Charge distributions of fission fragments of low- and high-energy fission of Fm, No, and Rf isotopes

The charge (mass) distributions of fission fragments resulting from low- and high-energy fission of the even-even nuclei ${}^{254-260,264}\mathrm{Fm}$, ${}^{258-264}\mathrm{No}$, and ${}^{262-266}\mathrm{Rf}$ are studied with the statistical scission-point model. The calculated results are compared with the available experimental data. In contrast to the experimental data, the calculated mass distribution for ${}^{258}\mathrm{Fm}$(s.f.) is strikingly similar to the experimental one for ${}^{257}\mathrm{Fm}$(s.f.). The transformation of the shape of charge distribution with increasing isospin and excitation energy occurs gradually and in a similar fashion like that of the mass distribution, but slower. For ${}^{254}$Fm(i.f.), ${}^{257}$Fm($n_{th}$,f), and ${}^{260}\mathrm{Fm}$(s.f.), the unexpected difference (symmetric or asymmetric) between the shapes of charge and mass distributions is predicted for the first time. At some critical excitation energy, the saturation of the symmetric component of charge (mass) yields is demonstrated.

Figure 1

The calculated mass distributions (solid lines) resulting from the spontaneous ($E^{*}=0$ MeV, the first column) and induced ($E^{*}=15$ MeV, the third column) fission of the indicated nuclei ${}^{254,256,258,260,264}\mathrm{Fm}$, and thermal-neutron-induced ($E^{*}\sim 6.3$ MeV, the second column) fission of nuclei ${}^{253,255,257,259,263}\mathrm{Fm}$. The calculations are performed for even-even mass and charge fragmentations. The distributions are normalized to unity. The open symbols represent experimental data of Refs. [3, 32, 33, 34, 35]. The spontaneous fission data for the ${}^{258}\mathrm{Fm}$ were multiplied by the factor 0.8. In (h), the dashed line represents the provisional mass deduced in Ref. [35], and the open square represent radiochemically deduced secondary yield, while the open circles are the derived primary distributions [33].

Figure 2

The calculated charge distributions (solid lines) resulting from the spontaneous ($E^{*}=0$ MeV, the first column) and induced ($E^{*}=15$ MeV, the third column) fission of the indicated nuclei ${}^{254,256,258,260,264}\mathrm{Fm}$, and thermal-neutron-induced ($E^{*}\sim 6.3$ MeV, the second column) fission of nuclei ${}^{253,255,257,259,263}\mathrm{Fm}$. The calculations are performed for even-even mass and charge fragmentations. The distributions are normalized to unity.

Figure 3

The same as in Fig. 1, but for $E^{*}=25$ MeV (the first column), $E^{*}=35$ MeV (the second column), and $E^{*}=50$ MeV (the third column) excitation energies.

Figure 4

The same as in Fig. 2, but for $E^{*}=25$ MeV (the first column), $E^{*}=35$ MeV (the second column), and $E^{*}=50$ MeV (the third column) excitation energies.

Figure 5

The calculated mass distributions (solid lines) resulting from the fission of the indicated nuclei ${}^{260,262,264}\mathrm{No}$ at excitation energies $E^{*}=0$ MeV (the first column), $E^{*}=25$ MeV (the second column), and $E^{*}=50$ MeV (the third column). The calculations are performed for even-even mass and charge fragmentations. The distributions are normalized to unity. In (a) and (g), the histograms represent experimental data of Refs. [3] and [36], respectively.

Figure 6

The calculated charge distributions (solid lines) resulting from the fission of the indicated nuclei ${}^{260,262,264}\mathrm{No}$ at excitation energies $E^{*}=0$ MeV (the first column), $E^{*}=25$ MeV (the second column), and $E^{*}=50$ MeV (the third column). The calculations are performed for even-even mass and charge fragmentations. The distributions are normalized to unity.

Figure 7

The same as in Fig. 5, but for the indicated nuclei ${}^{262,264,266}\mathrm{Rf}$. In (a), the symbols connected by line represent the experimental data of Ref. [37].

Figure 8

The same as in Fig. 6, but for the indicated nuclei ${}^{262,264,266}\mathrm{Rf}$.