_11/2. intruder orbital. Another collective band probably built on 9/2^－ level is also observed. Some important characteristics of the collective bands have been systematically discussed.     

Recent progress in AMS measurement of 182Hf at the CIAE

In order to improve the accuracy of accelerator mass spectrometry (AMS) measurement for ¹⁸²Hf/¹⁸⁰Hf, a series of measurements have been taken in the AMS laboratory at the China Institute of Atomic Energy (CIAE). The major ones include the instantaneous monitoring of ¹⁸⁰HfF₅^- current, testing the stability of transmission, the alternate measurements of an unknown sample and standard, and the origin identification and minimization of background ¹⁸²W. The experimental details and the improvement in the measurement accuracy, as well as some useful suggestions for better satisfying the requirements of certain practical applications, are presented in this paper.     

Research on Measurement of 182Hf with HI-13 AMS System

¹⁸²Hf with half-life of about (8.90±0.09) Ma is an extinct radionuclide and can only be produced by a supernova explosion in nature. Therefore ¹⁸²Hf is an ideal candidate nuclide for the study on possible supernova explosions in the vicinity of the earth within the last 100 million years. In addition, ¹⁸²Hf is a long-lived radionuclide of particular interest for nuclear engineering. Accurate measurement of ultra-trace ¹⁸²Hf is very important for reactor design,studies on nuclear cosmo-physics and other fields. With an accelerator mass spectrometry (AMS), it is possible to detect the trace amounts of ¹⁸²Hf. In this paper, the detection method of ¹⁸²Hf with HI-13 AMS system at China Institute of Atomic Energy (CIAE) and the chemical procedures to reduce ¹⁸²W interference are presented. The energy and TOF two-dimension spectra of ¹⁸²Hf and ¹⁸³W for blank and a series of standard samples have been obtained, respectively. The ¹⁸²W contribution to the counts in ¹⁸²Hf peak was corrected by ¹⁸³W normalization. The detection sensitivity of this AMS facility for ¹⁸²Hf/¹⁸⁰Hf ratio measurement is about 4.15±10^－11 at present.     

Particle-Number Conserving Calculation for Low-Lying Excited High-K Multi-Quasiparticle Bands in 172,174Hf

Using the particle-number conserving method for treating the cranked shell model,the microscopic mechanism of the variation of the kinematic moments of inertia with rotational frequency ω for the rare-earth deformed nuclei ^172,174Hf is investigated. The observed J⁽¹⁾ and angular momentum alignment are reproduced satisfactorily in the PNC calculation,in which no free parameters are involved. The PNC analysis shows that the difference between the variations of J⁽¹⁾ with ω for the high K multi-quasiparticle bands and for ground state band is mainly due to the Pauli blocking effect of high j intruder orbitals near the Fermi surface.     

Developments in accelerator mass spectrometry (AMS) method for 182Hf

The present detection limit for ¹⁸²Hf at CIAE HI-13 AMS systems could not satisfy various applications (e. g. detection of a nearby supernovae signal). Therefore, techniques were developed in this work to improve the AMS measurement of ¹⁸²Hf mainly on building a new injector and using a method that based on solid-phase reaction for the preparation of HfF₄ samples from HfO₂. The experimental results show that mass resolution of the injector can reached 630, and the F^－/O－ and beam current of ¹⁸⁰HfF₅^－ for HfF₄ samples produced by dry method is about 2—3 times and 1.5 times of that by previously method, respectively.     

High-Spin States and Negative Parity Levels in Neutron-Rich 116,118,120Cd Nuclei

High spin states in neutron-rich ^116,118,120Cd nuclei have been investigated by observing high-fold prompt γ-ray coincidence events from the spontaneous fission of ²⁵²Cf with the Gammasphere detector array. The yrast bands have been extended with spin up to 18h in¹¹⁸Cd and 16h in ^116,120Cd respectively. The band structures are calculated using the cranked shell model and possible origination for the backbends in the yrast bands is discussed. Proposed 5^－ and 7^－ levels are observed in each of these cadmium isotopes, and possible explanation for the negative states is discussed based on systematic comparison. A quasi-rotational band based on 7^－ level in ¹¹⁸Cd has been established.     

Particle-Number Conserving Analysis for High K Multi-Quasiparticle Bands in Odd-A Deformed Nuclei 173,175Hf

Using the Particle-number Conserving (PNC) method for treating the cranked shell model, the high K multi-quasiparticle bands in odd-A deformed nuclei ^173,175Hf are analyzed, including the variation with rotational frequency of the moment of inertia, angular momentum alignment and occupation probability of each cranked Nilsson orbital. No free parameters are involved in the PNC calculation and the experimental results are reproduced well. The microscopic mechanism of the difference between the multi-quasiparticle high K bands and the yrast bands in neighboring even-even nuclei is investigated, where the blocking effects of high j intruder orbitals near the Fermi surface play a crucial role.     

新同位素175Er

简介首次合成新核素１７5Ｅｒ及对其衰变纲图测定的实验方法和实验结果． the synthesis and γ decay scheme of new isotope175Er is reported for the first time.The related experimental process and main results are represented briefly also.     

ON THE BACKBENDING MECHANISM OF MUITIBAND STRUCTURE IN NUCLEUS 185Pt

The observation of multi-band structure in nucleus ¹⁸⁵Pt reported recently,once again raises the open question about whether the alignment of proton h_9/2 pair or neutron i_13/2 pair should be responsible to the backbending in five band.Blocking experiments prefer the proton h_9/2 pair while the Total Rothian Surface calculation supports neutron i_13/2 pair.Based on the analysis of assumptions implied in both approaches,a new theoretical calculation which includes the dynamic effect of band crossing is presented.Such a calculation indicates that the alignment of proton h pair should be the main cause for the observed backbendings.     

Measurement of Neutron-Removal Cross Section of Neutron-Rich Nucleus 8He by Using the Transmission Method

The neutron-rich nucleus ⁸He is selected by RIBLL from the breakup of 50MeV/u ¹³C on be target at HIRFL. The 2n-removal and 4n-removal cross section of ⁸He was measured by using the transmission method. The point that ⁴He is ⁸He core can be reduced from the experiment data via the Ogawa's theory.