摘要:

We report on the first application of the TDPAD method to measure the g factor of neutron‐rich isomeric states, produced and aligned in a projectile fragmentation reaction. The feasibility of similar measurement opens up a new, unexplored region of the nuclear chart for studies of the magnetic moments of microsecond isomers. Nuclei around68Ni were produced following the fragmentation of 61.6 MeV/u76Ge on a 145 mg/cm2Be target. The isotopes of interest were selected using the LISE spectrometer at GANIL, Caen, France, and were implanted in a high purity Cu foil fixed between the poles of an electromagnet. Two Ge Clover detectors, positioned in a plane perpendicular to the holding magnetic field, were used to observe the rotation of the nuclear spin ensemble and to derive the experimental R(t) function. The experimental result for the isomer in67Ni (J&pgr;= 9/2+, T1/2= 13.3 &mgr;s, Ex= 1007 keV), |g| = 0.125(6), is presented herein and is also compared to the theoretical expectations. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556646

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

An experiment was performed at GANIL to observe isomeric‐ and beta‐delayed gamma rays from very neutron‐rich nuclei around74Ni. Fragmentation products of the86Kr beam at 58 AMeV were studied using new devices: the LISE 2000 spectrometer and detectors from the EXOGAM germanium array. The primary aim of the experiment was to find the 8+microsecond isomer in76Ni and to perform beta decay spectroscopy of Co nuclei. We have successfully measured the beta delayed gammas from the decay of72Co to72Ni. The energies for the lowest excited states in72Ni are proposed, with the first 2+state at 1096 keV. These findings suggest a solution of the problem of the disappearance of the 8+isomer in72Ni. We also measured beta decay of other neutron‐rich Co isotopes including70Co. First evidence was found for a new short lived isomer, most likely the I&pgr;=8+state, in76Ni. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556647

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We review the experimental data on binding‐energy differences for nuclei along theN = Zline with emphasis on the odd‐odd nuclei. Qualitative pair blocking arguments are used to discuss the effect ofnppairing correlations. Calculations based on a single‐jshell model support these general arguments that seem to rule out the formation of a condensate of isoscalarnppairs. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556648

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The N = Z nucleus70Br has been investigated using a variety of reactions, beam energies and experimental techniques. A rather complete decay scheme has emerged, with low‐lying configurations of fp‐shell parentage based on the J = 0 groundstate and g‐shell parentage based on the J = 9 &bgr;‐decaying isomer, which is placed at 2293 keV. Comparison with other odd‐odd nuclei shows a surprisingly low‐level density in the first MeV of excitation energy. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556649

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Big Ge‐arrays like Euroball or Gasp have been built with the main purpose of studying high angular momentum phenomena in nuclei. When coupled with ancillary detectors they became also excellent instruments to explore the properties of very exotic nuclei far from &bgr;‐stability. A large fraction of the experiments has been therefore devoted to study both proton‐rich and neutron‐rich nuclei populated using stable beams provided by the Legnaro and Strasbourg accelerators. Nuclei lying close to the N=Z line are of particular interest being a laboratory where collective excitations as well as fundamental properties of the nuclear force can be tested, like isospin symmetry and isospin breaking terms, proton neutron pairing, dripline effects. Due to their special symmetry they allow to test nuclear models. An example is the impact of nuclear physics calculations on the predictions of the standard model of the electro‐weak interaction which requires unitarity for the Cabibbo‐Kobayashi‐Maskawa (CKM) matrix. Available data suggest that the CKM matrix fails the unitarity test, pointing to physics beyond the standard model. Since such result depends on corrections for nuclear isospin mixing which must be calculated for heavy N=Z nuclei it is very important to test experimentally the model predictions. The isospin mixing probability can be determined using isospin forbidden &ggr; transitions. If the charge symmetry of the nuclear force is exact, in the limit of long wavelengths, the E1 transition operator is purely isovector and therefore E1 transitions are forbidden in N=Z nuclei between states of equal isospin and have equal strength in mirror nuclei. Failure of this symmetry rule due to the isospin non conserving Coulomb interaction can be experimentally observed as an apparent “induced isoscalar term” through the presence of forbidden E1 transitions. An alternative method to test isospin symmetry is based on the investigation of the electromagnetic decay properties in mirror pairs. In such a case the determination of the isovector and isoscalar components of E1 transitions allow higher sensitivity compared to the determination of the transition probability of forbidden transitions in N=Z nuclei as a consequence of the interference between forbidden and allowed strengths. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556650

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

High‐spin states have been studied in72,73Kr using40Ca+40Ca and36Ar+40Ca reactions at 160, 164 and 145 MeV respectively. The properties and configurations of the bands observed are interpreted with the aid of unpaired cranked Nilsson‐Strutinsky/ cranked relativistic mean‐field calculations and paired total routhian surface and cranked relativistic Hartree‐Bogoliubov calculations. In73Kr the three previously known structures have been extended to a spin of ∼30ℏ and a fourth structure, which is believed to be the signature partner to the g9/2band, has been identified. The negative parity bands show evidence for an unusual type of band crossing. It is currently unclear whether this is a consequence of T=0 n‐p pairing. At the highest spins the unpaired calculations can reproduce the observed data, suggesting that there is little evidence for pairing correlations in this spin regime. In72Kr a new band has been identified that has the properties expected from the missing doubly aligned S‐band configuration. The properties of this band can be reproduced by the unpaired CNS/ CRMF calculations, again suggesting that the structure has little pairing. However, paired calculations appear to be necessary to reproduce the properties of the previously known structure in this nucleus. The72Kr results are also compared with projected shell model calculations. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556651

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Isospin mixing of excited states with isospin quantum numbersT= 0 andT= 1 in odd‐odd N=Z nuclei is analyzed. The measuredE2/M1 multipole mixing ratios and the branching ratios are used to estimate the degree of isospin breaking in54Co. The interference of the isospin and K‐quantum number selection rules in46V is examined. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556652

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The masses of very neutron‐deficient66As,68,70,71Se and71Br were measured for the first time and those of64,65Ge and67As remeasured, with total uncertainties ranging from 200 to 1000 keV, including systematic, extrapolation and statistical errors, using the SPEG direct time‐of‐flight method at GANIL. These new results are discussed and compared to other recent experimental data and mass predictions. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556653

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

It has been demonstrated that single‐nucleon knockout reactions in inverse kinematics at energies above 50 MeV/nucleon are a powerful spectroscopic tool for identifying single‐particle structure. Partial and differential cross sections to individual final levels are obtained by measuring the momentum of the projectile residue with a high‐resolution spectrograph in coincidence with gamma rays. The shape of the longitudinal momentum spectra identifies the orbital angular momentuml, while the absolute cross sections determine single‐nucleon spectroscopic factors. Examples of results with this technique are given. The method has an extremely high sensitivity, and experiments have been carried out with incident beams of less than one atom/second. An analysis of precise data from high‐energy experiments suggests that the method furnishes absolute occupancies and will allow the study of short‐range correlations caused by the hard core in the nucleon‐nucleon interaction. For the deeply boundp‐shell neutron states of16O and12C the occupancies are reduced by factorsRsof 0.56(3) and 0.51(3), respectively, relative to the many‐body shell model with effective interactions. Data for weakly bound neutron and proton states in radioactive nuclei suggestsRsvalues much closer to unity. We expect that the nuclear knockout method, in addition to being a tool for structure studies, will contribute to the understanding of the fundamentals of the shell model. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556654

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The one neutron removal from a secondary beam of14Be at 35MeV/A, produced at the LISE3 spectrometer, GANIL, has been used to study the near‐threshold structure of the unbound nucleus13Be. The relative energy in the12Be + n system has been reconstructed and suggests significant s‐wave strength in addition to a previously suggested d‐wave resonance at around 2MeV. The momentum distribution of the reconstructed13Be, parallel to the beam direction, consists of at least two components and requires the inclusion of d‐wave strength in the single‐particle structure of14Be, although it does not rule out the inclusion of p‐wave strength. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556655

出版商:AIP    

年代:1903

数据来源: AIP