Session 4WEB: Perspectives for Decay Spectroscopy with Fast Fragmentation Beams II

Decay spectroscopy at the NSCL

The National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University has a long list of successful experimental programs in fast-beam decay spectroscopy. The programs included studies of the evolution of nuclear structure away from the valley of stability, decay studies that drive astrophysical phenomena, the use of decays to probe fundamental interactions, and many more. To achieve such a diverse program, the NSCL hosted a plethora of experimental equipment, including implantation detectors, γ-ray arrays for high resolution spectroscopy, total absorption spectrometers, proton detectors, time projection chambers, and more. In this talk I will attempt to give an overview of the experimental decay program at the NSCL and provide some specific examples and their scientific impact. Looking towards the future, the decay spectroscopy program at FRIB is built on the success of the NSCL experimental program. It is therefore crucial to learn from the experiences of the decay spectroscopy users, and move forward as a community to tackle new scientific challenges at FRIB.   

Decay spectroscopy of neutron-rich nuclei produced in multinucleon transfer reactions at KISS

Multinucleon transfer (MNT) reactions have gained renewed interest in recent years as they provide a pathway to access neutron-rich nuclei that are difficult to produce by other methods such as complete fusion and fragmentation [1]. Because MNT reactions produce a wide variety of nuclides around both the projectile and target nuclei with wide angular and energy distributions, the development of experimental techniques to collect, separate, and identify the reaction products of interest is essential to perform their decay spectroscopy. In particular, exotic nuclei that are far from the projectile or target nuclei are produced very infrequently and may be buried among more abundant reaction products. Furthermore, for short-lived nuclei with lifetimes of less than a few minutes, rapid isolation becomes critical.

  We are developing the KEK Isotope Separation System (KISS) focusing on the extraction of MNT reaction products at the RIBF facility of the RIKEN Nishina Center [2]. This is an argon-gas-cell-based laser ion source coupled with an isotope separation online system. All reaction products are efficiently collected and neutralized by argon gas, and nuclides of interest are element-selectively ionized by laser resonance method to be accelerated and mass-separated with a bipolar electromagnet for their high-purity decay spectroscopy. We have performed decay spectroscopy of neutron-rich nuclei of refractory elements near the N = 126 region. Recently, we extracted the neutron-rich actinide nuclei produced by MNT reactions with ²³⁸U beams to extend our spectroscopic studies to the neutron-rich actinide region.

In this presentation, we will report the experimental methods and results of KISS, including the perspective of decay spectroscopy on the upgrade plan KISS-II.

 

References

[1] Y.X. Watanabe et al., Phys. Rev. Lett. 115, 172503 (2015).

[2] Y. Hirayama et al., Nucl. Instrum. Meth. B 353, 4 (2015).   

First Experiments with the FDSi at FRIB

The Facility for Rare Isotope Beams (FRIB) will provide unprecedented access to exotic nuclei; approximately 80% of the isotopes predicted to exist up to uranium (Z = 92) will be produced. The FRIB Decay Station (FDS) — an efficient, granular, and modular multi-detector system designed under a common infrastructure — will have a transformative impact on our understanding of nuclear structure, nuclear astrophysics, fundamental symmetries, and isotopes of importance to applications. The FRIB Decay Station Initiator (FDSi), led by the FDSi Coordination Committee and supported by the FDSi Group and Working Groups, is the initial stage of the FRIB Decay Station (FDS). The FDSi is primarily an assembly of the best detectors currently available in the community within an integrated infrastructure for Day One FRIB decay studies, ultimately providing a means for FRIB users to conduct world-class decay spectroscopy experiments with the best equipment possible and to transition to the FDS without interruption to the user program. The FDSi infrastructure will remain intact at FRIB, ready to receive community detectors that will nominally travel. 

An overview of the FDSi, scientific program, and first year of operation will be given. This will include recently published results from the first FRIB experiment.