This work was supported by the National Science Foundation Grants NSF PHY 78-22774 A03, NSF PHY 81-14339, and by Indiana Universit

Jacobs, W.W.

Kailas, S.

Karwowski, H.J.

Singh, P.P.

Soga, F.

Throwe, T.G.

Vigdor, S.E.

Ward, T.E.

Wark, D.L.

Wiggins, J.

English

IUScholarWorks

SYSTEMATICS OF THE K X-RAY MULTIPLICITY FOR TRANSITIONAL NUCLEI WITH A 200 
H.J. Karwowski, S.E. Vigdor, W.W. Jacobs, T.G. Throwe, D.L. Wark, 
S. Kailas, P.P. Singh, F.Soga, T.E. Ward, and J. Widgins 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
During the past year we have extended our R~K> for both smaller N (entering the strongly- 
measurements of the multiplicity (MK> of prompt K deformed, rare earth region) and larger N 
X-rays accompanying ( 6  >'~i,xn) reactions to several (approaching the shell closure at N=126). 
additional target-bombarding energy combinations. The The new data thus support the nuclear structure 
additional measurements were intended to complement scenario we had proposed previously to provide a 
those compiled in last year's Annual Report,l which qualitative explanation for our WK> measurements. In 
suggested an unexpectedly simple systematic behavior of this scenario we assume that the observed X-rays arise 
<MK> as a function of neutron number for the populated predominantly from internal conversion in M1 
residual nuclides. In fact, as shown in Fig. 1, the transitions among members of strongly-coupled 
complete data set very nicely defines this systematic rotational bands at moderately high spin (I-10-20h), 
dependence, indicating plateaus of high and constant associated with mildly deformed, high-K, 
multiplicity for the transitional-shape nuclides with few-quasiparticle intrinsic states. The high X-ray 
110 ( N (120, and rapid, nearly linear, falloffs in multiplicities suggest that such collective bands are a 
Figure 1. Compilation of 
I 
measured K X-ray multiplicities 
I I I 
Even -Z CN 'odd -2' CN for (Li,xn) reactions induced on 
4.0-GLi + ''ITa . 6 ~ i +  I 8 O ~ f  0 - the targets shown at bombarding 
185, 18fR, , '86W V energies from 75 to 124 MeV, 
194 plotted vs the neutron number N 
- 203,205 
- 
TI . averaged over the 
3.0 - 6 * 7 ~ i  + Ig7~u 
residual-nuclide production 
distribution appropriate to each 
A 
Y target and energy. [Typically, 
I - 
- two or three (Li,xn) residues 
v are significantly populated for 
2.0 - 
- 
a given target and energy.] The 
values of N are deduced to 
within 50.5 from systematics 
established by y-singles spectra 
1.0 - measured in the present 
experiment and the work of Ref. 
- - 4. The dashed curves guide the 
eye and are qualitatively 
I I I I I I I consistent with the nuclear 
/ 100 105 110 - 115 120 125 I30 structure arguments presented in 
N Refs. 2,3. 
much more general feature of the A=200 transitional 1) S.E. Vigdor et al., IUCF Scientific and Tecllnical 
Report 1980, p. 108. 
region than existing y-spectroscopy data indicate. The 
2) H.J. Karwowski et al., Phys. Rev. Lett. 47, 1251 
<MK> measurements and our nuclear structure inferences (1981). 
are described in detail in two recent publications .2r3 3) H.J. Karwowski et al., Phys. Rev. C, in press (IUCF 
preyrint no. 171). 
4) J. Kropp et al., Z. Phys. A280, 61 (1977). 
THE INFLUENCE OF DEFORMED-NUCLEUS LEVEL DENSITIES ON STATISTICAL MODEL CALCULATIONS FOR HIGH-SPIN FISSION 
S.E. Vigdor and H.J. Karwowski 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
During the past year we have continued our collective rotational bands built upon every intrinsic 
in~esti~ationl'~ of fission and particle emission from nucleon configuration are included in the level 
hot, high-spin nuclei by making substantial further density. For an axially symmetric nuclear shape 
improvements in the statistical model analysis of such characterized by moment of inertia with respect to 
data. We have specifically incorporated methods for an axis orthogonal to the symmetry axis, inclusion of 
estimating the effects of (1) the expected dilution of the rotational bands enhances the intrinsic level 
collective rotational bands with increasing temperature densities at nuclear temperature r by a factor gL~/li2. 
on the level densities for deformed nuclei, and (2) the In our previous analysis of measurements of fission- 
deformation of daughter nuclei on the barrier evaporation competition following 6~i-iaduced fusion 
transmission coefficients for particle emission. In reactions ,233 we incorporated this collective 
the process of introducing the latter change, we also enhancement of level densities at both the strongly 
found and corrected a significant long-standing error prolate saddle-point deformations relevant to fission 
in the widely used optical model subroutine TLJ. With and the mildly oblate equilibrium deformations used in 
these and the numerous other improvements we have evaluating particle emission widths. We were able to 
introduced over the past few years (see refs. 1-4), our reproduce very well the relative values of fission 
statistical model code now differs extensively from its cross sections (afiss) and anisotropies (yfiss) and 
progenitor MB-I1 (ref. 5 ) ,  and we have renamed the a-evaporation cross sections (a,) measured for various 
Indiana version MBEGAT. targets and bombarding energies, without ally adjustable 
We have previously stressed2 the importance, for parameters. [All nuclear structure properties needed 
the sake of consistency in calculations of fission- for the calculations were fixed according to 
evaporation competition, of generating level densities predictions of the rotating-liquid-drop (RLDM) and 
as a function of total angular momentum not by the non-interacting Fermi gas (NIFG) models, see Refs. 
conventional te~hnique,~ which implicitly assunes 2,3] .  However, after allowawce in the calculations for 
spherical symmetry, but rather by the K-summation pre-equilibrium nucleon emission manifested in the 
technique introduced for deformed nuclei by Bjornholm, observed proton energy spectra and (6~i,xn) residue 
Bohr, and Mottelson (BBM) .6 In the latter approach, mass distributions, the calculated absolute values 


Systematics of the K X-Ray Multiplicity for Transitional Nuclei with A = 200

https://scholarworks.iu.edu/dspace/bitstream/2022/2777/1/iucf_1981_100-101.pdf

Systematics of the K X-Ray Multiplicity for Transitional Nuclei with A = 200

Abstract

Similar works

Full text

Available Versions

IUScholarWorks