Alpha Decay of the Neutron-deficient Isotopes 215,216U

The most neutron-deficient isotopes 215;216U were produced in the complete-fusion reaction 180W(40Ar, 4-5n)215,216U. Evaporation residues recoiled from the target were separated in-flight from the primary beam by the gas-filled recoil separator SHANS and subsequently identified on the basis of correlated -decay chains. Two -decaying states were identified in 216U, one for the ground state and the other for the isomeric state with 8+(h9=2f7=2) configuration. The -decay properties for 215;216U and the systematics of 8+ isomeric state in N =124,126 isotones were investigated.     

Production and Identification of New Isotope ^265Bh（Z=107）

New Isotope ^265Bh was produced in bombardment of a ^243Am target with 168 MeV 26Mg ions. The experiment was carried out at the Sector Focus Cyclotron of Heavy Ion Research Facility in Lanzhou in 2003. The reaction products were transported and collected by using helium-jet technique and a set of rotating wheel system. Identification was made by observation of correlated a-particles between the new isotope ^265Bh and its ^261Db and ^257Lr daughter nuclei. A parent-daughter searching mode was used to facilitate detection of α-α correlations. A total of four pairs of PIPS detector (200mm^2 active area) were used to measure the kinetic energy of a particles. The a particle energy resolution was about 40 keV for the top detectors and 100 keV for the bottom detectors because of energy degradation in the polypropylene foil.     

New empirical formula for(γ, n) reaction cross section near GDR peak for elements with Z ≥ 60

A new empirical formula has been developed that describes the(7,n) nuclear reaction cross sections for isotopes with Z ≥ 60.The results were supported by calculations using TALYS-1.6 and EMPIRE-3.2.2 nuclear modular codes.The energy region for incident photon energy has been selected near the giant dipole resonance(GDR) peak energy.The evaluated empirical data were compared with available data in the experimental data library EXFOR.The data produced using TALYS-1.6 and EMPIRE-3.2.2 are in good agreement with experimental data.We have tested and presented the reproducibility of the present new empirical formula.We observe the reproducibility of the new empirical formula near the GDR peak energy is in good agreement with the experimental data and shows a remarkable dependency on key nuclei properties:the neutron,proton and atomic number of the nuclei.The behavior of nuclei near the GDR peak energy and the dependency of the GDR peak on the isotopic nature are predicted.An effort has been made to explain the deformation of the GDR peak in(γ,n) nuclear reaction cross sections for some isotopes,which could not be reproduced with TALYS-1.6 and EMPIRE-3.2.2.The evaluated data have been presented for the isotopes ~(180)W,~(183)W,~(202)Pb,~(203)Pb,~(204)Pb,~(205)Pb,~(231)Pa,~(232)U,~(237)U and ~(239)Pu,for which there are no previous measurements.     

Multi-guasiparticle excitations of ~(91)Ru

The level structure in neutron-deficient nucleus 91Ru was investigated via the 58Ni(36Ar,2 plnγ)Ru reaction at a beam energy of 111 MeV.Charged particles,neutrons,and y-rays were emitted in this reaction and detected by the DIAMANT CsI ball,Neutron Wall,and the EXOGAM Ge clover array,respectively.In addition to the previously reported levels in 91Ru,new low-to-medium spin states were observed.Angular correlation and linear polarization measurements were performed to unambiguously determine spins and parities of the excited states in 91 Ru.The low-spin states of 91 Ru exhibit a scheme of multi-quasiparticle excitations,which is very similar to that of the neighboring N=47 isotone.These excitations have been interpreted in terms of the shell model.The calculations performed in the configuration space(p3/2,f5/2,p1/2,g9/2)reproduce the experimental excitation energies reasonably well,supporting the interpretation of the newly assigned positive-parity states in terms of the three quasiparticle configurationsπ(g9/2)^-2v(g9/2^-1 and v(g9/2)^-3.     

266Bh的α衰变性质研究(英文)

报道了利用兰州重离子研究装置提供的26Mg重离子束流轰击243Am靶产生和鉴别已知超重核素266Bh的实验结果。利用转轮收集探测装置依靠母子核遗传关系通过观测Bh同位素与其子核Db和Lr之间的α-α关联事件来鉴别266Bh。实验中观测到266Bh的α能量为（9.03 ± 0.08）MeV, 与日本理化学研究所在合成113号元素中第一个衰变链中观测到266Bh的α能量为9.07 MeV相近。 266Bh的半衰期为0.66+0.59-0.26 s, 从实验得到的Qα也符合Z=107的Qα随中子数变化的系统性。The isotope of 266Bh was produced and identified definitely in bombardments of 243Am target with 162 MeV 26Mg ions at HIRFL. Identification was made by observation of correlated α particle decays between the Bh isotopes and their Db and Lr daughters using a rotating wheel system. The measured α energy for 266Bh is (9.03±0.08) MeV, and this value close to the 9.07 MeV for 266Bh observed in the first chain of element 113 at RIKEN. The half life of 266Bh is 0.66+0.59 -0.26 s. The Qα value derived from this experiment fits well into the general trend in a “Qα N systematics” for the isotopes with Z = 107.     

60 MeV/u 18O离子同天然铀反应钡同位素截面的测定

通过60MeV/u18O离子照射天然铀靶产生Ba放射性同位素,使用BaCl2沉淀法从大量铀和其它反应产物混合物中分离出Ba.通过离线γ谱学方法测量了Ba样品的γ射线单谱,根据Ba同位素特征γ射线峰的强度及其它相关数据计算了Ba同位素的生成截面.发现在厚铀靶的情况下,缺中子Ba同位素仍有较高的截面. The radioactive Ba isotopes were produced by 60 MeV/u~(18)O ion bombardment of natural uranium. Ba was separated from U and the reaction product mixture by BaCl_(2) precipitation. The Ba fraction was measured by off-line γ-ray spectroscopy. The cross sections of the individual Ba isotope were calculation based on the intensities of the character γ-ray peaks of Ba isotopes and other relative information. It was found that the n-deficient Ba isotopes have higher cross sections using the thick uranium targets.     

Dependence of the cross sections for Ir isotopes on the values of Qgg in the heavy ion collision

¹⁹⁷Au were irradiated with 47 MeV/u ¹²C ions. Iridium was produced via the multinucleon transfer reactions in bombardments of ¹⁹⁷Au with ¹²C. and was separated radiochemically from Au and the mixture of the reaction products. The γ radioactivities of Ir isotopes were measured by using a HPGe detector. The production cross sections of Ir isotopes were determined from activities of Ir isotopes at the end of bombardment and the other relative data. It has been found that the cross sections for neutron-rich isotopes of iridium show an exponential dependence on the values of Q_gg. Our experimental results also demonstrate lack of correlation between the cross sections and Q_gg in the case of neutron-deficient isotopes of iridium. The fact can be explained from that neutron-rich isotopes of iridium were produced in the deep inelastic transfer reactions.     

Spectral property and its shape transition on 72—84Kr isotopes in microscopic core plus two—quasiparticle approach

By using a microscopic sdIBM-2+2q.p. approach, the levels of the ground-band, γ-band and partial two-quasi-particle bands for {}^{72-84}Kr isotopes are calculated. The data obtained are in good agreement with the recent experimental results, and successfully reproduce the nuclear shape phase transition of {}^{72-84}Kr isotopes at zero temperature. The ground-state band is described successfully up to J^π=18^+ and E_x=10.0MeV. Based on this model, the aligned requisite minimum energy has been deduced. The theoretical calculations indicate that no distinct change of nuclear states is caused by the abruptly broken pair of a boson, and predict that the first backbending of Kr isotopes may be the result of aligning of two quasi-neutrons in orbit g_{9/2}, which gains the new experimental support of the measurements of g factors in the {}^{78-86}Kr isotopes.     

Spectral property and its shape transition on ^72-84Kr isotopes in microscopic core plus two-quasiparticle approach

By using a microscopic sdIBM-2 2q.p, approach, the levels of the ground-band, 7-band and partial two-quasi-particle bands for ^72-84Kr isotopes are calculated. The data obtained are in good agreement with the recent experimental results, and successfully reproduce the nuclear shape phase transition of ^72-S4Kr isotopes at zero temperature.The ground-state band is described successfully up to J^π=18^ and Ex=10.0MeV. Based on this model, the aligned requisite minimum energy has been deduced. The theoretical calculations indicate that no distinct change of nuclear states is caused by the abruptly broken pair of a boson, and predict that the first backbending of Kr isotopes may be the result of aligning of two quasi-neutrons in orbit g9/2, which galus the new experimental support of the measurements of g factors in the ^78-86Kr isotopes.     

Cross-section prediction for isotopes near neutron drip line in ~(70, 80)Zn projectile fragmentation reactions

The cross sections for ~(59,60)Ca, recently measured in the 345 A MeV ~(70)Zn+~9 Be reaction,were estimated using the FRACS parametrization and an empirical formula,which are in good agreement.The FRACS parametrization and the empirical formula are combined to predict the cross sections for extreme calcium isotopes ~(66,70)Ca in the~(70,80)Zn+~9 Be reactions at the incident energies of ~(60,80),and 345 A MeV.The dependence of emperical formula parameters on the reaction system,as well as the incident energy,are discussed.The results indicate that ~(66,70)Ca can be discovered in reactions of ~(60,80)A MeV ~(80)Zn+~9 Be.The predicted binding energy for extreme neutron-rich isotopes by the spherical relativistic continuum Hartree-Bogoliubov theory was adopted in the calculation.Hence,the planned Beijing Isotope-Separation-On Line Neutron-Rich Beam Facility(BISOL),which is a third generation radioactive ion beam facility,could provide the opportunity to discover ~(66,70) Ca and neighboring neutron-drip line nuclei.     

Binding energies of near proton-drip line Z = 22-28 isotopes determined from measured isotopic cross section distributions

A new method is proposed to determine the binding energy(B)of near proton-drip line isotopes from isotopic cross section distribution.To determine B of Z=22-28 isotopes(with T_z=-2 and-5/2),the lack of cross sections for proton-rich isotopes in the 345A MeV~(78)Kr+~9Be is overcome by predicting the proton-rich isotopes from a newly discovered scaling phenomenon found in the proton-rich isotopes measured in the 140A MeV~(40,48)Ca(~(58,64)Ni)+~9Be reactions.The cross sections for proton-rich isotopes are verified to exponentially depend on the average binding energy per nucleon,based on which B of the Z=22-28 isotopes with T_z=-2 and-5/2 are determined from cross sections.The determined B of the isotopes are justified from obeying the scaling phenomenon of the difference between the mass of mirror nuclei.The cross sections for the Z=22-28 isotopes with T_z=-1 and-3/2,which in potential can be experimentally studied in mass storage ring,are also predicted.     

Experimental determination of one-and two-neutron separation energies for neutron-rich copper isotopes

A method is proposed to determine the one-neutron S_n or two-neutron S_(2n) separation energy of neutronrich isotopes.Relationships between S_n(S_(2n)) and isotopic cross sections have been deduced from an empirical formula,i.e.,the cross section of an isotope exponentially depends on the average binding energy per nucleon B/A.The proposed relationships have been verified using the neutron-rich copper isotopes measured in the 64 A Me V ~(86)Kr+~9Be reaction.S_n,S_(2n),and B/A for the very neutron-rich ~(77,78,79)Cu isotopes are determined from the proposed correlations.It is also proposed that the correlations between S_n,S_(2n) and isotopic cross sections can be used to find the location of neutron drip line isotopes.     

Possibilities for synthesis of new neutron-deficient isotopes of superheavy nuclei

This study investigates the optimal projectile/target combination for the production of new neutron-deficient isotopes of superheavy nuclei(SHN). To this end, the dependence of the evaporation residue cross-section(ERCS) used to synthesize SHN on the mass asymmetry and the isospin of colliding nuclei are analyzed within the dinuclear system(DNS) concept. The predicted ERCSs for the production of new neutron-deficient isotopes of SHN were found to be quite large with the ~(36) S projectile, and the cross-section of SHN decreases slowly with the charge of compound nuclei owing to the increase in their survival probability,. Wsur is not canceled by the decreasing probability, PCN, that the system will evolve from a touching configuration to the compound nucleus in competition with the quasifission process.     

Fragment distribution in ~(78,86)Kr+~(181)Ta reactions

Within the framework of the isospin-dependent quantum molecular dynamics model, along with the GEMINI model, the ~(86)Kr+~(181)Ta reaction at 80, 120 and 160 MeV/nucleon and the ~(78)Kr+~(181)Ta reaction at 160 MeV/nucleon are studied, and the production cross sections of the generated fragments are calculated. More intermediate and large mass fragments can be produced in the reactions with a large range of impact parameter. The production cross sections of nuclei such as the isotopes of Si and P generally decrease with increasing incident energy.Isotopes near the neutron drip line are produced more in the neutron-rich system ~(86)Kr+~(181)Ta.     

Neutron drip line of Z=9–11 isotopic chains

A recent experimental breakthrough identified the last bound neutron-rich nuclei in fluorine and neon isotopes. Based on this finding, we perform a theoretical study of Z = 9, 10, 11, 12 isotopes in the relativistic mean field(RMF) model. The mean field parameters are assumed from the PK1 parameterization, and the pairing correlation is described by the particle number conservation BCS(FBCS) method recently formulated in the RMF model. We show that the FBCS approach plays an essential role in reproducing experimental results of fluorine and neon isotopes. Furthermore, we predict ~(39)Na and ~(40)Mg to be the last bound neutron-rich nuclei in sodium and magnesium isotopes.     

Measurement of the ~2H(~7Be,~6Li)~3He reaction rate and its contribution to the primordial lithium abundance

In the standard Big Bang nucleosynthesis(SBBN) model, the lithium puzzle has attracted intense interest over the past few decades, but still has not been solved. Conventionally, the approach is to include more reactions flowing into or out of lithium, and study the potential effects of those reactions which were not previously considered.~7Be(d,~3He)~6Li is a reaction that not only produces~6Li but also destroys~7Be, which decays to~7Li, thereby affecting~7Li indirectly. Therefore, this reaction could alleviate the lithium discrepancy if its reaction rate is sufficiently high.However, there is not much information available about the~7Be(d,~3He)~6Li reaction rate. In this work, the angular distributions of the~7Be(d,~3He)~6Li reaction are measured at the center of mass energies Ecm = 4.0 Me V and 6.~7Me V with secondary~7Be beams for the first time. The excitation function of the~7Be(d,~3He)~6Li reaction is first calculated with the computer code TALYS and then normalized to the experimental data, then its reaction rate is deduced. A SBBN network calculation is performed to investigate its influence on the~6Li and~7Li abundances. The results show that the~7Be(d,~3He)~6Li reaction has a minimal effect on~6Li and~7Li because of its small reaction rate. Therefore,the~7Be(d,~3He)~6Li reaction is ruled out by this experiment as a means of alleviating the lithium discrepancy.     

Oscillatory extraction — New method of similar elements and isotopes separation

The new separation extraction method was created based on oscillatory extraction/stripping process in two extractors coupled by bulk liquid membrane (LM). The experimental setup to investigate the kinetics of non-stationary processes was built in Saint Petersburg State Institute of Technology in the Rare Earth Department. To induce the oscillatory extraction-stripping process the cyclic Belousov-Zhabotinsky (BZ) reaction or cyclic electrochemical oxidation-reduction was used. The possibility to use oscillatory extraction approach to separate similar elements by using the differences in their kinetic properties is demonstrated. The experimental evidences of uranium, cerium and neodymium isotopes separation were obtained. The separation of ¹⁴²Ce and ¹⁴⁰Ce isotopes between aqueous phases of two extractors coupled by bulk LM in the experiments with cyclic chemical oxidation/reduction with enrichment factor about 2.5% was observed. Under the same conditions the separation of the Nd isotopes (heavy isotopes of Nd — ¹⁴⁴Nd, ¹⁴⁵Nd, ¹⁴⁶Nd, ¹⁴⁸Nd, and ¹⁵⁰Nd from the light isotope — ¹⁴³Nd) in the same experiment with enrichment factor about 0.7–1.4% was observed.     

Physical preseparation for chemistry experiments

The availability of physically preseparated isotopes for chemistry experiment opens up completely new possibilities, especially for chemical investigations of transactinide elements. Many restrictions present in conventional methods that were used very successfully in the past can be overcome by using preseparated isotopes. An overview of experiments that were performed with preseparated isotopes is given. Studies of β-diketonates of group 4 elements are described in some more detail and used as an example to demonstrate the power of the method. Production of preseparated long-lived transactinide isotopes is outlined and, lastly, the new preseparator TASCA which is currently being installed at GSI, Darmstadt, is briefly described.