Search

The isotope $^{220}\mathrm{Pa}$ produced in the reaction $^{40}\mathrm{Ar}+^{187}\mathrm{Re}$ at a beam energy of 198.7 MeV was reinvestigated via the $\ensuremath{\alpha}$-spectroscopic method. A new $\ensuremath{\alpha}$-decaying state in $^{220}\mathrm{Pa}$ has been observed with an energy ${E}_{\ensuremath{\alpha}}=9664(40)\phantom{\rule{0.28em}{0ex}}\mathrm{keV}$ and with a half-life ${T}_{1/2}={233}_{\ensuremath{-}56}^{+108}\phantom{\rule{0.28em}{0ex}}\mathrm{ns}$. The spin parity of the state is tentatively suggested to be (${3}^{\ensuremath{-}}$). The $\ensuremath{\alpha}$ energy and half-life of the (${1}^{\ensuremath{-}}$) ground state are measured to be ${E}_{\ensuremath{\alpha}}=9548(30)\phantom{\rule{0.28em}{0ex}}\mathrm{keV}$ and ${T}_{1/2}=0.75(8)\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{s}$, respectively. The reduced $\ensuremath{\alpha}$ width, inferred from the present data, fits well into the systematics for $N=129$ isotones.

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 $ \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 $ \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.

HIRFL is an accelerator complex consisting of 3 accelerators, 2 radioactive beams lines, 1 storage rings and a number of experimental setups. The research activities at HIRFL cover the fields of radio-biology, material science, atomic physics, and nuclear physics. This report mainly concentrates on the experiments of nuclear physics with the existing and planned experimental setups such as SHANS, RIBLL1, ETF, CSRe, PISA and HPLUS at HIRFL.

A master equation is constructed to treat the nucleon transfer process in heavy ion fusion reactions to form superheavy nucleus. The relative motion concerning the energy, the angular momentum and the fragment deformation relaxations is explicitly treated to couple with the diffusion process. The nucleon transition probabilities, which are derived microscopically, are thus time dependent. The calculated evaporation residue cross-sections for both cold and hot fusion are in good agreement with the known experimental data.

The ground state properties of Hs nuclei were studied to give an overview to the isotope chain. It is seen that more stable isotopes are located on the proton abundant side of the chain. The last stable nucleus to the proton drip line is 256 Hs . The most stable unknown Hs nucleus may be 268 Hs . The proton Fermi surfaces of Hs nuclei are close to zero, the conventional BCS treatment with constant pairing interaction can excite protons to the continuum, and causes the failure for pairing correction. The density dependent delta interaction results in more reasonable single-particle energy level distributions and nucleon occupation. Therefore it has improved the BCS treatment, and is available to describe the properties of nuclei in the superheavy region.

Various nuclear reactions like quasi-fission, fusion-fission or particle and cluster evaporation from excited compound nuclei were studied in heavy-ion reactions at the velocity filter SHIP of GSI. The velocity filter offers the possibility to detect all reaction products under zero degree relative to the beam direction. Together with the measurement of the product velocity distribution this allows for an identification of the underlying reaction mechanism. This article is focussed on reactions of 25Mg and 64Ni beams on 206, 207Pb targets at energies of 5.9×AMeV and 8.7×AMeV . Besides evaporation residues from 25Mg + 206Pb collisions we found evidence for rotation and quasi-fission of nuclear molecules formed in the entrance channel after the capture stage. The break-up of the systems showed a preferred clustering leading to isotopes in the region 84 ⩽ Z ⩽ 88 and 122 ⩽ N ⩽ 127 of the chart of nuclei.

An overview of present experimental investigation of superheavy elements is given. The data are compared with theoretical descriptions. Results are reported from an experiment to confirm production of element 112 isotopes in irradiation of 238 UF 4 with 48 Ca . One spontaneous fission event was measured, which agrees with three events of previously measured data which had been assigned to the decay of 283112. However, more experimental work is needed in order to obtain an independent and unambiguous confirmation of previous results.

Lifetime measurements were made for the $\ensuremath{\nu}{h}_{11/2}$ band in $^{101}\mathrm{Pd}$, which had been interpreted as a possible antimagnetic rotation band based on the comparison of $I\ensuremath{-}\ensuremath{\omega}$ behavior with the calculation of a semiclassical particle-rotor model in our previous study. Doppler broadened line shapes were analyzed for the decaying $\ensuremath{\gamma}$ rays in the band following the reaction $^{68}\mathrm{Zn}(^{37}\mathrm{Cl},\phantom{\rule{0.16em}{0ex}}\text{1p3n})^{101}\mathrm{Pd}$. The semiclassical particle-rotor model was modified to reproduce both the $I\ensuremath{-}\ensuremath{\omega}$ plot and the $B(E2)$ behavior simultaneously for the antimagnetic rotation bands in Pd and Cd nuclei, for which $B(E2)$ values had been measured so far. Reasonable agreements between the experiment and the calculation were obtained. It is concluded that the lower part of the $\ensuremath{\nu}{h}_{11/2}$ band in $^{101}\mathrm{Pd}$ can be interpreted as an antimagnetic rotor.

The new neutron-deficient isotope U-216 was produced in the complete-fusion reaction W-180(Ar-40,(4)n) U-216. The evaporation residues were separated from the primary beam in flight by the gas-filled recoil separator Spectrometer for Heavy Atoms and Nuclear Structure. The activities have been identified by the alpha-alpha position and time correlation measurements. Two alpha-decaying states with E alpha = 8384(30) keV, T-1/2 = 4.72(-1.57)(+4.72) ms for the ground state and E alpha = 10582(30) keV, T-1/2 = 0.74(-0.29)(+1.34) ms for an isomeric state were identified in U-216.

In the framework of the relativistic mean field (RMF) theory, the stability and ground properties of super-heavy nuclei are discussed. Our study indicated that the current synthesized super-heavy nuclei (SHN) actually appear in the stable region, and adding more neutrons will not increase their stability. The study of nuclei from 287115 α decay chain showed that they are usually deformed, the magnitudes of their shell gaps are much smaller than those of nuclei before the actinium region, so that the shell effect is weakened, and SHN are usually not stable. A common phenomenon is that the Fermi surface of the proton is close to the continuum, the resonant continuums exist in SHN, because the SHN are usually neutron deficient. Although bulk properties can be described by the RMF+BCS theory, further study is needed. Density dependent delta pairing interaction can improve the treatment of the pairing and thus improve the level distribution in the continuum.

An isotope of the element 105 with mass number 259 has been produced via the reaction 241Am(22Ne, 4n)259Db at Elab = 118 MeV. The reaction products were transported and collected using the helium-jet technique and the rotating wheel apparatus. The α-decays of the products and their daughter nuclides were detected by a set of Si(Au) detectors arranged ingeniously. The Z and A of the nuclide have been unambiguously identified by the genetic relationship between the new activity and the known nuclide 255Lr established by α-recoiled milking measurement. The new nuclide 259Db has a half-life of 0.51±0.16 s and decays by alpha-particle emission of Eα = 9.47 MeV. Furthermore, the nuclide 258Db and its daughter 254Lr have also been clearly observed using the same projectile-target combination. Their half-lives and α-particle energies determined in this work are in agreement with previous known data, thus also proving the reliability of our assignment of 259Db.

A new isotope (265)Bh was produced and identified at the Sector Focus Cyclotron of the Heavy Ion Research Facility in Lanzhou. This experiment was performed via the reaction of an Am-243 target with 168 MeV Mg-26 ions. Identification was made by observation of correlated alpha-particle decays between the new isotope (265)Bh and its (261)Db and Lr-257 daughter nuclei rising a set of rotating-wheels system. A total of 8 correlated decay events of (265)Bh and 4 decay events Of (264)Bh were observed. (265)Bh decays with a 0.94(-0.31)(+0.70) s half-life by emission of a-particles with an average energy of 9.24 +/- 0.05 MeV. The half-life and a decay energy of (265)Bh from this experiment are in agreement with theoretical predictions.

High-spin states of ${}^{101}$Pd were studied through in-beam $\ensuremath{\gamma}$-ray spectroscopy by using the reaction ${}^{68}$Zn(${}^{37}$Cl, $1p3n$). The band based on the ${h}_{11/2}$ neutron orbital was extended up to (${\frac{51}{2}}^{\ensuremath{-}}$), and the band based on the ${d}_{5/2}$ neutron orbital was revised. Various transitions decaying to these bands were observed, and consequently several side bands were established. Electric dipole transitions from the $\ensuremath{\nu}{h}_{11/2}$ band to the $\ensuremath{\nu}{d}_{5/2}$ band were also observed. The structure of the $\ensuremath{\nu}{h}_{11/2}$ band is discussed from the viewpoint of antimagnetic rotation based on a semiclassical particle-rotor model by taking neutron alignments into account. The possible existence of octupole correlations is also discussed on the basis of $B(E1)/B(E2)$ ratios for the decays of the $\ensuremath{\nu}{h}_{11/2}$ band.

The high-spin states of 145Tb have been studied in the 118Sn(32S, 1p4n) reaction at 32S energies from 161 to 175 MeV using techniques of in-beam γ-ray spectroscopy. Measurements of γ-ray excitation functions and γ-γ-t coincidences were performed with 12 BGO(AC)HPGe detectors. Based on the measured results of γ-γ coincidences, γ-ray anisotropies and DCO ratios, a level scheme for 145Tb was established for the first time. The observed excited states show typical irregular pattern in a spherical nucleus, and the low-lying levels have been interpreted qualitatively with a particle-core coupling.

Within the framework of a dinuclear system model, a new master equation is constructed and solved, which includes the relative distance of nuclei as a new dynamical variable in addition to the mass asymmetry variable so that the nucleon transfer, which leads to fusion and the evolution of the relative distance, which leads to quasifission (QF) are treated simultaneously in a consistent way. The QF mass yields and evaporation residual cross sections to produce superheavy nuclei are systematically investigated under this framework. The results fit the experimental data well. It is shown that the Kramers formula gives results of QF, which agree with those by our diffusion treatment, only if the QF barrier is high enough. Otherwise some large discrepancies occur.

With the commissioning of HIRFL‐CSR, HIRFL can provide heavy ion beams with energy covering the range of several MeV/u to 1 GeV/u. In this talk, the experiments on nuclear physics at different energies to be carried out with different experimental setups at HIRFL will be introduced.

The decay of 131Pm has been investigated by means of γ-ray spectroscopy. The 131Pm nuclei were produced by fusion-evaporation reaction of 106Cd(32S,3p4n) at the beam energy of 170 MeV. A helium-jet technique and a tape transport system were used to collect the activities and transfer them to a detecting position for X and γ rays measurement. Two γ rays of 185.0 and 220.0 keV were unambiguously identified to follow the β+ decay of 131Pm by results of X-γ and γ–γ coincidence. A growth-decay feature of the decay curve for 87.8 keV γ-ray of 131Nd confirmed the production of 131Pm nuclei. The half-life of 131Pm was measured to be 6.3 ± 0.8 s. A partial decay scheme of 131Pm is proposed on the basis of X-γ and γ–γ coincidence data in this experiment and the known structure information deduced from in-beam experiments of the daughter nucleus 131Nd.

The new transuranium neutron-deficient isotope 235Am was produced by bombarding of 238Pu with 35-MeV protons beam via the (p,4n) reaction. The reaction products were transported by a helium-jet system. A rapid radiochemical method was employed for separating the americium isotopes from the complex products. From the observed Kx-rays of Np, γ-ray of 235Pu and x-γ coincidence measurements, the new neutron-deficient isotope 235Am with a half-life 15±5min was definitely identified for the first time.

A new nuclide239Pa was produced by 50MeV/u18O bombardment of uranium. A radiochemical separation method was employed for preparing sources of239Pa. The protactinium isotope239Pa has been identified for the first time by the results observed from the decay of the239Pa and its daughter239U. The half-life of239Pa has been determined to be 106 ±30min.