This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Berg, G.P.A.

Grabmayr, P.

Lisantti, J.

Miller, D.W.

Mondry, A.

Nann, H.

Singh, P.P.

Stephenson, E.J.

Wagner, G.J.

Woldt, P.

English

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TRANSFER REACTIONS 
SHELL STRUCTURE STUDIES IN THE Pb-REGION 
P. Grabmayr, A. Mondry, G.J. Wagner and P. Woldt 
Universitat Tubingen, 0-7400 Tubingen, Germany 
G.P.A. Berg, J .  Lisantti, D.W. Miller, H. Nann, P.P. Singh and E.J. Stephenson 
Indiana University Cyclotron Facility, Bloomington, Indiana 474 08 
The depletion of shell model strength has been the subject of many studies which were 
prompted by the low occupancies of several many-body predictions. In particular the 3s 
proton occupancy in doubly magic 208Pb permits convenient access to the influence of the 
short-range correlations through the underlying characteristic shape of the 3s wave func- 
tion. For this purpose we have developed the CERES method (Combined Evaluation of 
Relative spectroscopic factors and Electron Scattering), which was successfully applied to 
- 
earlier low resolution proton transfer data (ref. 1,2). An increase of precision and a clarifi- 
cation of open spectroscopic problems were expected and obtained from our measurements 
at the IUCF of ( 2 , 3 ~ e )  cross sections and analyzing powers at 80 MeV incident energy, 
where cross sections for all three isotones, 204Hg, 205Tl and 206Pb, have been measured 
relative to that of 208Pb in the same setup. 
The measurements were performed with the K600 magnetic spectrometer. Targets 
of isotopically enriched 204Hg34S and 205Tl, evaporated on thin carbon backings, and 
206,208Pb, as self-supporting foils, were used. Particle identification was established via 
time of flight through the spectrometer. An energy resolution of 30 - 55 keV was achieved, 
depending on target thickness. The 30 keV resolution was enough to separate the 39 keV 
ground state doublet of 2 0 3 A ~ .  The 3He spectra taken on the four targets at Blab = 8.5' 
are shown in Fig. 1 where the states containing 3s-strength have been marked by a dot. 
Note that the fragmentation of strength observed in 205Tl and 206Pb is counterbalanced 
by shell effects in '04Hg. 
In Fig. 2 we present the angular distributions of cross sections measured on 204Hg 
in the range of 4O to 22". The distinct patterns allow for a unique -ej assignment and 
the extraction of relative spectroscopic factors by comparison to exact finite-range DWBA 
calculations (solid line fig. 2). A light mass contaminant was found in the 2 0 5 ~ l ( & 3 ~ e )  
reaction to have caused the previous erroneous l = 0 assignment at E, - 3.9 MeV (ref. 
2). The present proton transfer data agree well with earlier data (ref. 2 - 5) in the low 
excitation part, and extend to significantly higher excitation energies. 
Figure  1. 3He-spectra for 204Hg, 205Tl and 206j208Pb taken at Blab = 8.5". The 3s strength 
is marked by full dots. 
Combining all proton transfer and knockout data (refs. 2 - 6) we determined the 3s 
proton occupation number in 208Pb as n = 2.46(16)z, where z is the 3s part of the charge 
density difference of and 2 0 6 ~ b .  Using the most recent value of z = 0.64(6) (ref. 
7) we obtain n = 1.57(17). Note, that most of the uncertainty comes from z. With the 
present data we predict the 3s part of the charge density difference between 204Hg and 
2 0 6 ~ b  to be z' = 0.74(10), which is only 16% larger than the difference z between 205Tl 
and 206Pb. 
1. G. J. Wagner, Progr. Part. Nucl. Phys. 24, 17 (1990) 
2. P. Grabmayr, e t  al., Nucl. Phys. A494, 244 (1989) 
3. M.C. Radhakrishna, e t  al., Phys. Rev. C 37, 66 (1988) 
4. E.R. Flynn, e t  al., Phys. Lett. 105B, 125 (1981) 
5 .  E.N.M. Quint, e t  al., Phys. Rev. Lett. 58, 1088 (1987) 
6. P. Woldt, e t  al., Nucl. Phys. A518, 496 (1990) 
7. I. Sick and P.K.A. de Witt Huberts, Comments on Nuclear Physics, to be published. 
10' 1 203 204~g(d,3~e) Au Ed = 80 MeV 203 lo, 204~g(d,3~e) Au Ed = 80 MeV 
Figure 2. Differential cross sections for transitions on 204Hg. The solid curves represent 
exact finite-range D WB A calculations. 


Shell Structure Studies in the Pb-Region

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Shell Structure Studies in the Pb-Region

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