Α-decay Chains Research Articles

Measurement of Evaporation Residue and Fission Cross Sections of the Reaction 30Si + 238U at Subbarrier Energies

Effects of the prolate deformation of 238 U on fusion were studied in the reaction 30 Si + 238 U at bombarding energies close to the Coulomb barrier. The fission (capture) cross sections were measured at the JAEA tandem accelerator to see the enhancement of the cross sections in the subbarrier energy due to the lower Coulomb barrier in the collisions of projectile at the polar sides of 238 U. In order to obtain the direct evidence for complete fusion, evaporation residue cross sections were measured at UNILAC of GSI. At the subbarrier energy of Ec.m. = 133.0 MeV, where only polar collisions to 238 U occur, we measured three spontaneously fissioning nuclei which we assigned to the isotope 264 Sg. The obtained cross section (10 +10 – 6 ) pb was smaller than the calculation that the system captured at the polar collisions results in complete fusion, suggesting the competition between fusion and quasifission. At the above barrier energy of Ec.m. = 144.0 MeV, where collisions on the equatorial side of 238 U start to contribute, we observed α-decay chains starting from 263 Sg and the cross section was determined to be (67 +67 ) pb. The data was reproduced by the calculation that the system captured from the equatorial side of 238 U results in complete fusion.

Self-consistent Dirac quasi-particle blocking approximation applied to the α-decay scheme of the superheavy element 287115

A Dirac–Hartree–Bogoliubov formalism for axially deformed nuclei is used to study the ground-state properties of odd–even and odd–odd mass nuclei. The effect of odd proton/neutron numbers is treated by using a self-consistent Dirac quasi-particle blocking method. The approach is tested by studying the ground-state properties of known medium-mass proton-rich odd–odd and even–odd nuclei. The method is applied to the 287115 and 288115 nuclei where the ground state and low-lying single-particle states and deformations are calculated. Results for the α energies and half-lives in the α-decay chain of 287115 are compared with experimental data and other calculations.

Microscopic description of superheavy nuclei

The results of extensive microscopic relativistic mean field (RMF) calculations for the nuclei appearing in the α-decay chains of recently discovered superheavy elements with 109 ⩽ Z ⩽ 118 are presented and discussed. The calculated ground-state properties like total binding energies, Q-values, deformations, radii, and densities closely agree with the corresponding experimental data, where available. The root mean square radii closely follow A 1/3 law ( A being the mass number) with the constant r o = 0.9639 ± 0.0005 fm. The double folding ( tρρ) approximation is used to calculate the interaction potential between the daughter and the α, using RMF densities along with the density-dependent nucleon–nucleon interaction (M3Y). This in turn is employed within the WKB approximation to estimate the half-lives without any additional parameter for α-decay. The half-lives are highly sensitive to the Q-values used and qualitatively agree with the corresponding experimental values. The use of experimental Q-values in the WKB approximation improves the agreement with the experiment, indicating that the resulting interaction potential is reliable and can be used with confidence as the real part of the optical potential in other scattering and reaction processes.

Ground State Properties of New Element Z = 113 andIts Alpha Decay Chain

We investigate the ground state properties of the new element278113 and of the α-decay chain with different models, wherethe new element Z = 113 has been produced at RIKEN in Japan bycold-fusion reaction [Morita et al. J. Phys. Soc. Jpn.73 (2004) 2593]. The experimental decay energies are reproduced by thedeformed relativistic mean-field model, by the Skyrme–Hartree–Fock (SHF)model, and by the macroscopic-microscopic model. Theoreticalhalf-lives also reasonably agree with the data. Calculations further showthat prolate deformation is important for the ground states of thenuclei in the α-decay chain of 278113. The commonpoints and differences among different models are compared and discussed.

Evidence for the formation of sodium hassate(VIII)

SummaryHassium, element 108, was produced in the fusion reaction between26Mg and248Cm. The hassium recoils were oxidizedin-situto a highly volatile oxide, presumably HsO4, and were transported in a mixture of He and O2to a deposition and detection system. The latter consisted of 16 silicon PIN-photodiodes facing a layer of NaOH, which served, in the presence of a certain partial pressure of water in the transport gas, as reactive surface for the deposition of the volatile tetroxides. Six correlated α-decay chains of Hs were detected in the first 5 detectors centred around detection position 3. In analogy to OsO4, which forms Na2[OsO4(OH)2], an osmate(VIII), with aqueous NaOH, HsO4presumably was deposited as Na2[HsO4(OH)2], a hassate(VIII).

Production and Decay Properties of272111 and its Daughter Nuclei

The production and decay of 272 111 has been investigated using a gas-filled recoil ion separator in irradiations of 209 Bi targets with 64 Ni beam at 320, 323 and 326 MeV. We have observed 14 α-decay chains in total, that can be assigned, on the basis of their time correlations, to subsequent decays from 272 111 produced in the 209 Bi( 64 Ni,1n) reaction. The present result is the first clear confirmation for the discovery of 272 111 and its α-decay products, 264 Bh and 268 Mt, reported previously by a GSI group. New information on their half-lives and decay energies as well as the excitation function is presented.

Relativistic mean field study of the newly discovered α-decay chain of 287115

The single particle structure of the low lying levels in the nuclei belonging to the newly observed α-decay chain starting from 287115 has been studied. Relativistic mean field calculation with two forces NL1 and NL3 has been performed in the blocked BCS approximation. Q-values for possible decay have been calculated and compared with experiment. Lifetime estimates obtained from phenomenological relations have also been compared.

Status of heavy element research using GARIS at RIKEN

A gas-filled recoil separator GARIS was installed at the RIKEN Linear Accelerator facility. Using the separator, two reactions, 208 Pb( 64 Ni, 1n), and 209 Bi( 64 Ni, 1n), were investigated. In the first reaction we observed fourteen α-decay chains which were assigned to be the decays starting from the isotope 271 Ds(Z=110). The α-decay energies as well as the decay times coincided well with the values reported by GSI group. Existence of an isomeric state in 271 Ds became clear from the present work. In the second reaction we have observed 14 α-decay chains that can be assigned to subsequent decays from 272 111. The present result is the first clear confirmation for the discovery of 272 111 and its α-decay products, 264 Bh and 268 Mt, reported previously by a GSI group. New information on their half-lives and decay energies is presented.

Status of heavy element research using GARIS at RIKEN

A gas-filled recoil separator GARIS was installed at the RIKEN Linear Accelerator facility. Using the separator, two reactions, 208Pb( 64Ni, 1n), and 209Bi( 64Ni, 1n), were investigated. In the first reaction we observed fourteen α-decay chains which were assigned to be the decays starting from the isotope 271Ds(Z=110). The α-decay energies as well as the decay times coincided well with the values reported by GSI group. Existence of an isomeric state in 271Ds became clear from the present work. In the second reaction we have observed 14 α-decay chains that can be assigned to subsequent decays from 272111. The present result is the first clear confirmation for the discovery of 272111 and its α-decay products, 264Bh and 268Mt, reported previously by a GSI group. New information on their half-lives and decay energies is presented.

STRUCTURE OF SUPERHEAVY NUCLEI WITH THE GOGNY FORCE

This contribution summarizes the predictions obtained in the domain of superheavy nuclei from self-consistent microscopic calculations employing the Gogny force. Results concerning shell gaps, fission barriers and stability against alpha-decay are recalled. Recent work involving α-decay chains in odd nuclides is also presented and discussed.

Elements discrimination in the study of super-heavy elements using an ionization chamber

Dedicated ionization chamber (IC) was built and installed to measure the energy loss of very heavy nuclei at 2.7 MeV/ u produced in fusion reactions in inverse kinematics (beam of 208 Pb ). After going through the IC, products of reactions on 12 C , 18 O targets are implanted in a Si detector. Their identification through their α-decay chain is ambiguous when their half-life is short. After calibration with Pb and Th nuclei, the IC signal allowed us to resolve these ambiguities. In the search for rare super-heavy nuclei produced in fusion reactions in inverse or symmetric kinematics, such a chamber will provide direct information on the nuclear charge of each implanted nucleus.

Structure effects in the region of superheavy elements via the α-decay chain of 293118

The α-decay chain of 293118, first proposed in the Berkeley cold fusion experiment 208Pb(86Kr, 1n) and now retracted, is calculated by using the preformed cluster model (PCM) of one of the authors (RKG). Also, the possible branchings of α-decays to heavier cluster decays of all the parents in this chain are calculated for the first time. The calculated Q-values, penetrabilities and preformation factors for α-decays suggest that the 285114 nucleus with Z = 114, N = 171 is a magic nucleus, either due to the magicity of Z = 114, or N = 172 or both. The N = 172 is proposed to be a magic number in certain relativistic mean-field calculations, but with Z = 120. The calculated cluster decays point to new interesting possibilities of 14C decay of the 281112 parent, giving rise to a (reasonably) deformed Z = 106, N = 161, 267106 daughter (N = 162 being now established as the deformed magic shell) or to a doubly magic 48Ca cluster emitted from any of the parent nucleus in the α-decay chain. Apparently, these are exciting new directions for future experiments.

Production of Super Heavy Elements at GANIL: Present Status and Perspectives

Ins. Fyziki Uniw., Krakow, Polandproceeding to the ASR2001 Conference, to be publishedin the Journal of Nuclear and Radiochemical Sciences (june 2002)AbstractExperiments on the production and study of superheavy nuclei have been un-dertaken at GANIL taking advantages of the powerful velocity filter LISE3 andthe high intensity ECR ion sources. A complete set-up has been built: - reactionchamber containing large rotating wheels, - slits and beam profiler at mid-filter,- detection chamber with time-of-flight and Silicon detectors for identifying evap-oration residues and their decay products. The response was checked via fusionreactions with known cross sections producing known α-decay chains and fissionfragments. Excellent transmission of evaporation residues and rejection factor forthe primary beam were obtained. This device is presented together with the resultsobtained in our last experiments and our future plans are discussed.

Mass mapping of a new area of neutron-deficient suburanium nuclides

The masses of 64 short-lived neutron-deficient nuclides covering the element range from tungsten to uranium have been obtained for the first time. They have been evaluated by combining directly measured masses from Schottky mass spectrometry with linked experimental Q-values in α-decay chains. Based on these new mass data we have determined the one-proton and two-proton drip-lines as well as the size of the “littoral shallow” of the sea of instability. No evidence of a Thomas–Ehrman shift has been found in the region of the investigated heavy nuclides. A peculiar behavior of two-proton separation energies has been observed in the lead region. The predictive power of various mass models is investigated.

Superdeformation in the newly discovered superheavy elements

The structures of newly discovered superheavy elements with the proton number Z=110–112, 114, 116, 118 and of their α-decay chain nuclei are investigated using the self-consistent relativistic mean-field (RMF) theory. Extensive calculations show that the experimental data on the α-decay energies are well reproduced by the RMF theory. We find sometimes shape coexistence in superheavy nuclei and a superdeformed prolate configuration becomes the ground state of the new superheavy elements. The superdeformation could lead to a slightly deeper binding and give a longer lifetime for superheavy nuclei than expected. This may be a new mechanism for the appearance of the superheavy island. A systematic comparison with other models for the calculated binding energies and deformations is carried out, and predictions on the properties of unknown neighbouring superheavy nuclei are made for further comparison with future experiments.

The new isotope 270110 and its decay products 266Hs and 262Sg

The even-even nucleus 270110 was synthesized using the reaction 64Ni + 207Pb. A total of eight α-decay chains was measured during an irradiation time of seven days. Decay data were obtained for the ground-state and a high-spin K isomer. The new nuclei 266Hs and 262Sg were identified as daughter products after α-decay. Spontaneous fission of 262Sg terminates the decay chain. The measured data are in agreement with calculations using the macroscopic-microscopic model and with self-consistent HFB calculations with Skyrme-Sly4 interaction.

Masses and Proton Separation Energies Obtained from Q α and Q p Measurements

For many nuclei beyond the proton drip line in the Z > 72, N > 82 region, both proton and α emission are energetically allowed. In the case of some proton emitters, there are α-decay chains emanating from both parent and daughter nuclei. This means that if the mass excess of one member of an α-decay chain is known, then the mass excesses for all members of both chains can be obtained. In addition, proton separation energies may be derived for nuclei in the α-decay chain of the proton emitter. The method of time- and space-correlations also allows the identification of isomeric states in these nuclei. As an example, a large number of mass excesses and proton separation energies for ground and metastable states have been derived from Q α and Q p values obtained from the proton emitters 165,166,167Ir, 171Au, 177Tl and their daughters.

Fine Structure in the alpha decays of 226U and 230Pu

The nuclei 226U and 230Pu have been populated via reactions involving 208Pb targets bombarded by 22Ne and 26Mg projectiles. Fusion-evaporation residues were separated in-flight using a gas-filled recoil separator. A position-sensitive Si-strip detector was employed at the focal plane in order to identify correlated α-decay chains. Two fine structure α-decay lines have been observed. The first, with an energy of 7385(5) keV, is assigned as the α decay from 226U to the first excited 2+ state of 222Th. The second line, observed for the first time in this work, has an energy of 6961(30) keV and is assigned as the α decay from 230Pu to the first excited 2+ state of 226U. The excitation energy of the first excited 2+ state in 226U was determined to be 96(25) keV, giving an estimate of the deformation parameter β2≃ 0.20.

Alpha-decay characteristics of neutron-deficient 190Po, 189Bi and 186Pb isotopes

The neutron-deficient 190Po and 189Bi isotopes have been produced in the 2n respectively p2n channels of the 48Ti +144 Sm reaction. Cross sections for different reaction channels are given. For 190Po, improved values of α-energy Eα = 7550(15) keV and half-life T1/2 = 1.9−0.4+0.6 ms were measured. By using correlated α-decay chains an α-branching ratio of 0.50(25) was deduced for 186Pb. The reduced α-width systematic is extended for both of these isotopes, confirming a persistence of the saturation towards the lighter Po isotopes and the absence of any anomalies for the neutron-deficient Pb isotopes. For 189Bi improved values of Eα = 7300(15) keV and T1/2 = 4.8(5) ms were measured.

Nuclear Data Sheets for A = 194

Abstract:Experimental data pertaining to all nuclei with mass A = 194 were evaluated. Level schemes from both radioactive decay and reaction studies are presented, along with associated tables of experimental data and adopted properties for levels and γ rays. The literature cutoff date for this revision is September 30, 1996. This revision replaces 89SiO1. Extensive high-spin experiments using large gamma-detector arrays have revealed superdeformed structures in 194Hg (three SD bands: Yrast and pair of excited signature partners), 194Tl (six SD bands: Three pairs of signature partners), and 194Pb (three SD bands: Yrast and pair of excited signature partners). For yrast bands (SD-1) in 194Hg and 194Pb, connecting transitions between the SD band and normal bands have recently (96Kh04, 96Lo12,96Br07) been reported. Several dipole (oblate) bands in 194Pb, some based on high-K (oblate) states have been reported from similar in-beam γ-ray experiments. New γγ coincidence measurements (93Ko59, 94KoZQ) using the 193Ir(n,γ) reaction helped to place several transitions in the level scheme and established the 31.85-ms 194Ir isomer at 147.078 KeV 5. Results from the first study of the 193Ir(d,p) reaction (94Ga30) agree with those from (n,γ). Unpublished (95TeZZ) γγ coincidence results (using HERA, an array of 20 intrinsic germanium detectors) revealed a new level in 194Pt at 1737.4 KeV. It also provided correct placement in the decay scheme for many γ rays from 194Au ϵ decay. Recent measurements (92Hu04) of the α-decay chain 202Fr– 196At– 194Bi confirm the existence of 194Bi isomers, and show population to previously unknown levels at 218 and 396 KeV in 194Bi. Cutoff Date:All data received by September 30, 1996 were evaluated. General Policies and Organization of Material:See the January issue of Nuclear Data Sheets. Acknowledgments:Evaluators wish to thank R.R.P. Teixeira (95TeZZ) for making available their unpublished data on 194Au ϵ decay. General Comments:The analysis of γ-ray data is described in detail in 86BrZQ. The γ-ray energies given by various authors were fit to a level scheme for each data set through a weighted least-squares analysis. The scales for the corresponding intensities, which were assumed to be linearly related, were adjusted using the methods of Tepel (80TeZW) and Lederer (92LeZJ). Uncertainties of absolute γ-ray intensities were determined using the method of Browne (86Br21).