Fission-product formation in the thermal-neutron-induced fission of odd Cm isotopes

Thermal-neutron-induced fission of ${}^{243}\mathrm{Cm}$ was studied at the Lohengrin mass separator. The light-mass peak of the fission-yield curve was investigated, and yields of masses from $A=72$ to $A=120$ were obtained. Independent-product yields were determined for nuclear charges $Z=28–37$. The yield of masses in the superasymmetric region was found to be identical to other fission reactions studied at Lohengrin. The multimodal approach to fission and the macroscopic-microscopic method for the calculation of charge-distribution parameters in isobaric chains were used to analyze experimental results from the fission of ${}^{243}\mathrm{Cm}$ and ${}^{245}\mathrm{Cm}$. A systematics on fission modes was derived from the analysis and extended to the ${}^{247}\mathrm{Cm}$ case. The weight of the ${}^{132}\mathrm{Sn}$ mode was found to decrease in ${}^{243}\mathrm{Cm}$, relative to the ${}^{245}\mathrm{Cm}$ nucleus. A prediction of the ${}^{78}\mathrm{Ni}$ yield in the fission of Cm isotopes was made. The feasibility of the study of ${}^{78}\mathrm{Ni}$ at Lohengrin has been demonstrated.

Figure 1

Experimental burn-up data (points) obtained from the integration of the $A=100$ kinetic-energy distribution. The solid line is a fit with one-exponential function.

Figure 2

Fission-product mass scatter plot, taken with an ionization chamber in $\Delta E\text{‐}E$ mode at the separator settings $A∕q=4$ and $E∕q=4.5$, plotted in coordinates of “specific energy loss $\Delta E$, total kinetic energy $E_{\text{TOTAL}}$.” Measuring time was 25 min. The numbers under the peaks (masses) are the mass $A∕q$ parameters. Events forming the diagonal line $(E_{\text{TOTAL}}\approx \Delta E)$ and the tail under it are, respectively, the fragments stopped in collisions with the separating grid placed between the two $\Delta E$ anode sections and those scattered from it.

Figure 3

Absolute mass yields for the light-mass peak from the reactions ${}^{243}\mathrm{Cm}(n_{\mathit{th}},f)$ (this work) and ${}^{245}\mathrm{Cm}(n_{\mathit{th}},f)$ [2, 4]. The uncertainties shown are equivalent to one standard deviation.

Figure 4

Absolute mass yields for the light-mass peak from the reactions ${}^{235}\mathrm{U}(n_{\mathit{th}},f)$ [22, 23], ${}^{237}\mathrm{Np}(n_{\mathit{th}},f)$ [8, 24], ${}^{239}\mathrm{Pu}(n_{\mathit{th}},f)$ [25, 26], ${}^{242m}\mathrm{Am}(n_{\mathit{th}},f)$ [27], ${}^{243}\mathrm{Cm}(n_{\mathit{th}},f)$ (this work), ${}^{245}\mathrm{Cm}(n_{\mathit{th}},f)$ [2, 4], and ${}^{249}\mathrm{Cf}(n_{\mathit{th}},f)$ [28]. The error bars $\left(1\sigma \right)$ are shown only for ${}^{243}\mathrm{Cm}$.

Figure 5

Comparison between experimental (connected points) and calculated (dashed lines) mass yields for ${}^{243}\mathrm{Cm}$ and ${}^{245}\mathrm{Cm}$. The insets are the same data but on a linear scale.

Figure 6

Calculated prompt-neutron multiplicities used in the yield calculations for the ${}^{243}\mathrm{Cm}$ (solid line) and ${}^{245}\mathrm{Cm}$ (dotted line) targets.

Figure 7

Comparison between experimental (solid points) and calculated (open points) isotopic distributions from the ${}^{243}\mathrm{Cm}(n_{\mathit{th}},f)$ reaction.

Figure 8

Experimental (solid points) and calculated (open symbols) mean isobaric charge $\overline{Z}$ for masses $A=77–80$, obtained from the thermal-neutron-induced fission of different nuclei, as a function of the neutron-to-proton ratio of the corresponding compound systems. The data for ${}^{241}\mathrm{Pu}$ were taken from [4]; for other references, see Fig. 4. The straight lines are for legibility only.

Figure 9

Calculated absolute yields of Ni isotopes from fission of the ${}^{244}\mathrm{Cm}^{*},{}^{246}\mathrm{Cm}^{*}$, and ${}^{248}\mathrm{Cm}^{*}$ compound nuclei. Black points are the experimental data.