9th SUNFLOWER Workshop

Friday 28 Jul 2023, 09:00 → 17:00 Europe/London

ISA on Campus East, Room 135 (University of York)

Pieter Doornenbal (RIKEN)

The 9th SUNFLOWER workshop will take place at the University of York, UK and online via ZOOM on the 28th of July 2023. The meeting's main purpose is to discuss the current status and future in-beam gamma-ray spectroscopy experiments at the RIBF.

Presentations and discussions about current and future detector developments related to in-beam gamma-ray spectroscopy will be held. Current status from previous in-beam gamma experiments are encouraged to be presented. In addition, proponents intending to submit a SUNFLOWER proposal to the next Program Advisory Committee for Nuclear Physics experiments at RIBF held this December, are expected to attend the workshop and present their ideas.

This workshop will be followed by the symposium on "Direct reactions and spectroscopy with hydrogen targets: past 10 years at the RIBF and future prospects"  to be held at the Hilton Hotel York from July 31st to August 4th 2023. Results involving DALI2+ and MINOS are encouraged to be presented at that symposium. 

09:00 → 09:10 Welcome

Speaker: Marina Petri

09:10 → 09:40 Status of Sunflower

Speaker: Pieter Doornenbal (RIKEN)

09:40 → 10:20 Overview of the HiCARI project at the RIBF

In-beam gamma-ray spectroscopy at the Radioactive Isotope Beam Factory (RIBF), RIKEN, Japan has primarily been carried out in the moderate energy resolution regime using the high-efficiency NaI array DALI2. To perform high-resolution gamma-ray spectroscopy, a high-purity germanium array, known as the HIgh-resolution Cluster Array at the RIBF (HiCARI), was realised at the RIBF. The array comprised six Miniball detectors, two GRETA-type tracking detectors, and four clover detectors sourced from around the world.

Three experimental campaigns, exploring many key regions of the nuclear chart, were carried out during 2020 and 2021, yielding excellent preliminary results across a range of physics topics. This talk will provide details of the HiCARI configuration, the physics cases addressed, and some preliminary results from the campaigns.

Speaker: Frank Browne (RIKEN Nishina Center)

10:20 → 10:50 Coffee Break

10:50 → 11:20 Status and Results of NP1612-RIBF149 and NP1712-RIBF162

Speaker: Andrea Jungclaus (Instituto de Estructura de la Materia - CSIC)

11:20 → 11:50 Coulomb excitation of N=52 isotones towards 100Sn

Report on the NP1712-RIBF153R1

Speaker: Martha Liliana Cortes (RIKEN Nishina Center)

11:50 → 12:20 Coulomb excitation of the semi-magic nucleus 130Cd

Speaker: He Wang (RIKEN)

12:20 → 13:30 Lunch Break

13:30 → 13:50 Evolution of collectivity in the N=50 isotones towards 100Sn

We propose to measure the reduced transition probabilities B(E2; 0+g.s.→2+1) of 96Pd and 98Cd by means of inelastic scattering at intermediate energies. The radioactive 96Pd and 98Cd beams are produced by fragmentation of a 345 MeV/u 124Xe beam on a 9Be target. The isotopes of interest are selected and identified with the BigRIPS separator, then impinged on the secondary target. A Au and a Be secondary targets are used for the inelastic scattering. The gamma-rays emitted from the excited states are measured with the DALI2+ array, and the outgoing particles are identified with the ZeroDegree Spectrometer. The cross sections populating to the 2+1 states on the Au and the Be targets are extracted from the observed gamma-ray intensities. The excitation of the 2+1 state is caused by both the electromagnetic and the nuclear interaction between target and projectile. To extract the reduced transition probability B(E2), reaction model calculations will be performed and the nuclear deformation length and B(E2) value for the projectile nucleus will be adjusted to reproduce simultaneously the measured cross sections on the Au and the Be targets.

The 96Pd and 98Cd are only 4 and 2 valence protons below the doubly magic 100Sn. The measurement of this experiment will allow for a detailed comparison of the nuclear structure between the 56-78Ni (Z=28) isotopes versus the 78Ni-100Sn (N=50) isotonic chain, both regions sharing the same p3/2, f5/2, p1/2 and g9/2 orbitals for valence neutrons and protons, respectively. The shell model calculations in the f5/2, p, g9/2 model space in Ref.[1] predict a decrease of collectivity towards the complete occupation of the g9/2 orbitals, with B(E2; 2+1→0+g.s.) value of about 150 e2fm4 for 98Cd. Nevertheless, it is well known that the single-particle d5/2 orbital above the magic number 50 for neutrons and protons, together with the quasi-SU3 partner g9/2 can give rise to collectivity [2]. In Ref.[2], it is suggested that the findings of B. Cederwall and collaborators in 92Pd [3] indicates the necessity to consider the d5/2 orbital above the magic number 50 to describe the nuclei in this region. With the B(E2) measurements of this experiment, the role of the d5/2 orbital in the structure of the nuclei approaching 100Sn will be explored.

[1] R. M. Pérez-Vidal, et al., Phys. Rev. Lett. 129, (2022) 112501
[2] A. P. Zuker, et al., Phys. Rev. C 92, (2015) 024320
[3] B. Cederwall, et al., Nature (London) 469, (2011) 69

Speaker: Dr Sidong Chen (University of York)

13:50 → 14:10 Intermediate-energy Coulomb excitation of 94Ru, 96Pd, and 98Cd

$^{94}$Ru, $^{96}$Pd, and $^{98}$Cd are semi-magic isotones with N=50, and their B(E2;0+ $\to$ 2+) values are still missing or with large uncertainty. We propose an experiment to measure the B(E2;0+ $\to$ 2+) of these isotones by means of intermediate-energy Coulomb excitation. These results will help to verify the seniority scheme in the g9/2 shell. The measurement of $^{98}$Cd will also help us to understand the relatively larger B(E2;0+ $\to$ 2+) observed in $^{102-106}$Sn. In $^{94}$Ru and $^{96}$Pd, it may be possibly to observe Coulomb excitation from the isomeric states.

Speaker: Liu Xiaoyu (The University of Hong Kong)

14:10 → 14:30 Ideas for the next PAC

The Atomki group would like to propose two ideas for the next PAC. (1) Shape evolution of proton-rich nuclei beyond the N=Z line, (2) study of sulfur and silicon isotopes reaching the neutron drip line.

Specifically, we intend to propose to investigate the proton and neutron distribution in 58Zn, 62Ge, and 66Se as well as the matter deformation in 52Ni, 56Zn, and 60Ge. For the neutron-rich nuclei, we plan to map the low-lying states of 46,47,48Si as well as that of the 43,44Si isotopes.

Speaker: Zoltan Elekes (MTA ATOMKI)

14:30 → 14:50 Coffee Break

14:50 → 15:20 New Scintillation Array

Speaker: Pieter Doornenbal (RIKEN)

15:20 → 16:00 Discussion