Search

Gamma-ray production cross section excitation functions have been measured for $30$, $42$, $54$ and $66$ MeV proton beams accelerated onto targets of astrophysical interest, $^{nat}$C, C + O (Mylar), $^{nat}$Mg, $^{nat}$Si and $^{56}$Fe, at the Sector Separated Cyclotron (SSC) of iThemba LABS (near Cape Town, South Africa). The AFRODITE array equipped with 8 Compton suppressed HPGe clover detectors was used to record $\gamma$-ray data. For known, intense $\gamma$-ray lines the previously reported experimental data measured up to $E_{p}\simeq$ $25$ MeV at the Washington and Orsay tandem accelerators were extended to higher proton energies. Our experimental data for the last 3 targets are reported here and discussed with respect to previous data and the Murphy \textit{et al.} compilation [ApJS 183, 142 (2009)], as well as to predictions of the nuclear reaction code TALYS. The overall agreement between theory and experiment obtained in first-approach calculations using default input parameters of TALYS has been appreciably improved by using modified optical model potential (OMP), deformation, and level density parameters. The OMP parameters have been extracted from theoretical fits to available experimental elastic/inelastic nucleon scattering angular distribution data by means of the coupled-channels reaction code OPTMAN. Experimental data for several new $\gamma$-ray lines are also reported and discussed. The astrophysical implications of our results are emphasised.

CITATION: Ndayishimye, J. 2019. Competition of rotation around the intermediate and long axes in 193Tl. Physical Review C, 100(1):014313, doi:10.1103/PhysRevC.100.014313.

CITATION: Kaya, B. D. C. K., et al. 2018. Comparison of double-folding effective interactions within the cluster model. Physical Review C, 98(4):044308, doi:10.1103/PhysRevC.98.044308.

CITATION: Liu, L., et al. 2018. Evolution from quasivibrational to quasirotational structure in 155Tm and yrast 27/2− to 25/2− energy anomaly in the A ≈ 150 mass region. Physical Review C, 97(4):044306, doi:10.1103/PhysRevC.97.044306.

CITATION: Niu, C. Y., et al. 2018. Spectroscopic study of the possibly triaxial transitional nucleus 75Ge. Physical Review C, 97(3):034322, doi:10.1103/PhysRevC.97.034322.

Experiments in physics, Astro-particle physics and cosmology that require careful shielding against cosmic rays include dark matter searches, studies of radioactive decays, and neutrino detection experiments. The need for such shielding has motivated the construction of laboratory caverns in mines and adjacent to tunnels under mountains. There are currently about a dozen such laboratories, in existence or under construction, all in the Northern Hemisphere. A motivation has been made for the establishment of a Southern Hemisphere facility. In this paper a feasibility study of measurements of radon in air (using electret ion chambers and alpha spectroscopy), background gamma ray measurements (inside/outside) the tunnel using scintillator (inorganic) detectors, cosmic ray measurements using organic scintillators and radiometric analyses of representative rock samples for the establishment of such a facility in the South Africa is presented.

High-spin states in $^{155}\mathrm{Yb}$ have been studied via the $^{144}\mathrm{Sm}(^{16}\mathrm{O},5n)^{155}\mathrm{Yb}$ reaction at a beam energy of 118 MeV. One negative-parity and one positive-parity cascade built on the $\ensuremath{\nu}{f}_{7/2}$ and $\ensuremath{\nu}{i}_{13/2}$ states, respectively, are established for the first time. The structures observed in $^{155}\mathrm{Yb}$ are compared with those in the neighboring $N=85$ isotones and with semiempirical shell-model (SESM) calculations. According to adiabatic and configuration-fixed constrained triaxial covariant density functional theory (CDFT) calculations, a coexistence of prolate and oblate shapes is predicted to exist in $^{155}\mathrm{Yb}$.

Spectator fragments resulting from relativistic heavy ion collisions, consisting of single protons and neutrons along with groups of stable nuclear fragments up to nitrogen $(Z=7)$, are measured in PHOBOS. These fragments are observed in Au+Au $(\sqrt{{s}_{{}_{NN}}}=19.6\phantom{\rule{0.16em}{0ex}}\mathrm{GeV})$ and Cu+Cu (22.4 GeV) collisions at high pseudorapidity $(\ensuremath{\eta})$. The dominant multiply-charged fragment is the tightly bound helium $(\ensuremath{\alpha})$, with lithium, beryllium, and boron all clearly seen as a function of collision centrality and pseudorapidity. We observe that in Cu+Cu collisions, it becomes much more favorable for the $\ensuremath{\alpha}$ fragments to be released than lithium. The yields of fragments approximately scale with the number of spectator nucleons, independent of the colliding ion. The shapes of the pseudorapidity distributions of fragments indicate that the average deflection of the fragments away from the beam direction increases for more central collisions. A detailed comparison of the shapes for $\ensuremath{\alpha}$ and lithium fragments indicates that the centrality dependence of the deflections favors a scaling with the number of participants in the collision.

A selection of experimental results from the PHOBOS Collaboration relevant for probing high-energy nuclear collisions with high transverse momentum particles is presented. The inclusive yields of charged particles and comparisons between nuclear and elementary collisions already reveal a large amount of parton energy loss in the hot and dense medium created in heavy ion collisions. Remarkable scaling and factorization features are observed, unifying the data taken at various collision energies, centralities and nuclear sizes. To further analyze the nature of the energy loss, a measurement of pseudorapidity (Δη) and azimuthal angle (Δφ) correlations between high transverse momentum charged hadrons (pT>2.5 GeV/c) and all associated charged particles is presented at both short-range (small Δη) and long-range (large Δη) over a continuous detector acceptance covering −4

Two pairs of positive-and negative-parity doublet bands together with eight strong electric dipole transitions linking their yrast positive- and negative-parity bands have been identified in ^{78}Br. They are interpreted as multiple chiral doublet bands with octupole correlations, which is supported by the microscopic multidimensionally-constrained covariant density functional theory and triaxial particle rotor model calculations. This observation reports the first example of chiral geometry in octupole soft nuclei.

CITATION: Ndayishimye, J. et al. 2017. Chiral Bands in 193TI. Acta Physica Polonica B, 48(3):343-346, doi:10.5506/APhysPolB.48.343.

The centrality dependence of the midrapidity charged-particle multiplicity density (|η| < 1) is presented for Au + Au and Cu + Cu collisions at RHIC over a broad range of collision energies. The multiplicity measured in the Cu + Cu system is found to be similar to that measured in the Au + Au system, for an equivalent Npart, with the observed factorization in energy and centrality still persistent in the smaller Cu + Cu system. The extent of the similarities observed for bulk particle production is tested by a comparative analysis of the inclusive transverse momentum distributions for Au + Au and Cu + Cu collisions near midrapidity. It is found that, within the uncertainties of the data, the ratio of yields between the various energies for both Au + Au and Cu + Cu systems are similar and constant with centrality, both in the bulk yields and as a function of pT ,u p to at least 4 GeV/c. The effects of multiple nucleon collisions that strongly increase with centrality and energy appear to only play a minor role in bulk and intermediate transverse momentum particle production.

Antiparticle to particle ratios for identified protons, kaons, and pions at {radical}(s{sub NN})=62.4 and 200 GeV in Cu+Cu collisions are presented as a function of centrality for the midrapidity region of 0.2 / ratio at {approx_equal}0.51 GeV/c, we observe an average value of 0.50{+-}0.003{sub (stat)}{+-}0.04{sub (syst)} and 0.77{+-}0.008{sub (stat)}{+-}0.05{sub (syst)} for the 10% most central collisions of 62.4 and 200 GeV Cu+Cu, respectively. The values for all three particle species measured at {radical}(s{sub NN})=200 GeV are in agreement within systematic uncertainties with that seen in both heavier and lighter systems measured at the same RHIC energy. This indicates that system size does not appear to play a strong role in determining the midrapidity chemical freeze-out properties affecting the antiparticle to particle ratios of the three most abundant particle species produced in these collisions.

We present the first measurements of the pseudorapidity distribution of primary charged particles in Cu+Cu collisions as a function of collision centrality and energy, \sqrtsnn = 22.4, 62.4 and 200 GeV, over a wide range of pseudorapidity, using the PHOBOS detector. Making a global comparison of Cu+Cu and Au+Au results, we find that the total number of produced charged particles and the rough shape (height and width) of the pseudorapidity distributions are determined by the number of nucleon participants. More detailed studies reveal that a more precise matching of the shape of the Cu+Cu and Au+Au pseudorapidity distributions over the full range of pseudorapidity occurs for the same Npart/2A value rather than the same Npart value. In other words, it is the collision geometry rather than just the number of nucleon participants that drives the detailed shape of the pseudorapidity distribution and its centrality dependence at RHIC energies., Submitted to Physical Review Letters

We present results on two-particle angular correlations in proton-proton collisions at center-of-mass energies of 200 and 410 GeV. The PHOBOS experiment at the BNL Relativistic Heavy Ion Collider has a uniquely large coverage for charged particles, giving the opportunity to explore the correlations at both short- and long-range scales. At both energies, a complex two-dimensional correlation structure in $\ensuremath{\Delta}\ensuremath{\eta}$ and $\ensuremath{\Delta}\ensuremath{\phi}$ is observed. In the context of an independent cluster model of short-range correlations, the cluster size and its decay width are extracted from the two-particle pseudorapidity correlation function and compared with previous measurements in proton-proton and proton-antiproton collisions, as well as PYTHIA and HIJING predictions.

We present transverse momentum distributions of charged hadrons produced in Cu+Cu collisions at {radical}(s{sub NN})=62.4 and 200 GeV. The spectra are measured for transverse momenta of 0.25