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β-­‐decay of neutron-­‐rich nuclei with Z≈60
− The origin of rare-­‐earth elements −
Jin Wu
Collaborators
S. Nishimura, G. Lorusso, Z.Y. Xu, E. Ideguchi, G. Simpson, H. Baba,
F. Browne, R. Daido, P. Doornenbal, Y.F. Fang, T. Isobe, Z. Li, Z. Patel, S. Rice,
L. Sinclair, P.A. Sӧderstrӧm, T. Sumikama, H. Watanabe, A. Yagi, R. Yokoyama,
N. Aoi, F.L. Bello Garrote, G. Benzoni, G. Gey, A. Gottardo, K. Kobayashi,
I. Kojouharov, N. Kurz, H. Nishibata, A. Odahara, H. Sakurai, H. Schaffner,
M. Tanaka, J. Taprogge and the EURICA collaboration
Mo<va<on Solar r-process abundance distribution
N=126 wai<ng point
The REE peak
N=82 wai<ng point
Z
N
2
Mo<va<on Solar r-process abundance distribution
N=126 wai<ng point
The REE peak
N=82 wai<ng point
Z
N
3
Mo<va<on Solar r-process abundance distribution
N=126 wai<ng point
???
The REE peak
N=82 wai<ng point
Z
N
4
Mo<va<on The REE Peak is sensi<ve to : Solar r-process abundance distribution
²  late &me r-­‐process condi&ons (freeze out) ²  Nuclear structure (deforma&on) N=126 wai<ng point
???
The REE peak
N=82 wai<ng point
Z
N
5
Fission model (β,f), spontaneous
The REE peak A≈278
Fig. r-­‐process abundance distribu=ons obtained with three different models
S. Goriely et al, PRL 111, 242502 (2013)
M. Arnould et al, Phys. Rep. 450, 97 (2007).
The 110<A<170 nuclei originate from the spontaneous and β-­‐delayed fission of nuclei with A≈278.
Deformed Subshell Closure ?
S2n(N,Z) − S2n(N +2,Z) (MeV)
S2n (MeV)
N=100 deformed subshell closure? Fig..Experimental energy levels for Z = 64(Gd), Z = 66(Dy), Z = 68 (Er), Z = 70 (Yb), and Z = 72 (Hf) isotopes with N = 94 −108. P.-A. Söderström, et al, PRC 81, 034310(2010)
Fig. The two-­‐neutron separa=on energy S2n and the S2n-­‐
differen=al (S2n(N,Z) − S2n(N +2,Z)) obtained in the rela=vis=c mean field theory. L. Satpathy et al, J. Phys.30(2004)771
Deformed Subshell Closure ?
S2n(N,Z) − S2n(N +2,Z) (MeV)
S2n (MeV)
N=100 deformed subshell closure? Fig..Experimental energy levels for Z = 64(Gd), Z = 66(Dy), Z = 68 (Er), Z = 70 (Yb), and Z = 72 (Hf) isotopes with N = 94 −108. P.-A. Söderström, et al, PRC 81, 034310(2010)
The of a deformed subshell Fig. Tpresence he two-­‐neutron separa=on energy S2n and the S2n-­‐
differen=al (
S
(N,Z) −
S
(N +
2,Z)) o
btained i
n t
he closure around N=100 may result in 2n
2n
rela=vis=c mean field theory. sudden of neutron-­‐capture.
d
Lrop . Satpathy et al, J. Phys.30(2004)771
Why do we study β-­‐decay half-­‐lives (T1/2) and β-­‐delayed neutron emission probability (Pn)? Hot r-­‐process
Cold r-­‐process
1. Nuclear Masses (n, γ)çè(γ, n) 2. β-­‐decay rates equilibrium
3. Pn No (γ, n) 1.  Neutron capture rate(n, γ) 2.  β-­‐decay rates 3. Pn Ø Nuclear Masses Sn-­‐value (Neutron Separa3on Energy) => r-­‐process path Ø Neutron capture rates Ø β-­‐decay proper=es T1/2(Half-­‐lives) => r-­‐process progenitor abundances Pn(β-­‐delayed Neutron Emission Probability)=>modula3on abundance through re-­‐capture Experimental Setup
238U
RRC fRC
IRC
EURICA SRC
BigRIPS+ZeroDegree Detector system
Ø Neutron-rich heavy nuclei were implanted in the beta-decay counting system
(WAS3ABi) which consisted of a stack of five DSSSDs and two plastic scintillators.
Ø Twelve high-purity germanium cluster detectors (EURICA) and eighteen LaBr3
detectors were responsible for detecting γ-rays emitted from implanted nuclei.
Experimental Techniques
e-
Beam
Y-­‐strip
DSSSDs
X-­‐strip
Experimental Techniques
Heavy Ion e-
Beam
e-­‐ Time stamp e-­‐ e-­‐ e-­‐ e-­‐ Y-­‐strip
e-­‐ Posi=on Correla=on X-­‐strip
DSSSDs
t
Time Correlation
Time(10ns) Par<cle Iden<fica<on
Setting One
161Pm
158Nd
156Pr
154Ce
151La
New β-decay
half-lives
Setting Two
157Pr
Totally, 27 new beta-­‐decay half-­‐lives are measured
154Ce
152La
151Ba
14
Counts/50ms
Figng β-­‐decay curve (150La)
150La
(3+)
Chi-square
0.0
β4+
208.7 keV
2+
0+
97 keV
150Ce
Time(s)
Maximum Likelihood
Time(10ns) keV
β-γ coincidence
β-γ coincidence
15
Counts/50ms
Figng β-­‐decay curve (150La)
150La
(3+)
Chi-square
0.0
β4+
208.7 keV
2+
0+
97 keV
150Ce
Time(s)
Maximum Likelihood
Time(10ns) keV
β-γ coincidence
β-γ coincidence
16
β-­‐delayed neutron emission probability Pn (150Ba) β -n
150Ba ββ -n
150La 149La β-
149Ce β -n
148Ce Analysis is ongoing...... 97 keV 150Ce β-
X01(t1)—From 0 to t1, detected the number of parent nuclei (150La) occurring beta decay. X02(t2)—From 0 to t2,detected the number of daughter nuclei (150La) occurring beta decay. I—β-­‐delayed γ intensity. Nγ1(208.7keV)= X01(t1)*ϵγ*I Nγ2(208.7keV)= X02(t2)*ϵγ*I*(1-­‐Pn) 150La -­‐> 150Ce
Nγ1
208.7 keV Nγ 2
97 keV 150Ba -­‐> 150La -­‐> 150Ce Nγ2 208.7 keV X 01 (t1 )
Pn = 1 −
•
N γ 1 X 02 (t 2 )
17
Systema<c tendency of T1/2 as the func<on of neutron number T1/2 (ms) Preliminary
Preliminary
Preliminary
Preliminary
KTUY+GT2 FRDM+QRPA T1/2 (ms) Previous Preliminary
Preliminary
Preliminary
Neutron number This Work Systema<c tendency of T1/2 as the func<on of neutron number T1/2 (ms) Preliminary
Preliminary
Preliminary
Preliminary
KTUY+GT2 ???
T1/2 (ms) Preliminary
Preliminary
Preliminary
Neutron number FRDM+QRPA Previous This Work Summary Ø Rare-­‐earth elements are produced by the r-process . However,
the production mechanism is not well understood. Ø To address this problem, a β-decay spectroscopy experiment
was performed at RIBF (RIKEN) to study the neutron-­‐rich isotopes of Ba, La, Ce, Pr, Nd, Pm. Ø Data analysis is ongoing. The experimental results will provide inputs to the r-­‐process calcula&on, constrains our theore&cal stellar models, and provide the insight to the nuclear structure of exo&c nuclei. 20
1/--pages
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