# Fileset

[105_Ito.pdf](https://mdr.nims.go.jp/filesets/9f4d6591-7a05-4083-851d-36ff4d57c4e5/download)

## Creator

M. Ito, K. Imamura, S. Akimoto, A. Takamine, K. Kikuchi, R. Mitsuyasu, T. Miwa, A. Gladkov, M.Tajima, S. Go, M. Mukai, H. Endo, S.Sasamori, S. Takahashi, Y. Fukuzawa, [M.Hase](https://orcid.org/0000-0003-2717-461X), K. Kawata, A. Kitagawa, T. Wakui, H. Ueno, Y. Matsuo

## Rights

[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

## Other metadata

[Measuring the stopping position of the energetic radioactive Rb beams in superfluid helium](https://mdr.nims.go.jp/datasets/9bb8b7b5-b829-4eca-8528-d9830fcaa321)

## Fulltext

RIKEN Accel. Prog. Rep. 56 (2023)Measuring the stopping position of the energetic radioactive Rbbeams in superfluid heliumM. Ito,∗1,∗2 K. Imamura,∗1 S. Akimoto,∗1,∗2 A. Takamine,∗1 K. Kikuchi,∗1,∗2 R. Mitsuyasu,∗1,∗2 T. Miwa,∗1,∗2A. Gladkov,∗1 M. Tajima,∗1 S. Go,∗1 M. Mukai,∗1 H. Endo,∗1,∗2 S. Sasamori,∗1,∗2 S. Takahashi,∗1,∗2Y. Fukuzawa,∗1,∗2 M. Hase,∗3 K. Kawata,∗1,∗4 A. Kitagawa,∗5 T. Wakui,∗5 H. Ueno,∗1 and Y. Matsuo∗1,∗2We are developing a laser spectroscopy techniquecalled OROCHI (Optical RI-atom Observation in Con-densed Helium as Ion-catcher) to study the nuclearstructure of short-lived and low-yield radioisotopesproduced at accelerator facilities.1) In OROCHI, ionbeams are injected into superfluid helium (He II),where the ions are slowed down, stopped in a smallvolume, and neutralized with nearly 100% efficiency.Nuclear spins/moments are derived from the measure-ments of the Zeeman/hyperfine splitting energy usingthe laser-radio frequency (RF)/laser-microwave (MW)double resonance. The feasibility of this method formeasuring the hyperfine splitting energy with an ac-curacy of six orders of magnitude was demonstratedin off-line experiments conducted with Cs atoms.2)Therefore, this method is expected to be promisingfor short-lived unstable nuclei applications.In previous online experiments,1) our group ob-served laser-RF double resonance spectra for 84–87Rbion beams provided by the RIKEN RIPS at∼60 MeV/nucleon. In the future, we plan to conductmeasurements on low-yield unstable nuclear atoms,such as Ag, which are provided at energies as highas ∼300 MeV/nucleon at the RIKEN BigRIPS facility.To demonstrate the applicability of our method to highenergy beams, we conducted experiments at the QST-HIMAC SB2 beamline, which can deliver a beam inexcess of 350 MeV/nucleon. Among the single-valence-electron alkali atoms, Rb is one of the atoms whosebehavior in superfluid helium is well studied. Further-more, 84Rb is estimated to be produced with the high-est yield with a primary beam of 84Kr according to theLISE++ simulation. This is why we employed 84Rb asthe target atom in our experiments. Because the num-ber of atoms stopped in the observation region in HeII is small, a LIF (laser-induced fluorescence) detectionmechanism with high efficiency is needed. Therefore,the accurate measurement of the beam stopping posi-tion at HIMAC SB2 beamline is one of the importantdevelopments for the future double resonance measure-ment of atoms with unstable nuclei.So far, in FY2019, we measured the beam yields of ahigh-energy 84Rb beam at the HIMAC SB2 beamline∗1 RIKEN Nishina Center∗2 Department of Advanced Sciences, Hosei University∗3 National Institute for Materials Science (NIMS)∗4 Center for Nuclear Study, University of Tokyo∗5 Institute for Quantum Medical Science, National Insti-tutes for Quantum and Radiological Science and Technology(QST-iQMS)using liquid nitrogen as a stopping material to esti-mate the number of stopped atoms in the possible LIFobservation region.3) Then, in FY2021, we successfullyobserved the LIF of 84Rb atoms in superfluid helium(He II) at the HIMAC SB2 beamline.4)In FY2022, the number of measurement points wasincreased compared to the beam experiment conductedin FY2021 to more precisely determine the beam stop-ping position. Two measurement methods were per-formed as shown in Fig. 1. (1) measurement of thenumber of injected ions that penetrated the plasticscintillator placed in the center of the cryostat in nor-mal fluid liquid helium and (2) measurement of LIFfrom atoms stopped in superfluid helium in the cryo-stat. A taper-amplified laser light5) was used for theirradiation of the cryostat center with a cross sectionsize of 3 mm × 6 mm. These two types of measure-ments were performed while varying the thickness ofthe Al degrader every 100 µm to optimize the degraderthickness for efficient LIF collection from 84Rb atoms.We are currently in the process of data analysis.Fig. 1. Schematics of RI beam introduction to helium atHIMAC SB2 beamline.References1) X. F. Yang et al., Phys. Rev. A 90, 052516 (2014).2) K. Imamura et al., Hyperfine Interact. 73, 230 (2015).3) K. Tsubura et al., RIKEN Accel. Prog. Rep. 53, 132(2020).4) K. Tsubura et al., RIKEN Accel. Prog. Rep. 55, 91(2022).5) R. Mitsuyasu et al., in the abstract of 25th Congress ofthe International Commission for Optics (2022).RIKEN Accel. Prog. Rep. 56 (2023)Ⅱ-9. Instrumentation- 105 -