CRIBの低エネルギー不安定核ビームを使った最近の天体核反応研究成果
Hidetoshi Yamaguchi (山口英斉)

CNS, the Univ. of Tokyo (東京大学原子核科学研究センター)

宇宙核物理グループ(Nuclear astrophysics group) members:
Seiya Hayakawa (早川勢也), Nanru Ma (馬南茹),Hideki Shimizu (清水英樹), Kodai Okawa(大川皓大)in Collaboration with:RIKEN, KEK, Kyushu, Tsukuba, Tohoku, Osaka (Japan),
McMaster (Canada), CIAE, IMP, Beihang (China), SKKU, Chung-Ang,IBS, Ehwa, SKKU (Korea), INFN LNL/LNS (Italy), Edinburgh (UK),IOP(Vietnam), ULB (Belgium) and others.

Topics••

Brief introduction of our RI beam separator CRIB (CNS, U-Tokyo)
Recent Highlights of experimental projects at CRIB:
1. Resonant scattering with thick-target method in inverse
kinematics (TTIK)
25Al+p: study for the 22Mg(α,p) reaction in X-ray bursts

Project in collaboration with IMP, Lanzhou, China
Paper submitted to Phys. Rev. Lett., review in progress.
2. Trojan Horse experiment with RI beam
7Be(n,p)/(n,α) in BBN
Project by Seiya Hayakawa (CNS, U-Tokyo)
Paper accepted at Astrophys. J. Lett. in May, 2021.
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CRIB/OEDO in RIBF
Facilities operated by CNS, the University of Tokyo in RIBF (RIKENNishina center)• CRIB: RI beam separator for low-mass, low-energy (<10 MeV/u)
RI beams• SHARAQ: high resolution spectrometer• OEDO: new low-energy (20-50 MeV/u) beamline for exoticbeams
AVF+OEDO (2017-)
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CRIB
•

CNS Radio-Isotope Beam separator , constructed and operated byCNS, Univ. of Tokyo, located at RIBF (RIKEN Nishina Center).

 Low-energy(<10MeV/u) RI beams by in-flight method.
 Primary beam from K=70 AVF cyclotron.
 Momentum (Magnetic rigidity) separation by “double achromatic” system,and velocity separation by a Wien filter.
 Orbit radius: 90 cm, solid angle: 5.6 msr, momentum resolution: 1/850.

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Low-Energy RI beam Productionsat CRIB
2-body reactions such as(p,n), (d,p) and (3He,n) in
inverse kinematics aremainly used for theproduction….large crosssectionMany RI beams havebeen produced at CRIB:
typically 104-106 pps
Higher intensity for 7Be
beam with cryogenic H2target: 3 x 108 pps.

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CRIB is collaborative• Recent proposer group of CRIB experiments:

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Method: the thick-target method
in inverse kinematics
Measurement ofresonance scattering

H. Yamaguchi@Tsukuba2021

 Inverse kinematics…
measurement is possible forshort-lived RI which cannot beused as the target.
 Simultaneous measurementof the excitation function forcertain energy range.(Smallsystematic error, no need tochange beam energy.)
 The beam can be stopped in
the target…measurement atθcm=180 deg. (where thepotential scattering is minimal)is possible.
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Courtesy of Dr. Hu Jun@IMP

Measurement of 25Al+p elastic scattering relevant to
the 22Mg(α,p)25Al reaction

Jun Hu, X.D. Tang, S.W. Xu, L.Y. Zhang, S.B Ma, N.T. Zhang, J.J. He,H. Yamaguchi. K. Abe, S. Hayakawa, L. Yang, H. Shimizu, D. Kahl,
T. Teranishi, J. Su. H.W. Wang, B. Guo et al.,Institute of Modern Physics, Chinese Academy of Sciences,
CNS, the University of Tokyo,
National Astronomical Observatories,
The University of Edinburgh,CIAE, SINAP

1.1 αp-process in Type I X-ray bursts

X-ray burst(α,p) reactions：14O(α,p)17F(p,γ)18Ne(α,p)21Na(p,γ)22Mg(α,p)25Al(p,γ)26Si(α,p)29P(p,γ)30S(α,p)33Cl(p,γ)34Ar(α,p)37K(p, γ)38Ca(α,p)41Sc

14O(α,p)17F

18Ne(α,p)21Na

22Mg(α,p)25Al

26Si(α,p) 29P

30S(α,p)33Cl

34Ar(α,p)37K

38Ca(α,p)41Sc

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1.2 Sensitivity study to the light curve of X-ray burst(α, p) reactions that impact the burst light curve in themulti-zone x-ray burst model.
Rankαp-process reaction

Source of reaction rates adopted bymulti-zone model

1.

22Mg(α,p)25Al

Non-SMOKER

2.

14O(α,p)17F

Hu etetal.al.PRC
Hahn
PRC9054(2014)(1996)025803
1999

3.

18Ne(α,p)21Na

Matic80 (2013)(2009)055804
He et al. PRC 88012801

4.

26Si(α,p)29P

Non-SMOKER

5.

30S(α,p)33Cl

6.

34Ar(α,p)37K

7.

38Ca(α,p)41Sc

Non-SMOKER
D. Kahl etal. PRC 97 (2018)015802
Non-SMOKER
Non-SMOKER

Ref: Cyburt et al., ApJ, 830 (2016) 55
22Mg(α,p)25Al could be the most sensitive reaction in the αp-process and may

have a prominent impact on the burst light curve.
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2.2 Status of level properties in 26Si
Experimental
techniqueβ-delayed
protonmeasurementof 26P Thomaset al. 2004

Eres

Jπ

Γp0

Γp′

Γα

√
Ex>10 MeV−
Shell model
calculation−−−

Matic et al.
2011√Ex<10 MeV−
Analog state
assignment−−−

25Al+p√Excitation
functionmeasurement√−

28Si(p,t)26Si

scattering
measurement
above the αthreshold of 26Si
(will be done)√R-Matrixfitting√

25Al (p,25Al (p, p′)25Alp)25Al

All the previous measurements didn’t touch the astrophysicalinterested energy region.
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2.3 Status of 22Mg(α,p)25Al astrophysical reaction rate

The shaded area is theuncertainty of a factor
100 based on NonSMOKER calculation.

Large difference
between theexperiment andtheoretical calculation.

The 22Mg(α,p)25Al reaction rate as a function of the temperature for the Hauser-Feshbach
predictions TALYS and non-SMOKER

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MSU experiment
Randhawa et al., Phys. Rev.
Lett (2020):First direct measurement of22Mg(α, p) with a 900 cps 22Mg
beam
Only for T>2.6 GK (cf. mostrelevant T range they claim:below 1 GK).
Reaction rate evaluated byextrapolation: close to thestatistical-model calculation.
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Experimental
Setup at F3 focal
plane
25Al beam:

2 x 105 pps, 80%
purityH. Yamaguchi@Tsukuba2021

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Particle Identification for the Recoiling Particles
Si telescope @0°

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R-Matrix Fit Result

1. We observed 13
resonance states in 26Si.
2. Elastic scattering andinelastic scattering spectra
were fitted with commonparameters.
2. The spin parities of 5states above the α thresholdwere determined for thefirst time … reaction rateevaluated with parametersof those resonances

α threshold

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X-ray burst simulations
Light curves with new XRB model… Improved
reproducibility

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Cosmological 7Li problem

Iocco et al. Phys. Rep. 2009

A. Coc et al. J. Cos. Astropart. Phys. 2014
●7Li problem... disagreement between theory and observation by a factor of 3−4–Due to CMB obs.? Low-metallicity stars obs.? Standard BBN model? Nuclear Physics?

–7Be abundance in the end of BBN determines 7Li predominantly–p(n,γ)d, 3He(d,p)4He, 7Be(n,p)7Li, 7Be(n,α)4He, 7Be(d,p)2α, etc.
H. Yamaguchi@Tsukuba2021●Temperature ~ 1010 − 3×108 K, Energy: 1 MeV − 25 keV#22

Trojan Horse Method for RI + neutronTrojan Horse method: (Spitaleri+ Phys. Atom. Nucl. 2011)
 7Be(n,p)7Li, 7Be(n,α)4He via 2H(7Be,7Lip)1H, 2H(7Be,αα)1HPWIA applicable when Quasi-free mechanism is dominantpdn⊗

Virtual Decayp7Be7Liorαα=

Virtual reaction

2(Kinematic Factor)·|Φ (Ps)|Calculated byMonte Carlo simulationn×dσHOES∝dΩ
Half-off energy-shell
2-body cross sectiondn

7Bep (spectator)
αpor
7Li
α

3-body Reaction
3dσdΩp dΩ7Li dEcm
Measured at
Ed-7Be > Coulomb barrier

σOES = Normalization × σHOES × Penetrability

7Be(n, p)7Li (Q = 1.644 MeV)

(Adahchour & Descouvemeont 2003)?
BBN energy~ 100 keV

@0.478 MeV

 Sensitivity: ∂logY 7Li / ∂log〈σv〉7Be = −0.71 (Coc & Vangioni 2010, Cyburt+ 2016, etc.)
If 5×higher rate ➡ 7Li problem solved Direct measurement up to 13.5 keV, time-reversal reactions at higher energies.
 R-matrix analysis: Adahchour & Descouvemont 2003.
 New n_TOF measurement: enhancement below BBN energies (Damone+ PRL 2018)

7Be(n, α)4He (Q = 18.990 MeV)BBN energy
Observed@n_TOF>200 keV@RCNP

Barbagallo+PRL2016<10 keV@n_TOF
Kawabata+ PRL2017

 Hou et al. PRC 2015: evaluation from 4He(α,p)7Li
 Barbagallo et al. PRL 2016: s-wave measurement @ nTOF
 Kawabata et al. PRL 2017: p-wave measurement @RCNP Lamia et al. APJ 2017: evaluation of 7Li(p,α) data measured by THM.
 Recent works consistent... Yet no direct data in the BBN range.

Experimental setup

 6 ΔE-E position sensitive
silicon telescopes
7Be beam:

7Li

22.12 ± 0.1 MeV
on target
PPAC ap (spectator)
CD2target

PPAC b Tracking
 PIDCD2p34°
56°

 CD2: 64 μg/cm2➡ ΔEbeam ~ 150 keV➡ To resolve Ex(7Li1st) = 478 keV

Au12° 7Li-p and α-α coincidence
measurements… spectator not measured

 Hamamatsu Charge-division PSD:
position resolution ~ 0.5 mm

CH2

#5 #4
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➡ Total angular resolution(PPACs & PSDs & alignment)〜 0.5° ➡ ΔEcm ~ 60 keV#2#1

Q-value spectra of the 3-body channels

7Be(d,2α)p7Be(d,7Lip)p

E1st = 478 keVReactionp+2α
7Li+2p7Be+n+p
5He+p+3He

Q-value (MeV)
16.766-0.589-2.225-4.547

Threshold (MeV)
Q3body0 = E1 + E2 + E3 – Ebeam
22.602 ~ √(ΔE 2 + ΔE 2 + ΔE 2 +ΔEΔQ
3body
123beam )9.975~ 200 keV expected with 64 μg/cm2 CD220.387

Gaussian fitting to Q-value spectra
3+2-(n,p0)(n,p1)

Isotropy assumed (as nostrong angular dependenceseen)Checked systematic changeof widths & peaks➡ Reduces errors

7Be(n,p ), (n,p ) & (n,α ) cross sections by CRIB
010BBN
7Be(n,p )07Be(n,p )7Li* (@478 keV)
1s waves wave☑ p0/p1 ratio from Gaussianfitting☑ s-wave penetrability correction... leads “upper limit”

7Be(n,α)p wave→ consistent w/Kawabata2017

(Preliminary) R-matrix fitting by AZURE2

BBN

Procedure:
Condition (starting from simple assumptions):☑ Start from (n,p0) channel with Ada.&Desc.2003 parameters.
☑ Fix known Jπ and Eresonance (except 1-)☑ Fit only (n,p1) and (n,α) channels.
☑ Adopt l ≦ 3☑ Fit (n,p0) channels again.
☑ Exclude no neutron emission states☑ Fix converged parameters and iterate.
☑ Fit Only Ec.m. < 1.2 MeV☑ χ2 converged (preliminary): χ2p0/NDF = 1.59, χ2p1/NDF = 1.33, χ2α/NDF = 0.68

Revised 7Be(n,p) Reaction rate
n_TOF result (Damone+ PRL2018):~ 5% higher rate in BBN range➡ 96% 7Li abundanceThis work:~ 15±15% higher rate (preliminary)➡ ~ 90% 7Li abundance (preliminary)(with the sensitivity∂logY 7Li / ∂log〈σv〉7Be = −0.71)

BBN

Recent 7Be+d work @ FSU(Rijal+ PRL122, 182701 (2019)):
Resonance of (d,α) channel just inBBN Gamow window➡ ~ 87% 7Li abundance?
-> (Errata) the effect seems to bemuch smaller.

Summary
CRIB is a low-energy RI beam facility in RIBF operated by CNS,
University of Tokyo, providing low-energy ( < 10MeV/u) RI beams ofgood intensity and purity.
Interests on indirect determination of astrophysical reactions, using RI
beams:
Proton/alpha resonant scattering to study resonance properties
Indirect method measurements (THM and ANC)
26Al isomeric beam for the cosmic gamma-rays (not discussed today)
Visit CRIB webpage for more information. http://www.cns.s.utokyo.ac.jp/crib/crib-new/

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