Search

Schottky mass spectrometry was applied to stored and cooled neutron-deficient 152Sm projectile fragments at the experimental storage ring (ESR) facility at GSI Darmstadt, Germany. 311 different nuclides were identified by means of their revolution frequency spectra. The measured frequencies were used to investigate the shape of the momentum-compaction-factor of the ESR.

An analytical description for guiding of ions through nanocapillaries is given on the basis of previous work. The current entering into the capillary is assumed to be divided into a current fraction transmitted through the capillary, a current fraction flowing away via the capillary conductivity and a current fraction remaining within the capillary, which is responsible for its charge-up. The discharging current is assumed to be governed by the Frenkel–Poole process. At higher conductivities the analytical model shows a blocking of the ion transmission, which is in agreement with recent simulations. Also, it is shown that ion blocking observed in experiments is well reproduced by the analytical formula. Furthermore, the asymptotic fraction of transmitted ions is determined. Apart from the key controlling parameter (charge-to-energy ratio), the ratio of the capillary conductivity to the incident current is included in the model. Differences resulting from the nonlinear and linear limits of the Frenkel–Poole discharge are pointed out.

Two low-lying isomeric states in 169Ta have been identified via 159Tb(16O, 6nγ)169Ta reaction. Their half-lives are measured to be 28 ± 5 ns for the 9/2- level and 17 ± 4 ns for the 5/2- level by using the delayed γ-γ coincidence method. These two isomeric states are considered to be the bandheads with 9/2-[514] and 1/2-[541] configurations, respectively. Possible neutron quasiparticle configuration for the ground state of 169W is discussed.

The characteristics of intermediate mass fragments (IMFs: 3, 13 pages, 15 figures

Excitation functions of the dissipative products in the reaction 19F + 51V have been measured from 102.25 to 109.50 MeV by 250 keV steps at θl = 21.7°, 36.1° and 40.5°. The rotation angular velocities ω and the energy coherence widths Γ of the corresponding dinuclear systems were extracted. The coherence rotation and its importance in the reaction process have been discussed.

Particle correlation functions from central $^{129}\mathrm{Xe}+^{197}\mathrm{Au}$ collisions at $50A\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ have been measured with a large area $\text{silicon}\text{\penalty1000-\hskip0pt}\text{strip}∕\mathrm{Cs}\mathrm{I}$ detector array. A new technique of spin determination from particle correlation functions is proposed. Two examples of correlation functions are studied. The spin of the first excited level of $^{8}\mathrm{B}$ at $0.774\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ is determined as $J=1$.

Alpha particles emitted from an excited projectile-like fragment (PLF*) formed in a peripheral collision of two intermediate-energy heavy ions exhibit a strong preference for emission towards the target-like fragment (TLF). The interplay of the initial deformation of the PLF* caused by the reaction, Coulomb proximity, and the rotation of the PLF* results in the observed anisotropic angular distribution. Changes in the shape of the angular distribution with excitation energy are interpreted as being the result of forming more elongated initial geometries in the more peripheral collisions., 4 figures

Using symmetric 112Sn+112Sn, 124Sn+124Sn collisions as references, we probe isospin diffusion in peripheral asymmetric 112Sn+124Sn, 124Sn+112Sn systems at an incident energy of E/A=50 MeV. Isoscaling analyses imply that the quasiprojectile and quasitarget in these collisions do not achieve isospin equilibrium, permitting an assessment of isospin transport rates. We find that comparisons between isospin sensitive experimental and theoretical observables, using suitably chosen scaled ratios, permit investigation of the density dependence of the asymmetry term of the nuclear equation of state.

Isotopic yields for light particles and intermediate mass fragments have been measured for central $^{112}\mathrm{Sn}+^{112}\mathrm{Sn}$, $^{112}\mathrm{Sn}+^{124}\mathrm{Sn}$, $^{124}\mathrm{Sn}+^{112}\mathrm{Sn}$, and $^{124}\mathrm{Sn}+^{124}\mathrm{Sn}$ collisions at $E∕A=50\phantom{\rule{0.3em}{0ex}}\text{MeV}$ and compared with predictions of stochastic mean field calculations. These calculations predict a sensitivity of the isotopic distributions to the density dependence of the asymmetry term of the nuclear equation of state. However, the secondary decay of the excited fragments modifies significantly the primary isotopic distributions and these modifications are rather sensitive to theoretical uncertainties in the excitation energies of the hot fragments. The predicted final isotope distributions are narrower than the experimental data and the sensitivity of the predicted yields to the density dependence of the asymmetry term is reduced.

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 $\alpha$-decay chains which were assigned to be the decays starting from the isotope $^{271}$Ds(Z=110). The $\alpha$-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 $\alpha$-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 $\alpha$-decay products, $^{264}$Bh and $^{268}$Mt, reported previously by a GSI group. New information on their half-lives and decay energies is presented.

The European physical journal / Web of Conferences 93, 05003 (2015). doi:10.1051/epjconf/20159305003, Published by EDP Sciences, Les Ulis

The defining characteristics of fragment emission resulting from the non-central collision of 114Cd ions with 92Mo target nuclei at E/A = 50 MeV are presented. Charge correlations and average relative velocities for mid-velocity fragment emission exhibit significant differences when compared to standard statistical decay. These differences associated with similar velocity dissipation are indicative of the influence of the entrance channel dynamics on the fragment production process.

The performance of a double sided silicon strip detector (DSSSD), which is used for the position and energy detection of heavy ions, is reported. The analysis shows that although the incomplete charge collection (ICC) and charge sharing (CS) effects of the DSSSD give rise to a loss of energy resolution, the position information is recorded without ambiguity. Representations of ICC/CS events in the energy spectra are shown and their origins are confirmed by correlation analysis of the spectra from both the junction side and ohmic side of the DSSSD.

In order to satisfy high precision requirement for the modern nuclear physics experiment detectors and radiologic imaging technology equipments, we do some researches in improving the resolution of the detector with LaBr3:Ce scintillator.

Total recombination rate coefficients of Sn-112(35+) ions have been firstly measured by employing the electron-ion merged-beams technique on the main cooler storage ring at Lanzhou. Using an electron beam energy detuning system, we precisely tuned the relative energies from 0 to 6.0 eV between the electron beam and the ion beam (momentum spread Delta p/p similar to 5 x 10(-4)). A multi-configuration Breit-Pauli calculation utilizing kappa-averaged relativistic orbitals has been carried-out for the recombination rate coefficients. We find that there are obvious differences between the experimental total rate coefficients and the theoretical calculations.

Different statistical multifragmentation models have been used to study isoscaling, i.e., the factorization of the isotope ratios from two reactions, into fugacity terms of proton and neutron number, ${R}_{21}{(N,Z)=Y}_{2}{(N,Z)/Y}_{1}(N,Z)=C\mathrm{exp}(\ensuremath{\alpha}N+\ensuremath{\beta}Z).$ Even though the primary isotope distributions are quite different from the final distributions due to evaporation from the excited fragments, the values of $\ensuremath{\alpha}$ and $\ensuremath{\beta}$ are not much affected by sequential decays. $\ensuremath{\alpha}$ is shown to be mainly sensitive to the proton-to-neutron composition of the emitting source and may be used to study isospin-dependent properties in nuclear collisions, such as, the symmetry energy in the equation of state of asymmetric nuclear matter.

Calculations predict a connection between the isotopic composition of particles emitted during an energetic nucleus-nucleus collision and the density dependence of the asymmetry term of the nuclear equation of state (EOS). This connection is investigated for central 112Sn+112Sn and 124Sn+124Sn collisions at E/A=50 MeV in the limit of an equilibrated freezeout condition. Comparisons between measured isotopic yields ratios and theoretical predictions in the equilibrium limit are used to assess the sensitivity to the density dependence of the asymmetry term of the EOS. This analysis suggests that such comparisons may provide an opportunity to constrain the asymmetry term of the EOS., Comment: 14 Pages, 2 figures

Isoscaling, where ratios of isotopes emitted from two reactions exhibit an exponential dependence on the neutron and proton number of the isotope, has been observed over a variety of reactions including evaporation, strongly damped binary collision, and multifragmentation. The conditions for isoscaling to occur as well as the conditions when isoscaling fails are investigated., 13 pages, 5 figures

Neutrons and isotopically resolved light charged particles have been detected in coincidence with evaporation residues produced in the reaction $E/A=11 \mathrm{MeV}$ ${}^{60}\mathrm{Ni}{+}^{100}\mathrm{Mo}.$ Multiplicities of evaporated particle-unstable clusters have been determined from correlations in the emission of these light particles. The decay of the short-lived ${}^{5}\mathrm{He}$ and ${}^{8}\mathrm{Be}$ ${(E}^{*}=3.04 \mathrm{MeV})$ states was found to be affected by the Coulomb field of the compound nucleus in accordance with theoretical estimates. The contributions to the measured kinetic-energy distributions of stable fragments from the sequential decay of the unstable clusters was examined. Overall, the contributions from secondary fragments do not greatly influence the spectral shapes and specifically the location of the spectral peaks are not significantly shifted down in energy due to the presence of these secondary fragments. Therefore contrary to the suggestion of Charity et al. [Phys. Rev. C 56, 873 (1997)], the lower peak energy of the experimental $\ensuremath{\alpha}$-particle spectrum as compared to standard statistical-model calculations cannot be attributed to sequential $\ensuremath{\alpha}$ particles from ${}^{5}\mathrm{He}$ and other clusters. Only for the extreme ``subbarrier'' regions of the $\ensuremath{\alpha}$-particle, deuteron, ${}^{6,7}\mathrm{Li},$ and ${}^{8}\mathrm{Be}$ spectra was the sequential contribution found to be dominant. Statistical-model calculations incorporating large initial deformations are shown to provide enhancements in the yield of low-energy fragments which are roughly appropriate for all the detected isotopes. This suggests that the origin of the sub-barrier enhancements may be a result of evaporation from highly deformed systems which are either produced dynamically during the fusion process or by thermal shape fluctuations.

The n-p asymmetry of the material found in the midvelocity or ‘‘neck’’ region of an intermediate energy heavy-ion reaction is determined. In order to accomplish this task, data from two different experiments are utilized. While the n-p asymmetry of the light particles ( Z

Isotopic distributions for light particles and intermediate mass fragments have been measured for 112Sn+112Sn, 112Sn+124Sn, 124Sn+112Sn and 124Sn+124Sn collisions at E/A=50 MeV. Isotope, isotone and isobar yield ratios are utilized to obtain an estimate of the isotopic composition of the gas phase, i.e., the relative abundance of free neutrons and protons at breakup. Within the context of equilibrium calculations, these analyses indicate that the gas phase is enriched in neutrons relative to the liquid phase represented by bound nuclei., 14 paged, 3 figures

The longitudinal Schottky spectra of a radio-frequency (RF) bunched and electron cooled 22Ne10+ ion beam at 70 MeV/u have been studied by a newly installed resonant Schottky pick-up at the experimental cooler storage ring (CSRe), at IMP. For an RF-bunched ion beam, a longitudinal momentum spread of has been reached with less than 107 stored ions. The reduction of momentum spread compared with coasting ion beam was observed from Schottky noise signal of the bunched ion beam. In order to prepare the future laser cooling experiment at the CSRe, the RF-bunching power was modulated at 25th, 50th and 75th harmonic of the revolution frequency, effective bunching amplitudes were extracted from the Schottky spectrum analysis. Applications of Schottky noise for measuring beam lifetime with ultra-low intensity of ion beams are presented, and it is relevant to upcoming experiments on laser cooling of relativistic heavy ion beams and nuclear physics at the CSRe., Comment: to be published in Chinese Physics C

Laser cooling is one of the most promising techniques to reach high phase-space densities for relativistic heavy-ion beams. Preparations for laser cooling of relativistic lithium-like ions, such as C3+ and N4+, are being made at the experimental cooler storage ring (CSRe) in Lanzhou, China. In December 2011, a new buncher was installed and tested with a 70 MeV u−1 22Ne10+ ion beam by electron cooling at the CSRe. The longitudinal momentum spread of the bunched ion beam was measured by the new resonant Schottky pick-up. As a result, Δp/p ≈ 2 × 10−5 has been reached at ion numbers less than 107. According to this test result, the RF-buncher is suitable for the upcoming experiment of laser cooling at the CSRe. Laser cooling of heavy-ion beams will also be applied at future storage ring facilities, e.g. FAIR in Darmstadt, and HIAF in Lanzhou.

A gas-filled recoil separator was designed and built newly at Institute of Modern Physics (IMP) in Lanzhou. With the recent commissioning of the separator, the decay properties of 271Ds were studied via the 208Pb (64Ni, n) reaction at a beam energy of 313.3 MeV. One α-decay chain for 271Ds was established in total. The experimental result is consistent with the values reported in the literature.

A storage ring equipped with an electron cooler is an ideal platform for dielectronic recombination (DR) experiments. In order to fulfill the requirement of DR measurements at the main Cooler Storage Ring, a detuning system for the precision control of the relative energy between the ion beam and the electron beam has been installed on the electron cooler device. The test run using 7.0 MeV/u C6+ beam was performed with recording the Schottky spectra and the ion beam currents. The influence of pulse heights and widths of the detuning voltage on the ion beam was analyzed. For the small pulse height, the experimental results from the Schottky spectra were in good agreement with the theoretical results. The frequency shift in the Schottky spectra was significantly reduced for the short pulse width. For the large pulse height, an oscillation phenomenon was observed and some effective ways to reduce the oscillation were pointed out. The detailed description of the phenomenon and the theoretical model based on the plasma oscillation is discussed in this paper. The overall results show that the new detuning system works properly, and could fulfill the requirements of future DR experiments.

An electron beam energy detuning system has been installed to the electron cooler device at the cooler storage ring in Lanzhou. The system is tested by using 7 MeV/u C6+ beam. The detuning system is feasible for future dielectronic recombination experiments.

With the recent commissioning of a gas-filled recoil separator at Institute of Modern Physics (IMP) in Lanzhou, the decay properties of (271)Ds (Z = 110) were studied via the Pb-208(Ni-64, n) reaction at a beam energy of 313.3MeV. Based on the separator coupled with a position sensitive silicon strip detector, we carried out the energy-position-time correlation measurements for the implanted nucleus and its subsequent decay alpha's. One alpha-decay chain for (271)Ds was established. The.. energy and decay time of the (271)Ds nucleus were measured to be 10.644 MeV and 96.8 ms, which are consistent with the values reported in the literature.

We report some recent progress in constraining the symmetry energy Esym(ρ) at high densities using high-energy heavy-ion collisions. Circumstantial evidence of a soft Esym(ρ) at supra-saturation density is obtained by comparing the pion ratio π−/π+ measured recently with FOPI at GSI and the IBUU04 model calculations. Detailed studies indicate that the power of determining the Esym(ρ) from π−/π+ is enhanced with decreasing the beam energy to near the pion production threshold, showing a correlation to the increasing nuclear stopping. Among several heavy-ion reaction facilities in the world, the cooling storage ring (HIRFL-CSR), newly commissioned at Lanzhou, delivering heavy-ion beams up to 1 A GeV, to be coupled with advanced detectors will contribute significantly to further studies of the equation of state of asymmetric nuclear matter.