摘要:

The availability of fast radioactive beams offers the possibility for studies ofE1‐strength in projectiles via Coulomb excitation. Theoretical calculations predict that a significant fraction of this strength is shifted towards lower excitation energies in neutron‐rich systems (e.g., [1]). At the NSCL, virtual photon scattering was used to probe the discrete structure of both18O and20O for levels in the region between 1 and 8 MeV. Two 1−levels at 5.35(10) and 6.85(5) MeV were observed for the first time in20O [2]. The observed &ggr;‐ray spectrum for20O is, in fact, dominated by transitions resulting fromE1 excitations to these states. The extractedB(E1) ↑ values of ∼0.062(16) e2fm2and ∼0.035(9) e2fm2for the 5.35 and 6.85 MeV levels, respectively, are larger than shell model calculations predict [3, 4]. Such large dipole strengths are not observed for low‐lying 1−states in18O, indicating a shift of dipole strength towards lower energies as one approaches the neutron drip‐line. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556656

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The angular momentum projected Generator Coordinate Method, with the quadrupole moment as collective coordinate and the Gogny force as the effective interaction, is used to describe the properties of the ground state and low‐lying excited states of the even‐even Magnesium isotopes20–40Mg. It is found that the ground states of the N=2032Mg and N=2840Mg nuclei are deformed and therefore the corresponding shell closures are not preserved. Rather good agreement with experimental data for many observables is obtained. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556657

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Carbon and oxygen isotopes very close to the neutron drip‐line have been studied using in beam gamma spectroscopy with fragmentation reactions of radioactive secondary beams. No &ggr;‐ray transitions have been observed in both23O and24O suggesting that probably only the ground state of these two oxygen isotopes is bound with respect to particle emission. In the case of19C and20C only a single line has been observed in each of the corresponding &ggr;‐ray spectra. The interpretation of the results is made by comparison to shell model calculations. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556658

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

One‐nucleon removal reactions at relativistic energies have been used as spectroscopic tool to obtain information about the ground state properties of8B and23O. Using the FRS at GSI, the longitudinal momentum distributions of the emerging fragments after breakup and the one‐nucleon removal cross‐sections were measured. The relative contributions of the remaining fragments (7Be and22O) in their ground and excited states have been determined from measurements of &ggr; rays in coincidence with the longitudinal momentum distributions. In the8B case, the experimental breakup data on two different targets (C and Pb) allow a determination of the weight of the7Be*component in the8B ground state wave function as (13.3±2.2) &percent;. These results are discussed in the context of a theoretical three‐body model. Preliminary results on23O indicate a spin and parity assignment of 1/2+in agreement with shell model predictions. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556659

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Radioactive ion beams of 55 MeV11C from the BEARS project at LBNL and a thick‐target technique were used to study resonant states in12N. With a reaction in inverse kinematics an excitation function of elastic scattering cross section was measured in a single exposure covering the center of mass energy range between 300 keV to 1100 keV. The elastic scattering reaction11C(p,p)11C is related to the reaction11C(p,&ggr;)12N, an important branch point in the hot pp chains and a determinant of the evolution of supermassive stars. The data was analyzed using the R‐matrix code MULTI. Preliminary results suggests that the first excited state in12N (0.96 MeV) might play a more important role in determining the11C(p,&ggr;)12N reaction rate than previously believed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556660

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The radiative capture reaction involving heavy ions is a relatively unexplored reaction mechanism which affords the possibility of gaining insights into molecular structure in nuclei and exotic, highly‐deformed nuclear shapes. The12C(12C,&ggr;) reaction has been studied using an unconventional application of gamma‐ray spectroscopy using the Gammasphere array. A resonance for this reaction has been located for Ebeam=15.8 MeV. Favored population of the K=2 rotational band in24Mg as well as particular states around 10 MeV in excitation is observed. Using a Monte Carlo simulation of the previously uncharacterised high energy efficiency of Gammasphere, we set a lower limit on the cross‐section for the species of decays observed of 1&mgr;b. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556661

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The Rare Isotope Accelerator (RIA) is a next generation radioactive beam facility designed to provide experimental access to large unexplored regions of the nuclear landscape. To do this, RIA makes use of standard ISOL and in‐flight fragmentation technology together with novel approaches to handle high primary beam power and remove existing limitations in the extraction of short‐lived isotopes. The use of a versatile primary accelerator allows various production and extraction schemes to be used to optimize production of specific isotopes. These isotopes are then available for studies at ion source energy or can be further accelerated by a superconducting linac whose novel injection system allows the efficient acceleration from ion source energy of singly‐charged heavy ions with masses up to 240 amu. The high‐intensity radioactive beams at RIA will be made available to experimental areas spanning the energy regime from ion source energy to primary beam energy. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556662

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Gamma ray energy tracking is a new concept for detecting gamma rays. It can be implemented as a 4&pgr; array of highly segmented Ge detector, which would advance detection sensitivity by three orders of magnitude in certain applications. Such an array will provide tremendous discovery potential at current stable and exotic beam facilities, as well as at future facilities. The development of a tracking array for nuclear structure physics has brought together scientists from different areas. Technical advances made in the last 5 years have demonstrated that the construction of a gamma ray energy‐tracking array is feasible, and a plan for constructing a US array is in place. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556663

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Miniball is a dedicated Ge detector array which has been developed for the investigation of rare &ggr; decays at the new radioactive beam facility REX‐ISOLDE [1, 2] at CERN. The array is optimised for high full‐energy peak efficiency and for high granularity needed to perform Doppler corrections of &ggr;‐rays emitted by fast moving nuclei. Miniball will finally consist of 40 six‐fold segmented, encapsulated detectors which are clustered in eight cryostats with three detectors each and four cryostats with four detectors, respectively. It is shown that from an analysis of the pulse shapes and of the amplitudes of the mirror charges in the adjacent segments the effective granularity of Miniball can be enhanced from 240 to ≈ 4000. The properties of Miniball are compiled on the basis of experimental data. Examples of the first data measured with Miniball are presented. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556664

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The feasibility of the entire process of &ggr;‐ray tracking is demonstrated experimentally for the first time. The accurracy of the results is verified by the capability to carry out Doppler correction of &ggr;‐rays emitted in flight. The resolution of the 847.8 keV transition detected with the MARS detector after Coulomb excitation of a56Fe beam could be improved from 15 keV to below 5 keV (FWHM). © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1556665

出版商:AIP    

年代:1903

数据来源: AIP