Spallation and fission of nuclei as a result of the capture of stopped negative pions

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

“…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. This refers to our results, too.…”

“…However, the calculated shapes for the multiplicity distribution for a27I [23] shows, that this stronger broadening of the distribution for the (pxn)-channel could be caused by e-particle absorption. Thus, the eparticle absorption could be responsible also for the broadening of the distribution for channels with higher proton multiplicity like for the (3px n)-channel for Nb.…”

“…In the case of 133Cs the experimental results are insufficient to discern clearly a structure in the distribution. 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.…”

“…As a significant feature of the calculations of Iljinov etal. [23] appears the influence of the e-particle absorption mechanism where the transformation of the pion mass in excitation energy should occur more efficiently and consequently, nuclear spallation should be stronger. 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 measurements of the isobaric yield ratio (independent yields of two isobars) for heavy nuclei proposed by Iljinov etal. [23] should give information about the probability of the absorption on np-and pp-pairs. Although the ratio of the intensity of the (re ,xn)-reactions to that of the (~ ,pxn)-reactions (133Cs) agrees well with the results for heavier nuclei the isobaric yield ratio for 133Cs (~-, 10n, p9n) was found to be 0.65_+0.25 whereas for 169Tm(~z-,10n, p9n) it is 9.9_+2.9 [25].…”