Post on 21-Jan-2021
GAN Zaiguo
Institute of Modern Physics, Chinese Academy of Sciences
Alpha decay of the neutron-deficientisotopes 215-217U
Institute of Modern Physics, Chinese Academy of Sciences
Outline
Lanzhou Gas-filled Separator – SHANS
Isotope 216U and its isomer 216mU
Search for the isotope 215U
-decay lines of isotope 217U
Summary
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Gas-filled recoil separator in Lanzhou
HIRFL-CSR layout
SFC: Sector Focusing Cyclotron
K ~ 70 MeV (Ek<10 AMeV)
I ~ 3×1013 pps (C-Ne)
~ (1-5)×1012 pps (Mg-Zn)
Spectrometer for Heavy Atoms and Nuclear Structure
Gas-filled recoil separator – SHANS
Institute of Modern Physics, Chinese Academy of Sciences
Gas-filled recoil separator – SHANS
Fixed target
Detection system
Configuration Qv-D-Qv-Qh
Trajectory length 6.5 m
Acceptance280mmmrad (h)
450mmmrad (v)
Central trajectory
radius
1.8 m
Bending angle of D 52
Max. magnetic
rigidity
2.88 Tm
The gas-filled separators use the different magnetic
rigidities of the recoils and projectiles traveling through a
low-pressure (about 1 mbar) gas-filled volume in a
magnetic dipole field. 0 0
0 1/3 1/30
( / ) ( / )( ) 0.0227 0.0227 0.0227 [T m]
( / )
ave
A v v A v v AB
q Z v v Z
Institute of Modern Physics, Chinese Academy of Sciences
Motivation
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Search for most neutron-deficient uranium isotope 215,216U
Institute of Modern Physics, Chinese Academy of Sciences
Excitation function calculated by HIVAP
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Institute of Modern Physics, Chinese Academy of Sciences
Experiment
Reaction channels: 40Ar+180W216U+4n;40Ar+180W215U+5n
Beam: 40Ar12+
– Energy: 189.5 MeV ( for 216U), 103 hours
204.5 MeV (for 215U), 89 hours
207.6 MeV (for 215U), 157 hours
– Delivered by the SFC of HIRFL in Lanzhou
– Typical intensity: 150–250 pnA
Target: enriched 180W
– 180W (91.4% 180W and 8.5% 182W)
– thickness:41g/cm2(C)+481g/cm2(W) +14g/cm2(C)
– Beam energy at the center of target:
187.2 MeV, 202.4 MeV and 205.5 MeV
Experimental setup: Gas-filled recoil separator SHANS
– He pressure:0.6 mbar
Detection system : 2 MWPC + Si-box + Veto+gamma
Calibration: source + test reaction
Data acquisition system:VME
– Dead time: <16 s
Institute of Modern Physics, Chinese Academy of Sciences
EVR - α1 (216U)
8
Vetoed with MWPC and
punch-through detectors
Ecot=187.2 MeV
Dt (EVR-1) = 50 ms
Institute of Modern Physics, Chinese Academy of Sciences
EVR - α1 - α2 (216U)
9
Dt (EVR-1) = 50 ms
Dt (1-2) = 6 s
Institute of Modern Physics, Chinese Academy of Sciences
216U
A.P. Leppänen et al., Phys. Rev. C 75(2007)054307
Institute of Modern Physics, Chinese Academy of Sciences 11
maoshh@impcas.ac.cnmaoshh@impcas.ac.cn
α decay with an energy of 8335keV
following an implanted recoil nucleus after 5.5ms
Physics Letters B 748 (2015) 199–203
Institute of Modern Physics, Chinese Academy of Sciences
RIKEN
12
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Search for isotope 215U
Institute of Modern Physics, Chinese Academy of Sciences 14
Search for isotope 215U
Institute of Modern Physics, Chinese Academy of Sciences 15
Search for isotope 215U
Institute of Modern Physics, Chinese Academy of Sciences
Search for the isotope 215U
16
Dt (EVR-1) = 100 ms
Dt (1-2) = 5 s
Dt (EVR-1) = 100 ms
Nuclide E T1/2
215U 8.428(30) MeV1.330.290.73 ms
Ecot=205.5 MeV
Institute of Modern Physics, Chinese Academy of Sciences
Cross sections for the 215U and 216U
17
Institute of Modern Physics, Chinese Academy of Sciences
-decay lines of isotope 217U
21.31/2 5.7
8.005(20) MeV
15.6 ms
E
T
The research status of 217U
40Ar+182W->217U+5n
O.N. Malyshev et al., Eur. Phys. J. A 8, 295(2000)
Institute of Modern Physics, Chinese Academy of Sciences
RIKEN Accel.
Prog.Rep.45(2012)
They tentatively assigned this events to the decays of an isomeric state of 217U.
18 events
82Kr+138Ba->217U+3n
8200 keV
Institute of Modern Physics, Chinese Academy of Sciences
Two alpha energies : 8.215(30)MeV,8.098(30) MeV
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The 217U observed in this work
However, we prefer to assigned
the 8.215(30) MeV to the
decay of 217U from ground state
to ground state transitions (1/2-
5/2-) and 8.098(30) MeV was
assigned to the decay of 217U
populating one low-lying excited
state in 213Th (1/2-1/2- ). In
addition, the previously reported
value 8.005(20) MeV can be
assigned to the decay of 217U
from the ground state to an
another excited state in 213Th
(1/2-3/2-). It is inappropriate to
assign this two particle
energies to the decays of
isomeric states.
Institute of Modern Physics, Chinese Academy of Sciences
Based on the -decay schemes of the 125-neutron isotopes (215Th, 213Ra, 211Rn and 209Po), more than one decay energies (with much large decay branch) should be
exist in the decay of 217U from the ground state.
isotones
P.Kuusiniemi et al., Eur. Phys. J. A 30, 551(2006)
Institute of Modern Physics, Chinese Academy of Sciences
K.Valli et al., Phys. Rev. 176,1377(1968)
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The particle energies were predicted
by extrapolation method
Institute of Modern Physics, Chinese Academy of Sciences 23
Institute of Modern Physics, Chinese Academy of Sciences
we put the measured value 8.215(30) MeV on the plot, the value fits well into the
systematic regularities.
Alpha particle energies of ground state to ground state transitions for neutron-deficient Rn, Fr, Ra,
Ac, Th, Pa and U isotopes (except 209Th). Open squares refer to literature values taken from
appropriate references. The red solid squares refer to the values measured in this work.
Institute of Modern Physics, Chinese Academy of Sciences
Outlook and Summary
25
A.P. Leppänen et al., Phys. Rev. C 75(2007)054307
Institute of Modern Physics, Chinese Academy of Sciences
Outlook and Summary
26
Search for most neutron-deficient uranium isotope 214U
Institute of Modern Physics, Chinese Academy of Sciences
Outlook and Summary
Two neutron-deficient uranium isotopes 215,216U were synthesized on the gas-filled
recoil separator SHANS
The -particle energies and half-lives were determined to be 8.384(30) MeV and
4.72(- 1.57/+4.72) ms for the ground state of 216U and 10.582(30) MeV and 0.74(-
0.29/+1.34) ms for an isomeric state (8+). The -particle energy and half-life of 215U
were determined to be 8.428(30)MeV and 0.73(-0.29/+1.34) ms, respectively.
Two lines with energies of 8.215(30) MeV and 8.098(30) MeV were observed for
the known isotope 217U.
The 8.215(30) MeV line was assigned to the decay of 217U from ground state to
ground state transitions and the 8.098(30) MeV and 8.005(20) MeV are the decays
of 217U populating the low-lying two excited states. In addition, an improved half-
life of 20.4(-6.3/+16.5) ms for 217U was obtained.
However, our conclusions about 217U (unpublished) need further verification due to
the low statistics (five decay chains were observed).
Institute of Modern Physics, Chinese Academy of Sciences
Collaboration
Thank you for your attention!
IMP-CAS: Zaiguo Gan, Zhiyuan Zhang, Long Ma, Jianguo Wang, Lin Yu,
Huabin Yang, Jian Jiang, Tianheng Huang, Zhong Liu,
Xiaohong Zhou
Nanjing Univ.: Zhongzhou Ren
ITP-CAS: Shangui Zhou