Post-accelerated Radioactive Ion Beams Research Articles

Opportunities for nuclear reaction studies at future facilities

Opportunities for investigations of nuclear reactions at the future nuclear physics facilities such as radioactive ion beam facilities and high-power laser facilities are considered. Post-accelerated radioactive ion beams offer possibilities for study of the role of isospin asymmetry in the reaction mechanisms at various beam energies. Fission barrier heights of neutron-deficient nuclei can be directly determined at low energies. Post-accelerated radioactive ion beams, specifically at the future facilities such as HIE-ISOLDE, SPIRAL-2 or RAON-RISP can be also considered as a candidate for production of very neutron-rich nuclei via mechanism of multi-nucleon transfer. High-power laser facilities such as ELI-NP offer possibilities for nuclear reaction studies with beams of unprecedented properties. Specific cases such as ternary reactions or even production of super-heavy elements are considered.

Nuclear-Structure Physics with MINIBALL at HIE-ISOLDE

The MINIBALL spectrometer utilizes successfully a variety of post-accelerated radioactive ion beams provided by the new HIE-ISOLDE accelerator at CERN. In-beam γ-ray spectroscopy after Coulomb excitation (CE) or transfer reactions is performed with optimized setups of ancillary detectors for particle detection. The physics program covers a wide range of shell model investigations. Exotic heavy ion beams will enable unique studies of collective properties up to the actinide region. First data taking with HIE-ISOLDE beams started recently. The higher energies and intensities of the new post-accelerator provides a promising perspective for a new generation of MINIBALL experiments. Intriguing first results were obtained by employing beams of 74,76,78Zn, 110,132Sn, 144Xe with beam energies in the range of 4.0 - 5.5 MeV/u for CE experiments at ‘safe’ energies. In all cases first results for various B(Eλ) values for these isotopes were obtained.

Neutron effective single-particle energies above Ni78 : A hint from lifetime measurements in the N=51 isotones Se85 and Kr87

Background: While the N=50 shell-gap evolution towards Ni78 is presently in the focus of nuclear structure research, experimental information on the neutron effective single-particle energy sequence above the Ni78 core remain scarce. Direct nucleon-exchange reactions are indeed difficult with presently available post-accelerated radioactive-ion beams (especially for high orbital-momentum orbitals) in this exotic region. Purpose: In this study we probe the evolution of the ν1g7/2 effective single-particle energy which is a key to understanding the possible evolution of the spin-orbit splitting due to the proton-neutron interaction in the Ni78 region. To achieve this goal, a method based on lifetime measurements is used for the first time. The obtained lifetimes of the 7/21+ states in Kr87 and Se85 are used to investigate the ν1g7/2 evolution. Method: Yrast and near-yrast states in the light N=51 isotones Se85 and Kr87 were populated via multinucleon transfer reactions, using a Se82 beam and a U238 target at the LNL tandem-ALPI facility. The prompt γ rays were detected by the AGATA Demonstrator and particle identification was performed using the PRISMA spectrometer. Lifetime measurements were performed by using the Cologne plunger device for deep inelastic reactions and the Recoil Distance Doppler Shift technique. Results: We obtain τ(7/21+)=0.4−0.4+1.6 ps for Kr87. In the case of Se85 an upper limit of 3(2) ps is obtained for the τ7/21+ value. Conclusion: For Kr87, the measured (7/21+) lifetime is consistent with a core-coupled 2+⊗ν2d5/2 configuration for this state. This result is consistent with that obtained by direct reaction, which validates our method. For Se85, the measured 7/21+ lifetime limit indicates a very small contribution of the ν1g7/2 configuration to the wave function of this state.8 MoreReceived 13 December 2016Revised 20 June 2017DOI:https://doi.org/10.1103/PhysRevC.96.044320©2017 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasEnergy levels & level densitiesLifetimes & widthsNuclear structure & decaysShell modelProperties59 ≤ A ≤ 89Nuclear Physics

Injected 1+ ion beam as a diagnostics tool of charge breeder ECR ion source plasmas

Charge breeder electron cyclotron resonance ion sources (CB-ECRIS) are used as 1+ →n+ charge multiplication devices of post-accelerated radioactive ion beams. The charge breeding process involves thermalization of the injected 1+ ions with the plasma ions in ion–ion collisions, subsequent ionization by electron impact and extraction of the n+ ions. Charge breeding experiments of 85Rb and 133Cs ion beams with the 14.5 GHz PHOENIX CB-ECRIS operating with oxygen gas demonstrate the plasma diagnostics capabilities of the 1+ injection method. Two populations can be distinguished in the m/q-spectrum of the extracted ion beams, the low (1+ and 2+) charge states representing the uncaptured fraction of the incident 1+ ion beam and the high charge states that have been captured in ion–ion collisions and subsequently charge bred through electron impact ionization. Identification of the uncaptured fraction of the 1+ ions allows estimating the lower limit of ion–ion collision frequency of various charge states in the ECRIS plasma. The collision frequencies of highly charged ions (∼107 Hz) are shown to exceed their gyrofrequencies (∼106 Hz) at least by an order of magnitude, which implies that the dynamics of high charge state ions are dictated by magnetically confined electrons and ambipolar diffusion and only low charge state ions can be considered magnetized. Furthermore, it is concluded that the plasma density of the ECRIS charge breeder is most likely on the order of 1011 cm−3 i.e. well below the critical density for 14.5 GHz microwaves.

Coulomb excitation of exotic nuclei at REX-ISOLDE with MINIBALL

In this contribution nuclear structure studies with post-accelerated radioactive ion beams from the REX-ISOLDE facility at CERN are presented. The method employed is γ -ray spectroscopy with the MINIBALL array following “safe” Coulomb excitation. Recent results concerning the investigation of nuclear shapes are presented and discussed.

Low-energy radioactive ion beam induced nuclear reactions

Low-energy post-accelerated radioactive ion beams have been used to study nuclear reactions addressing important nuclear structure and nuclear astrophysics questions. A high-granularity, large-solid-angle silicon strip detector array has been used to account for the low reaction products' yields. First experiments using a He beam on thin C targets show the feasibility of direct reaction studies with good angular resolution and a detection limit in access of 0.1 mb cross sections. The measurement of the six -decay channel in a N-induced reaction on a B target shows the capabilities of this experimental technique even for sophisticated reaction studies. The study of stellar properties in ground-based experiments, in particular break-out reactions from the hot-CNO, i.e. Ne, can be pursued using these beams. Experiments are being performed to study these reactions by measurement of O and , which might provide an alternative breakout route.