Heavy elements above Fm (Z = 100) are nuclei with vanishing liquid-drop fission barriers and are therefore entirely stabilized by quantum shell effects. Due to the large density of single-particle levels and strong polarized Coulomb fields, theoretical predictions of magic numbers are extremely model dependent. Furthermore, shell closures for one nucleon species depend strongly on the number of the other species. Reliable experimental data is needed in order to test and constrain theory. As there is a lack of such data in the region, new data is needed along with the confirmation of previous data. A detection system dedicated to the spectroscopy of transfermium nuclei was constructed in 2004 and installed at the focal plane of the VASSILISSA separator at the FLNR, Dubna, by a Franco-Russian collaboration. The results from the 2009 campaign will be presented.

New high-statistics data have been obtained on the decay properties of No-253 and its daughters using the reaction Pb-207(Ca-48, 2n)No-253. This was made possible thanks to an improved transmission of fusion evaporation residues through the VASSILISSA recoil separator and an increased efficiency of the GABRIELA detector setup. The decay schemes of No-253 and Fm-249 have been revisited. The known level scheme of Fm-249 has been confirmed, including a new level at 669 keV excitation energy. The observation of L X-rays in coincidence with the a decay of Fm-249 gives additional support to the ground-state configuration of 1/2(+)[631] instead of 5/2(+)[622] for Cf-245. In both Fm-249 and Cf-245, the interpretation of the data has been checked by comparing experimental a-particle and gamma-ray spectra with realistic simulations of the decay cascades and of the interaction of particles and photons in the detectors of GABRIELA. The population of a 0.7 ms isomeric state attributed to No-253 is confirmed by an a-tagged calorimetric measurement and the corresponding gamma and electron decay spectra are presented. Possible evidence for more than one isomer is given and a tentative partial decay scheme is discussed in the light of the available experimental data, systematics and theoretical expectations. (C) 2011 Elsevier B.V. All rights reserved.

An IN2P3-JINR collaboration has launched a project called GABRIELA at the Flerov Laboratory for Nuclear Reactions (FLNR) within the Joint Institute for Nuclear Research (JINR) in Dubna (Russia). The goal of the project is to perform gamma-ray and internal conversion electron spectroscopy of heavy nuclei produced in fusion-evaporation reactions and transported to the focal plane of the recoil separator VASSILISSA. During five experimental campaigns of GABRIELA, the detection system has gained in sensitivity and new spectroscopic information has been obtained for Fm-249, Fm-251, No-253 and Lr-255. In this contribution new results for No-253 will be discussed.

We report on the first determination of the magnetic moment of the 981.1 keV, ${J}^{\ensuremath{\pi}}={8}^{+}$ level in $^{72}\mathrm{As}$, a nucleus that belongs to the $A\ensuremath{\approx}70$ mass region dominated by rapidly changing deformations and shapes. The ${8}^{+}$ level is the bandhead of a collective sequence of positive parity levels coexisting with low-spin and medium-spin spherical shell-model states. The magnetic moment was measured by the time-integral perturbed angular distributions method to be $\ensuremath{\mu}=\ensuremath{-}(4.272\ifmmode\pm\else\textpm\fi{}0.280){\ensuremath{\mu}}_{N}$. This value is in disagreement with the presumed $[\ensuremath{\pi}(1{g}_{9/2}),\ensuremath{\nu}(1{g}_{9/2})]$ configuration and points to a more complex configuration involving two neutrons in the $1{g}_{9/2} $orbital.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation K. Hauschild, A. Lopez‐Martens, O. Dorvaux, J. Piot, D. Curien, B. Gall, A. V. Yeremin, M. L. Chelnokov, V. I. Chepigin, A. V. Isaev, I. N. Izosimov, A. P. Kabachenko, D. E. Katrasev, A. N. Kuznetsov, O. N. Malyshev, A. G. Popeko, E. A. Sokol, A. I. Svirikhin, T. Wiborg‐Hagen, H. T Nyhus, S. Siem, G. Drafta, D. Pantelica, N. Scintee, A. Görgen, T. Kutsarova, S. Mullins, Š. Šáro; Spectroscopy of transfermium nuclei using the GABRIELA set up at the focal plane of the VASSILISSA recoil separator. AIP Conference Proceedings 1 June 2010; 1238 (1): 337–342. https://doi.org/10.1063/1.3455962 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

We report on the first determination of the magnetic moment of the 981.1 keV, J(pi) = 8(+) level in As-72, a nucleus that belongs to the A approximate to 70 mass region dominated by rapidly changing deformations and shapes. The 8(+) level is the bandhead of a collective sequence of positive parity levels coexisting with low-spin and medium-spin spherical shell-model states. The magnetic moment was measured by the time-integral perturbed angular distributions method to be mu = -(4.272 +/- 0.280)mu(N). This value is in disagreement with the presumed [pi(1g(9/2)),nu(1g(9/2))] configuration and points to a more complex configuration involving two neutrons in the 1g(9/2) orbital.

The alpha-decay chain Xe-109 -> Te-105 -> Sn-101 was identified at the Holifield Radioactive Ion Beam Facility. Advances in digital electronics have made possible the identification of both alpha emitters in the same experiment despite the disparate half-lives of 13 +/- 2ms and 620 +/- 70ns for Xe-109 and Te-105, respectively. Two alpha-decay transitions were observed from Xe-109 with Q(alpha) values of 4067 +/- 10 and 4217 +/- 8 keV. One transition between the ground states of Te-105 and Sn-101 was observed with a Q(alpha) value of 4889 +/- 6 keV. Using the measured half-lives, branching ratios, and Q(alpha) values the reduced alpha-decay widths, delta(2), were determined. Comparison of the delta(2) value for Te-105 with Po-213 indicates a "superallowed" character in the alpha emission of Te-105.

The α-decay chain 109Xe → 105Te → 101Sn was identified at the Holifield Radioactive Ion Beam Facility. Advances in digital electronics have made possible the identification of both alpha emitters in the same experiment despite the disparate half-lives of 13 ±2 ms and 620 ±70 ns for 109Xe and 105Te, respectively. Two α-decay transitions were observed from 109Xe with Qα values of 4067 ±10 and 4217 ±8 keV. One transition between the ground states of 105Te and 101Sn was observed with a Qα value of 4889 ±6 keV. Using the measured half-lives, branching ratios, and Qα values the reduced α-decay widths, δ2, were determined. Comparison of the δ2 value for 105Te with 213Po indicates a “superallowed" character in the α emission of 105Te.

Two new alpha emitters 109Xe and 105Te were identified through the observation of the 109Xe --> 105Te --> 101Sn alpha-decay chain. The 109Xe nuclei were produced in the fusion-evaporation reaction 54Fe(58Ni,3n)109Xe and studied using the Recoil Mass Spectrometer at the Holifield Radioactive Ion Beam Facility. Two transitions at Ealpha = 4062 +/- 7 keV and Ealpha = 3918 +/- 9 keV were interpreted as the l = 2 and l = 0 transitions from the 7/2+ ground state in 109Xe (T1/2 = 13 +/- 2 ms) to the 5/2+ ground state and a 7/2+ excited state, located at 150 +/- 13 keV in 105Te. The observation of the subsequent decay of 105Te marks the discovery of the lightest known alpha-decaying nucleus. The measured transition energy Ealpha = 4703 +/- 5 keV and half-life T1/2 = 620 +/- 70 ns were used to determine the reduced alpha-decay width delta2. The ratio delta105Te(2)/delta213Po(2) of approximately 3 indicates a superallowed character of the alpha emission from 105Te.

Two new alpha emitters Xe-109 and Te-105 were identified through the observation of the Xe-109 -> Te-105 -> Sn-101 alpha-decay chain. The Xe-109 nuclei were produced in the fusion-evaporation reaction Fe-54(Ni-58,3n)Xe-109 and studied using the Recoil Mass Spectrometer at the Holifield Radioactive Ion Beam Facility. Two transitions at E-alpha=4062 +/- 7 keV and E-alpha=3918 +/- 9 keV were interpreted as the l=2 and l=0 transitions from the 7/2(+) ground state in Xe-109 (T-1/2=13 +/- 2 ms) to the 5/2(+) ground state and a 7/2(+) excited state, located at 150 +/- 13 keV in Te-105. The observation of the subsequent decay of Te-105 marks the discovery of the lightest known alpha-decaying nucleus. The measured transition energy E-alpha=4703 +/- 5 keV and half-life T-1/2=620 +/- 70 ns were used to determine the reduced alpha-decay width delta(2). The ratio delta Te-105(2)/delta Po-213(2) of similar to 3 indicates a superallowed character of the alpha emission from Te-105.

Two new $\\ensuremath{\\alpha}$ emitters $^{109}\\mathrm{Xe}$ and $^{105}\\mathrm{Te}$ were identified through the observation of the $^{109}\\mathrm{Xe}\\ensuremath{\\rightarrow}^{105}\\mathrm{Te}\\ensuremath{\\rightarrow}^{101}\\mathrm{Sn}$ $\\ensuremath{\\alpha}$-decay chain. The $^{109}\\mathrm{Xe}$ nuclei were produced in the fusion-evaporation reaction $^{54}\\mathrm{Fe}(^{58}\\mathrm{Ni},3n)^{109}\\mathrm{Xe}$ and studied using the Recoil Mass Spectrometer at the Holifield Radioactive Ion Beam Facility. Two transitions at ${E}_{\\ensuremath{\\alpha}}=4062\\ifmmode\\pm\\else\\textpm\\fi{}7\\text{ }\\text{ }\\mathrm{keV}$ and ${E}_{\\ensuremath{\\alpha}}=3918\\ifmmode\\pm\\else\\textpm\\fi{}9\\text{ }\\text{ }\\mathrm{keV}$ were interpreted as the $l=2$ and $l=0$ transitions from the $7/{2}^{+}$ ground state in $^{109}\\mathrm{Xe}$ (${T}_{1/2}=13\\ifmmode\\pm\\else\\textpm\\fi{}2\\text{ }\\text{ }\\mathrm{ms}$) to the $5/{2}^{+}$ ground state and a $7/{2}^{+}$ excited state, located at $150\\ifmmode\\pm\\else\\textpm\\fi{}13\\text{ }\\text{ }\\mathrm{keV}$ in $^{105}\\mathrm{Te}$. The observation of the subsequent decay of $^{105}\\mathrm{Te}$ marks the discovery of the lightest known $\\ensuremath{\\alpha}$-decaying nucleus. The measured transition energy ${E}_{\\ensuremath{\\alpha}}=4703\\ifmmode\\pm\\else\\textpm\\fi{}5\\text{ }\\text{ }\\mathrm{keV}$ and half-life ${T}_{1/2}=620\\ifmmode\\pm\\else\\textpm\\fi{}70\\text{ }\\text{ }\\mathrm{ns}$ were used to determine the reduced $\\ensuremath{\\alpha}$-decay width ${\\ensuremath{\\delta}}^{2}$. The ratio ${\\ensuremath{\\delta}}_{^{105}\\mathrm{Te}}^{2}/{\\ensuremath{\\delta}}_{^{213}\\mathrm{Po}}^{2}$ of $\\ensuremath{\\sim}3$ indicates a superallowed character of the $\\ensuremath{\\alpha}$ emission from $^{105}\\mathrm{Te}$.