Gamma and electron spectroscopy of transfermium

isotopes at Dubna: Results and plans

A YEREMIN¹, O MALYSHEV¹, A POPEKO¹, A LOPEZ-MARTENS²,

K HAUSCHILD², O DORVAUX³, S SARO⁴, D PANTELICA⁵ and S MULLIN⁶

¹Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research,

Joliot Curie Str. 6, 141980 Dubna, Russia

²CSNSM, IN2P3-CNRS, Orsay Campus, F-91405 Orsay, France

³IPHC, IN2P3-CNRS, F-67037 Strasbourg, France

⁴Comenius University, SK84215 Bratislava, Slovakia

⁵Inst. for Physics and Nuclear Engineering, Bucharest Magurele, P.O. Box MG6, Romania

⁶iThemba Labs, South Africa

^*Corresponding author. E-mail: eremin@jinr.ru

Abstract. Detailed spectroscopic information of excited nuclear

states in deformed transfermium nuclei is scarce. Most of the

information available today has been obtained from investigations of

fine-structure $\alpha$-decay. Although $\alpha$ decay gives access

to hindrance factors and lifetimes which are strongly correlated to

shell/subshell closures and the presence of isomers, only the

combined use of $\gamma$ and conversion electron spectroscopy allows

the precise determination of excitation energy, spin and parity of

nuclear levels.

In the years 2004--2009 using the GABRIELA set-up [Hauschild {\it

et al}, {\it Nucl.\ Instrum.\ Methods} {\bf A560}, 388 (2006)] at the

focal plane of VASSILISSA separator [Malyshev {\it et al}, {\it

Nucl.\ Instrum.\ Methods} {\bf A440}, 86 (2000); {\bf A516}, 529

(2004)] experiments with the aim of $\gamma$ and electron

spectroscopy of the isotopes from Fm to Lr, formed by complete

fusion reactions with accelerated heavy ions were performed. In the

following, the preliminary results of decay studies using

$\alpha$--$\gamma$ and $\alpha$--$\beta$ coincidences at the focal

plane of the VASSILISSA recoil separator are presented.

Accumulated experience allowed us to perform ion optical

calculations and to design the new experimental set-up, which will

collect the base and best parameters of the existing separators and

complex detector systems used at the focal planes of these

installations. In the near future it is planned to study

neutron-rich isotopes of the Rf--Sg in the `hot' fusion reactions

with $^{22}$Ne incident projectiles and $^{242}$Pu, $^{243}$Am and

$^{248}$Cm targets.

Keywords. Recoil separator; heavy ion-induced reactions; properties

of nuclei with $220 \leq A$; $\gamma$-transitions and level energies.

PACS Nos 23.20.Lv; 23.60.+e; 27.90.+b; 29.30.Kv