Role of isospin and its conservation in neutron-rich fission fragments

Abstract

Following upon our earlier paper [1] containing some initial results, we present detailed discussion and complete results in this paper, which provide the first direct evidence for the validity of isospin as a nearly good quantum number in neutron-rich systems. The evidence comes from the reproduction of the general features of the partition-wise relative yields of neutron-rich fission fragments produced in two heavy-ion induced fusion fission reactions, namely 208 Pb ( 18 O, f) and 238 U ( 18 O, f), by using the concept of isospin conservation. To fix the isospin values and use the isospin algebra, we invoke what we term as Kelson's conjectures. We present a consistent scheme for isospin assignments based on these considerations. Our calculated results confirm that isospin behaves as an approximately good quantum number in neutron-rich systems, in this case, the fission fragments.

Measurement of relative isotopic yield distribution of even-even fission fragments from U235 ( nth,f ) following Dey1, Biswas2, Chakraborty3 et al. 2021Phys. Rev. C3020View full textAdd to dashboardCite

“…Subsequent calculations for the relative yields of the fission fragments were carried out based on the assigned isospin and related algebra. The formalism has already been tested for the relative isotopic yields of the correlated even-even fission fragments produced through heavy-ion-induced fusion-fission reactions and thermal neutron-induced fission of 245 Cm [42][43][44]. A very good agreement was obtained between the theoretical and the experimental relative yields for the correlated even-even fission fragment pairs.…”

Measurement of relative isotopic yield distribution of even-even fission fragments from $^{235}$U($n_{th}$,$f$) following $γ$ ray spectroscopy

“…The values of the total isospin (T) and the third component of isospin (T 3 ) of all the even-even fragment nuclei that are possible in the 235 U(n th ,f ) reaction have been uniquely assigned (following the prescription proposed by Jain and collaborators [42][43][44]), and are tabulated in Table III. A pictorial representation of the assigned values of T and T 3 for different fragment nuclei is shown in Fig.…”

“…These are: (a) the higher the number of neutrons (ν) emitted in a fission process, the greater is the probability for the formation of highly excited states with T > T 3 , and (b) the fission fragment nuclei are preferably formed in isobaric analog states (IAS). It has already been explained that for the IAS, it is sufficient to consider three member isobaric multiplets (see Table III) for assigning a proper isospin value (T) to the fragment nuclei of a particular mass number [43].…”

Empirical Evidence of Isospin Memory in Compound Nuclear Fission

“…We have recently applied the idea of isospin purity in heavy mass nuclei which are naturally neutron-rich systems (N > Z) to reproduce the fission fragment distributions [10,11,12,13,14]. We have calculated the relative yields of fission fragments in heavy ion and thermal neutron induced reactions based on the premise of conservation of isospin in CN fission with remarkable success.…”