A novel experimental approach to study
beta-delayed neutron emissions• Recent experimental activities• A new method to determine Pxn
Bao-Hua Sun Beihang university
NSFC-JSPS collaboration workshop, Tsukuba

1Recent experimental activitiesl Decays close to the proton drip line at JYFL, Finland (2011-)
The quenching of the experimental spectroscopic factor for proton emission
from the short-lived d3/2 isomeric state in 151mLu was a long-standing
problem.

Proton formation
probability

Ø F. Wang, BHS, Z. Liu, et al., Phys. Lett. B 770 (2017) 83–87
Spectroscopic factor and proton formation probability for thed3/2 proton emitter 151mLu
Ø Wang, BHS et al., to be sumitted to Phys. Rev C (2017)
Ø Tian, BHS et al., half-life measurements of 156mLu
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Recent experimental activitiesl Decays close to the proton drip line at JYFL, Finland (2011-)
l TOF-Br-dE method for nuclear mass measurements (2012-)
One of the most precise timing detectors
st~5psNeutron-Rich Nd to Dy
BUAA&GSINIMA823,41(2016)
Many many thanks for sharing the beam time at HIMAC!

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Recent experimental activitiesl Decays close to the proton drip line at JYFL, Finland (2011-)
l TOF-Br-dE method for mass measurements of exotic nuclei(2012-)
l Charge-changing c.s. measurements at RIBLL2-ETF (2014.12,2017.01)
à Charge radii
à Charge density distribution

Beihang-IMP
collaboration

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Recent experimental activitiesl Decays close to the proton drip line at JYFL, Finland (2011-)
l TOF-Br-dE method for mass measurements of exotic nuclei(2012-)
l Charge-changing c.s. measurements at RIBLL2-ETF (2014.12,2017.01)~300 MeV/u

TOF-Stop

T0

TOF-Start

F2ETFF16

Recent experimental activitiesl Decays close to the proton drip line at JYFL, Finland (2011-)
l TOF-Br-dE method for mass measurements of exotic nuclei(2012-)
l Charge-changing c.s. measurements at RIBLL2-ETF (2014.12,2017.01)
l Steller lifetime measurement of 63Cu at RCNP, Osaka Univ. (2016-)

63Ni, t =100 y
1/2

core He burning
T»300 MK, nn~106cm-3

shell C burning
T» 1GK, nn>1011cm-3
RCNP proposal: E501

A novel experimental approach to study
beta-delayed neutron emissions• Beta-delayed neutron-emission (Pxn)• A new method to determine Pxn (SAMRAI)• Summary

Bao-Hua Sun ()Beihang university
Collaborators: T. Kabayashi, I. Tanihata, X.D. Xu, J.W. Zhao et al.
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Beta-decays towards neutron drip-linel The Qb value increases far
from stability.
l b-decay may populate statesin the daughter above theparticle separation energy (S).
This happens when S < Qb.
l b-delayed proton/neutron/alpharadioactivity
l While neutrons are emitted
promptly, the proton emission isfurther delayed by the Coulombbarrier.
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Beta-delayed neutron emission: an example
S(b)f(Z,Qb)lbSS(b)f(Z,Qb)

Shalev, Rudstam, PRL28,687(1972)

β-delayed neutron spectrum can reveal a great deal about theunderlying wave functions involved and hence is interesting for
nuclear structure investigations.

Pxn required for r-process
Beta delayed neutrons are of great relevance in reshaping theabundance during/after the neutron freeze-out, providing later timeneutrons in r-process nucleosynthesis and in the determination of rprocess lifetimes: change elemental abundance, provide neutrons15

Beta-delayed neutron emission
Sequential model of the multineutron emission process

Miernik, PRC90,054306(2014)l After beta transition, the daughter nucleus can be a in state of excitationenergy Ei
l The (Ei,Ji) state may de-excite by gamma emissions or (whenenergetically allowed) by neutron emissions. neutron-gamma emission
competition, generally gamma-emission is much smaller (<10%)l the subsequent de-excitation of the daughter nuclides

Beta-delayed neutron emission

P2n

P3n

P1n
P0
Pxn: the probability of a beta-delayed x-neutron decay event
occurring, i.e., the probability of populating the (A-x,Z+1) nucleus.
P0: the probability that beta decay occurs without neutron emission.
Pn: total neutron emission probability, i.e., the probability that any
neutron activity occurs
Qbn: energy window or phase space available for b-decayed neutrondecay. Going from stability, Sn decreasing, Qb/Pxn increasing
Birch et al., Nuclear Data sheets 128(2015)131

Pxn required for r-process

P2n
P1n

P3n
K. Miernik, PRC88, 041301(R)(2013); PRC90,054306(2014)

P018

Beta strength and nuclear lifetime/branching ratio
N. J. Stone (2014)

Strength function
Beta-ray (DSSD)
3He, liquid/plastic

scintillator

SnMany experimental
difficulties (efficiency, energy dependent)
4-pi NaI(Tl)• Complex detector array• Coincidence measurements for b, gHPGe/Cloverand neutron• Hard (impossible) for weak transition due to theenergy phase space• Low efficiency for beta-delayed multi-neutron
emission decay (P2n/P3n)

Charge-exchange reaction at ≥ 100 MeV/uCex at intermediate beam energies has long been a powerful
technique to study β-transition strength, especially can probe
excitation regions, which are inaccessible to β-decay.
Proportionality relationship between Cex and β-transition strength
for allowed GT/F transition for E~100 AMeV and above: (~10%)" dσ %⌢$' = σ (A, E)B(GT )# dΩ &q=0

Unit cross Transition
strengthsectionBertsch, Esbensen, Rep. Prog. Phys. 50(1987)607
Osterfeld, Rev. Mod. Phys. 64(1992)491

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Proposal at BIGRIPS-SUMRAI, RIBF
28Na: P =0.58(12)%n29Na: P =25%,unknown Pn2nS2n=12.159
Sn=3.655

PHYSICAL REVIEW C 85, 034310 (2012)

Proposal at BIGRIPS-SUMRAI, RIBF
30Na: Pn=30(4)%, P =1.15(25)%2nS2n=10.007
Sn=3.652

Summaryp We propose to have the first experiment to demonstrate thepossibility of studying beta-decay of neutron-rich nuclide relevant to rprocess via nuclear charge-exchange reactions of Na isotopes in inverse
kinematics at > 100 MeV/u.
p This method can be very robust to determine precisely the branchingratios of beta-delayed neutron emissions and also the individualtransitions, and can be applied to study very neutron-rich nuclei relevant
for r-process study.
p More details will be presented in the coming SUMRAI workshop

Looking forward to collaborating with you!
Beihang-RIBF-Tohuku-Tsukuba-Saitama…

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