alpha decay of the neutron-deficient isotopes...

GAN Zaiguo

Institute of Modern Physics, Chinese Academy of Sciences

Alpha decay of the neutron-deficientisotopes 215-217U


Outline

Lanzhou Gas-filled Separator – SHANS

Isotope 216U and its isomer 216mU

Search for the isotope 215U

-decay lines of isotope 217U

Summary

2

Institute of Modern Physics, Chinese Academy of Sciences 3

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


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


Motivation

5

Search for most neutron-deficient uranium isotope 215,216U


Excitation function calculated by HIVAP

6


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


EVR - α1 (216U)

8

Vetoed with MWPC and

punch-through detectors

Ecot=187.2 MeV

Dt (EVR-1) = 50 ms


EVR - α1 - α2 (216U)

9

Dt (EVR-1) = 50 ms

Dt (1-2) = 6 s


216U

A.P. Leppänen et al., Phys. Rev. C 75(2007)054307


[email protected]@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


RIKEN

12


Search for isotope 215U


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


Cross sections for the 215U and 216U

17


-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)


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


Two alpha energies : 8.215(30)MeV,8.098(30) MeV

20

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.


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)


K.Valli et al., Phys. Rev. 176,1377(1968)

22

The particle energies were predicted

by extrapolation method


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.


Outlook and Summary

25

A.P. Leppänen et al., Phys. Rev. C 75(2007)054307


Outlook and Summary

26

Search for most neutron-deficient uranium isotope 214U


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).


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

alpha decay of the neutron-deficient isotopes...

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