Experimental methods for heavy element research will be presented. Recent experimental results are discussed together with recent theoretical predictions. New instrumental developments and future plans will be discussed.

抄録全体を表示

The paper presents results on the synthesis of superheavy nuclides with Z=114 and 116 in the fusion reactions with ⁴⁸Ca ions. In the irradiation of targets made from enriched ²⁴⁴Pu and ²⁴⁸Cm isotopes with beam doses of 1.5×10¹⁹ and 2.3×10¹⁹, respectively, the detector array situated in the focal plaaane of the gas-filled separator registered heavy atoms of new elements undergoing sequential a decays terminated by spontaneous fission. The time of the decay chains is approximately one minute. Decay properties of the synthesized nuclei are consistent the consecutive α decays originating from the parent nuclides ²⁸⁸ 114 and ²⁹⁶ 116 produced in the 4n-evaporation channels with the cross section of about a picobarn. Comparison of T_SF and T_α values for the nuclei with Z=110 and 112 with those obtained earlier for lighter isotopes of these elements points to an enhanced stability of heavy nuclei with an increase in the neutron number. The α-decay energies Q_α measured experimentally in the chains 116-α₁-1l4-α₂-112-α₃-110 are compared with theoretical predictions of different nuclear models. This comparison shows that the difference between the experiment and theory is in the range of ±0.5 MeV. From this it follows that the theoretical models predicting the decisive influence of the nuclear structure on the stability of superheavy elements are well-founded not only qualitatively but in some sense also quantitatively. The prospects of further investigations in the field of superheavy nuclei are discussed briefly.

抄録全体を表示

Experiments on the production and study of superheavy nuclei have been undertaken at GANIL taking advantages of the powerful velocity filter LISE3 and the high intensity ECR ion sources. A complete setup has been built: -reaction chamber containing large rotating wheels, - slits and beam profiler at mid-filter, - detection chamber with time-of-flight and Silicon detectors for identifying evaporation residues and their decay products. The response was checked via fusion reactions with known cross sections producing known α-decay chains and fission fragments. Excellent transmission of evaporation residues and rejection factor for the primary beam were obtained. This device is presented together with the results obtained in our last experiments and our future plans are discussed.

抄録全体を表示

A new mechanism of the fusion-fission process for a heavy nuclear system is proposed, which takes place in the (A₁, A₂) space, where A₁ and A₂ are two nuclei, surrounded by a certain number of shared nucleons ΔA. The nuclei A₁ and A₂ gradually lose (or acquire) their individualities with increasing (or decreasing) a number of collectivized nucleons ΔA. The driving potential in the (A₁, A₂) space is derived, which allows the calculation of both the probability of the compound nucleus formation and the mass distribution of fission and quasi-fission fragments in heavy ion fusion reactions. The cross sections of super-heavy element formation in the "hot" and "cold" fusion reactions have been calculated up to Z_CN=118.

抄録全体を表示

The fusion-fission process for synthesis of superheavy elements is studied on the basis of the fluctuation-dissipation dynamics. Recently at Dubna the experiments on the fission of superheavy nuclei were carried out and they presented the fusion-fission cross section. We calculated the fusion-fission cross section of these systems and compared with these experimental data.

抄録全体を表示

We developed a combined approach for the calculation of the fusion cross section and the evaporation residue cross sections in reactions with heavy ions. The method consists of two parts. The first part is a Langevin dynamics with which we can calculate the touch probability of the incident ions P_touch and the formation probability of the compound nucleus P_form. Their product gives the fusion probability P_fus. The second part is a statistical calculation. We employ the code HIVAP for calculations of the survival probability P_surv of the compound system. The approach is tested on the reaction ⁴⁸Ca+²³⁸U and is applied to ⁴⁸Ca+²⁴⁴Pu system. The preliminary results are presented.

抄録全体を表示

The cold fusion reactions related to ²⁰⁸Pb and ²⁰⁹Bi targets leading to superheavy elements with Z=104-112 have been successfully considered in our model recently. Here we briefly discuss this model and extend our consideration to another type of fusion reactions. The interaction potential between heavy ions around the touching point is calculated for various Skyrme forces in the extended Thomas-Fermi approximation by using the frozen Hartree-Fock-Bogoliubov densities of the individual nuclei. The shape of fragment mass distribution in the case of ternary fission mode is discussed in detail.

抄録全体を表示

Angular distributions of elastic scatterings for ¹⁹F+²⁰⁸Pb system have been measured at six energies around the Coulomb barrier. It is found that the real and imaginary potentials show pronounced energy dependence in terms of the phenomenological optical model analysis. The real parts of potentials extracted from the fusion data are similar to those from the elastic data. A comparison with the neighbouring systems of ¹⁶O+²⁰⁸Pb and ¹⁶O+²⁰⁹Bi reveals that the ¹⁹F deformations play an important role in the fusion reaction. Based on the deformed and energy dependent barrier penetration model, the calculated fusion cross sections and mean-square spin distribution agree with the experimental data well. Moreover, it is indicated that the enhancement of fusion cross sections attributes to the dynamic polarization effects around the barrier, and to the static deformation effects further below the barrier.

抄録全体を表示

In heavy element synthesis, the population surviving quasi-fission and fusion-fission is far out in the tail of the distribution of reaction outcome probabilities, and should be sensitive to slight changes in the reaction conditions. Because of the extremely low yields of very heavy elements, it is difficult to make detailed and systematic experimental studies. However, studies of less-fissile systems can give valuable information relevant to the formation of super-heavy elements. Measurements made at the ANU, Canberra, to study the influence of entrance-channel properties on the subsequent reaction dynamics are presented. New and surprising data show that the entrance-channel mass-asymmetry plays a role in the compound nucleus formation probability, even when forming a nucleus as light as ²¹⁶Ra. The influence of different physical configurations, related to different contact barrier energies, on superheavy element formation is discussed.

抄録全体を表示

The dependence of the fusion probability on the orientation of deformed nucleus was investigated for the reactions ^{60, 64}Ni+¹⁵⁴Sm and ⁷⁶Ge+¹⁵⁰Nd. Evaporation residues were measured for these reaction systems by the JAERI recoil mass separator in the vicinity of the Coulomb barrier and the fusion probability was extracted as a function of bombarding energy. It was found that the fusion probability depends strongly on the orientation of the nuclear deformation. The fusion probability is considerably reduced when the projectiles collide at the tip of the deformed nuclei. On the other hand, when the projectiles collide at the side of the deformed nuclei, the fusion occurs without hindrance. This phenomenon is understood qualitatively by comparing the distance between the mass centers of two colliding nuclei at touching with the position of the saddle point of the compound nucleus. The dependence of the fusion probability on the nuclear shell closure was also investigated for the reactions ⁸²Se+^{134, 138}Ba, where the nucleus ¹³⁸Ba has a closed neutron shell of N=82 and the nucleus ¹³⁴Ba has the neutron number N=78, four neutrons less than the closed shell. The measured evaporation residue cross section for the reaction ⁸²Se+¹³⁸Ba was well reproduced by statistical model calculations taking into account a subbarrier fusion enhancement, while the evaporation residue cross section for the reaction ⁸²Se+¹³⁴Ba was about 100 times smaller than that for the fusion reaction ⁸²Se+¹³⁸Ba. This suggests that the shell closure plays an important role in the fusion process.

抄録全体を表示

We present a method for finding very general reflection asymmetric equilibrium (saddle-point) nuclear shapes, as solutions of an integro-differential equation, without giving a shape parametrization. By introducing phenomenological shell corrections one obtains minima of deformation energy for binary fission of parent nuclei ²³⁸U, ^{232, 228}That a non-zero mass asymmetry, leading to the same mass number of the heavy fragment A₁=125. Applications for fission into more than two and three fragments are also illustrated.

抄録全体を表示

At GSI, Darmstadt, an experimental program on fission with relativistic heavy-ion beams is in progress. A large range of excitation energies, combined with low angular momentum and small shape distortion is accessible. Full nuclide identification of the reaction residues is achieved by applying inverse kinematics. The nuclide production and the kinematics of fission fragments from a variety of primordial and radioactive projectiles reveal new insight into the influence of shell effects and dissipation on the fission process. The present contribution gives an overview on the experimental methods, the experimental results, and the prospects for future progress.

抄録全体を表示

The process of fusion-fission of superheavy nuclei with Z=102-122 formed in the reactions with ²²Ne, ²⁶Mg, ⁴⁸Ca, ⁵⁸Fe, and ⁸⁶Kr ions at energies near and below the Coulomb barrier has been studied. The experiments were carried out at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR) using a time-of-flight spectrometer of fission fragments CORSET and a neutron multi-detector DEMON. As a result of the experiments, mass and energy distributions of fission fragments, fission and quasi-fission cross sections, multiplicities of neutrons and γ-quanta, and their dependence on the mechanism of formation and decay of compound superheavy systems have been studied.

抄録全体を表示

In order to clarify the relationship between a mass distribution and shell structure of the fission fragments in nuclear fission, the fragment mass and the kinetic energy distributions in the proton-induced fission of plutonium isotopes, ^{239, 242, 244}Pu, were precisely measured using a double time-of-flight system. It was found that the position of the light side of the heavy asymmetric mass distributions shifts to a larger fragment mass number according to the neutron-proton ratio, N_f/Z_f, of the fissioning nucleus. The result is qualitatively explained by the change of the most probable mass number of fission fragments for Z=50 proton shell.

抄録全体を表示

We investigate fission modes of ²⁷⁰Sg with 3-dimensional Langevin equation. The shell correction energy is included in the total energy. The mass distribution and the total kinetic energy (TKE) distribution of fission fragments are calculated and are compared with the experimental results. Mass asymmetric fission dominates in the mode with the lower TKE, which is in agreement with the experimental result. The dynamics from saddle to scission is also discussed.

抄録全体を表示

The two stage approach to the description of fusion-fission reactions is suggested. On each stage (fusion or fission) the tree-dimensional Langevin equation for the variables describing the shape of nuclear system is solved. The results obtained on the first stage are used as the input data for description of fission dynamics. In this way it turned out possible to describe for the reaction ¹⁸O + ²⁰⁸Pb simultaneously both fusion and fission cross sections, the energy and mass distribution of fission fragments, the probability of the evaporation residue formation, the dependence of pre-fission neutron multiplicities on the fragment mass number. From the results of the computations it follows that the observed quantities of the fission process can be reproduced without formation of compound nucleus. At the same time the duration of the process is so large that events of quasi-fission and "true" fission of compound nucleus can not be distinguished.

抄録全体を表示

We investigate the formation and the decay of heavy systems which are above the fission barrier. By using a microscopic simulation of constrained molecular dynamics (CoMD) on Au+Au collision, we observe composite states stay for very long time before decaying by fission.

抄録全体を表示

Recent experimental investigations are pointing to the existence of a new type of nuclear phenomenon which consists in the formation of a long living molecule during the cold fragmentation of ²⁵²Cf. For such long times it is possible that the nuclear molecules rotate and vibrate like atomic molecules making thus possible the study of a new type of spectroscopy. We present in this paper the basic ideas which are leading to the calculation of rotational and vibrational bands of three-clusters molecules.

抄録全体を表示

The transactinide nuclei, ²⁶¹Rf and ²⁶²Db, have been produced in the ²⁴⁸Cm (¹⁸O, 5n) reaction at beam energies of 91, 94, and 99 MeV, and in the ²⁴⁸Cm (¹⁹F, 5n) reaction at 106 MeV, respectively. The production cross sections are evaluated from the mother-daughter correlations of α energies between ²⁶¹Rf and ²⁵⁷No, and ²⁶²Db and ²⁵⁸Lr. The maximum cross section of the ²⁴⁸Cm (¹⁸O, 5n) reaction is measured to be 13±3 nb at around 94 MeV, while the production cross section of ²⁶²Db in ²⁴⁸Cm (¹⁹F, 5n) is 1.3±0.4 nb at 106 MeV.

抄録全体を表示

Fusion probabilities for the ⁷⁶Ge + ¹⁵⁰Nd and ⁸²Se + ^natCe reactions were obtained near the Coulomb barrier, and the effects of nuclear deformation on the fusion process were discussed. The former reaction represents fusion involving the prolately deformed target ¹⁵⁰Nd, whereas the latter reaction is the fusion with the spherical target ^natCe. We obtained the fusion probability by measuring the evaporation residue (ER) cross sections. The system ⁸²Se + ^natCe showed fusion hindrance in the form of the extra -extra-push energy of 27±5 MeV, whereas the system ⁷⁶Ge + ¹⁵⁰Nd does not show any hindrance at the bombarding energy corresponding to the Coulomb barrier for the collision of ⁷⁶Ge on the side of ¹⁵⁰Nd. Our results suggest that the reaction starting from the compact touching point (side collision) results in a higher fusion probability.

抄録全体を表示

Prompt neutron spectra for Am isotopes (²⁴¹ Am, ^242mAm, ²⁴³Am) were calculated on the basis of a modified version of the Madland-Nix model combined with multimodal fission model. The predicted spectra were found to be in fair agreement with recent data.

抄録全体を表示

The average angular momentum of the primary fission fragments as a function of their masses was calculated using the wave function of the bending mode excitation at the scission point. The scission configuration was assumed to be determined by the prescission shapes of fissioning nucleus within the multimodal fission model. Results in ²³⁵U (n_th, f) is in good agreement with the recent experimental data.

抄録全体を表示

The fission cross sections and fragment angular distributions for the complete fusion-fission reactions of ¹¹B + ²³⁸U, ²³⁷Np, ¹²C + ²³⁷Np, ¹⁶O + ²³²Th, ²³⁸U, and ¹⁹F + ²³²Th at near-and sub-barrier energies have been measured by the fragment folding angle technique. It is revealed that the anomalous anisotropies of fission fragments in latter three systems are existence. Based on the experimental observations and Dφssing and Randrup's theory, a new version model of preequilibrium fission is put forward to explain the anomaly.

抄録全体を表示

The deformation properties of heavy nuclei undergoing the individual fission paths are studied. To understand the nuclear mass division process at low energy, fission events for the symmetric and asymmetric fission paths are analyzed from the overall fission events. The fragment mass-yield distributions for the symmetric and asymmetric fission paths in the fission processes of ²¹⁰Po, ²²⁷Ac, ²³³Pa, ²⁴⁹Bk, and ²⁵⁹Md are systematically studied. Fission characteristics including the deformation of the fissioning nucleus at the scission configuration, the fragment massyield distributions, and the total kinetic energy release for individual fission paths are presented.

抄録全体を表示

A first prediction of the chemistry of superheavy elements has been given 30 years ago using many-electron relativistic atomic structure calculations in the quality of that time. The first relativistic molecular calculation for a system with a transactinide element was published in 1977. Since then relativistic atomic and molecular structure calculations have been considerably improved and applied to many atoms and molecules. In this review we try to outline the general theory and the development of the quality of such calculations with less and less approximations as well as better and better numerical methods and higher accuracy. But even if one has quite accurate total energies, quantities like effective charges, overlap populations or radii of the outermost wavefunctions are still a very valuable information for an effective prediction of the chemical behavior of the superheavy elements.

抄録全体を表示

The chemistry of transactinides and superheavy elements has reached element 108. Preparations are under way to leap to element 112 and beyond. This development, its current status and future perspectives are reviewed from an experimental point of view. The atom-at-a-time situation of transactinide chemistry is briefly outlined. Experimental techniques and important results enlightening the chemical properties of elements 104 through 108 are presented in an exemplary way with emphasis on the aqueous chemistry of the lighter ones. From the results of these experiments it is justified to place these elements in the Periodic Table of the Elements into groups 4 through 8, respectively. However, strongly due to the influence of relativistic effects, it is no longer possible to deduce detailed chemical properties of these superheavy elements from this position. Perspectives for future research programs are given.

抄録全体を表示

The SISAK liquid-liquid extraction system was used to extract 4.0-s ²⁵⁷Rf. The ²⁵⁷Rf was produced in the reaction ²⁰⁸Pb (⁵⁰Ti, 1n) ²⁵⁷Rf with 237-MeV beam energy on target, separated in the Berkeley Gas-filled Separator (BGS) and transferred to a gas jet using the Recoil Transfer Chamber (RTC). The activity delivered by the gas jet was dissolved in 6-M HNO₃ and Rf was extracted into 0.25-M dibutyl-phosphoric acid in toluene. This was the first time a transactinide, i. e., an element with Z≥104, was extracted and unequivocally identified by the SISAK system. Thus, this pilot experiment demonstrates that the fast liquid-liquid extraction system SISAK, in combination with liquid-scintillation detectors, can be used for investigating the chemical properties of the transactinides. The extraction result is in accordance with the behaviour shown by the Rf group IV homologues Zr and Hf.

抄録全体を表示

The paper considers a programme of development of radiochemical investigations at the FLNR in the light of recent results on the synthesis of isotopes of elements 108-116 in reactions between ⁴⁸Ca and ²³⁸U, ²⁴²Pu, ²⁴⁴Pu, ²⁴⁸Cm. Three main lines of the investigation are discussed: chemical identification and study of chemical properties of superheavy elements (SHE), on-line mass separation for the detection of SHE, and the setting of new experiments on the search of SHE in Nature.

抄録全体を表示

The present status of heavy element nuclear chemistry research at JAERI (Japan Atomic Energy Research Institute) is reviewed. Successful production of the transactinide nuclei, ²⁶¹Rf and ²⁶²Db via the reactions of ²⁴⁸Cm (¹⁸O, 5n) and ²⁴⁸Cm (¹⁹F, 5n), respectively at the JAERI tandem accelerator is presented. Aqueous chemistry of Rf is being carried out with a newly developed rapid ion-exchange separation apparatus. Anion-exchange behavior of Rf in HCl solution is shortly discussed. Recent experimental results on decay studies of neutron-deficient actinide nuclei using the gas-jet coupled JAERI-ISOL are also given. Prospects for the near future studies are briefly considered.

抄録全体を表示

The chemistry of superheavy element 114 is reviewed. The ground state of element 114 is closed shell [112]7s²7p²_1/2 and shows a distinct chemical inertness (low reactivity). This inertness makes it rather difficult to study the atom-ata-time chemistry of 114 in the gas or liquid phase.

抄録全体を表示

Fully relativistic electronic structure calculations have been performed for gas phase and aqueous phase compounds of elements 104 through 108. Based on these calculations, volatility and complex formation, as well as trends in these properties, have been predicted. The transactinide compounds were shown to exhibit properties very similar to those of the lighter homologs in the respective chemical groups. Some deviations from the observed trends were established.

抄録全体を表示

A short review is given on our current anion-exchange studies of element 104, rutherfordium (Rf), in HCl and HNO₃ solutions. The distribution coefficients of the Rf homologues Zr, Hf, and Th (IV), and Pu (IV) on an anion-exchange resin were measured in 1.0-11.5 M HCl and 1.1-13.1 M HNO₃ with a batch method using the radiotracers ⁸⁸Zr, ¹⁷⁵Hf, ²³⁴Th, and ²³⁷Pu. In experiments for the short-lived ²⁶¹Rf, the isotopes ⁸⁵Zr, ¹⁶⁹Hf, and ¹⁶⁹Rf were produced in the ¹⁸O-induced reactions on ^natGe, ²⁴⁸Gd, and ²⁴⁸Cm targets, respectively, and their anion-exchange behavior in 4.0-11.5 M HCl and 8.0 M HNO₃ was investigated using the Automated Ion-exchange separation apparatus coupled with the Detection system for Alpha spectroscopy (AIDA). In the HCl system, the percent adsorption of Rf on the anion-exchange resin increases steeply with increasing HCl concentration from 7.0 M to 11.5 M. This adsorption behavior is similar to that of the group-4 elements Zr and Hf, and is quite different from that of the pseudo-homologue Th (IV). The percent adsorption decreases in the order Rf>Zr>Hf. In the HNO₃ system, Rf behaves like Zr and Hf in 8.0 M HNO₃ but not like Pu (IV) and Th (IV), implying the formation of cationic or neutral species.

抄録全体を表示

Nobelium (²⁵⁹No, T_1/2=58 min) was produced in bombardment of ²⁴⁸Cm target with ¹⁸O⁵⁺ ions. Next, it was oxidised by H₅IO₆ and loaded together with lanthanide tracers on a chromatographic column filled with cryptomelane MnO₂. In the HNO₃ elution curve two peaks are observed. First one is related to the nonoxidized No²⁺ and the second corresponds to No³⁺ close to positions of elution peaks of Ho³⁺ and Y³⁺. The ionic radius deduced from the elution position of No³⁺ is to be 89.4±0.7 pm.

抄録全体を表示

The oxidation state of actinide elements encapsulated in fullerenes is studied. HPLC elution behavior of actinidefullerenes is classified into two groups; the elution behavior of the first group, encapsulating U, Np, and Am, issimilar to that of the light lanthanide fullerenes, such as La, Ce, Pr, and Nd, while the behavior of the second group, encapsulating Th and Pa, is quite different from that of any lanthanide fullerenes. The chemical species in the mainHPLC elution peak of each group were identified as M @C₈₂ and M @C₈₄ (M=metal atom) from the mass of the U and Th fullerenes, respectively. The oxidation states of the U and Th atoms in the fullerenes were deduced to be 3+ and 4+, respectively, from the UV/vis/NIR absorption and XANES spectroscopy.

抄録全体を表示

An anion exchange in mineral acid and methanol system was examined in view of rapid chemical separation. An elution behavior of Bk in hydrochloric acid-methanol system was obtained using ²⁵⁰Bk. An elution behavior of Bk in nitric acid-methanol system was predicted from the relationship between an elution position and an ionic radius . The separation was completed for nitric acid-methanol system and for hydrochloric-methanol system within 40 and 25 min, respectively.

抄録全体を表示

The extension of the periodic system into various new areas is investigated. Experiments for the synthesis of superheavy elements and the predictions of magic numbers with modern meson field theories are reviewed. Furtheron, different channels of nuclear decay are discussed including cluster radioactivity, cold fission, and cold multifragmentation. A perspective for future research is given.

抄録全体を表示

Ground-state collective properties of heaviest nuclei, such as deformations and rotational energies, are studied. In particular, the role of deformations of various multipolarities in the rotational energies is discussed. A large region of even-even nuclei with proton, Z = 82-126, and neutron, N = 126-190, numbers is considered.

抄録全体を表示

The gas-filled recoil separator RITU in conjunction with germanium detector arrays and the SACRED conversion electron array has been used for studies of nuclear structure in the region around ²⁵⁴No. Rotational spectra have been extracted using in-beam measurements with recoil gating or recoil decay tagging. Results from completed in-beam γ-ray studies of ^{252, 254}No as well as preliminary data from in-beam conversion electron measurements of ^{253, 254}No and γ-ray studies of ²⁵⁰Fm are presented. These measurements give strong support to the prediction that nuclei in this region of the nuclear chart are quadrupole-deformed in their ground state with β₂∼0.27. There are indications of an upbend occurring in the moment of inertia of ²⁵²No and ²⁵⁰ Fm at a frequency around 180 keV. Future prospects for these studies as well as for focal plane decay spectroscopy in the transfermium region using RITU are discussed.

抄録全体を表示

The stability of the superheavy elements depends on the shell corrections which are governed by the single-particle spectra. Ideally one would like to experimentally determine the single-particle levels in the superheavy nuclei but the production of only a few atoms of these nuclides precludes such measurements. One therefore has to identify single-particle levels in the heaviest nuclei which are available in at least nanoCurie amounts. We have studied the structure of such heavy nuclei in the Z=98 region and identified many single-particle states. In particular, we have studied the structure of ²⁵¹Cf and ²⁴⁹Bk by measuring the radiations emitted in the α decay of ²⁵⁵Fm and ²⁵³Es. These single-particle spectra can be used to test theoretical models for superheavy elements.

抄録全体を表示

A new isotope of ²⁵⁹Db has been produced via the reaction ²⁴¹Am (²²Ne, 4n) at E_lab=118 MeV, and its half-life of 0.51 ± 0.16 s and α-decay energy of 9.47 MeV were determined in this work. The americium targets with thickness ranged from 0.7 to 1.0 mg/cm₂ were prepared by molecular plating method through a single electrodeposition cycle. The reaction products were transported and collected using a helium jet technique and a rotating wheel apparatus. The α decays of both the products and their daughter nuclides were detected by a series of Si (Au) surface barrier detectors arranged ingeniously. The identification of ²⁵⁹Db was performed based on the genetic relationship between the new activity and the known ²⁵⁵Lr established by α-recoiled milking measurement. The Q_α value of ²⁵⁹Db derived from the present experiment is in good agreement with theoretical prediction.

抄録全体を表示

The EC and α decays of neutron-deficient Am and Cm nuclei have been studied using a gas-jet coupled on-line isotope separator. Decay schemes of the EC decay of ^{235, 236}Am have been constructed, and weak α decays of ^{233, 235, 236}Am and ^{237, 238}Cm have been observed. The efficiency of the on-line mass separation of Bk nuclei was measured to be ∼1%. The Q_α values, α-decay partial half-lives, and proton-neutron configurations are discussed.

抄録全体を表示

A relativistic point coupling model is discussed focusing on a variety of aspects. In addition to the coupling using various bilinear Dirac invariants, derivative terms are also included to simulate finite-range effects. The formalism is presented for nuclear structure calculations of ground state properties of nuclei in the Hartree and Hartree-Fock approximations. Different fitting strategies for the determination of the parameters have been applied and the quality of the fit obtainable in this model is discussed. The model is then compared more generally to other mean-field approaches both formally and in the context of applications to ground-state properties of known and superheavy nuclei. Perspectives for further extensions such as an exact treatment of the exchange terms using a higher-order Fierz transformation are discussed briefly.

抄録全体を表示

The structures of the nuclei with the proton number Z=106-110 are systematically investigated using the deformed relativistic mean-field (RMF) theory. The calculated binding energies are in good agreement with experimental ones. The experimental data of α-decay energies are well reproduced by the calculations. Calculations show clearly that a prolate deformation is important for the ground state of these nuclei. The properties of the nuclei on the α-decay chain of ²⁶⁹Mt are predicted.

抄録全体を表示

We estimate α-decay half-lives from Q_{α} values with phenomenological formulas. The parameter values of the formulas are adjusted by using experimental half-lives and Q values of the Evaluated Nuclear Structure Data File (ENSDF) for a wide nuclidic region. The half-lives T_{α} for unknown nuclei are estimated by this phenomenological formula with the use of Q_{α} values taken from KUTY mass formula. In addition to the half-lives, we estimate spontaneous fission barriers calculated by the method to obtain the shell energies of KUTY formula. In the superheavy region, the barrier heights of the nuclei near the nucleus ³⁰⁴ 122 are about 8 MeV and their widths are fairly wide. Therefore these spontaneous-fission half-lives are expected to be very long. On the other hand, there are some neutron-deficient nuclei whose spontaneous-fission half-lives expected to be rather short because their fission barrier heights are small and the widths of them are narrow.

抄録全体を表示

The structure of nuclei in ultrastrong magnetic fields relevant for supernovas and neutron stars is considered. The dependence of shell-correction energy on magnetic field is analyzed and systemized by employing the shell model with spherical harmonic oscillator confining potential.

抄録全体を表示

A recoil mass separator has been in operation at the JAERI tandem-booster facility since 1995, for in-flight separation of low-yield reaction products recoiling out in the beam direction. The current status and future plan together with a brief description of the design performance are presented.

抄録全体を表示

In this contribution the emphasis will be on the capabilities of the new generation of Ge arrays based on a new concept of detection using Gamma Ray Tracking and recent advances in crystal segmentation technology which will enable in-beam spectroscopy towards super heavy elements.

抄録全体を表示

Experimental methods for the identification of newly synthesized heaviest isotopes of elements Z=112 and 114 with the use of ⁴⁸Ca beams are discussed.

抄録全体を表示