Direct Measurement of Superheavy Element Z & A at the Berkeley Gas-Filled Separator by Dr. Gregory Pang (LBL )

Monday 1 Jul 2013, 10:30 → 11:30 Asia/Tokyo

Small Seminar room at Nishina Hall (RIKEN Wako)

Location: Small Seminar room at Nishina Hall. Time: 10:30, 1st July (Mon.) Speaker: Dr. Gregory Pang from LBL Abstract: Several new superheavy elements (SHE) have been produced in fusion evaporation reactions using 48Ca beams on actinide targets [Oga2007,Oga2011]. The α-decay chains of these superheavy elements (SHE) terminate by spontaneous fission, before reaching the part of the chart of the nuclides where Z and A are well-established. The SHE Z and A assignments have been made by comparing experimental α-particle decay energies with model calculations [Sob2007], supplemented with cross-bombardment information. Thus, neither Z nor A have been directly measured. Before using measured α-decay energies to adjust mass models, these Z and A assignments must be proven to be correct. Otherwise a situation could arise where data from incorrect assignments are used to modify mass models which, in turn, reinforce the incorrect assignments. Using the Berkeley Gas-Filled Separator (BGS) at the 88-inch cyclotron at Lawrence Berkeley National Laboratory, the Heavy Element Group plans to simultaneously identify both Z and A for 289Fl [Oga2004] produced in the fusion evaporation reaction of244Pu(48Ca,3n). In order to achieve this feat, the BGS needs several upgrades to its detection setup, its means for mass determination, and its method of matching the output of the BGS to the acceptance of the mass analyzer. The detection scheme needs to allow for α - K x-ray coincidences, to provide Z-identification [Bem1973], also known as x-ray fingerprinting. Further coupling of this detection scheme with a mass analyzer, then provides a simultaneous determination of A and Z. The acceptance matching between the BGS and the mass analyzer is achieved by a RF gas catcher and RFQ trap. The detection setup, the RF gas catcher and RFQ trap, mass analyzer and the impact of the measurement will be discussed. [Oga2007] Y.T. Oganessian, J. Phys. G 34, R165 (2007). [Oga2011] Y.T. Oganessian, Radiochim. Acta 99, 429 (2011) [Sob2007] A. Sobiczewski et al., Prog. Part. Nucl. Phys. 58, 292 (2007). [Oga2004] Y.T. Oganessian et al., Phys. Rev. C 69, 054607 (2004). [Bem1973] C.E. Bemis et al., Phys. Rev. Lett. 31, 647 (1973).