Analysis of the shape of multiplicity distributions of prompt neutrons emitted in spontaneous fission

International audienceThe current work discusses the experimental evaluation technique for the prompt neutron multiplicity distribution (PNMD) emitted is the spontaneous fission (SF). The restoring technique for the detector efficiency correction is shown as well as the comparison of two regularization parameter choice methods. The shape of the PNMD helps to achieve the information according the dynamic of the SF. The work also compiles all currently published PNMDs in the transfermium (Z > 100) region and discusses their shapes, providing a physical interpretation of the distortion of these distributions

Pulse-height defect in single-crystal CVD diamond detectors

International audienceThe pulse-height versus deposited energy response of a single-crystal chemical vapor deposition (scCVD) diamond detector was measured for ions of Ti, Cu, Nb, Ag, Xe, Au, and of fission fragments of$^{252}$ Cf at different energies. For the fission fragments, data were also measured at different electric field strengths of the detector. Heavy ions have a significant pulse-height defect in CVD diamond material, which increases with increasing energy of the ions. It also depends on the electrical field strength applied at the detector. The measured pulse-height defects were explained in the framework of recombination models. Calibration methods known from silicon detectors were modified and applied. A comparison with data for the pulse-height defect in silicon detectors was performed

Structure of the prompt neutron multiplicity distribution in the spontaneous fission of 256Rf

An experimental study of 256Rf spontaneous fission following the fusion reaction of 50Ti+208Pb was performed using the velocity filter SHELS of the Flerov laboratory at JINR. The average number of neutrons of ν‾=4.30±0.17 and variance of σν2=3.2 from the prompt neutron multiplicity distribution were obtained. The alpha decay branching ratio of bα=0.003−0.003+0.005 and the half-life of T1/2=(6.7±0.2) ms of the isotope were determined. For the first time, our neutron detector system allowed us to extend investigation of the prompt neutron multiplicity study to the superheavy element region

Observation of new neutron-deficient isotopes with Z≥92 in multinucleon transfer reactions

In deep inelastic multinucleon transfer reactions of 48Ca + 248Cm we observed about 100 residual nuclei with proton numbers between Z=82 and Z=100. Among them, there are five new neutron-deficient isotopes: 216U, 219Np, 223Am, 229Am and 233Bk. As separator for the transfer products we used the velocity filter SHIP of GSI while the isotope identification was performed via the α decay chains of the nuclei. These first results reveal that multinucleon transfer reactions together with here applied fast and sensitive separation and detection techniques are promising for the synthesis of new isotopes in the region of heaviest nuclei

Prompt neutron emission in 250^{250}No spontaneous fission associated with ground and isomeric state decays

International audienceThe complete-fusion reaction $^{204}$Pb($^{48}$Ca,2n)$^{250}$No was used to study two activities of $^{250}$No with distinct half-lives. A total of 1357 events were observed in the SFiNx neutron detection system. The average number of neutrons emitted per spontaneous fission of $^{250}$No was determined to be . The unusually symmetrical shape of the prompt neutron multiplicity distribution was restored and presented for the first time. Statistical tests were performed to compare the prompt neutron multiplicity distributions associated with the ground state and K-isomer state decays

Spontaneous fission of 246^{246}Fm

An experiment on the study of the $^{246}$Fm spontaneous fission was conducted using the SHELS separator. The isotope was synthesized in the complete fusion reaction of $^{40}$Ar beam ions and $^{208}$Pb target nuclei. The neutron yields of $^{246}$Fm spontaneous fission ($\overline{\nu} = 3.79\pm0.30$, $\sigma^{2}_{\nu} = 2.1$) were obtained using the SFiNx detector system. The multiplicity distribution of emitted prompt neutrons was restored using the Tikhonov method of statistical regularisation ($\overline{\nu}_{r} = 3.79\pm0.20$, $\sigma^{2}_{\nu r} = 2.8$). The spontaneous fission branching ratio ($b_{SF} = 0.061\pm0.005$) and the half-life ($T_{1/2} = 1.50^{+0.08}_{-0.07}$ s) of the isotope were determined. The experimental data were compared with scission point model predictions. Excellent convergence was observed in the average number of neutrons per spontaneous fission process. However, the forms of the experimental and model prompt neutron multiplicity distributions differ significantly