Muon capture rates in233U,234U,235U,236U,238U,and237Np

The time spectra for muon induced fission of²³³U,²³⁴U,²³⁵U,²³⁶U,²³⁸U, and²³⁷Np were measured simultaneously, detecting both fragments in coincidence in a fast multi parallel plate avalanche detector. The observed mean lifetimes τ are 68.9 ± 0.3 ns, 70.6 ± 0.2 ns, 72.2 ±0.2 ns, 74.3 ± 0.3 ns, 77.0 ±0.4 ns, and 69.8 ±0.2 ns for the above isotopes, respectively. No second time component, tentatively ascribed to a possible fission isomer, was observed. The deduced total capture rates are compared with theoretical predictions.     

Classical microscopic description of U + U collisions

Calculations simulating head-on collisions between two mass-235 nuclei are made using classical kinematics, Monte-Carlo methods, and nucleon-nucleon cross sections. The calculated ratio of maximum particle density to the pre-collision nuclear density is ≈ 2 or 3, depending on details of the nucleon-nucleon scattering mechanism used.     

Event selection in CSR-ETF U+U collision

Uranium on uranium target (U+U) collision experiment has been proposed to be performed on Cooling Storage Ring (CSR), External Target Facility (ETF), which is to be built at Lanzhou, China, delivering the uranium beam up to 520 MeV/nucleon. It is predicted that the tip-tip U+U collision patterns can produce significant high baryon density and long duration nuclear matter to study the nuclear Equation of State (EoS). As the random orientation in U+U collisions, it is necessary to select the interested tip-tip events from the large trivia background. A Relativistic Transport (ART1.0) Model is applied to compute the random mini-biased U+U collisions to select our most favorable tip-tip events. It is found that applying various combination cut on the forward neutron multiplicity and forward charged particle multiplicity of the random U+U mini-biased sample, we can select the tip-tip configuration with certain purity and efficiency.     

Specific heat of amorphous U−Fe,U−Co and U−Ni-alloys

Alloys of U-X with X=Fe, Co, Ni were prepared by rapid quenching in the concentration range between 50 and 83 at% U. The samples were obtained in the amorphous state as determined by X-ray diffraction. Parts of the samples were used to measure the specific heat by the relaxation method. The calculated density of states is twice as large as that of transition metals like amorphous Zr-alloys. Therefore these results are discussed within the frame of the paramagnon model by taking into account values of the magnetic susceptibility and the supercon-ducting transition temperature.     

Reactions of40Ar with233U,235U,and238U at the barrier

Production cross sections for target-like transfer products in reactions of⁴⁰Ar with^233,235,238U at the barrier were determined using radiochemical techniques. The heaviest products detected are isotopes of californium (Z=98). In addition to the quasi-elastic component of the isotopic distributions observed in the vicinity of uranium, there are also relaxed contributions throughout the entire region. The peak positions of the isotope distributions of this component for fixed atomic number, after the transfer of > 3 charges, approach closely the minimum of the potential energy surfaces (PES). The experimental results thus indicate the cold formation of the reaction products. A search for long-lived heavy actinides produced, by fusion-evaporation, via isotopes of element 110 and their subsequent decay through α-decay chains, remained unsuccessful at a cross section limit of 21 pb.     

U + U potential in the sudden and adiabatic approximation

A recent approach for calculating both the real and imaginary parts of the ion-ion potential has been modified to produce the ground state properties of separate nuclei. This approach is used to study both the energy and orientation dependence of the optical potential between two U nuclei adopting the sudden and adiabatic approximations.     

Electrofission of 234U, 236U and 238U: Angular distributions and E2 strength functions

The electrofission angular distributions for ²³⁴U in the energy range 5.5 to 25 MeV were measured and are analyzed together with those obtained previously for ²³⁶U and ²³⁸U. The competition between the K = 0 and K = 1 fission channels following E2 excitation is established, showing a dominance of the K = 0 channel for near-barrier fission. The E2 fission strength functions for ²³⁴U, ²³⁶U and ²³⁸U are deduced as well, and the E2 fission probabilities (at energies below the pairing gap) are estimated. A substantial concentration of E2 strength near the fission barrier is found, in good agreement with earlier photofission angular-distribution studies.     

Cold fragmentation in thermal-neutron-induced fission of 233U and 235U

The mass spectrometer Lohengrin of the Institut Laue-Langevin in Grenoble was used to measure fission-fragment mass yields in the mass range 80 ≤ A ≤ 107 for light-fission-fragment kinetic energies up to about 115 MeV for the reactions ^233,235U(n_th, f). The kinetic energies corresponding to a common fixed yield level for each isobar reflect the influence of the proton pairing energy, but not of the neutron pairing energy. By using calculated Q-values for the different mass splits, mass distributions at fixed total excitation energy are deduced from the data. At a fixed total excitation energy of about 7 MeV, the yield increases from very asymmetric mass splits (A_L ≈ 80) to more symmetric mass splits (A_L ≈ 105) by more than two orders of magnitude. This strong dependence on the mass split seems to be correlated with the decreasing surface-to-surface distance of the unaccelerated fission fragments in this range of mass splits, as calculated under the assumption that the total Q-value is represented by the mutual Coulomb repulsion of the two fragments. The influence of the fission-fragment ground-state deformations on the yield in cold fragmentation could not be detected unambiguously.     

Testing the chiral magnetic effect with central U+U collisions

A quark interaction with topologically nontrivial gluonic fields, instantons and sphalerons, violates P and CP symmetry. In the strong magnetic field of a noncentral nuclear collision such interactions lead to the charge separation along the magnetic field, the so-called chiral magnetic effect (CME). Recent results from the STAR collaboration on charge dependent correlations are consistent with theoretical expectations for CME but may have contributions from other effects, which prevents definitive interpretation of the data. Here I propose to use central body-body U+U collisions to disentangle correlations due to CME from possible background correlations due to elliptic flow. Further, more quantitative studies can be performed with collision of isobaric beams.     

Anisotropic flow and jet quenching in ultrarelativistic U+U collisions

Full-overlap U+U collisions provide significantly larger initial energy densities at comparable spatial deformation, and significantly larger deformation and volume at comparable energy density, than semi-central Au+Au collisions. We show quantitatively that this provides a long lever arm for studying the hydrodynamic behavior of elliptic flow in much larger and denser collision systems and the predicted nonlinear path-length dependence of radiative parton energy loss.     

Lattice parameters and superconductivity of the compounds U6Mn,U6Fe,U6Co and U6Ni and alloys between them

Lattice parameter measurements were made on the tetragonal compounds U₆Mn, U₆Fe, U₆Co, and U₆Ni and alloys between them. Parameter a was found to have a minimum at U₆Fe while c decreased steadily from U₆Mn to Uin6Ni. There appears to be a correlation between a and the superconducting transition temperature.     

Meson production inp+U,O+U and S+U interactions at 200 GeV/nucleon

Meson production in proton, oxygen and sulphur interactions with uranium targets at 200 GeV/nucleon is studied. We measure the inclusive meson cross-section d /dP _T ² and its evolution fromp+U to S+U. The cross-section fitted with an exponential gives an inverse slopeP _T0 of the order of 210 MeV/c. As a function of the neutral transverse energy,P _T0 values show a slight rise followed by a plateau. The normalized difference (⁺–^–)/^– between positive and negative meson cross-sections is found to increase withE _T .also at ISEL     

Fission in238U+238U collisions below the Coulomb barrier

Integral fission cross sections in the system²³⁸U+²³⁸U were measured at beam energies below the interaction barrierV _C. Scattering angle dependent probabilities and integral cross sections for Coulomb fission were calculated. It is concluded that earlier observed discrepancies between measured and calculated angular distributions for the one-neutron transfer product²³⁹U cannot be explained by sequential fission. Multi-nucleon transfer induced fission is observed down to energies (0.90±0.02)×V_C.     

The octupole states in odd uranium isotopes233U and235U

The behaviour of some excited states in odd uranium isotopes is compared with octupole vibrational states in even-even uranium isotopes. The possibility to interpret the states in odd isotopes as octupole vibrations is discussed.     

The reaction238U +238U at 7.42MeV/u

One-particle-inclusive measurements have been performed for the charge, kinetic energy and angular distributions of reaction products from²³⁸U +²³⁸U at 1 766MeV (7.42MeV/u) incident energy. The deep inelastic products exhibit features similar to those seen in reactions induced by medium heavy nuclei: increasing particle transfer is observed with increasing energy damping, the angular distributions are peaked near the grazing angle, they broaden significantly with increasing energy loss and/or charge transfer. The dominant reaction mechanism, however, is found to be sequential fission of one or both primary reaction products. The reconstructed primaryZ- andQ-value distributions show more particle transfer at a given energy loss than in other systems, i.e. the diffusion process seems to proceed colder in this system. This is confirmed by relatively large cross sections for surviving deep inelastic reaction products belowZ=92. A direct search forα-decay or fission of superheavy nuclei being produced in a deep inelastic reaction and being implanted in a surface barrier detector resulted in an upper cross section limit of 2 ×10^?32cm².     

Total spontaneous and isomer fission half-lives of U,U and Pu

Using the recently proposed coupled channel decay theory, we have reproduced here the observed absolute yield curves; total decay probabilities from the spontaneous and the isomeric fission states of ²³⁴U, ²³⁶U, and ²⁴⁰Pu, and the average kinetic energies. Our predicted yield curve for the decay of isomer fission state seems to be in agreement with preliminary observation.     

U impurities in Au

The properties of U impurities in Au have been studied by magnetic susceptibility, electrical resistivity, and electron spectroscopic measurements. The results indicate that U forms a well-defined local magnetic moment of 3.6 _B , giving rise to a Kondo resistance anomaly at low temperature. This is in agreement with spectroscopic data, which show localized impurity states well removed from the Fermi level. Comparison to calculated atomic multiplets shows the need for inclusion of crystal or ligand field effects for the multiplets. The intra-5f Coulomb correlation energy is found to be 2.6 eV.     

Structure of high-spin states in 232Th, 234U and 236U

Multiple Coulomb excitation of ²³²Th, ²³⁴U and ²³⁶U by 5.3 $\text{MeV}\text{u}$²⁰⁸Pb ions has been studied using γ-ray spectroscopy. Excitation of ground-band levels is observed up to spin I^π = 26⁺ (tentatively 28 ⁺) in ²³²Th and ²³⁴U and I^π = 28⁺ (tentatively 30⁺)in ²³⁶U. High-spin levels of the K^π = 0^? octupole-vibrational bands are also observed in these nuclei. The measured transition energies between ground-band levels suggest that at $\text{I≈ 28}\text{h}\text{?}$ several units of angular momentum are carried by single particles aligned with the rotation axis.This result can be understood in terms of a super band built on aligned two-quasiparticle configurations which crosses the ground-state rotational band at a rotational frequency of $\text{h}\text{?}\text{ω ? 0.25}\text{MeV}\text{(I ? 28}\text{h}\text{?}\text{)}$. The E2 transition-matrix elements deduced from the experimental γ-yields agree within their errors with the rigid-rotor predictions up to the highest spins observed.The experimental results are discussed using the concept of rotation alignment and are compared with predictions of the rotation-vibration model and the interacting-boson model.