宇宙での元素合成過程とRIBFでの不安定核の質量測定
Nucleosynthesis in Cosmos& Mass measurements at RIBF/RIKEN
石山 博恒
理化学研究所仁科加速器科学研究センター
宇宙史研究センター2023年度第2回構成員会議・成果報告&交流会
筑波大学、2023年12月8日

Contents
1. Introduction- Beginning of Nuclear Astrophysics- Rapid neutron capture (r) process- Candidates for r-process astrophysical sites- Nuclear Physics inputs
2. Mass measurements at RIBF/RIKEN
3. Mass measurements with SLOWRI/ZD-MRTOF
4. Future programs

1. Introduction~ The origin of Gold and Platinum~This year, 2023 marks the 76th anniversaryof the beginning of ‘Nuclear Astrophysics’.
Nuclear Astrophysics started from B2FH
paper and Cameron paper published in 1957.
The origins of elements were clarified
with several process in this paper.
Especially, beyond iron, half of elements
are produced in ‘rapid neutron capture process’.

Nobel prize in 1983

However, until now, the site of r-process still remains as a mystery.

Element abundance in solar system

Mass ratio
H: 70.7%
He: 27.4%
Others: 1.9%
Heavy elements (> Ni): 4E-4%
Big Bang Nucleosynthesis:
Main production of H, He (Li, Be)
No stable isotope : A = 5, 8

Thermo-nuclear reactions (charged particle) in Stars:
Up to Fe
Fe: Maximal binding energy / nucleon ⇒ Stable
Beyond Fe ⇒ neutron capture reactions: (n, )
Why do two peaks exist?
Slow (s-) process
Rapid (r-) process
B2FH, Rev. Mod. Phys. 29 (1957) 547.

Beyond Fe, why do several peaks exist? (before double peaks problem)
Shell model⇒ Magic number = 2, 8, 20, 28, 50, 82, 126,..
We call ‘Shell closure’.
Typically, 4He, 16O, 20Ne, 40Ca (double magic nuclei)
Neutron separation energy (Sn)High Sn around magic numbers = stable⇒ Reversely speaking, neutron capture is not easy after magic number nuclei.
⇒ Suppression of neutron capture reaction⇒ Peak formation (accumulation at around magic number)Why are double peaks generated?

Clayton, Principles of stellar Evolution
And Nucleosynthesis (1983)

A ~ 90A ~ 80A ~ 138

A ~ 208Pb
A ~ 130
A ~ 196
Pt, AuNeutron capture process along stable nuclei⇒ - slower than -decay, Slow(s-) process
Neutron capture process on radioactive nuclei⇒ faster than -decay, Rapid (r-) process

Proton Number Z

Features of r-process- Neuron capture is faster than beta decay- Uranium, Th, etc. productions beyond Bi- (n, ) – (, n) equilibrium @ high temperature
T ~ 109 K
neutron capture reactions & photo-distinguishreactions equilibrium- Waiting point nuclei
N = 50, 82, 126 : Sn ⇒ high,
Magic number + 1: Sn ⇒ low⇒ Neutron capture reaction ceases on
those nuclei have to wait for -decay‘Waiting point nuclei’⇒ Peak formation- High neutron density > 1020 cm-3

Recent Astronomical observations ofr-process abundance in galactic halo stars
R-process has already occurred in the early stage
in galaxy.

56 < Z < 78 (Universality )Main r-process ?
Single episode / Single event ?
2nd-3rd peak
2nd peak : Ba
3rd peak : Os, Ir, Pt, Au

C. Sneden, et al., 2003
Z < 56 (Dispersive)
-processand/or weak r-process ?
1st peakZ > 78 (Dispersive ) ?
Cosmo-chronometer:
238U (4.5Gy) / 232Th (14Gy)
Stellar chronometer ?
Pb, Actinoides

Candidates for r-process site
Rapid neutron capture・high temperature (T9 ~ 1)
・High neutron number density(1020 ~ 1030/cm3)
・Short time scale ( several seconds)➔Stellar explosion ?
High S/k site
Neutrino driven wind in type Ⅱ Sne(NDW)
S/k ~ several 100
Ye ~ 0.45

High Ye value?
High S/k ?

Site parameters・Ye (electron fraction):
Yp = Ye, Yn = 1-Ye
・S/k (entropy)∝ T3/ (density @ same T）
・ dyn (dynamic time scale)～ duration time for -process& r-process

Low Ye site
MHD jet/Collapsar

Nuclear physics inputs
・Nuclear massS/k < several 10-> Sn, r-process pathYe < 0.2
・Half life
Neutron star merger-> r-process speed, waiting point・neutron branching ratio-> r-process abundance pattern・neutron capture rate & otherreaction-> r-process path when the equilibrium
is broken
Event rate, early universe ?

Network calculation for r-process nucleosynthesis
Simulation(Woosley et al. 1994; Meyer 1995)

Effect of (unknown) nuclear physics inputs
For example, MASS

microscopic: (a) HFB-2, (b) HFB-7 (Goriely et al. 2002, 2003)
macroscopic: (c) FRDM (Möller et al. 1995), (d) Hilf et al. 1976

Known masses

Made by Wanajo

Status of measurements
for mass, half lifeand n-branching ratio
Made by HI in 2009

: Mass (exp.): half life (exp.): n branching ratio (exp.): r-process path

128Te

129Xe

130Xe

131Xe

132Xe

N = 82

-126Te

Z = 50

128Sb

129Sb

131Sb

131Sb

132Sb

133Sb

134Sb

135Sb

136Sb

127Sn

128Sn

129Sn

130Sn

131Sn

132Sn

133Sn

134Sn

135Sn

136Sn

126In

127In

128In

129In

130In

131In

132In

133In

134In

135In

126Cd

127Cd

128Cd

129Cd

130Cd

131Cd

132Cd

132Cd

134Cd

126Ag

127Ag

128Ag

129Ag

130Ag

131Ag

132Ag

133Ag

126Pd

127Pd

128Pd

0.038

0.035

129Pd

130Pd

131Pd

132Pd

125Rh

126Rh

127Rh

128Rh

129Rh

130Rh

131Rh

: Mass (exp.)

0.059: half life (exp.): n branching ratio (exp.): r-process path(n, )

0.0265 0.019

0.052

0.02

Waiting-point nuclei

127I

Present status (2023) for mass, half life, neutron
branching ratio at around N = 82

0.042

0.031

0.163

0.082

0.035

0.124

0.064

0.028

137Sb

0.35

0.103

0.065

2. Mass measurements at RIBF/RIKEN

1. B-TOF
at OEDO-SHARAQ

TOF ∝ L √E/M

3. MRTOF-MS

2. Rare RI Ring (R3)
To be published
in RIKEN Accelerator Progress
Report 56 (2023)

1. B-TOF at OEDO-SHARAQ
3. MRTOF(multi-reflection time-of-flight)-MS

2. Rare RI Ring (R3)3. Mass measurementswith SLOWRI/ZD-MRTOF

GARIS
II (稼働中)
MRTOF-MSHe GC + MRTOFGARIS III (開発中)He GC + MRTOF

BigRIPS/ZDS (稼働中)
He GC + MRTOF
From 2020
BigRIPS/F5 (開発中)He GC + MRTOF

RF carpet typeHe gas catcher
KISS (KISS+1.5) (稼働中）
Ar GC/He GC + MRTOF

BigRIPS/F2 （開発中）
Ar GC + MRTOF

RFGC-I: RF carpet type He gas cell + ZD-MRTOF @F11
RI

Ion mirror(inject)

MRTOF

Ion trap

Ion mirror (exit)

Detector
RFGCion1st carpet(DC +RF)He gas cellp ~ 150 Torr, L = 50 cm
Cryogenic operation(T = 80 K)

exit hall

2nd carpet(gutter, RF+AC)Symbiotic mass measurements with RFGC/ZD-MRTOF
Z = 50N = 82Mass measured but well known (AME2020)

Z = 20N = 28N = 50

Improved precision
more than a factor of 2 c.w. AME2020
First mass determination

Sc, Ti, V region
Non-existence of N = 34
sub-shell closure
on Ti isotope

Well known mass (AME2016)

Improved precision
more than a factor of 2 c.w. AME2020- Published in PRLFirst mass determination
c.w. AME2020- Press-releasedon Jan. 2023
- Dr Thesis for Iimura-san

A ～ 90 region

No effect for N = 56

Ratio of reaction rates
I = <v>exp./<v>AME2020

Well known mass (AME2016)- Accepted forImproved
publicationin PRC
precision

more than a factor of 2 c.w. AME2020
First mass determination c.w. AME2020

4. Future programs

Future programs for mass measurements with SLOWRI/ZD-MRTOF
NP2112-RIBF211 (11 days)
Jenny Lee,in the vicinity of 100Sn
NP2212-RIBF205R1 (2 days)
S. Kimura,Zr, Mo proton-rich RIs

In planning,
S. Iimura,in the vicinity of N = 126
isotones

NP2212-RIBF216 (4 days)
Phong Vi,
Escaping path from 2nd
peak on r process
abundance

BigRIPS/ZDS

PE22-01 (5 days)
Symbiotic experiment
KanugoCa isotopes

NP2312-RIBF172R1 (6 days)
P. Doonenbal
NP2312-RIBF202 (5 days)
M. Rosenbush
in the vicinity of 78Ni

In planning,
C. Fu
Around Ti isotopes

NP2112-RIBF207 (8.5 days)
S. Nishimura,r process path on rare earth elements

In planning,
A. Takamine,in the vicinity of 129Ag

Total Beam Time
= 41.5 days

Thank you for your attention!