The mechanism of fusion of two heavy nuclei is formulated within the concept of transmission across a mildly absorptive effective fusion barrier (EFB). The intensity of transmitted waves across such a barrier could be represented by the product $T_R{P}_S$ where $T_R$ stands for the transmission coefficient across the corresponding real barrier and $P_S$ is a factor of survival probability against absorption under the complex barrier. The justification of this result and the physical basis of the above EFB transmission model of fusion, which is complementary to the definition of fusion based on absorption in the interior region known as the direct reaction model (DRM), are demonstrated in the case of a complex square well potential with a complex rectangular barrier. Based on a WKB approach, expressions for $T_R$ for different partial waves utilizing a realistic nucleus-nucleus potential are derived. Using the resulting expressions for the fusion cross section $\left({\sigma }_F\right),$ the experimental values of ${\sigma }_F$ and the corresponding data of the average angular momentum of the fused body are explained satisfactorily over a wide range of energy around the Coulomb barrier in various heavy ion systems such as ${}^{16}{\mathrm{O}+}^{152,154}\mathrm{Sm},$ ${}^{58,64}{\mathrm{N}\mathrm{i}+}^{58,64}\mathrm{Ni},$ ${}^{64}{\mathrm{N}\mathrm{i}+}^{92}\mathrm{Zr},$ and ${}^{64}{\mathrm{N}\mathrm{i}+}^{100}\mathrm{Mo}.$

Measurements of dielectron production in $p+p$ and $p+d$ collisions with beam kinetic energies from 1.04 to 4.88 GeV are presented. The differential cross section is presented as a function of invariant pair mass, transverse momentum, and rapidity. The shapes of the mass spectra and their evolution with beam energy provide information about the relative importance of the various dielectron production mechanisms in this energy regime. The $p+d$ to $p+p$ ratio of the dielectron yield is also presented as a function of invariant pair mass, transverse momentum, and rapidity. The shapes of the transverse momentum and rapidity spectra from the $p+d$ and $p+p$ systems are found to be similar to one another for each of the beam energies studied. The beam energy dependence of the integrated cross sections is also presented.

We analyze recent results of SU(3) lattice QCD calculations with a phenomenological parametrization for the quark-gluon plasma equation of state based on a quasiparticle picture with massive quarks and gluons. At high temperature we obtain a good fit to the lattice data using perturbative thermal quark and gluon masses from an improved HTL scheme. At temperatures close to the confinement phase transition the fitted masses increase above the perturbative value, and a nonzero (but small) bag constant is required to fit the lattice data.

We have shown that recent experimental data on radial flow, both from AGS and SPS energies, are in agreement with the equation of state (EOS) including the QCD phase transition. A new hydrokinetic model (HKM) is developed, which incorporates a hydrodynamical treatment of the expansion and proper kinetics of the freeze-out. We show that the freeze-out surfaces for different secondaries and different collisions are very different, and they are not at all isotherms $T$=const (as was assumed in most previous hydrodynamics works). Comparison of HKM results with the cascade-based event generator RQMD is also made in some detail: we found that both the EOS and flow are in rather good agreement, while the space-time picture is still somewhat different.

By using the output of a thermal model as the input to a hadronic cascade, we investigate the role of kinetic and chemical equilibrium in the breakup stage of $158A\hspace{0.5em}\mathrm{GeV}/c$ Pb+Pb collisions at CERN. Gross features of experimental pion and proton spectra are fit, as well as the transverse energy and baryons per unit rapidity. However, experimental source sizes extracted from pion correlations and the low $p_t$ behavior of pion spectra are not reproduced. We argue that pionic phase space has become overpopulated compared to equilibrium considerations. Other issues regarding chemical and kinetic equilibration are also explored.

We study the disintegration of nuclei by strong electromagnetic fields induced by ultrarelativistic heavy ions. The proposed multistep model includes (1) the absorption of a virtual photon by a nucleus, (2) intranuclear cascades of produced hadrons, and (3) statistical decay of the excited residual nucleus. The combined model describes well existing data on projectile fragmentation at energy 200 GeV per nucleon. Electromagnetic multifragmentation of nuclei is predicted to be an important reaction mechanism at RHIC and LHC energies.

We investigate the space-time structure of the classical gluon field produced in an ultrarelativistic collision between color charges. The classical solution which was computed previously in a perturbative approach is shown to become unstable on account of the non-Abelian self-interaction neglected in the perturbative solution scheme. The time scale for growth of the instabilities is found to be of the order of the distance between the colliding color charges. We argue that these instabilities will eventually lead to thermalization of gluons produced in an ultrarelativistic collision between heavy nuclei. The rate of thermalization is estimated to be of order $g^2\mu$, where $g$ is the strong coupling constant and ${\mu }^2$ the transverse color charge density of an ultrarelativistic nucleus.

A self-consistent relativistic integral-differential equation of the Boltzmann-Uehling-Uhlenbeck type for the $N^{*}$(1440) resonance is developed based on an effective Lagrangian of baryons interacting through mesons. The closed time-path Green’s function technique and semiclassical, quasiparticle, and Born approximations are employed in the derivation. The nonequilibrium RBUU-type equation for the $N^{*}$(1440) is consistent with that of the nucleon’s and delta’s which we derived before. Thus, we obtain a set of coupled equations for the $N$, $\Delta$, and $N^{*}$(1440) distribution functions. All the $N^{*}$(1440)-relevant in-medium two-body scattering cross sections within the $N$, $\Delta$, and $N^{*}$(1440) system are derived from the same effective Lagrangian in addition to the mean field and presented analytically, which can be directly used in the study of relativistic heavy-ion collisions. The theoretical prediction of the free $p\overrightarrow{p}{\mathrm{pp}}^{*}\mathrm{}\left(1440\right)\mathrm{}$ cross section is in good agreement with the experimental data. We calculate the in-medium $N+\overrightarrow{N}{N+N}^{*}$, $N^{*}+\overrightarrow{N}N+N$, and $N^{*}+\overrightarrow{N}{N}^{*}+N$ cross sections in cold nuclear matter up to twice the nuclear matter density. The results show that the density dependence of predicted in-medium cross sections is sensitive to the $N^{*}{N}^{*}$ coupling strengths used.

The production of the isoscalar $J^{\pi }{=3\mathrm{}}^{+}$ didelta dibaryon $d^{*}$ by proton inelastic scattering from deuteron targets is described in a double-scattering Glauber approximation. Each scattering changes a target nucleon into a Δ with the help of the isovector tensor force transmitted by π and ρ mesons. The differential cross section constructed from empirical Love-Franey nucleon-nucleon $t$ matrices and a simple model of $d^{*}$ shows a maximum of some 10 μb/sr at 70° (c.m.) for 500 MeV protons. The partial width of the decay $d^{*}\to \mathrm{NN}$ caused by the exchanges of the same mesons is found for this simple model of $d^{*}$ to be about 9 MeV if the $d^{*}$ mass is 2100 MeV. The implications of these results are discussed.

The modified quark-meson coupling (MQMC) model is applied to describe the properties of finite nuclei. The concept of a density-dependent bag constant is used to calibrate the model at equilibrium nuclear matter density. By a redefinition of the scalar meson field, the MQMC model can be cast in a form similar to a quantum hydrodynamics (QHD) type mean-field model. Binding energies, charge radii, and single-particle spectra of spherical nuclei are analyzed and compared with QHD calculations and with results based on the original quark-meson coupling model. The accurate reproduction of the effective nucleon mass in the MQMC model leads to a realistic description of single-particle spectra and spin-orbit splittings. Changes of the internal quark structure of the nucleon in the nuclear environment are also discussed.

We calculate the full static interaction of a Skyrmion and an anti-Skyrmion as a function of separation and relative grooming. From this, using projection methods and Born-Oppenheimer mixing, we obtain the nucleon- antinucleon interaction. We find agreement with the major features of the empirical interaction including the strong central attraction and the sharp onset of annihilation at about 1 fm.

Semileptonic heav$\overrightarrow{\mathrm{y}}$heavy and heav$\overrightarrow{\mathrm{y}}$light meson transitions are studied as a phenomenological application of a heavy-quark limit of Dyson-Schwinger equations. Employing two parameters, $E$, the difference between the mass of the heavy meson and the effective mass of the heavy quark, and $\Lambda$, the width of the heavy-meson Bethe-Salpeter amplitude, we calculate $f_{+}\mathrm{}\left(t\right)\mathrm{}$ for all decays on their entire kinematically accessible $t$ domain. Our study favors $f_B$ in the range $0.135$–$0.17$ GeV and with $E=0.44\mathrm{}$ GeV and $1/\Lambda =0.14\mathrm{}$ fm we obtain $f_{+}^{B\pi }\mathrm{}\left(0\right)=0.46\mathrm{}$. As a result of neglecting ${1/m}_c$ corrections, we estimate that our calculated values of ${\rho }^2=0.87\mathrm{}$ and $f_{+}^{\mathrm{DK}}\mathrm{}\left(0\right)=0.62\mathrm{}$ are too low by approximately 15%. However, the bulk of these corrections should cancel in our calculated values of Br$\left(\overrightarrow{D}\pi \mathcal{l}\nu \right)/\mathrm{Br}\left(\overrightarrow{D}K\mathcal{l}\nu \right)=0.13\mathrm{}$ and $f_{+}^{D\pi }{\mathrm{}\left(0\right)/f}_{+}^{\mathrm{DK}}\mathrm{}\left(0\right)=1.16\mathrm{}$.

The partial-wave expansion used to treat the distortion of scattered electrons by the nuclear Coulomb field is simpler and considerably less time-consuming when applied to the production of muons and electrons by low- and intermediate-energy neutrinos. For angle-integrated cross sections, however, a modification of the “effective-momentum” approximation seems to work so well that for muons the full distorted-wave treatment is usually unnecessary, even at kinetic energies as low as 1 MeV and in nuclei as heavy as lead. The method does not work as well for electron production at low energies, but there a Fermi function often proves perfectly adequate. Scattering of electron neutrinos from muon decay on iodine and of atmospheric neutrinos on iron is discussed in light of these results.

We present the results of two separate measurements of the half-life of ${}^{44}\mathrm{Ti}$ relative to those of ${}^{22}\mathrm{Na}$ and ${}^{207}\mathrm{Bi},$ respectively. By comparing the numbers of 1157-keV γ rays from ${}^{44}\mathrm{Ti}$ to those of 1274-keV γ rays from ${}^{22}\mathrm{Na}$ observed from a mixed source over a period of approximately 2 yr, we determined the half-life of ${}^{44}\mathrm{Ti}$ to be $61.5\pm 1.0\mathrm{yr}.$ From an approximately 1-yr-long study of another mixed source, where we compared the numbers of 1157-keV γ rays from ${}^{44}\mathrm{Ti}$ to those of 1064-keV γ rays from ${}^{207}\mathrm{Bi},$ we determined the ${}^{44}\mathrm{Ti}$ half-life to be $62\pm 5\mathrm{yr}.$ From these two results, we have obtained a best value of $62\pm 2\mathrm{yr}$ for the half-life of ${}^{44}\mathrm{Ti}.$ The astrophysical implications of this result are discussed.

${}^7$Be electron capture decay to ${}^7$Li has been investigated by means of a cryogenic $\mu$ calorimeter. A cryogenic particle detector, due to its low energy threshold and good energy resolution, allows us to detect for the first time the complete ${}^7$Be calorimetric energy spectrum with a peak width of 24 eV full width at half maximum at 112 eV. The observed decrease in the rate of the absorber activity corresponds to the expected ${}^7$Be half-life of 53 days. This kind of detector has an important application in the environment of a lithium radiochemical solar neutrino experiment which is in progress in Moscow. A discussion about the possible processes which take place inside the BeO absorber during the energy thermalization is reported.

Clayton and Jin have proposed that ${}^{26}\mathrm{Al}$ in the early solar system was made by oxygen-rich cosmic rays through the ${}^{12}\mathrm{C}{(}^{16}\mathrm{O}{,x)}^{26}{\mathrm{Al}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}$ reaction. To test their proposal we have measured the yield of ${}^{26}{\mathrm{Al}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}$ from this reaction using the activation method. We find that the yield is too low to explain the ${}^{26}\mathrm{Al}{/}^{27}\mathrm{Al}$ ratio that has been observed in carbonaceous chondrite meteorites.

The prediction of cross sections for nuclei far off stability is crucial in the field of nuclear astrophysics. We calculate direct neutron capture on the even-even isotopes ${}^{124-145}$Sn and ${}^{208-238}$Pb with energy levels, masses, and nuclear density distributions taken from different nuclear-structure models. The utilized structure models are a Hartree-Fock-Bogoliubov model, a relativistic mean field theory, and a macroscopic-microscopic model based on the finite-range droplet model and a folded-Yukawa single-particle potential. Due to the differences in the resulting neutron separation and level energies, the investigated models yield capture cross sections sometimes differing by orders of magnitude. This may also lead to differences in the predicted astrophysical $r$-process paths.

From an experiment with Gammasphere and a ${}^{252}\mathrm{Cf}$ spontaneous fission source, a new negative-parity band in ${}^{154}\mathrm{Nd}$ and new negative-parity levels in ${}^{152}\mathrm{Nd}$ were identified and the yrast bands were extended to ${18}^{+}$ in ${}^{154}\mathrm{Nd}$ and ${20}^{+}$ in ${}^{152}\mathrm{Nd}$ 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 $J_1$ values for the negative-parity band in ${}^{152}\mathrm{Nd}$ and $J_1$ for the similar negative-parity band in ${}^{154}\mathrm{Nd},$ however, their $J_2$ values are essentially identical. These bands indicate a new kind of identical band.

We measured the cross sections for the ${}^{17}\mathrm{O}{\mathrm{}(n,p)\mathrm{}}^{17}\mathrm{N}$ and ${}^{17}\mathrm{O}{\mathrm{}(n,d)\mathrm{}}^{16}\mathrm{N}$ reactions at a neutron bombarding energy of 14 MeV. A small DT generator was used to produce 14 MeV neutrons which irradiated known mixtures of ${}^{16}\mathrm{O}$ and ${}^{17}\mathrm{O}.$ The resulting ${}^{16}\mathrm{N}$ and ${}^{17}\mathrm{N}$ activities were transported to a remote counting station where a germanium detector was used to measure the characteristic gamma rays emitted in the beta decays of these isotopes. By using the cross section for the ${}^{16}\mathrm{O}\mathrm{}(n,p)\mathrm{}$ reaction as a reference, we determined the cross sections for the ${}^{17}\mathrm{O}\mathrm{}(n,p)\mathrm{}$ and ${}^{17}\mathrm{O}\mathrm{}(n,d)\mathrm{}$ reactions to be 27.4±6.1 and 5.6±1.9 mb, respectively.

In order to test the possibility of using ${}^{144}\mathrm{Pm}$ as a clock to measure the mean cosmic-ray confinement time in the Galaxy, we counted a highly purified 1.4 μCi source of this isotope in GAMMASPHERE and searched for its astrophysically interesting ${\beta }^{+}$ decay branch through the observation of positron-annihilation γ rays in coincidence with the characteristic 697-keV γ ray. Analysis of 57 h of source counting and 15 h of background shows no net signal and results in an upper limit of 3.7 of 511-511-697 keV coincident events. From this result we establish a 90% confidence level upper limit on the branch for this decay mode to be $7.4\times {10}^{-6}\%.\mathrm{}$ The implications of this result for the ${}^{144}\mathrm{Pm}$ cosmic-ray chronometer problem are discussed.