Transcript Document

J. Pereira
b-decay studies of r-process nuclei
near 137Sb
Jorge Pereira
NSCL/MSU
Frontiers 2005, MSU, August 2005
J. Pereira
Some recent r-process motivated experiments
ANL/CPT (Cf source)
Re-measured masses with high precision
Clark, Savard et al.
ORNL (ISOL)
(d,p) and Coulex
GSI (in-flight fission)
Masses (IMS)
GSI (in-flight fission)
Half-lives, Pn values
Schatz et al.
Matos, Scheidenberger et al.
ISOLDE (ISOL)
Decay spectroscopy
Dillmann, Kratz et al.
MSU/NSCL (fragmentation)
Half-lives, Pn values
GANIL (fragmentation)
Decay spectroscopy
Sorlin et al.
Hosmer et al.
Montes et al.
J. Pereira
A=130 abundance peak
Freiburghaus, et al. 1999
- Closed Shell
- Waiting point nuclei
- b-decay measurement
ETFSI-Q (Pearson, et al. 1996)
ETFSI-1 (Aboussir, et al. 1995)
The b-decay half-lives and Pn values are crucial
to understanding the r-process
J. Pereira
Production of n-rich nuclei around 132Sn by
projectile-fission of 238U @ 750MeV/u on 208Pb
238U
accelerated up to 750MeV/u
A B e


Z b m0
Z  E
b 
In-flight isotopic separation with the
FRS
L
1

c  ToF 1  ( L / c  ToF) 2
 x  M 2  xd
B  ( B ) 0  1  a
D2




J. Pereira
b-decay properties of n-rich U-fission fragments
MUSIC
Chamber
Collimator
Scintillator
neutron
beam
b
Mainz Neutron
Long Counter
Degrader
Multiwire
Proportional
Counter (MWPC)
Silicon Detectors
(veto)
Silicon Stack
(implantation region)
J. Pereira
Analysis of b-decay half-lives
Identified fragments
After implantation:
Position-correlated decay-events
observed within correlation time
(10 sec)
Implanted fragments
J. Pereira
Analysis of b-decay half-lives
T1/2=1449±46 msec
T1/2=1450±30 msec
T1/2=1775±19 msec
T1/2=2490±50 msec !!!
T1/2=530±5 msec
T1/2=530±20 msec
J. Pereira
The background problem
Decay-curves fits were done assuming
constant background
“High-energy” decay-events follow
spill beam pattern
Light-particles
(Beam-induced background)
Background must be calculated on a
time-dependent basis
J. Pereira
Outlook
•n-rich fission fragments produced in 238U at 750MeV/u) on208Pb
have been separated and identified in the FRS (including 134Sn,
136Sn, 137Sb and 142Te waiting points)
•Position correlated decay-events were measured after
implantation events within a correlation time of 10 sec
•Background determination (per detector, strip and settinig) on a
time-dependent basis (IN PROGRESS)
•Half-lives will be determined with MLH-method
•Pn values must be determined
J. Pereira
Collaborators
R. Kessler (Diploma Thesis), Universität Mainz
P.Santi, H. Schatz, NSCL
F. Attallah, H. Geissel, M. Hausmann, M. Hellström, G. Münzenberg, C.
Scheidenberger, K. Schmidt, K. Sümmerer, GSI
H. Mahmud, P.J. Woods, University of Edinburgh
J. Stadlmann, Universität Giessen
M.N. Mineva, Lund University
M. Hannawald, K.-L. Kratz, B. Pfeiffer, Universität Mainz
T. Faestermann, R. Schneider, A. Stolz, E. Wefers, TU München
U. Giesen, University of Notre Dame
J. Pereira
b-decay studies of n-rich nuclei around 137Sb at GSI
•Electromagnetic-induced fission
of 238U on 208Pb provides maximum
productions of n-rich nuclei
around 132Sn
e.g. 238U + 208Pb
T.Enqvist et al., Nucl. Phys. A658 (1999) 47
•Isotopic separation of
fission fragments: in-flight
separation
•Transmission:
Very low for high-mass fission
fragments
Better at high energies
SIS + FRS at GSI: Fission reaction
238U(750MeV/u)+208Pb at GSI