Half-life of the first
excited state of 201Hg
V. Méot, J. Aupiais, P.Morel, G. Gosselin ,
CEA/DIF
BP 12, 91680 Bruyères-le-Châtel, France
F.Gobet, J.N. Scheurer , M.Tarisien
Université Bordeaux 1; CNRS/IN2P3
Centre d’Etudes Nucléaires de Bordeaux Gradignan, UMR 5797
Chemin du Solarium, BP120, 33175 Gradignan cedex
The energy of the first excited state of 201Hg is very low: 1.565 keV
Such a low-lying level could be excited in plasma created by a laser
Motivation: Study of the resonant coupling between
the atom and the nucleus in plasma
(Nuclear Excitation by Electronic Transition)
32.1 keV 60 ps
26.3 keV 630 ps
3/25/2-
t1/2???
1.565 keV
1/23/2+
M1+E2
0
Stable
201Hg
We need to have a precise knowledge of the 1.56 keV lifetime
To calculate the nuclear excitation rate
To have a clear signature of the experimental process
How to produce the 1.565 keV level
for the lifetime measurement?
Populated by the electron-capture decay of 201Tl (3.038 days)
Produced by the reaction 203Tl (p,3n)201Pb followed by the 201Pb decays ( 9.4 hours half-life) to 201Tl.
The 201Tl source is supplied as
thallium chloride
in solution by CIS Bio
International
Delayed coincidence
between a conversion
electron (a=6.5 104) and
g-rays
electroplating
on platinum disk
initial activity of 10 MBq
700 eV< kinetic electron energy< 1500 eV
Experimental set-up
g detector
1”×1” LaBr3:Ce crystal scintillator
Lanthanum Bromide BrilLanCe® 380
•Fast decay time (16 ns)
•Good energy resolution 3% @661 keV
deposit
Photon
135. keV
g-ray spectrum of the 201Tl deposit
in coincidence with electrons
201Tl
201Tl
→201Hg
Electron detector :
channeltron
electron
Platinum
backing
10-7 mbar
V= +600 Volts
Distance between channeltron-crystal= 10 mm
→202Hg
(12 days)
202Tl
g-ray spectrum of the 201Tl deposit
in coincidence with electrons
TAC spectrum (+600 Volts)
201Tl
TAC Spectrum
(Time)
Intense prompt peak due to:
Huge number of auger electrons emitted by the EC decay
g-ray spectrum of the 201Tl deposit
in coincidence with electrons
TAC spectrum (+600 Volts)
t1/2 = 81±5 ns
201Tl
c2=1.021
202Tl
202Tl
Tac spectrum gated
by the 202Tl transition
flat
439 keV
Relative intensity
Variation of the delayed signal as function of the bias voltage on target
The delayed signal disappears beyond +1.6 KVolt
(The underlying spectrum is different from the prompt peak)
t1/2 = 81±5 ns
+
Internal conversion coefficient
+
Multipole mixing ratio
Nuclear reduced matrix element
B(E2;1/2-→3/2-)= 0.2490.082 e2b2
B(M1;1/2-→3/2-)= (2.00.7)10-3 mN2
Nuclear Excitation by Electronic Transition
NEET: resonant phenomenon
M. Morita, Progr. Theor. Phys. 49, 1574 (1973)
E.V.Tkalya Nucl. Phys.A539 209(1992)
M. Harston Nucl.Phys A690 447(2001)
P. Morel et al, Phys. Rev. A69, 063414 (2004)
R12  
 2 
 1  
2
 1   2 1  2  
 

4


2
NEET probability
PNEET
Observed in 197Au and 189Os for isolated atoms
197Au
189Os
PNEET = 5.0±0.6 10-8
PNEET< 4.5 10-10
S.Kishimito et al, Phys. Rev C74, 031301 (2006)
K.Aoki et al Phys. Rev. C 64, 044609 (2001)
The NEET probability strongly depends on the atomic properties
which can be easily modified in a plasma
Nuclear Excitation by Electronic Transition for 1.565 keV of 201Hg
Several resonant atomic transitions for different charge states:
Q ~ 44+
6s1/2  4s1/2
6p1/2  4p1/2
and
5p3/2  4p1/2
5s1/2  4p1/2
Q ~ 61+
In a thermodynamic equilibrium plasma these charge states could be
reached for T~240
(r~10-2
eV and T~630 eV
The NEET rate is defined as :
g/cm3)
Total decay rate of
the initial configuration
c
 PNEET
P (c) 
NEET T , r  


c  configuration
Probability of the initial configuration
k max


 Ec  m  pci 

i 1
P(c)  exp  


kT




Nuclear transition rate
by the NEET process
R12  
  
 1  2 
2
 1   2  1  2 
4
2
PNEET
Nuclear Excitation by Electronic Transition rates in plasma
P. Morel et al, Phys. Rev. A69, 063414 (2004)
It strongly depends on thermodynamic conditions (T,r)
The NEET rate is high enough to allow us to design a forthcoming experiment
 (s-1)
105
1.565 keV
5p3/2  4p1/2
5s1/2  4p1/2
1/2-
3/2+
201Hg
104
0.8
0.6
6s1/2  4s1/2
6p1/2  4p1/2
0.4
0.2
10-2
10-1
100
101
Conclusions
The half-life of the first excited state of 201Hg was measured at
t1/2 = 81±5 ns (accepted for publication in PRC2007)
The Reduced matrix element B(E2) and B(M1) were extracted
We derived the NEET rate in a thermodynamic equilibrium
plasma
Next step: Excitation of 201mHg in laser plasma