J. Pereira

-decay studies of r-process nuclei near 137Sb

Jorge PereiraNSCL/MSU

Frontiers 2005, MSU, August 2005

J. Pereira

Some recent r-process motivated experiments

GSI (in-flight fission)Half-lives, Pn values

Schatz et al.

ISOLDE (ISOL)Decay spectroscopy

Dillmann, Kratz et al.

GSI (in-flight fission)Masses (IMS)

Matos, Scheidenberger et al.

GANIL (fragmentation)Decay spectroscopy

Sorlin et al.

ANL/CPT (Cf source) Re-measured masses with high precision

Clark, Savard et al.

ORNL (ISOL)(d,p) and Coulex

MSU/NSCL (fragmentation) Half-lives, Pn values

Hosmer et al. Montes et al.

J. Pereira

A=130 abundance peakFreiburghaus, et al. 1999

ETFSI-1

(Pearson, et al. 1996)ETFSI-Q

(Aboussir, et al. 1995)

The -decay half-lives and Pn values are crucial to understanding the r-process

- Closed Shell

- Waiting point nuclei

--decay measurement

J. Pereira

Production of n-rich nuclei around 132Sn by projectile-fission of 238U @ 750MeV/u on 208Pb

EZ

0m

eB

Z

A

2)/(1

1

ToFcLToFc

L

2

20 1)(

D

xMxBB da

238U accelerated up to 750MeV/u In-flight isotopic separation with the FRS

Multiwire

Proportional

Counter (MWPC)

MUSIC

ChamberScintillator

Degrader

Collimator

Silicon Detectors

(veto) Silicon Stack

(implantation region)

Mainz Neutron

Long Counterbeam

neutron

J. Pereira

-decay properties of n-rich U-fission fragments

J. Pereira

Analysis of -decay half-lives

Identified fragments Implanted fragments

After implantation: Position-correlated decay-events

observed within correlation time (10 sec)

J. Pereira

Analysis of -decay half-lives

T1/2=1449±46 msec T1/2=1450±30 msec T1/2=530±5 msec

T1/2=530±20 msec

T1/2=1775±19 msec T1/2=2490±50 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

P.Santi, H. Schatz, NSCLF. Attallah, H. Geissel, M. Hausmann, M. Hellström, G. Münzenberg, C. Scheidenberger, K. Schmidt, K. Sümmerer, GSIH. Mahmud, P.J. Woods, University of EdinburghJ. Stadlmann, Universität GiessenM.N. Mineva, Lund UniversityM. Hannawald, K.-L. Kratz, B. Pfeiffer, Universität MainzT. Faestermann, R. Schneider, A. Stolz, E. Wefers, TU MünchenU. Giesen, University of Notre Dame

R. Kessler (Diploma Thesis), Universität Mainz

J. Pereira

-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:

Better at high energies

Very low for high-mass fission fragments

SIS + FRS at GSI: Fission reaction 238U(750MeV/u)+208Pb at GSI