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研究会「原子核物理でつむぐｒプロセス」 ＠ 京大基研 May 22, 2019 R プロセスの研究：実験的検証と挑戦 [ 現状と今後の戦略 ] 西村俊二 （理研）

Nucleosynthesis of Heavy Elements (r-Process) J.J.Cowan C.Sneden, Nature 440 (2006) Atomic number (Z) Mass number (A) Neutron-Star Mergers Supernovae Mass … r-proces path (n, γ ) ⇄ ( γ ,n) Half-lives … process speed/abundance Delayed neutron emission & Fission … freeze-out path, odd-even Nuclear Structure - Neutron Magic (N=50, 82, 126) , Deformation, Quenching

Contents 1. Experiments for r-process nucleosynthesis at RIBF (ZDS) 2. Decay Spectroscopy at RIBF 1. EURICA 2. BRIKEN Experiments Nuclear Theory 3. VANDLE / CAITEN [ Feedback to Theory ] 4. DTAS 5. Future Plan 3. Other Activities 1. Heavy-ion Collisions (EOS) Experiments Nuclear Theory 4. Summary [ Feedback from Theory ]

RI Production

Location of Decay Station at RIBF 238 U … 345 MeV/u, Intensity = 5 – 12 pnA à 70pnA ! ZDS KISS OEDO H. Miyatake-san N. Imai-san

Question: Accessible r-nuclei Which part of that nuclear physics data is already known, which part remains yet unmeasured, and which part will be accessible in the new RIB-facilities? Korobkin 2012 超重元素 N=126 N=82 N=50

RI Beam Production : RIBF vs FAIR (FRIB) RIBF goal = 1000 pnA (current int. = 70 pnA) Pb beam Beam line transport should be taken into account

Decay Spectroscopy Experiment

Decay Exp. Programs at ZDS (Past, Present, Future) 2021 2022 2019 2020 EURICA ① Beta-gamma Campaign ⑤ Ge-detector array from Lanzhou Gr. ( IBS + Other Institutes?) BRIKEN ② β delayed neutron emission probabilities (Pn) CAITEN/NiGIRI/LaBr3(Ce) array ③ β delayed neutron: energy spectra (E n ) VANDLE/HAGRID ④ Total absorption: Heavier RI γ energy spectra (E γ ) ⑥ N=126 and beyond! MRTOF & β -TOF ( Mass & Decay : R&D ) DTAS

Beam Production & Decay Station 238 U 9 Be Ø The implantation of an identified RI is associated with the following β-decay events that are detected in the same silicon pixel (DSSSD).

Beta-gamma spectroscopy

440 Exotic Isotopes Surveyed by EURICA half-life （ sec ） EURICA Data( 2012 – 2016 ) Isomer … 14~ Z (number of protons) New Isotopes … 34 Delayed γ … 37 ~ New β -decay half-life Delayed neutron … 6 ~ 18 à 125 (N sum = 284) Proton emission … 3~ 82 50 50 28 28 U-beam int. = 5 ~ 10 pnA N (number of neutrons)

First Excited States of RI (Even-Z, Even-N) Z.Xu et al, PRL 2014) R. Taniuchi et al., Nature (2019) In-beam gamma exp. EURICA 実験

~284 Half-lives (New T 1/2 ~125) Measured at RIBF SN et al., PRL (2011) G.Lorusso et al., PRL (2015) J. Wu et al., PRL (2017)

Feedback to Network Calculation G.Lorusso et al., PRL (2015) 重元素の成分比（ｒ過程 ） 理論予想 1 st ピーク 2 nd ピーク RIBF で得たデータを使用 テルル、キセノン 128 Te 130 Xe 3 rd ピーク 金、白金 希土類元素 232 Th 238 U ウラン 235 U 80 100 120 140 160 180 200 220 240 Assumption: Hot r-process 質量数（陽子数 + 中性子数） (n, γ ) ⇄ ( γ , n) equilibrium.

BRIKEN (2016 – 2021) Beta-delayed neutron emission probabilities

Impact of β -delayed neutrons in R-Process R. Surman, at Gordon conf., June 2013, at ARIS conf., June 2014 post r-process abundances Y(A) with β -delayed neutrons neutron density without beta-delayed neutrons mass in r-process β -delayed neutron à (n, γ ) reactions at freeze-out time

BRIKEN: Highest neutron detection eff. BRIKEN @ RIBF BELEN (Spain) 3Hen (ORNL) A.Tarifeno-Saldivia et al. KAKENHI (Japan) BRIKEN design, simulation Jour. Instrum. 12, P04006 (2017)

BRIKEN Experiments (2016 - 2018) Commissioning & Experiments (Parasitic Mode) (1) 2016 Oct. 77 Ni RIBF123R1 (Takechi Exp.) … 2 days A.Tolosa-Delgado et al. (2) 2016 Nov. NIMA 925 (2019) 133 40 Mg RIBF03R1 (Fallon Exp.) ... 6.5 days ( 81,82 Ga, 80 Zn) (3) 2017 Mar. DA16-01 (Ahn Exp.) ... 3 days 11.5 days 40 Mg 2017 May-June BRIKEN Campaign-1 (4) RIBF127R1 (Rykaczewski) ... 4.5 days 78 Ni (N ~ 50) (5) RIBF128 (Estrade) ... 6.5 days 128 Pd (N~82) (6) RIBF148 (Kiss) ... 2 days/11 days RIBF139 (Nishimura) C Rare earth (A ~ 150-160) ancelled. B.C.Rasco et al. ( 77 Cu) 2017 Oct.-Nov. BRIKEN Campaign-2 NIM A 911 (2018) 79 (7) DA17-02 (Rykaczewski) ... 10 days 82 Cu (8) RIBF139 (Nishimura) ... 5.5 days R.Yokoyama et al. ( 86,87 Ga) Mid-shell (A ~ 90-125) (submitted) 2018 Nov. BRIKEN Campaign-3 Total : ~ 34.5 days RIBF148 (Kiss) ... 6 days (+2 days..)

Delayed neutron of 78 Ni on N = 50 (Experiment ßà Theory) Z.Xu PhD thesis (2014) 78 Ni 77 Co

Sensitivity Study of Decay Properties in r-Process P n T 1/2 low entropy hot wind M.R. Mumpower et al.(2016) high entropy hot wind N=82 N=82 Z=50 Z=50 cold wind NS merger

133 Cs 136 Xe 132 Xe 134 Xe T 1/2 : 126 ms (7) … EURICA

BRIKEN 2017 Nov. Spokespersons: S. Nishimura (RIKEN), A. Algora (IFIC-CSIC) 5.5 days 123 Ru 113 Zr 90 Ge WAS3ABi (Si) YSO (U.Tennessee) 7 isomers (known) 6 isomers (unknown)

Summary of BRIKEN @ RIBF BRIKEN (Accepted) BRIKEN 2018 BRIKEN 2017 - 284 ( à ~ 340) T 1/2 - 6 ( à ~ 150) P n , P 2n , .. - Excited States, Isomers - Magic / Deformation Survey of decay properties is in progress.

Decay Spectroscopy toward Heavier RI

Origin of Rare-Earth Elements

3 rd r-Process Peak ( N = 126 Region ) 120 Pt, Au Super-Heavy Z (number of protons) Lanthanide Elements s 100 U Nuclear Decay Heat r-process path 80 60 Origin of r-Process Elements ! Lanthanides (Pt?, Au?, and U?) 40 20 RIBF: Breakhrough Techniques Needed ( RI Separation & Identification ) 0 0 20 40 60 80 100 120 140 160 180 N (number of neutrons)

Decay Program with ZD-MRTOF N~126 … . Upgrade of detectors & Better Optics (BigRIPS – ZDS) Gas Catcher & MRTOF BigRIPS/ZDS Experiments à MRTOF (Symbiotic Collaboration) - In-beam, New isotopes, Interaction cross-section, Decay & Mass Workshop 2018 Sep. for Gas-Cell & MRTOF development with exotic nuclei ZD-MRTOF & Decay for heavy RI (N = 126)

Summary ü Beta-gamma spectroscopy 2009, 2012-2016, ü Successful Campaigns with EURICA (~ 100 days) Cluster Detectors are shipped back to GSI ü Beta-Neutron & gamma spectroscopy in progress ü Successful Campaigns with BRIKEN (~35 days) à 284 (EURICA) à ~ 340 T 1/2 , 6 (EURICA) à ~150 P xn ü Future Plan ü Decay experiments around N = 126 ü 2 nd Beta-gamma campaign ü Delayed neutron energy / Fast γ -decay ü BigRIPS-ZDS à MR-TOF à Decay Station