Search results for " Barrier"
showing 10 items of 540 documents
Multinucleon transfer reactions in closed-shell nuclei
2007
Multinucleon transfer reactions in 40Ca+96Zr and 90Zr+208Pb have been measured at energies close to the Coulomb barrier in a high resolution gamma-particle coincidence experiment. The large solid angle magnetic spectrometer PRISMA coupled to the CLARA gamma-array has been employed. Trajectory reconstruction has been applied for the complete identification of transfer products. Mass and charge yields, total kinetic energy losses, gamma transitions of the binary reaction partners, and comparison of data with semiclassical calculations are reported. Specific transitions in 95Zr populated in one particle transfer channels are discussed in terms of particle-phonon couplings. The gamma decays fro…
Weak channels in backscattering of20Ne onnatNi,118Sn, and208Pb
2012
To further our understanding of the influence of weakly coupled channels on the distribution of Coulomb barrier heights, we have measured transfer cross sections for ${}^{20}$Ne ions backscattered from ${}^{\mathrm{nat}}$Ni, ${}^{118}$Sn, and ${}^{208}$Pb targets at near-barrier energies. The $Q$ value spectrum in the case of ${}^{208}$Pb target has been determined too. The transfer channels appear to be especially important for ${}^{208}$Pb, whose double-closed-shell nature leads to a relatively low level density for noncollective inelastic excitations.
Competition between binary reactions and fusion in heavy-ion collisions at the Coulomb barrier
1992
Mass and charge distributions for binary reaction channels have been measured for the reactions86Kr with76Ge,104Ru and130Te at the Coulomb barrier using chemical separations andγ-ray spectroscopy. These systems span the region where dynamical hindrance to complete fusion sets in. The binary reactions can be subdivided into two components associated withi) reflection from the outer potential barrier (quasielastic), andii) reseparation after passing the barrier (complex reactions). The sum of complex-reaction channels and evaporation residues from complete fusion can be reproduced by a barrier passing calculation. The fraction of the barrier passing flux leading to reseparation increases from…
Spin distributions at the Coulomb barrier in the $^{58}$Ni+$^{60}$Ni fusion reaction from gamma-ray multiplicity measurements
2002
Abstract Heavy-ion fusion barrier distributions are now routinely obtained directly from experimental data. Measurements of the total γ-ray multiplicity for the fusion channels of the 58 Ni + 60 Ni system, which has striking yet well understood barrier structures, confirm the theoretical predictions that very high spins can be populated at energies close to (and even below) the nominal Coulomb barrier. The mapping from multiplicities to spin populations shows that structures in the barrier distribution are still evident in the γ-ray results.
Testing refined shell-model interactions in thesdshell: Coulomb excitation ofNa26
2015
Background: Shell-model calculations crucially depend on the residual interaction used to approximate the nucleon-nucleon interaction. Recent improvements to the empirical universal $sd$ interaction (USD) describing nuclei within the $sd$ shell yielded two new interactions---USDA and USDB---causing changes in the theoretical description of these nuclei.Purpose: Transition matrix elements between excited states provide an excellent probe to examine the underlying shell structure. These observables provide a stringent test for the newly derived interactions. The nucleus $^{26}\mathrm{Na}$ with 7 valence neutrons and 3 valence protons outside the doubly-magic ${}^{16}\mathrm{O}$ core is used a…
The decay of $^{31}$Ar
1990
10 pages, 1 table, 4 figures.
Mass distributions of the system136Xe+208Pb at laboratory energies around the Coulomb barrier: A candidate reaction for the production of neutron-ric…
2012
Reaction products from the system ${}^{136}\mathrm{Xe}+{}^{208}$Pb at ${}^{136}$Xe ions laboratory energies of 700, 870, and 1020 MeV were studied by two-body kinematics and by a catcher-foil activity analysis to explore the theoretically proposed suitability of such reaction as a means to produce neutron-rich nuclei in the neutron shell closure $N=126$. Cross sections for products heavier than ${}^{208}$Pb were measured and were found sensibly larger than new theoretical predictions. Transfers of up to 16 nucleons from Xe to Pb were observed.
Deeply bound pionic atoms from the $(\gamma,p)$ reaction in nuclei
2002
We study the $(\gamma,p)$ reaction on $^{208}Pb$ leading to $^{207}Pb$ with a bound pion attached to it in the lowest 1s or 2p pionic levels. The reaction can be made recoilless to optimize the production cross section but we must choose a bit higher photon energy to overcome the Coulomb barrier in the proton emission. The cross sections obtained are easily measurable and can be larger than 50 per cent of the background from inclusive ($\gamma$,p). This makes it a clear case for the detection of the pionic atom signals, converting this reaction into a practical tool to produce deeply bound pionic atoms.
Effects of weakly coupled channels on quasielastic barrier distributions
2009
Heavy-ion collisions often produce fusion barrier distributions with structures displaying a fingerprint of couplings to highly collective excitations. Similar distributions can be obtained from large-angle quasielastic scattering, although in this case, the role of the many weak direct-reaction channels is unclear. For $^{20}\mathrm{Ne}+^{90}\mathrm{Zr}$, we have observed the barrier structures expected for the highly deformed neon projectile; however, for $^{20}\mathrm{Ne}+^{92}\mathrm{Zr}$, we find significant extra absorption into a large number of noncollective inelastic channels. This leads to smearing of the barrier distribution and a consequent reduction in the ``resolving power'' o…
Two-proton emission in the decay of Ar-31
1998
18 pages, 7 figures, 2 tables.-- PACS nrs.: 23.40.Hc; 27.30.+t.