Search Results (15 total)

We have measured the yields of protons and A=2–4 nuclei in collisions between 10.8A GeV/c Au beams and targets of Al, Cu, and Au. The data, which cover a broad rapidity range at low transverse momenta, were measured as a function of collision centrality using a focusing beam line spectrometer and a high-rate centrality detector. We investigate the dependence of coalescence parameters on event geometry. The data are compared with the predictions of an RQMD+coalescence model.

From an experiment with Gammasphere and a ²⁵²Cf spontaneous fission source, a new negative-parity band in ¹⁵⁴Nd and new negative-parity levels in ¹⁵²Nd were identified and the yrast bands were extended to 18⁺ in ¹⁵⁴Nd and 20⁺ in ¹⁵²Nd in a triple gamma coincidence study. These new negative-parity bands are consistent with octupole vibrational mode. There is a constant difference as a function of spin between the J₁ values for the negative-parity band in ¹⁵²Nd and J₁ for the similar negative-parity band in ¹⁵⁴Nd, however, their J₂ values are essentially identical. These bands indicate a new kind of identical band.

Experiment E878 at the BNL-AGS has measured the invariant cross sections of antiprotons produced near p_t=0 in interactions of 10.8 GeV/c Au beams with targets of Al, Cu, and Au. The data were measured for a wide range of centralities and rapidities using a focusing beamline spectrometer and a high-rate centrality detector. We compare our data with the predictions of simple models and sophisticated transport models to explore the physics of antiproton production and annihilation.

Ten new transitions in ¹⁰⁷Mo have been observed and levels in ¹⁰⁹Mo are identified for the first time in a γ-γ-γ coincidence study from the spontaneous fission of ²⁵²Cf with 72 Compton suppressed Ge detectors in Gammasphere. Two sets of bands, each set intertwined by E1 transitions are observed in ¹⁰⁷Mo and one such set in ¹⁰⁹Mo. The observed level schemes are interpreted in terms of possible octupole deformation originating from the strong interaction of the h_11/2 and d_5/2 neutron shells.

A Reply to the Comment by Y. Pang, D. E. Kahana, and S. H. Kahana.

The γ transitions in ¹⁴⁷Ba, ¹⁴⁹Ce, and ^151,153Nd have been identified from γ-γ-γ, γ-γ, x-γ, and x-γ-γ coincidence studies of spontaneous fission of ²⁵²Cf. The yrast positive parity band in ¹⁴⁹Ce is assigned to an i_13/2, neutron favored signature. The yrast negative parity band in ¹⁴⁹Ce is assigned a h_9/2 proton favored signature. The positive parity band in ¹⁵¹Nd corresponds to the positive parity band in ¹⁴⁹Ce. The negative parity band in ¹⁵³Nd corresponds to the negative parity bands of ¹⁴⁹Ce and ¹⁶¹Er. The band observed in ¹⁴⁷Ba is built on the h_9/2 orbital. The plots for J₁ in these isotopes are remarkably similar, supporting our assignments. © 1996 The American Physical Society.

Coincidence γ-ray data from the spontaneous fission of ²⁴²Pu were collected at the Lawrence Berkeley Laboratory high purity Ge (HPGe) array, GAMMASPHERE. Data from several cold-fission (0 neutron emission) isotopic pairs were observed and are presented. An interesting trend in the fractional population of cold-fission events was observed and is discussed. Relative yields of Zr-Xe, Sr-Ba, and Mo-Te pairs were measured. The Zr-Xe system has the most complete data set. Some speculations on the trend in the number of neutrons emitted as a function of the mass of the Xe isotope populated are presented. Comparisons between the yields from the spontaneous fission of ²⁴²Pu and the yields from thermal-neutron-induced fission of ²⁴¹Pu are also presented. © 1996 The American Physical Society.

We have measured the yields of antiprotons in Au + Au interactions in the rapidity range 1.2<y<2.8 as a function of centrality using a beam line spectrometer. The shapes of the invariant multiplicity distributions at p_t=0 are used to explore the dynamics of antiproton production and annihilation.

We have investigated particle production using a zero degree two-segment focusing beam-line spectrometer, examining 2×10¹²  Au+Au interactions at a beam momentum of 10.8A  GeV/c. We have measured invariant cross sections for protons, various light nuclei (through A  =  6), antiprotons, and have set upper limits on the production of heavier nuclei, antideuterons, and strangelets. There is no evidence, within the sensitivity of our measurements, for the formation of new particles having lifetimes >100  ns

The levels in^108,110,112Ru have been investigated in the spontaneous fission of ²⁵²Cf using γ-γ-γ-, γ-γ-, x-x-, x-γ-, and x-γ-γ-coincidence techniques. The levels up to 16⁺ and 9⁺ in the yrast bands and γ-vibrational bands have been identified with very little energy staggering in ^108,110,112Ru. The ground bands in ^108,110Ru have identical γ-ray transition energies up to 8⁺. These are the lightest observed even-even nuclei with extended identical ground bands. Calculations in a collective model which includes rotations and vibrations reproduce the level energies and γ band branching ratios above the 3⁺ state rather well, while rigid triaxial rotor model calculations reproduce the branching ratios for the 2⁺ and 3⁺ states.

With prompt γ-ray and x-ray spectroscopy on fission fragments, several new transitions in ^109,111Ru have been identified. Angular correlation analysis of several of the new transitions yield evidence of a stretched E2 band structure. Qualitative Nilsson model arguments, systematics, and triaxial rotor+particle calculations support our hypothesis that the observed band is built on the unique parity νh_11/2 orbital.

Large discrepancies have existed, factor of ∼2.5 (∼5σ), between a variety of cascade-type theoretical models and published experimental results for the inclusive protonlike production corss sections at the 20° polar laboratory angle for relativistic La + La collisions. In view of this discrepancy the present work was undertaken to check the experimental cross sections for 0.76 GeV/nucleon La + La collisions using a small-acceptance magnetic spectrometer. The 20° cross sections were determined by measuring the appropriate range of polar laboratory angles and momenta which, when transformed into the projectile frame, produce the cross sections at 20°. Cross sections have been determined from 30° to 75° for protons and light nuclei with rigidities from 0.5 to 2.0 GeV/c in the laboratory frame. Cross sections were also deduced at 15° and 20° in the projectile frame for nucleon momenta from 0.9 to 1.5GeV/c. The original experimental results for the larger polar laboratory angles (40° and 60°) were confirmed; however, the 20° cross sections disagree by a factor of about 1.5 (∼2σ). At large polar laboratory angles (40°-70°) the model calculations disagrees in the low-momentum range with the present data by a factor of 1.5 (∼3σ). The discrepancy at small polar angles (15° and 20°) has been significantly reduced from the original factor of 2.5 down to a value of 1.2 (∼3σ).

Bose-Einstein correlations of negative pions in heavy ion collisions have been investigated for the reaction ¹³⁹La+^natLa→2π^-X at 12.6 GeV/nucleon at two acceptances, centered at laboratory observation angles of approximately 0° and 45° with respect to the beam axis. A scintillation counter array downstream of the target was used to sample the charged particle multiplicity of each event and hence give some information on the impact parameter of the collision. Including results from previous experiments, space-time dimensions of the pion source are now available for mass-symmetric collisions in the mass range of A=40 to 139. The sources are oblate for nearly all systems, except for La+La central collisions viewed near 45° in the laboratory (90° in the center of mass) where the source is spherical. The perpendicular radius R_⊥ is never less than 4 fm, regardless of the centrality of the La+La collision. Furthermore, R_⊥ seems independent of the mass of the collision system.

Results are presented for pion interferometry measurements of 1.2A GeV La+La at the Lawrence Berkeley Laboratory Heavy Ion Spectrometer System. The experiment’s acceptance is at forward angles in the center-of-mass system. The fit parameters R, τ, λ, R_⊥, and R_∥ are presented. The extracted shape of the pion source is oblate. The correlation between the extracted size of the pion source and the centrality of the collision is investigated as well as the dependence of the source size on the mean momentum of the pion pairs. We conclude that the fitted radius parameters scale with mass for symmetric systems. We observe a dependence of the fitted size of the pion source on the mean momentum of the pion pairs. Comparisons are made with previous results.