Speaker
Description
The interplay between single-particle and collective degrees of freedom in $^{251}$Fm was investigated using combined internal conversion electron (ICE) and $\gamma$-ray spectroscopy. Excited states in $^{251}$Fm were populated via the $\alpha$-decay of $^{255}$No produced in the fusion-evaporation reactions: $^{208}$Pb($^{48}$Ca, 1n)$^{255}$No and $^{209}$Bi($^{48}$Ca, 2n)$^{255}$Lr. The intense beams were delivered by the U-400 cyclotron at the FLNR, JINR, Dubna. The separators VASSILISSA [1] and SHELS [2] were used to select the fusion evaporation residues. At the focal planes of these separators the GABRIELA [3] spectrometer was used to perform a time and position correlated measurement of the characteristic decay properties to further isolate the nuclei of interest. ICE spectroscopy of $^{251}$Fm was performed for the first time [4]. These measurements allowed the multipolarities of several transitions in $^{251}$Fm to be established, and, the M2/E3 mixing ratio in the decay of the low-lying 5/2+ isomer to be determined. The extracted B(E3) value will be compared to those found in other members of the N=151 isotonic chain and to theoretical calculations.
Time permiting, recent results from on-going measurements will also be presented. In particular, "pxn cross-sections” and the implications of accessing nuclei closer to the "island of stability". Upgrades to the detection system and electronics of GABRIELA can also be mentioned.
References:
[1] A. Yeremin, et al., Nucl. Instr. Meth. A 350 (1994) 608
[2] A.G. Popeko , et al., Nucl. Instr. Meth. B 376 (2016) 140
[3] K. Hauschild, et al., Nucl. Inst. and Meth. A 560 (2006) 388
[4] K. Rezynkina: "Structure des noyaux les plus lourds: spectroscopie du noyau 251Fm et d?éveloppement pour des traitements numériques du signal, thesis, Université Paris Sud, Orsay, 2016
