Entrance channels and alpha decay half-lives of the heaviest elements

The barriers standing against the formation of superheavy elements and their consecutive decay have been determined in the quasimolecular shape path within a Generalized Liquid Drop Model including the proximity effects between nucleons in a neck, the mass and charge asymmetry, a precise nuclear radius and the shell effects given by the Droplet Model. For moderately asymmetric reactions double-hump potential barriers stand and fast fission of compact shapes in the outer well is possible. Very asymmetric reactions lead to one hump barriers which can be passed only with a high energy relatively to the superheavy element energy. Then, only the emission of several neutrons or an particle can allow to reach an eventual ground state. For almost symmetric heavy-ion reactions, there is no more external well and the inner barrier is higher than the outer one. Predictions for partial decay half-lives are given.     

Production and properties of the heaviest elements

This article reviews the following topics which were discussed at the 375th Wilhelm and Else Heraeus-Seminar Workshop on the Atomic Properties of the Heaviest Elements held from September 25–27, 2006 at the Abtei Frauenw?rth im Chiemsee, Germany: (i) the recent progress in the production of the heaviest elements, the investigation of their nuclear structure, and prospects for direct mass measurements in Penning traps. (ii) Recent studies of their chemical properties with the aid of volatile species and single-atom aqueous-phase chemistry; (iii) the current status and future prospects for the investigation of atomic and ionic properties such as optical spectroscopy in gas cells and ion traps, including fully relativistic calculations of the atomic level structure with predictions for the element nobelium; and (iv) ionic charge radii measurements in buffer gas filled drift cells, and ion chemical reactions in the gas phase.     

Relativistic effects on atomic and molecular properties of the heaviest elements

Interaction of superheavy element 112 and its homolog Hg with inert and gold surfaces was studied on the basis of atomic and molecular fully-relativistic (4-component) DFT electronic structure calculations. Performance of additional non-relativistic calculations allowed one to demonstrate the role and magnitude of relativistic effects on adsorption energies and bond distances of the studied systems. For example, on quartz, element 112 will be stronger adsorbed than Hg by about 5 kJ/mol (or at 5 degrees higher temperatures) due to the stronger van der Waals interaction. This is caused by the relativistically contracted smallest atomic radius of element 112. Non-relativistically, the trend would be opposite. On surface of gold, element 112 will be about 20 kJ/mol weaker adsorbed than Hg (i.e., it will be deposited at about 100 degrees lower temperatures than Hg). Such a decrease in ΔH_ads comes at the account of the weaker interaction of the relativistically stabilized 7s_1/2(112) orbital with valence orbitals of gold. Still, the relatively large adsorption energy of element 112 is indicative that it is a transition metal forming intermetallic compounds with Au and other metals due to the involvement of the relativistically destabilized 6d orbitals. The influence of relativistic effects on the adsorption energy depends, however, on the adsorption position.     

Entrance and exit channels for the heaviest elements

The potential barriers governing the entrance and α decay channels of the heaviest elements have been determined within a Generalized Liquid Drop Model including the asymmetry, the proximity effects, an adjustment to reproduce the Q value and within the asymmetric two-center shell model and the Strutinsky method. In cold fusion reactions double-hump barriers stand and incomplete fusion may occur. Warm fusion paths lead to one-hump potential barriers but also to very excited systems cooling down by neutron or even α particle evaporation. Partial half-lives for α decay have been calculated and compared with the new available experimental data.     

Excitation effects on the nuclear-fission process in the heaviest elements

Calculations have been carried out of the fission barriers of excited nuclei for elements with Z = 102?108. The effect of nuclear heating is taken into account according to conventional quantum-statistical formulae. A realistic Woods-Saxon potential is employed to calculate single particle states. The- degree of deviation of the fissioning nucleus shape from axial symmetry and changes in the depth of the intermediate minimum are discussed.     

Systematic study of properties of Hs nuclei

The ground-state properties of Hs nuclei are studied in the framework of the relativistic mean-field theory. We find that the more relatively stable isotopes are located on the proton abundant side of the isotopic chain. The last stable nucleus near the proton drip line is probably the ²⁵⁵Hs nucleus. The a \alpha -decay half-lives of Hs nuclei are predicted, and together with the evaluation of the spontaneous-fission half-lives it is shown that the nuclei, which are possibly stable against spontaneous fission are ^263-274Hs . This is in coincidence with the larger binding energies per nucleon. If ^271-274Hs can be synthesized and identified, only those nuclei from the upper Z = 118 isotopic chain, which are lighter than the nucleus ²⁹⁴118 , and those nuclei in the corresponding a \alpha -decay chain lead to Hs nuclei. The most stable unknown Hs nucleus is ²⁶⁸Hs . The density-dependent delta interaction pairing is used to improve the BCS pairing correction, which results in more reasonable single-particle energy level distributions and nucleon occupation probabilities. It is shown that the properties of nuclei in the superheavy region can be described with this interaction.     

Level densities of heaviest nuclei

The intrinsic level densities of superheavy nuclei in the α-decay chains of ^296,298,300120 are calculated using the single-particle spectra obtained with the modified two-center shell model. The role of the shell and pairing effects on the level density as well as their quenching with excitation energy are studied. The extracted level density parameter is expressed as a function of mass number, ground-state shell correction, and excitation energy. The results are compared with the phenomenological values of level density parameters used to calculate the survival of excited heavy nuclei.     

Calculated masses of heaviest nuclei

Masses of heaviest nuclei are calculated within a macroscopic-microscopic approach. Even-even, odd-A, and odd-odd nuclides are considered. A large region of nuclei with proton and neutron numbers of Z=82–128 and N=126–192, respectively, is analyzed. The results are compared with those of other macroscopic-microscopic and of recent microscopic Hartree-Fock-BCS calculations. Alpha-decay energies are also given.     

Dilation-analyticity and decay properties of interactions

LetH=H ₀+V be a Schrödinger operator onL ²(? ⁿ ). We show that the more dilation analyticV is, the slower it must decay at infinity.     

Spectroscopy and decay properties of charmonium

The mass spectra of charmonium are investigated using a Coulomb plus linear(Cornell)potential.Gaussian wave functions in position space as well as in momentum space are employed to calculate the expectation values of potential and kinetic energy respectively.Various experimental states(X(4660)(5~3S_1),X(3872)(2~3P_1),X(3900)(2~1P_1),X(3915)(2~3P_0)and X(4274)(3~3P_1)etc.)are assigned as charmonium states.We also study the Regge trajectories,pseudoscalar and vector decay constants,electric and magnetic dipole transition rates,and annihilation decay widths for charmonium states.     

Some decay properties of 183Ir

The isotope ¹⁸³Ir was produced at the Yale Heavy Ion Accelerator via the ¹⁷⁵Lu(¹²C, 4n)¹⁸³Ir reaction and from the decay of ¹⁸³Pt, which was formed in the ¹⁶⁹Tm(¹⁹F, 5n)¹⁸³Pt reaction. The half-life of ¹⁸³Ir was found to be 55±5 min. Singles and coincidence γ-ray measurements were performed using 30–40 cm³ Ge(Li) detectors. X-ray measurements were carried out using an intrinsic Ge detector. The following γ-rays were found to belong to the decay of ¹⁸³Ir: 30.8, 87.7, 96.2, 102.2, 107.7, 136.8, 165.7, 194.5, 228.5, 236.7, 250.6, 254.4, 282.4, 286.1, 296.3, 314.4, 319.1, 342.2, 347.7, 392.4, 411.2, 457.7, 461.9, 498.4, 617.4, 655.1, 670.8, 692.2, 706.1, 724.8, 800.1 and 896.7 keV. A tentative decay scheme for ¹⁸³Ir is proposed verifying levels in ¹⁸³Os.     

Spectrum and decay properties of diquonia

Using the interquark potential due to Bhaduri et al., the properties ofq ² q ^?2 systems are studied within a non-relativistic quark model. A systematics over the various flavorsu, d, s, c, b, over the total spinS and over the orbital angular momentumL=0, 1, 2, 3 is carried out, while the parity is taken as the natural one. Not only the spectrum, but also the decay properties of each state are evaluated and the wave functions are analyzed in term of dumbbell structure. We propose a number of new resonances which could have a very narrow width.     

A possible probe of neutrinoless double-beta decay nuclear matrix elements

Future experiments on the search for the 0??|? decay will be sensitive to the effective Majorana mass in the region of the inverted mass hierarchy. If a positive signal is observed, a possibility to test models of calculation of nuclear matrix elements of the process will appear. We discuss this possibility in some detail.     

Systematic study of a decay half-lives within the Generalized Liquid Drop Model with various versions of proximity energies

It is universally acknowledged that the Generalized Liquid Drop Model(GLDM)has two advantages over other a decay theoretical models:introduction of the quasimol...     

可能合成的超重核的alpha衰变能和半衰期

本文考察和研究了将来可能在实验上合成的超重新元素和新核素的基态性质。研究的重点主要放在原子核的alpha衰变能和半衰期。详细比较和讨论了不同理论模型计算的alpha衰变能和半衰期。通过这些计算和比较,从理论上提出了将来在实验上比较容易合成的超重新元素和新核素的性质。理论计算结果可为将来的超重核实验提供理论参考。     

Description of α-decay half-lives of heaviest nuclei

The accuracy in describing α-decay half-lives T _α of heavy and superheavy nuclei is studied. A simple five-parameter phenomenological formula, expressing T _α as a function of the α-decay energy Q _α, is considered. It is found that such a formula can describe measured values of T _α within a factor of 1.3 for even-even, 2.1 for odd-even, 3.2 for even-odd, and 4.0 for odd-odd nuclei when measured values of Q _α are taken. This accuracy is decreased by a factor of about 4 when theoretical values of Q _α are used. The latter are obtained within a macroscopic-microscopic approach and reproduce the experimental values of Q _α of the same nuclei with an average accuracy of about 190 keV for even-even, 270 keV for odd-even, 260 keV for even-odd, and 330 keV for odd-odd nuclei. In the analysis, 201 nuclei with proton number Z = 84–111 and neutron number N = 128–161, with measured values of both Q _α and T _α, are taken. The text was submitted by the authors in English.