Background: Experimental setups commonly used to study fission properties of nuclei in the exotic neutron-deficient ${}^{180}\mathrm{Hg}$ region are based on the time-of-flight technique for the fission-product identification. In best cases, the obtained fragments mass (FFMD) and total kinetic energy (TKE) resolution does not exceed 2 u and 6 MeV, respectively. In addition, the nuclei of interest are created via fusion reactions and at excitation energies of several tens of MeV. The deduced final FFMDs are in general structureless, which makes the identification of fission modes, along with their properties, ambiguous and analysis dependent.

Purpose: To develop a robust analysis approach aiming at identification of a number of major fission modes in FFMDs from fusion-fission reactions.

Method: FFMD data with known composition are used to calculate the second derivative which is then inspected for presence of minima. Number of detected minima is relevant to the number of fission modes present in the FFMD and thus determines the structure of the fit function to use for the FFMD and TKE data description.

Results: The resolution effect is found to broaden the simulated FFMD and TKE data, as well as to smear structures in the second derivatives thus limiting the sensitivity of the method to a few per-cent level in the fission-mode weight. Direct fit of the resolution-affected FFMD data is shown unable to find the asymmetric-mode positions nor to reproduce the modes weights, especially if the used fit-function composition does not correspond to the input data. The fission-modes characteristic TKE values are also not reproduced in a non-constrained fit. In contrario, the simulated data could be safely reproduced with fit functions constructed with help of the second derivative curves, the detected minima being the signature of number of fission modes detectable in the resolution-affected data. The power of the derivative method is demonstrated on example of real experimental FFMDs for the ${}^{180}\mathrm{Hg}$ nucleus.

Conclusions: The derivative analysis applied to limited-resolution FFMDs appears to provide consistent results on the number and parameters of fission modes, even in cases of strong symmetric-mode dominance, i.e., for Gaussian-like FFMD shapes. The method is shown to work also on data sets with limited statistics (real experimental data with integral of a few tens of thousands of events).

Close

PrevNext

View figure in article

• Fission
• Nuclear fusion
• Nuclear reactions
• 150 ≤ A ≤ 189