High spin states and neutron multiplicities after pion capture in181Ta and209Bi

Abstract

The absorption of stopped n in 181Ta and 2~ has been investigated by studying prompt and delayed 7-ray spectra. Absolute cross-sections for the yield of isotopes per captured n-in (n-, xn) reactions, as well as the relative probability of populating nuclear states of different spins have been measured for the hafnium and lead isotopes, respectively. A spin as high as 20 has been observed in the production of 2~ The ground-state rotational bands of the hafnium isotopes are excited to spin values up to 16. Neutron multiplicities as large as 15 have been observed for both targets. A neutron multiplicity of -8 is most probable for both tantalum and bismuth targets. The strong interaction monopole energy shift e o and width F o for the 4f level are found to be e0(~81Ta)=540+100 eV; ~o(2~ 1790_+150 eV; Fo(181Ta)=225 +57 eV; F0(2~ = 1166 _+ 70 eV. The quadrupole moments, determined from the hyperfine splitting of the 4f pionic atom level, are Q=3.30+0.06b and Q=-0.50+0.08b for 181Ta and 2~ respectively.

Nuclear reactions induced by stopped negative pions in133Cs,93Nb and45Sc

“…2, 3 respectively. The mean number of emitted neutrons ,2foundfor 133Cs (~=6.2) and for 95Nb (E =5.0) is consistency with the data for 197 Au (.~=6.5) [14], for 2~ (~=7.5) [13], for aSlTa (X=7.9) [13] and for 75As (~=4.5) [14] and is also in agreement with the calculations of Gadioli and Gadioli-Erba [22]. The shapes of the neutron multiplicity distribution for 127I and VSAs were calculated by Iljinov et al [23] suggesting 75 ~o quasideuteron absorption and 25~o e-particle absorption and a good agreement with earlier experiments was obtained, however the calculations fail to reproduce the distribution for small x.…”

“…Finally, in respect with this consideration one should suggest that ~z-are not absorbed only on the nuclear surface, which is in agreement with the conclusion of Beetz etal. [13].…”

“…It was found that the maximum of the distribution for e-particle absorption should be displaced to higher x relative to that for quasideuteron absorption. The superposition of both types of distributions may lead to a broadening or possibly to a structure with two maxima which should be revealed for Pb [9] and probably for 2~ [13]. In the case of 133Cs the experimental results are insufficient to discern clearly a structure in the distribution.…”

“…The population of high-spin states of rotational bands in heavy nuclei was observed in SIN [8,14] and in CERN [13]. In our experiments several isomeric methastable states were identified from which the isomeric yield ratio for the isomeric pairs sTm, gy and 86~,gy induced in (n-,p5n) and (re ,p6n) reaction respectively were determined.…”

“…For the lighter nuclei the distance of both types of distribution should decrease and such structure cannot be observed [23]. If we compare the neutron multiplicity distribution of the (xn)-and (pxn)-channels for 197Au [14], 2~ [13], 181Ta [13] and our findings, we can establish that the distribution of the (pxn)-reactions for a33Cs and 93Nb proves to be broader relatively to that of the (~-, x n)-reactions for high x (Figs. 2, 3).…”