Bulletin of the American Physical Society
4th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 59, Number 10
Tuesday–Saturday, October 7–11, 2014; Waikoloa, Hawaii
Session DG: Mini-Symposium on Super Heavy and Heavy Elements I |
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Chair: Walter Laveland, Oregon State University Room: King's 3 |
Thursday, October 9, 2014 9:00AM - 9:30AM |
DG.00001: Superheavy Elements: Status and Future Invited Speaker: Jacklyn Gates In 1966 Myers and Swiatecki predicted a new, spherical closed shell, centered at an element with Z$=$126 and A$=$310. In this region, now referred to as the ``Island of Stability,'' shell-effects were predicted to stabilize these spherical ``superheavy'' elements (SHE) with Z$\approx $114-126 against fission, leading to predicted half-lives of years or longer. In 2000, more than 30 years after these predictions were made, scientists at the Flerov Laboratory of Nuclear Reactions reported on the first successful experiments aimed at approaching this region of spherical superheavy elements. Since that time, six new elements and more than fifty new isotopes with Z $\ge$ 112 have been discovered. More recently experiments have transitioned away from discovery and towards understanding production, chemistry and investigating the level structure of SHE. On the other side, theoreticians have been looking for reactions that may reach the Island of Stability. In this talk, an overview of SHE research will be presented, with a focus on recent results and new directions in the field. [Preview Abstract] |
Thursday, October 9, 2014 9:30AM - 9:45AM |
DG.00002: Research of Superheavy Element at RIKEN Kosuke Morita An isotope of the 113$^{\mathrm{th}}$ element, $^{278}$113, were produced by the $^{209}$Bi($^{70}$Zn, $n)$ reaction using gas-filled recoil ion separator (GARIS). Three decay chains originating from $^{278}$113 were observed. Two of them consisted of four consecutive alpha decays followed by spontaneous fission (SF). One consisted of six consecutive alpha decays. These were assigned to the decay, $^{278}$113(alpha) $\to$ $^{274}$Rg(alpha) $\to$ $^{270}$Mt(alpha) $\to$ $^{266}$Bh(alpha) $\to$ $^{262}$Db(SF/alpha) $\to$ $^{258}$Lr(alpha) $\to$. The reaction $^{248}$Cm + $^{48}$Ca was studied using GARIS. Five decay chains terminated by SF were observed. The decay properties of the chains agree well with the chains observed, and assigned to $^{292}$Lv and $^{293}$Lv, at Dubna and at GSI in the same reaction. Possible new alpha decay branch of $^{284}$Cn and subsequent SF of possible new isotope $^{280}$Ds were observed. [Preview Abstract] |
Thursday, October 9, 2014 9:45AM - 10:00AM |
DG.00003: Recent results from the field of superheavy element research in Europe Andreas Tuerler With the discovery of six new elements in the past decade an extraordinary expansion of the Periodic Table took place, so that now all elements of the 7th period have been synthesized. This success was possible by exploiting the concept of ``warm'' fusion using the available, neutron-rich actinide target materials and the tightly bound, doubly magic projectile $^{48}$Ca [1]. Most of these discovery experiments were conducted by the Dubna-Livermore collaboration at the Flerov Laboratory in Dubna, Russia and a number of independent experiments have been able to confirm these findings [2-5]. In this contribution I will highlight different nuclear aspects of superheavy element research in the context of experiments performed by the TASCA collaboration. Attempts to push beyond Z$=$118 using the reactions $^{50}$Ti $+ \quad^{249}$Bk and $^{50}$Ti $+ \quad^{249}$Cf have failed so far, while reaching rather low upper limit production cross sections. It appears, as if only new, more powerful accelerators and associated experimental equipment would allow the synthesis of even heavier elements in the 8th row of the Periodic Table. Noteworthy is also the possible observation of X-rays in the alpha-particle decay chains of element 115 isotopes [6], paving the way towards X-ray fingerprinting of new elements. [1] Yu.Ts Oganessian, J. Phys. G: Nucl. Part. Phys. 34, R165 (2007) [2] L. Stavsetra et al., PRL 103, 132502 (2009) [3] Ch.E. Duellmann et al., PRL 104, 252701 (2010) [4] S. Hofmann et al., EPJA 48, 1 (2012) [5] J. Khuyagbaatar et al., PRL 112, 172501 (2014) [6] D. Rudolph et al., PRL 111, 112502 (2013) [Preview Abstract] |
Thursday, October 9, 2014 10:00AM - 10:15AM |
DG.00004: Recent Super Heavy Element Experiments at GSI-SHIP M. Stoyer, S. Hofmann, S. Heinz, R. Mann, J. Maurer, J. Khuyagbaatar, D. Ackermann, S. Antalic, W. Barth, H.G. Burkhard, V.F. Comas, L. Dahl, K. Eberhardt, R. Henderson, J.A. Heredia, F.P. Hessberger, J. Kenneally, B. Kindler, I. Kojouharov, J.V. Kratz, R. Lang, M. Leino, B. Lommel, K. Moody, G. Munzenberg The synthesis of element 116 (Lv) in fusion-evaporation reactions of a $^{48}$Ca beam with $^{248}$Cm targets was studied at the velocity filter SHIP of GSI in Darmstadt. At excitation energies of the compound nuclei of 40.9 MeV, four decay chains were measured, which were assigned to the isotope $^{292}$Lv, and one chain, which was assigned to $^{293}$Lv. Measured cross-sections of (3.4$+$2.7 $-$1.6) pb and (0.9$+$2.1$-$0.7) pb, respectively, and decay data of the chains agree with data measured previously at the Flerov Laboratory of Nuclear Reactions in Dubna. We measured the velocity spectra of the 116 isotopes and transfer products which reveal the reaction type underlying the synthesis of the nuclei. The experience gained in this experiment will serve as a basis for future experiments to study still heavier elements at the velocity filter SHIP. Searches for element 120 in fusion-evaporation reactions of a $^{54}$Cr beam with $^{248}$Cm targets were studied later at SHIP and progress in the analysis will be discussed. [Preview Abstract] |
Thursday, October 9, 2014 10:15AM - 10:30AM |
DG.00005: Random Probability Analysis of $^{48}$Ca$+^{239}$Pu Experimental Data S.Y. Strauss, R.A. Henderson, M.A. Stoyer, A.F.Sh. Abdullin, N.T. Brewer, S.N. Dmitriev, R.K. Grzywacz, J.H. Hamilton, M.G. Itkis, K. Miernik, Yu.Ts. Oganessian, A.N. Polyakov, J.B. Roberto, K.P. Rykaczewski, A.V. Sabelnikov, R.N. Sagaidak, I.V. Shirokovsky, M.V. Shumeyko, V.G. Subbotin, A.M. Sukhov, Yu.S. Tsyganov, V.K. Utyonkov, A.A. Voinov, G.K. Vostokin Element 114 (Fl), was discovered at the Flerov Laboratory of Nuclear Reactions (FLNR) using the $^{48}$Ca $+ ^{244}$Pu reaction and the Dubna Gas-Filled Recoil Separator (DGFRS) [1]. The structural properties of the super heavy elements are still largely unknown. The extent of the region of enhanced stability near Z$=$114 and N$=$184 is not completely known. To examine these properties, a new experimental data set has been taken using the $^{48}$Ca $+ ^{239}$Pu reaction at the DGFRS, in an effort to look for lighter isotopes of Fl. Progress on the production of lighter isotopes of Fl, cross-section measurements, and any nuclear decay properties will be discussed. Comparisons with reactions using heavier $^{242,244}$Pu targets and Monte Carlo random probability analysis will be highlighted[2]. \\[4pt] [1] Yu.Ts.~Oganessian, \textit{et al}., Phys. Rev. C 62, 041604(R) (2000).\\[0pt] [2] N.J. Stoyer \textit{et al.,} Nuc. Inst. Meth. A 455 (2000). [Preview Abstract] |
Thursday, October 9, 2014 10:30AM - 10:45AM |
DG.00006: An evidence for SF decay of 284Fl Krzysztof Rykaczewski, Nathan Brewer, Robert Grzywacz, Krzysztof Miernik, Vladimir Utyonkov, Yury Oganessian, Alexandr Polyakov, Yury Tsyganov, Alexei Voinov, Max Shumeyko In order to expand our knowledge of the properties of superheavy nuclei and to partially fill the gap between the Island and Mainland, experiments with 239,240Pu targets and 48Ca beams were initiated at Dubna in November 2013. These studies are being performed using a new digital detection system commissioned by the ORNL-UTK team and implemented at the DGFRS (FLNR, JINR Dubna). An on-line test at the DGFRS using the 48Ca$+$natYb reaction allowed direct observation of alpha decay from thorium isotopes including 1-$\mu$s activity of 219Th. Irradiation of the 239Pu target, with a total beam dose of about 1.3 $\times$ 10$^{19}$, was performed between December 2013 and February 2014. The evidence for a new sub-millisecond isotope 284Fl will be presented and discussed. [Preview Abstract] |
Thursday, October 9, 2014 10:45AM - 11:00AM |
DG.00007: FIONA: A new mass analyzer for superheavy elements Nicholas Esker, Jacklyn Gates, Kenneth Gregorich, Gregory Pang, Heino Nitsche Six new superheavy elements (SHE, $Z = 112 - 118$) and over fifty new transactinide isotopes ($Z > 104$) have been synthesized in compound nuclear reactions using $^{48}\mathrm{Ca}$ on actinides. These SHE are short-lived; their decay chains end in spontaneous fission before reaching a known mass region. Direct mass determination was unavailable and their $A$ assignments remain unconfirmed. At LBNL, we use the 88''-cyclotron to produce high intensity beams ($10^{13}$ particles per second) and the Berkeley Gas-Filled Separator (BGS) to isolate and study such transactinides at a rate of atoms per week. Unfortunately, the BGS's high beam suppression comes at the cost of mass resolution. Ongoing upgrades to the BGS, including beam thermalization and fast ion transport, will allow us to couple a dedicated mass analyzer to the BGS. This Facility for Identification Of Nuclide $A$ (FIONA) is a novel mass separator based on an unbalanced Wien velocity filter. It has been designed for 100\% transmission with an expected mass resolution of $\approx$2000 A/$\Delta$A. We present the current progress in commissioning the FIONA mass analyzer using a $^{nat}\mathrm{Xe}$ ion source and the future directions of the project, including the first direct mass measurement of a superheavy element. [Preview Abstract] |
Thursday, October 9, 2014 11:00AM - 11:15AM |
DG.00008: Prospects for Production of New Superheavy Elements using Projectiles with Z \textgreater 20 Charles Folden Recent experiments have produced superheavy elements with atomic numbers up to Z $=$ 118 in complete-fusion evaporation reactions using projectiles of $^{48}$Ca, although projectiles with Z$_{\mathrm{p}}$ \textgreater 20 will be required for the discovery of heavier elements. A systematic study of the reactions of projectiles of $^{44,48}$Ca, $^{45}$Sc, $^{50}$Ti, and $^{54}$Cr with a variety of lanthanide targets has been conducted at Texas A{\&}M University. The products of these reactions are spherical, shell-stabilized nuclei near the N $=$ 126 shell. Excitation functions have been measured for numerous reaction combinations, and the data show a substantial reduction in cross section for reactions with Z$_{\mathrm{p}}$ \textgreater\ 20 compared to the reactions of $^{48}$Ca with the same targets. These data have been compared to a simple theoretical model which suggests that the probability of compound nucleus formation and the survival of compound nuclei are both negatively affected by the change from $^{48}$Ca. In these reactions, significant collective effects decrease the survival of the compound nuclei and defy the assumption that strong shell-stabilization will increase the cross section. These results suggest that the production of new spherical, shell-stabilized superheavy elements with Z \textgreater\ 118 could be very difficult. This talk will discuss the most recent results and their implications. [Preview Abstract] |
Thursday, October 9, 2014 11:15AM - 11:30AM |
DG.00009: A New Gas Stopper for Heavy Element Chemistry Research at the Texas A{\&}M University Cyclotron Institute Marisa Alfonso, Evgeny Tereshatov, Michael DeVanzo, Jordan Sefcik, Megan Bennett, Dmitriy Mayorov, Tyler Werke, Charles Folden A Recoil Transfer Chamber (RTC) to facilitate the chemical study of the heaviest elements, created via fusion-evaporation reactions, has been fabricated at the Cyclotron Institute at Texas A{\&}M University. This gas stopper is a hybrid of previously used RTCs in the transactinide field and one used at Michigan State University for stopping products from projectile fragmentation reactions. Our RTC uses laminar gas flow and a series of electrodes that create a potential gradient to efficiently transport evaporation residues to an appropriate chemistry experiment. The RTC was characterized offline using $^{216}$Po recoils from a $^{228}$Th source and online using a high cross section fusion-evaporation reaction, $^{118}$Sn($^{40}$Ar, 6n)$^{152}$Er. Results show an online extraction efficiency of (70 $+$/- 9) {\%}, which is comparable to devices used worldwide. This talk will discuss the design of the RTC and present results from offline and online experiments. [Preview Abstract] |
Thursday, October 9, 2014 11:30AM - 11:45AM |
DG.00010: Isomers and Enhanced Stability of Superheavy Elements Filip Kondev There has been continuing activity addressing the complex question of whether excited isomeric states would lead to enhanced stability of superheavy nuclei, given changes in the fission barriers, $\alpha$-decay probabilities and the effects of nuclear structure (such as K-hindrance). Recently, we have carried out new studies of the $^{254}$Rf isotope using the $^{50}$Ti+$^{206}$Pb reaction at Argonne National Laboratory and Lawrence Berkeley National Laboratory. A digital data acquisition system was deployed in both experiments, which allowed the identification of implant and decay events that were separated by time as short as hundreds of nanoseconds. Two isomeric states were discovered in $^{254}$Rf with half-lives of $\sim$4 $\mu$s and $\sim$300 $\mu$s, the latter being an order of magnitude longer lived than the ground state. In addition, K-isomers in $^{244}$Cm and $^{246}$Cm were also studied following $\beta^{-}$ decays of $^{244}$Am (K$^{\pi}$=6$^{+}$) and $^{246}$Am (K$^{\pi}$=7$^{-}$) mass-separated sources, respectively. The emphasis was on elucidating details of the level schemes, which allowed reliable values for the strength of the K-forbidden transitions to be determined and compared with systematics in other regions of the nuclear chart. [Preview Abstract] |
Thursday, October 9, 2014 11:45AM - 12:00PM |
DG.00011: The Importance of Closed Shell Structures in the Synthesis of Super Heavy Elements J.H. Hamilton, S. Hofmann, Y.T. Oganessian In 1965, macroscopic models predicted that nuclei beyond Z $\approx $ 100 could not be synthesized because their fission barrier would go to zero. Then came microscopic models with shell corrections. Microscopic-macroscopic models predicted large gaps in the single-particle energy levels for protons and neutrons at Z $=$ 102, 108 and N $=$ 152, 162 for deformed shapes. The reinforcement of the Z $=$ 102, N $=$ 152 and Z $=$ 108, N $=$ 162 level gaps at the same deformations provided the stability for nuclei in these regions to be observed. Also predicted were shell gaps for spherical shapes for N $=$ 184 and Z $=$ 114, 120 or 126 forming an ``Island of Stability'' with very long half lives for fission and alpha decay. Cold fusion reactions involving beams of Ca to Zn and targets of stable $^{208}$Pb and $^{209}$Bi were pioneered at GSI and used to synthesize new elements for Z $=$ 107 to 112 and in Japan a new isotope of 113. Hot fusion reactions between radioactive actinide targets and neutron-rich $^{48}$Ca beams were pioneered in JINR leading to the synthesis of new elements with Z $=$ 113 to 118. Data showing the importance of reinforcement of the Z $=$ 102, N $=$ 152 and Z $=$ 108, N $=$ 162 single particle level gaps at the same deformation and Z $=$ 114-126, N $=$ 184 shell gaps in the synthesis of super heavy elements 107 to 118 will be presented along with the latest results on their synthesis. [Preview Abstract] |
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