SUNFLOWER Workshop

2 Sept 2025, 08:00 → 4 Sept 2025, 18:40 Asia/Shanghai

 

This workshop serves as a platform for discussing the ongoing and upcoming SUNFLOWER and experiments conducted at the Radioactive Isotope Beam Factory (RIBF) of the RIKEN Nishina Center and discuss first in-beam gamma experiments at the High Intensity Heavy-ion Accelerator Facility (HIAF) of the Institute of Modern Physics of the Chinese Academy of Sciences.

Our objectives for this collaborative workshop are multi-faceted, including:

i) Providing updates on the SUNFLOWER and collaboration.

ii) Presenting comprehensive reports on past experiments.

iii) Exploring new physics proposals and innovative concepts for the next NP-PAC.

iv) Offering insights into new projects and advancements such as HYPATIA and GT-5.

v) First in-beam gamma experiments at HIAF.

The workshop will be carried out in hybrid form (ZOOM and on-site) and will follow an engaging format with presentations and interactive discussions for two days, and a one-day facility tour of the HIAF.

Tuesday 2 September

15:00 → 15:10 Welcome

Speaker: He Wang

15:10 → 15:30 Overview of Sunflower

Speaker: Pieter Doornenbal (RIKEN)

15:30 → 15:50 Overview HYPATIA

Speaker: Stefanos Paschalis

15:50 → 16:10 GAGG Development

Speaker: William Marshall (University of York)

16:10 → 16:30 CeBr3 development

Speaker: Luke Tetley

16:30 → 16:50 Break

16:50 → 17:10 GT-5 status and future directions

In-beam gamma-ray spectroscopy is a powerful experimental tool for elucidating the structure of unstable nuclei and has served as a major workhorse at radioactive beam facilities. The high resolution, enabled by the use of tracking Ge detectors, will further enhance spectroscopic capabilities and broaden the scope of experimental explorations. This was exemplified by the HiCARI campaign, which combined available Ge detectors, including those possessing the gamma-ray tracking capability, and high-quality radioactive beams at RIBF. Following the success of this experimental campaign in 2020, a new GRETINA-type tracking detector module has been delivered to RIBF and the first experiments are planned to begin in the near future. The project is named GT-5 and it is funded as part of the RIKEN Transformative Research Innovation Platform (TRIP). The current status of the tracking detectors, results of simulation studies, and future directions will be discussed.

Speaker: Nori Kitamura

17:10 → 17:30 RIBF170R1 I

Speaker: Sidong Chen

17:30 → 17:50 RIBF170R1 II

Speaker: Heather Crawford

17:50 → 18:10 RIBF181 I

Speaker: Massyl Kaci (IJCLab)

18:10 → 18:30 Break

18:30 → 18:50 RIBF181 II

Speaker: William Marshall (University of York)

18:50 → 19:10 RIBF196

Speaker: Freddy Flavigny

19:10 → 19:30 RIBF190

Speaker: Usama Ahmed (Institute for nuclear physics, TU Darmstadt)

19:30 → 19:50 In-beam gamma-ray spectroscopy of 136Te within the HiCARI project

With the arrival of the HiCARI campaign [1] to the RIBF facility at RIKEN (Japan), a series of in-beam gamma ray spectroscopy experiments was performed in order to expand the previous spectroscopic information on exotic, neutron-rich nuclei of intermediate mass.

Previously, incompatible results regarding the reduced transition probability for the decay of the first excited 2+ state, B(E2), in 136Te were reported from Coulex experiments and direct lifetime measurements using the fast-timing technique [2-5]. Due to the better energy resolution of the Ge detectors forming the HiCARI array, as compared to the previously used DALI2 NaI(Tl) array [6], in experiment NP1912-RIBF193 it was possible to extract, from the same data set, B(E2) values from the cross sections measured for the inelastic excitation on Au and Be targets on the one hand and the analysis of Doppler-shifted lineshapes on the other. The new results shed light on the conflict between transition strengths derived from Coulex and lifetime measurements reported for several nuclei in the literature.

In addition, lifetimes of additional excited states of 136Te populated following one-neutron removal from 137Te were measured, some of them for the first time, and others with smaller uncertainty compared to previous works, highlighting the potential of high resolution detectors in in-beam gamma spectroscopy experiments.

References

[1] https://www.nishina.riken.jp/collaboration/SUNFLOWER/devices/hrarray/index.php, accessed 12-01-2024
[2] J. M. Allmond et al., Phys. Rev. Lett. 118, 092503 (2017)
[3] M. Danchev et al., Phys. Rev. C 84, 061306(R) (2011)
[4] L.M. Fraile et al., Nucl. Phys. A 805, 218 (2008).
[5] V. Vaquero et al., Phys. Rev. C 99, 034306 (2019)
[6] S. Takeuchi et al., Nucl. Instr. Meth. A 763, 596 (2014)

Speaker: Jaime Acosta (CSIC)

Wednesday 3 September

15:00 → 15:20 RIBF187

Speaker: Byul Moon

15:20 → 15:40 Analysis update for experiment RIBF142/NP1912-RIBF191

We will provide an update on the analysis of RIBF142/NP1912-RIBF191, in which neutron-rich Titanium isotopes were produced and impinged on Be and Au secondary targets within the HiCARI gamma detector array. We measure $B(E2)$ values using the Coulomb excitation of $^{56,58}$Ti, as well as with lifetime measurements using doppler-shift techniques. We also investigate neutron orbital occupation using the parallel momentum distribution of reaction products following neutron knockout. These data will allow us to probe the existence of the $N=32,34$ shell closures observed in Ca, with the $N=34$ shell closure so far unobserved in neighbouring elements. We also measure lifetimes in the Sc isotopes produced in proton knockout reaction from $^{56,58}$Ti.

Speakers: Martha Reece (GSI), Wiktor Poklepa (GSI)

15:40 → 16:00 Coulomb Excitation Study on 50-54Ca - Progress Report

We report on the progress of a systematic study of $E2$ transition strengths in neutron-rich Ca isotopes, namely $^{50–54}$Ca, using the intermediate-energy Coulomb excitation method. This study aims to provide key insights into the shell structure along the Ca isotopic chain on the neutron-rich side and to supply critical experimental information regarding the magicity of $^{60}$Ca. Furthermore, the neutron sub-shell gaps of $^{52}$Ca [1] and $^{54}$Ca [2] have been reported, yet the large charge radii of $^{50,52}$Ca suggest the possibility of core-breaking proton excitations in the isotopic chain [3], thereby questioning the magicity of $^{52}$Ca. Through this study, the transition strength to the $2^{+}$ state is expected to be systematically probed, with the goal of providing decisive information about the shell structure and benchmarking theoretical calculations.

The experiment was carried out at RIBF using the BigRIPS separator, the ZeroDegree spectrometer, and the DALI2+ array. The neutron-rich Ca beams were produced via the fragmentation of a $^{70}$Zn primary beam impinging on a 7-mm-thick Be target at 345 MeV/nucleon. Two BigRIPS settings were tuned to study $^{50,51}$Ca and $^{52-54}$Ca separately. The neutron-rich Ca beams were transported to a 1-mm Au target to induce the Coulomb excitation. The contributions of the nuclear excitation were measured on a 6-mm Be target. In this report, we present the preliminary result of the recently conducted experiment including PID results and gamma-ray spectrum.

Bibliography

1. Gade A, Janssens RVF, Bazin D, Broda R, Brown BA, Campbell CM, et al. Cross-shell excitation in two-proton knockout: Structure of $^{52}$Ca. Phys Rev C Nucl Phys. 2006; 74. doi:10.1103/physrevc.74.021302
2. Steppenbeck D, Takeuchi S, Aoi N, Doornenbal P, Matsushita M, Wang H, et al. Evidence for a new nuclear “magic number” from the level structure of $^{54}$Ca. Nature. 2013; 502: 207–210. doi:10.1038/nature12522
3. Garcia Ruiz RF, Berger R, Billowes J, Binnersley CL, Bissell ML, Breier AA, et al. Spectroscopy of short-lived radioactive molecules. Nature. 2020; 581: 396–400. doi:10.1038/s41586-020-2299-4

Speaker: Ting Gao (University of York)

16:00 → 16:20 Intermediate-energy Coulomb excitation of $N=52$ isotones towards $^{100}$Sn

The Sn isotopes, containing the longest chain of isotopes between two doubly-magic nuclei, offer a fundamental testing ground for nuclear theories. Between the $N = 50$ and $N = 82$ shell closures, the $2^{+}_{1}$ energies of all Sn isotopes are well established and show an almost constant value, as expected in the generalized seniority scheme. Within the same framework, the B(E2) values should resemble an inverted parabola peaking at mid-shell. However, measurements in the most proton-rich Sn isotopes have shown a clear deviation from the expected behavior, with an enhancement of the transition probabilities towards $^{100}$Sn.
An experiment to measure for the first time the B(E2) in the $N=52$ isotones towards $^{100}$Sn, was performed at the Radioactive Isotope Beam Factory in Japan using the high-efficiency DALI2+ $\gamma$-detector array, composed of 226 NaI(Tl) detectors.
Preliminary results on the Coulomb excitation cross sections and transition probabilities for $^{98}$Pd, $^{100}$Cd and $^{102}$Sn will be presented, and their comparison with shell model and ab-initio calculations will be discussed.

Speaker: Martha Liliana Cortes (RIKEN Nishina Center)

16:20 → 16:40 Break

16:40 → 17:00 Analysis of RIBF211

The status of data analysis will be reported, mainly including preliminary results of 100Sn and 96Cd.

Speaker: Xiaoyu Liu (RIKEN/HKU)

17:00 → 17:20 RIBF211 II

Speaker: Zoltan Elekes

17:20 → 17:40 The process of In-99 and In-101 analysis

The doubly magic nucleus ^{100}Sn provides a crucial testing ground for nuclear structure studies, offering key insights into isospin symmetry and shell evolution. Based on the NP2112-RIBF211 in-beam experiment, we have analyzed the γ-ray spectra of ^{99}In and ^{101}In. Several new transitions have been observed in both nuclei, which have been tentatively assigned and incorporated into revised level schemes. These results are expected to provide valuable experimental evidence for the investigation of isospin-related phenomena and shell evolution in this region.

Speaker: 万 林峰 (近代物理研究所放射束室)

17:40 → 18:00 New/Update Proposal IV

Speaker: Jenny Lee

18:00 → 18:20 Break

18:20 → 18:40 HIRIBL separator + in-beam gamma@HIAF

Speaker: He Wang (IMP)

18:40 → 19:00 GAGG Status at Beihang University

Speaker: Yelei Sun (Beihang University)

19:00 → 19:20 lH2 target development at HIAF

Speaker: Hongna Liu (Beijing Normal University)

Thursday 4 September

08:30 → 14:30 HIAF Tour

Tour to HIAF facility by bus, together with participants of decay workshop

15:00 → 15:20 Shape coexistence in neutron-rich Zr beyond N = 60

We propose to study the shape coexistence in the unstable neutron-rich system $^{102}$Zr (N = 62). The shape coexistent phenomenon around N = 60 has been identified by measuring the low-lying excided 0$^+$ states recently. In this study, we probe the shape coexistence in $^{102}$Zr by measuring the second 0$^+$ states using the two-neutron transfer (p,t) reaction at 40 MeV/u. The OEDO beamline at RIBF is used to degrade the energy of the radioactive $^{104}$Zr beam. The emitted tritons are measured by the TiNA system. Reaction residues are identified by the SHARAQ spectrometer. Gamma rays emitted from de-excitation from the second 0$^+$ state are detected by DALI2. By measuring the differential cross section for (p,t), we investigate nature of the second 0$^+$ state and thereby study the different shapes inside the neutron-rich Zr beyond N = 60.

Speaker: Wenzheng Xu (Shandong University)

15:20 → 15:40 New/Update Proposal II

Speaker: Francesco Recchia

15:40 → 16:00 New/Update Proposal III

Speaker: Andrea Jungclaus (CSIC)

16:00 → 16:20 Break

16:20 → 16:40 Resubmission of RIBF246

The proposal RIBF246, In-beam γ-ray and mass spectroscopy of 90Rh and 94Ag, is planned to be resubmitted this year. The 94Ag setting will be removed, leaving only the 90Rh setting, and the in-beam+decay measurement of 86Tc will be added.

Speaker: Xiaoyu Liu (RIKEN/HKU)

16:40 → 17:00 Exploring the Low-$Z$ Shore of the $N$ = 40 Island of Inversion

We plan to propose a new experiment at RIBF employing the LISA active target in combination with the DALI2+ $\gamma$-ray spectrometer to investigate the evolution of collectivity from $^{64}$Cr$_{40}$ (center of the island of inversion) to $^{62}$Ti$_{40}$. By combining complementary observables—such as lifetimes, momentum distributions, and reaction cross sections—deduced from one- and two-proton removal reactions, we aim to gain new insights on the low-$Z$ shore of the island of inversion and the predicted shape coexistence.

Speaker: Zhiqiang Chen (GSI Helmholtzzentrum für Schwerionenforschung GmbH)

17:00 → 17:30 Free Discussion

17:30 → 17:40 Closing