Search

Directed flow measurements for {Lambda} hyperons are presented and compared to those for protons produced in the same Au+Au collisions (2A, 4A, and 6AGeV; b

Transverse and radial flow measurements are presented for Λ hyperons along with Λ-P correlations from Au + Au collisions at AGS energies. The flow measurements are compared with those of co-produced protons. The measurements indicate that Λ hyperons flow consistently in the same direction as protons but with a smaller magnitude for all beam energies. Comparisons with RQMD calculations show that the experimentally determined Λ sideward flow is consistently larger compared with the calculated value obtained from scattering processes only. The experimental transverse flow ratio Λ/P is consistent with predictions ( 2/3) of the quark counting rule at 2 A GeV but is found to decrease with increasing beam energy. These observations may be related to the detailed features of the Λ-nucleon potential for the nuclear densities produced. At 6 A GeV, Λp correlation functions are observed to be essentially flat (within statistical uncertainty), indicating little or no correlation between Λs and co-produced protons. This suggests that Λs may have a spacetime emission pattern which is different from that for protons. Further evidence from radial flow measurements also indicates that 6 A GeV Λ hyperons (at mid-rapidity) do not share the same emitting source characteristics as co-produced protons.

The first detailed measurements of the centrality dependence of strangeness production in p-A collisions are presented. {lambda} and K{sub S} dn/dy distributions from 17.5 GeV/c p-Au collisions are shown as a function of ''grey'' track multiplicity and the estimated number of collisions, {nu}, made by the proton. The {nu} dependence of the {Lambda} yield deviates from a scaling of p-p data by the number of participants, increasing faster than this scaling for {nu} {le} 5 and saturating for larger {nu}. A slower growth in K{sub S} multiplicity with {nu} is observed, consistent with a weaker {nu} dependence of KK-bar production than YK production.

We have measured the sideward flow of neutral strange (K{sup 0}{sub s} ) mesons in 6A GeV Au +Au collisions. A prominent antiflow signal is observed for an impact parameter range (b(less-or-similar sign)7 fm ) which spans central and midcentral events. Since the K{sup 0}{sub s} scattering cross section is relatively small in nuclear matter, this observation suggests that the in-medium kaon vector potential plays an important role in high density nuclear matter. (c) 2000 The American Physical Society.

We present the first excitation function of ${\ensuremath{\pi}}^{\ensuremath{-}}$ intensity interferometry at Alternating Gradient Synchrotron (AGS) energies (2--8 A GeV). The sensitivity of the multidimensional correlation functions to the geometry and dynamics of the pion-emitting system provides a stringent test of transport models of heavy ion collisions. Detailed comparisons with a realistic transport model, both with and without an explicit nuclear mean field, suggest that the beam energy evolution in the reaction dynamics is different in the model than in the data. A significantly increased ${\ensuremath{\pi}}^{\ensuremath{-}}$ emission time scale, which has been suggested as a signal of the onset of the transition to quark-gluon plasma, is not observed.

We present some of the latest results from the E895 experiment conducted at the BNL AGS accelerator. Au+Au collisions were recorded by the EOS Time Projection Chamber (TPC) at beam energies of 2, 4, 6, and 8 A GeV. The TPC detector permitted the reconstruction of individual collision events with almost 4π acceptance and good particle identification. This capability allowed E895 to study global observables and two particle correlations with respect to symmetries of the event. Flow excitation functions are examined and discussed in the context of the Nuclear Equation of State.

We have measured the proton elliptic flow excitation function for the Au + Au system spanning the beam energy range 2 -- 8 AGeV. The excitation function shows a transition from negative to positive elliptic flow at a beam energy, $E_{tr} \sim$ 4 AGeV. Detailed comparisons with calculations from a relativistic Boltzmann-equation are presented. The comparisons suggest a softening of the nuclear equation of state (EOS) from a stiff form (K \sim 380 MeV) at low beam energies (E_{Beam} \le 2 AGeV) to a softer form (K \sim 210 MeV) at higher energies (E_{Beam} \ge $ 4 AGeV) where the calculated baryon density $ \rho \sim 4 \rho_0$.

Fission fragment mass and angular distributions were measured from the ^{64}Ni+^{197}Au reaction at 418 MeV and 383 MeV incident energy. A detailed data analysis was performed, using the one-body dissipation theory implemented in the code HICOL. The effect of the window and the wall friction on the experimental observables was investigated. Friction stronger than one-body was also considered. The mass and angular distributions were consistent with one-body dissipation. An evaporation code DIFHEAT coupled to HICOL was developed in order to predict reaction time scales required to describe available data on pre-scission neutron multiplicities. The multiplicity data were again consistent with one-body dissipation. The cross-sections for touch, capture and quasi-fission were also obtained., Comment: 25 pages REVTeX, 3 tables, 13 figures, submitted to Phys. Rev C

A sample of Lambda's produced in 2 A*GeV Ni + Cu collisions has been obtained with the EOS Time Projection Chamber at the Bevalac. Low background in the invariant mass distribution allows for the unambiguous demonstration of Lambda directed flow. The transverse mass spectrum at mid-rapidity has the characteristic shoulder-arm shape of particles undergoing radial transverse expansion. A linear dependence of Lambda multiplicity on impact parameter is observed, from which a total Lambda + Sigma^0 production cross section of $112 +/- 24 mb is deduced. Detailed comparisons with the ARC and RVUU models are made.

Transverse kinetic energies of individual fragments have been measured over a broad range of emitter excitation energies for the reaction 1AGeV Au+C. For excitation energies leading to large intermediate mass fragment multiplicities, these transverse energies require large collective radial expansion of the emitting systems. However, the traditional decomposition of the transverse energy into a thermal component and a Coulomb and collective component proportional to the fragment mass cannot account for this expansion. Expansion velocities show an increase with decreasing fragment Z and thus indicate fractionation of the collective energy for the expanding system. This collective energy increases with emitter excitation up to about 50{percent} of the energy deposited for a nuclear system with total energy {approximately}12AMeV. The bulk of the collective energy is carried away by ejectiles of Z{le}3. {copyright} {ital 1998} {ital The American Physical Society}

The E895 experiment has undertaken a systematic and exclusive study of Au+Au collisions between 2–8 A GeV. Complete event-by-event data were obtained using the EOS time projection chamber (TPC) which provided good particle identification and continuous tracking over almost 4π solid angle. In central Au+Au collisions at 6 A GeV, the proton rapidity distribution indicates almost complete stopping, hence high baryon density. We present preliminary results on collective flow observables as a function of beam energy. Data are compared with theoretical predictions.

Previous work has examined light particle correlations from O+Al reactions over a range of energies within a framework of statistical emission from a composite source. The source of these light particles was assumed to be an excited composite nucleus because the excitation energy of the source was not so high that exotic processes such as fragmentation or preequilibrium emission were significant. In this Brief Report we examine correlation functions between light charged particles emitted from reactions of S+Al at 105 MeV and 215 MeV. As in previous work, the proton-proton and proton-deuteron correlations are well described by the results of Monte Carlo simulations based on statistical emission. In this Brief Report we will also compare the results of alpha-alpha and deuteron-alpha correlations to the predictions of models which include the emission of heavier unstable particles (such as {sup 8}Be and {sup 6}Li{sup *}) from the excited source. The results presented here can serve as additional validation of the correlation technique and also as tests of the statistical model.

Proton and {alpha}-particle energy spectra were measured in coincidence with evaporation residues from 252 and 295 MeV {sup 58}Ni+{sup 112}Sn fusion reactions. Residues were separated from the beam using an electrostatic deflector and detected with surface barrier detectors. Light charged particles were detected with arrays of NaI detectors. Statistical model calculations based on standard parameter choices reproduce the spectra from the cold, low spin {sup 170}Pt{sup *} system. The effects of employing different methods of calculating transmission coefficients were explored. The optical model, ingoing wave boundary condition model, and a simple one-dimensional barrier penetration model from a fusion systematics analysis produce comparable satisfactory predictions. The Hill-Wheeler approximation for transmission coefficients gives unrealistic results for protons.

Proton and [alpha]-particle spectral shapes and multiplicities have been measured in coincidence with evaporation residues from 145 to 220 MeV [sup 28]Si+[sup 165]Ho and 115 and 140 MeV [sup 16]O+[sup 197]Au,[sup 208]Pb fusion reactions. Evaporation residues were separated using an electrostatic deflector and detected with large area surface barrier detectors. Light charged particles were detected at forward and backward angles with 14 single NaI detectors. In the context of the statistical model, the charged particle spectra provide information about the shapes and level densities of the emitting systems. Deformed emitters are inferred, and to a varying degree, an energy-dependent level density parameter is compatible with the data in each of the three cases. Implications for current fusion and fission dynamics studies are discussed.

Evaporation residue excitation functions and \ensuremath{\alpha}-multiplicities from complete fusion of $^{16}\mathrm{O}$ with $^{197}\mathrm{Au}$ and $^{208}\mathrm{Pb}$ have been measured from the fusion threshold up to 140 MeV incident energy. The data allow the conclusion that strongly overdamped motion cannot be dominant at energies in the vicinity of the fusion barrier below ${\mathit{E}}^{\mathrm{*}}$\ensuremath{\approxeq}50 MeV. At excitation energies above 50 MeV the residue cross section for $^{16}\mathrm{O}$${+}^{208}$Pb is much greater than predicted from the statistical model with conventional parametrizations. The enhancement is not explained by incorporating dynamical effects into the analysis. An alternative suggestion based on deexcitation-chain dependent fission barriers is discussed.

Particle-particle coincidence measurements for both large and small separation angles are reported for the reactions 140 MeV $^{16}\mathrm{O}$${+}^{27}$Al\ensuremath{\rightarrow}p-p, p-d, d-d, \ensuremath{\alpha}-\ensuremath{\alpha}, d-\ensuremath{\alpha}, and p-\ensuremath{\alpha}. Two clusters of seven detectors were used at \ifmmode\pm\else\textpm\fi{}50\ifmmode^\circ\else\textdegree\fi{}, on both the right and left sides of the beam axis. Coincidence data were compared for nearest-neighbor and across-beam geometries. For p-p, p-d, and d-d pairs, the results of this symmetry test are consistent with independent particle evaporation. For the \ensuremath{\alpha}-\ensuremath{\alpha}, d-\ensuremath{\alpha}, p-\ensuremath{\alpha} pairs, the results indicate significant contributions from breakup of preformed fragments. These results suggest that small-angle correlations for the former pairs are useful as probes of the space-time extent of the emitters, but that the latter pairs are compromised for this task.

Mass, velocity, and angular distributions have been measured for heavy products and for light charged particles from the reaction 215 MeV $^{16}\mathrm{O}$${+}^{27}$Al. Coincidences between evaporation residues and light charged particles have also been measured. Statistical-model calculations, incorporating light-particle decay from either the compound nucleus or the composite nucleus formed in the direct emission of a beam velocity particle, cannot account for the observed cross sections or angular distributions of the heavy residues. More elaborate kinematic simulations, which include direct light-particle emission as observed in the light-particle inclusive data, also do not work. This supports the notion that heavy fragment production (Ag4) would be needed to account for the residue distributions.

An analysis of inclusive pion production in proton-beryllium collisions at 6.4, 12.3, and 17.5 GeV/c proton beam momentum has been performed. The data were taken by Experiment 910 at the Alternating Gradient Synchrotron at the Brookhaven National Laboratory. The differential $\pi^+$ and $\pi^-$ production cross sections ($d^2\sigma/dpd\Omega$) are measured up to 400 mRad in $\theta_{\pi}$ and up to 6 GeV/c in $p_{\pi}$. The measured cross section is fit with a Sanford-Wang parameterization., Comment: Submitted to Phys. Rev. C

Nuclear reactions often proceed via fusion of projectile and target into a thermalized compound nucleus. For hot compound nuclei of temperature ≈1–5 MeV one expects that a chain of particles (neutrons, protons, alphas…) will be evaporated with a variety of time intervals of ≈10-22-10-20 s. The determination ofthese emission times is a major challenge for nuclear physicists. Such time intervals are too short to measure directly, but they do lead to final-state interactions between charged-particle pairs due to their mutual Coulomb repulsions. Therefore, one expects correlations between the charged-particle pairs that depend on their velocities and separation distances at birth, i.e. the flight distance of the first particle before birth of the second. The KALLIOPI program is a reaction simulation designed to predict the particle-particle correlations as a function of predicted or assumed values of the mean emission times. By comparison of the simulated results to experimental data one can test the basic predictions of decay rates for particle ejection from hot nuclear emitter.

Preliminary results of an experiment to detect y-transitions between structures known in the 12C+12 C system at 25.8 MeV and 19.3 MeV (c.m.) are reported. The extracted upper limit for these transitions is evidence against fully collective γ-decay between intermediate width resonances at these energies, but is inconclusive with respect to differentiating gross structure resonances from non-resonant processes.

Brookhaven-AGS. Measuerment of the spectra of charged pions over nearly full rapidity coverage from target to beam rapidity in the centrality range 0-5pct in AU-AU collisions at beam energies from 2 to 8 A GeV/nucleon. The rapidity densities are extracted using a thermal paramatrization model to fit the transverse mass spectra.. Numerical values supplied by J Klay.. This part (1) covers the data at 2 GeV/nucleon. Brookhaven-AGS. Measuerment of the spectra of charged pions over nearly full rapidity coverage from target to beam rapidity in the centrality range 0-5pct in AU-AU collisions at beam energies from 2 to 8 A GeV/nucleon. The rapidity densities are extracted using a thermal paramatrization model to fit the transverse mass spectra.. Numerical values supplied by J Klay.. This part (2) covers the data at 4 GeV/nucleon. Brookhaven-AGS. Measuerment of the spectra of charged pions over nearly full rapidity coverage from target to beam rapidity in the centrality range 0-5pct in AU-AU collisions at beam energies from 2 to 8 A GeV/nucleon. The rapidity densities are extracted using a thermal paramatrization model to fit the transverse mass spectra.. Numerical values supplied by J Klay.. This part (3) covers the data at 6.0 GeV/nucleon. Brookhaven-AGS. Measuerment of the spectra of charged pions over nearly full rapidity coverage from target to beam rapidity in the centrality range 0-5pct in AU-AU collisions at beam energies from 2 to 8 A GeV/nucleon. The rapidity densities are extracted using a thermal paramatrization model to fit the transverse mass spectra.. Numerical values supplied by J Klay.. This part (4) covers the data at 8.0 GeV/nucleon. Brookhaven-AGS. Measurement of the spectra of charged pions over nearly full rapidity coverage from target to beam rapidity in the centrality range 0-5pct in AU-AU collisions at beam energies from 2 to 8 A GeV/nucleon. The rapidity densities are extracted using a thermal paramatrization model to fit the transverse mass spectra.. Numerical values supplied by J Klay.. This part (5) covers the data Rapidiy density data.

Source images are extracted from two-particle correlations constructed from strange and nonstrange hadrons produced in 6A GeV Au+Au collisions. Very different source images result from pp vs p Lambda vs pi(-)pi(-) correlations. Scaling by transverse mass can describe the apparent source size ratio for p/pi(-) but not for Lambda/pi(-) or Lambda/p. These observations suggest important differences in the space-time emission histories for protons, pions, and neutral strange baryons produced in the same events.

The yield for the multi-strange $\Xi^{-}$ hyperon has been measured in 6 AGeV Au+Au collisions via reconstruction of its decay products $\pi^{-}$ and $\Lambda$, the latter also being reconstructed from its daughter tracks of $\pi^{-}$ and p. The measurement is rather close to the threshold for $\Xi^{-}$ production and therefore provides an important test of model predictions. The measured yield for $\Xi^{-}$ and $\Lambda$ are compared for several centralities. In central collisions the $\Xi^{-}$ yield is found to be in excellent agreement with statistical and transport model predictions, suggesting that multi-strange hadron production approaches chemical equilibrium in high baryon density nuclear matter., Comment: Submitted to PRL

Rapidity distributions of protons from central ${}^{197}\mathrm{Au}{+}^{197}\mathrm{Au}$ collisions measured by the E895 Collaboration in the energy range from $(2--8)A\mathrm{GeV}$ at the Brookhaven AGS are presented. Longitudinal flow parameters derived using a thermal model including collective longitudinal expansion are extracted from these distributions. The results show an approximately linear increase in the longitudinal flow velocity, $〈\ensuremath{\beta}\ensuremath{\gamma}{〉}_{L}$, as a function of the logarithm of beam energy.

Differential cross-sections are presented for the inclusive production of charged pions in the momentum range 0.1 to 1.2 GeV/c in interactions of 12.3 and 17.5 GeV/c protons with Be, Cu, and Au targets. The measurements were made by Experiment 910 at the Alternating Gradient Synchrotron in Brookhaven National Laboratory. The cross-sections are presented as a function of pion total momentum and production polar angle $\theta$ with respect to the beam.

Inclusive and semi-inclusive measurements are presented for antiproton ($\bar{p}$) production in proton-nucleus collisions at the AGS. The inclusive yields per event increase strongly with increasing beam energy and decrease slightly with increasing target mass. The $\bar{p}$ yield in 17.5 GeV/c p+Au collisions decreases with grey track multiplicity, $N_g$, for $N_g>0$, consistent with annihilation within the target nucleus. The relationship between $N_g$ and the number of scatterings of the proton in the nucleus is used to estimate the $\bar{p}$ annihilation cross section in the nuclear medium. The resulting cross section is at least a factor of five smaller than the free $\bar{p}-p$ annihilation cross section when assuming a small or negligible formation time. Only with a long formation time can the data be described with the free $\bar{p}-p$ annihilation cross section.

Source imaging analysis was performed on two-pion correlations in central Au + Au collisions at beam energies between 2 and 8$A$ GeV. We apply the imaging technique by Brown and Danielewicz, which allows a model-independent extraction of source functions with useful accuracy out to relative pion separations of about 20 fm. We found that extracted source functions have Gaussian shapes. Values of source functions at zero separation are almost constant across the energy range under study. Imaging results are found to be consistent with conventional source parameters obtained from a multidimensional HBT analysis., Talk given at Bologna 2000 - Structure of the Nucleus at the Dawn of the Century, Bologna, Italia, May 29 - June 3, 2000

Experiment E910 has measured slow protons and deuterons from collisions of 18 $\mathrm{GeV}/c$ protons with Be, Cu, and Au targets at the BNL AGS. These correspond to the ``grey tracks'' first observed in emulsion experiments. We report on their momentum and angular distributions and investigate their use in measuring the centrality of a collision, as defined by the mean number of projectile-nucleon interactions. The relation between the measured ${N}_{\mathrm{grey}}$ and the mean number of interactions $\overline{\ensuremath{\nu}}{(N}_{\mathrm{grey}})$ is studied using several simple models, one newly proposed, as well as the RQMD event generator. RQMD is shown to reproduce the ${N}_{\mathrm{grey}}$ distribution, and exhibits a dependence of ${N}_{\mathrm{grey}}$ on centrality that is similar to the behavior of the simple models. We find a strong linear dependence of $\overline{{N}_{\mathrm{grey}}}$ on $\ensuremath{\nu}$, with a constant of proportionality that varies with target. For the Au target, we report a relative systematic error for extracting $\overline{\ensuremath{\nu}}{(N}_{\mathrm{grey}})$ that lies between 10 and 20 % over all ${N}_{\mathrm{grey}}.$

We present a preliminary excitation function of π - intensity inteferometry at AGS energies (2-8 AGeV). The sensitivity of the multidimensional correlation functions to both the geometry and dynamics of the hot pionemitting system provide a stringent test of transport models of heavy ion collisions. Detailed comparisons are performed with the RQMD transport model, both with and without an explicit nuclear meanfield. These comparisons suggest that the evolution in the reaction dynamics with beam energy is different in the model and the data. A suggested signal of the onset of the transition to quark-gluon plasma in the inteferometry excitation function is not observed.

A primary goal of high-enery heavy ion physics is to create and study the quark-gluon plasma (QGP), a phase of matter in which partonic- instead of hadronic- degrees of freedom describe the system. Several transport, hydrodynamic, and nucleation theories1,2,3,4 suggest that energy densities achieved in central collisions between heavy ions at AGS energies may be sufficient to create the QGP.

Using a relativistic hadron transport model, we investigate the utility of the elliptic flow excitation function as a probe for the stiffness of nuclear matter and for the onset of a possible quark-gluon-plasma (QGP) phase-transition at AGS energies 1 < E_Beam < 11 AGeV. The excitation function shows a strong dependence on the nuclear equation of state, and exhibits characteristic signatures which could signal the onset of a phase transition to the QGP., 11 pages, 4 Postscript figures, uses epsf.sty, submitted to Physical Review Letters

Experiment 910 at the Brookhaven National Laboratory AGS accelerator is a study of proton-nucleus collisions using 6, 12.5 and 18 GeV/c proton beams. E910 was designed to have close to 100% acceptance, and to provide a large enough data sample to allow particle production to be studied as a function of collision “centrality”. The E910 spectrometer is built around a large TPC, as shown schematically in fig. 1. Because the TPC does not provide good particle identification or momentum resolution at high momentum, these are obtained by including downstream tracking, a time of flight detector and a Cherenkov detector.

High-energy photon yields from the reactions [sup 12]C+[sup 112,124]Sn at 10 MeV/nucleon have been measured. The ratio of cross sections ([ital E][sub [gamma]][ge]30 MeV)[sigma]([sup 124]Sn)/[sigma]([sup 112]Sn) is 1.6[plus minus]0.2, which is larger than expected within the equal-participant model. The elementary [ital n]-[ital p]-[gamma] cross section is evaluated within the neutral scalar [sigma] meson exchange model, and implemented into a BUU code. The results of the BUU calculation suggest that the high-energy [gamma]-ray yield differences for the two Sn isotopes arise from the differences in nucelon phase-space distributions. The sensitivity of the high-energy photon production to the initial phase-space conditions is explored.

We present data for small-angle particle-particle correlations from the reactions 80, 140, 215, and 250 MeV {sup 16}O+{sup 27}Al{r arrow}{ital p}-{ital p} or {ital p}-{ital d}. The main features of these data are anticorrelations for small relative momenta ({le}25 MeV/{ital c}) that strengthen with increasing bombarding energy. Statistical model calculations have been performed to predict the mean lifetimes for each step of evaporative decay, and then simulate the trajectories of the particle pairs and the resulting particle correlations. This simulation accounts very well for the trends of the data and can provide an important new test for the hypothesis of equilibration on which the model is built.

The particle decay of the ground state of /sup 6/Be was observed following population in the /sup 6/Li(/sup 3/He,t)/sup 6/Be reaction. The ..cap alpha.. particle decay spectrum corresponds to the ordinary three body phase space shape for energies above about 100 keV in the /sup 6/Be center-of-mass system. At lower energies the relative yield exceeds the available phase space. It is shown that neither the phase space spectrum modified by the proton-proton final state interaction nor the spectrum corresponding to sequential decay through the /sup 5/Li ground state have shapes consistent with the data. The enhanced yield of low energy ..cap alpha.. particles is not accounted for by either process.

Using particle $\ensuremath{\gamma}$-coincident techniques, an upper limit of about 8 \ensuremath{\mu}b/sr is placed on the forward angle cross section for the excitation in ($p,{p}^{\ensuremath{'}}$) at ${E}_{p}=17.2$ MeV of the ${4}^{\ensuremath{-}}$ state in $^{90}\mathrm{Zr}$ at 2.738 MeV. This upper limit is consistent with distorted-wave Born-approximation calculations using realistic interactions and reasonable wave functions. A ${4}^{\ensuremath{-}}$ state in $^{92}\mathrm{Zr}$ is identified at 2.740 \ifmmode\pm\else\textpm\fi{} 0.010 MeV through the reaction $^{93}\mathrm{Nb}(d, ^{3}\mathrm{He})^{92}\mathrm{Zr}$ at ${E}_{d}=17.2$ MeV.NUCLEAR REACTIONS $^{90}\mathrm{Zr}(p,{p}^{\ensuremath{'}}\ensuremath{\gamma})$, $^{93}\mathrm{Nb}(d, ^{3}\mathrm{He})$, ${E}_{p}=17.2$ MeV, ${E}_{d}=17.2$ MeV; measured $\ensuremath{\sigma}({E}_{{p}^{\ensuremath{'}}}, \ensuremath{\theta})$, $\ensuremath{\sigma}({E}_{^{3}\mathrm{He}}, \ensuremath{\theta})$; calculated $\ensuremath{\sigma}({E}_{{p}^{\ensuremath{'}}}, \ensuremath{\theta})$ microscopic DWBA; $^{92}\mathrm{Zr}$ level measured, deduced ${J}^{\ensuremath{\pi}}$.

Photons with energies of 5--40 MeV have been measured in the $^{12}$C${+}^{112}$,124Sn reactions at incident energies of 7.5 and 10.5 MeV/nucleon and at laboratory angles of 60\ifmmode^\circ\else\textdegree\fi{}, 90\ifmmode^\circ\else\textdegree\fi{}, and 120\ifmmode^\circ\else\textdegree\fi{}. Statistical model calculations which describe the photon yields in the 5--20 MeV photon energy range cannot account for the relatively large yields measured at ${E}_{\ensuremath{\gamma}}$g20 MeV. For these energies, the angular distribution suggests photon emission from a source moving at the nucleon-nucleon center-of-mass velocity. The magnitude of the nonstatistical photon yields is roughly consistent with a scaling relationship based on nucleon-nucleon bremsstrahlung. However, this does not account for the observation that the $^{124}\mathrm{Sn}$ yield is considerably larger than the $^{112}\mathrm{Sn}$ yield and suggests differences in the neutron-proton dynamics play a role in these low energy collisions.

The properties of yrast states of $^{52}\mathrm{Fe}$ and $^{52}\mathrm{Mn}$ were studied using the $^{40}\mathrm{Ca}$ + $^{14}\mathrm{N}$ reaction. In-beam $\ensuremath{\gamma}$-ray singles, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence, and $n\ensuremath{-}\ensuremath{\gamma}$ coincidence data establish the positions of the lowest ${2}^{+}$ and ${4}^{+}$ states of $^{52}\mathrm{Fe}$ as 849.1\ifmmode\pm\else\textpm\fi{}0.3 and 2384.6\ifmmode\pm\else\textpm\fi{}0.7 keV, respectively. No $\ensuremath{\gamma}$ rays associated with other $^{52}\mathrm{Fe}$ states could be found. This is because an $^{52}\mathrm{Fe}$ isomer at 6.83 MeV ${\ensuremath{\beta}}^{+}$ decays to $^{52}\mathrm{Mn}$, diverting strength from the $^{52}\mathrm{Fe}$ $\ensuremath{\gamma}$ cascade. Delayed $\ensuremath{\gamma}$-ray singles and $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence data give information on the high-spin yrast states of $^{52}\mathrm{Mn}$ populated in the ${\ensuremath{\beta}}^{+}$ decay of the isomer. The results are consistent with several recently published works, and unambiguously establish that the $^{52}\mathrm{Mn}$ ${8}^{+}$ state is at 2286.0\ifmmode\pm\else\textpm\fi{}0.4 keV. The delayed spectra show no indication of direct $\ensuremath{\gamma}$ decay of the $^{52}\mathrm{Fe}$ isomer. An upper limit on the $\ensuremath{\gamma}$ decay branch is 4 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$. On the basis of the ${(1{f}_{\frac{7}{2}})}^{n}$ model with "bare" nucleon charges, direct $E4$ $\ensuremath{\gamma}$ emission should be the dominant decay mode. It is argued that the absence of $E4$ decay, taken together with known $B(E4)$ data on $^{44}\mathrm{Sc}$, $^{52}\mathrm{Mn}$ and $^{53}\mathrm{Fe}$, shows $E4$ effective charges in the ($1{f}_{\frac{7}{2}}$) shell are different for nuclei located near the beginning or end of the shell. Further, the effective charges near the end of the shell seem to be quite different from those found in $E2$ transitions, i.e., ${e}_{p}\ensuremath{\sim}0.5$, ${e}_{n}\ensuremath{\sim}\ensuremath{-}0.5$. First order perturbation calculations in the ${(1f,2p)}^{n}$ model offer qualitative, but not quantitative, insight as to the $E4$ effective charge behavior.RADIOACTIVITY $^{52}\mathrm{Fe}^{m}$; measured ${T}_{\frac{1}{2}}$. $\ensuremath{\beta}\ensuremath{\gamma}$ coin., $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$ and $\ensuremath{\gamma}\ensuremath{\gamma}$ coin; deduced $log\mathrm{ft}$, $E4$ limit. $^{52}\mathrm{Mn}$ deduced levels.NUCLEAR REACTIONS $^{40}\mathrm{Ca}$($^{14}\mathrm{N}$, $\mathrm{np}$)$^{52}\mathrm{Fe}$, $E=29 \mathrm{to} 38$ MeV; measured prompt $\ensuremath{\gamma}$ and $n\ensuremath{\gamma}$ coinc., deduced $^{52}\mathrm{Fe}$ levels.

The spin-isospin flip ( 6 Li, 6 He) reaction has been studied. The experiment was performed with a 34 MeV 6 Li beam incident upon 25, 26 Mg and 27 Al targets. Angular distributions associated with the lowest 5 2 + , 1 2 + , 7 2 + 25 Al , 5 + , 3 + , 1 + 26 Al and 5 2 + 27 Si states were measured. Microscopic DWBA calculations were performed using Yukawa central and r 2 . Yukawa ( r 2 · Y ) tensor ( μ = 1.0 fm −1 ) potentials averaged over the 6 Li( 6 He) cluster model wave functions. Knock-on (KO) exchange corrections corresponding to the central interaction are included using the local-energy approximation (LEA) method. The conclusion is that the quasi-elastic process is of major importance in the ( 6 Li, 6 He) transition studied in this work.

Evidence for population of $^{12}\mathrm{C}$ + $^{12}\mathrm{C}$ resonant states in the $^{12}\mathrm{C}(^{16}\mathrm{O}, \ensuremath{\alpha})^{24}\mathrm{Mg}^{*}$ transfer reaction at 130 MeV incident energy was sought in carbon-carbon coincidence data. Carbon momenta were measured with position sensitive telescopes centered at + 35\ifmmode^\circ\else\textdegree\fi{} and -30\ifmmode^\circ\else\textdegree\fi{}. Despite the fact that the experimental configuration discriminates against the prolific projectile breakup process, few events are observed in the kinematic regions corresponding to the resonances. A Monte Carlo simulation of the $^{12}\mathrm{C}(^{16}\mathrm{O}, \ensuremath{\alpha})^{24}\mathrm{Mg}^{*}\ensuremath{\rightarrow}^{12}\mathrm{C}+^{12}\mathrm{C}$ sequential reaction indicates that the transfer production cross section of resonant states is less than one-fourth the value in the literature based on $\ensuremath{\alpha}$-particle singles data at 145 MeV incident energy.

The /sup 54/Fe(/sup 6/Li,/sup 6/He)/sup 54/Co reaction was studied at an incident energy of 40 MeV. The results complement earlier (/sup 3/He,t) and (p,n) work. If one assumes approximate validity of one-step microscopic selection rules, and that the reaction strongly populates approx. =(1f/sub 7/2/)/sup -2/ states, the results suggest the previously unspecified 3/sup +/, 5/sup +/, and 6/sup +/ states of this configuration lie at 2.285, 2.149, and either 3.085 or 3.128 MeV in /sup 54/Co, respectively.

We investigated $^{206}\mathrm{Hg}$, the missing link for particle-vibration coupling studies around $^{208}\mathrm{Pb}$. In $^{18,17}\mathrm{O}$ induced reactions on $^{204}\mathrm{Hg}$ we identified $\ensuremath{\gamma}$ rays from states at 1.068 and 2.102 MeV in $^{206}\mathrm{Hg}$. Relying on theoretical arguments we propose spins ${2}^{+}$ and ${4}^{+}$, respectively.

Deep inelastic collisions between ''light'' heavy ions are considered in a formalism containing diffractive, diffusive, and statistical aspects. A closed-form diffractive cross section is derived, with the deflection function being parametrized in a classically-motivated way. A statistical argument is used to demonstrate how the observed double differential cross section is built up from different diffractive contributions each with its own weight. The form of the weighting function is derived. The observed forward-peaked exponentially-decaying form of deep inelastic collision angular distributions is accounted for. The possibility of exciting a nonzero spin state is explicitly included, enabling the same formalism to be used to explain the spin polarization occurring in deep inelastic collisions. This quantity is much more sensitive than the angular distribution to the choice of deflection function parametrization. Reasonable fits to data are obtained with only one free parameter, apart from an overall normalization factor.

Utilizing the $^{10}\mathrm{Be}(^{3}\mathrm{He},n)$ reaction the lowest ${0}^{+}$ $T=2$ state of $^{12}\mathrm{C}$ has been located at 27.611 \ifmmode\pm\else\textpm\fi{} 0.020 MeV. The result agrees with earlier ($p,t$) measurements on $^{14}\mathrm{C}$. The $T=2,1,0$ splitting of 2p-2h, ${0}^{+}$ states in $^{12}\mathrm{C}$ is discussed.

The mechanism of the reaction $^{27}\mathrm{Al}(^{16}\mathrm{O}, ^{12}\mathrm{C}\ensuremath{\alpha})^{27}\mathrm{Al}$ at 65.6-MeV incident energy has been examined with use of coincidence techniques. It is shown that the broad bell-shaped peak observed in $^{12}\mathrm{C}$ singles spectra corresponds to an $\ensuremath{\alpha}$-transfer-like process leading to fixed excitation energy in the $\ensuremath{\alpha}$+$^{27}\mathrm{Al}$ system. The $\ensuremath{\alpha}$-$^{12}\mathrm{C}$ angular correlation, however, is forward-peaked along the momentum-transfer direction, suggesting that the decay time of the system is less than required for equilibration into $^{31}\mathrm{P}$.

The ($^{3}\mathrm{He},d$), reaction cross sections on $^{90,92,94}\mathrm{Zr}$ and $^{92,94,96,98}\mathrm{Mo}$ targets have been measured to unbound isobaric analog states. All expected transitions are observed except those to $3{s}_{\frac{1}{2}}$ analog states which are inhibited. Distorted-wave Born approximation calculations do not explain the anomaly. Other possible explanations are suggested.

($^{3}\mathrm{He},t$) differential cross sections on $^{54}\mathrm{Fe}$, $^{58}\mathrm{Ni}$, and $^{60}\mathrm{Ni}$ targets have been studied at 24-MeV incident energy. Triton angular-distribution systematics are suggested by corroborative data from other work. On this basis several tentative spin-parity assignments in the copper isotopes are given. Distorted-wave Born-approximation calculations based on a microscopic effective-interaction model are presented for $^{54}\mathrm{Fe}$ and $^{58}\mathrm{Ni}$. These are in fair agreement with the data for the $^{54}\mathrm{Co}$ states thought to have ${(1{f}_{\frac{7}{2}})}^{\ensuremath{-}2}$ structure, and for the $T=1$ $^{58}\mathrm{Cu}$ states. However, these calculations generally do not yield consistent effective-interaction strengths or correct angular-distribution shapes for the $T=0$ $^{58}\mathrm{Cu}$ transitions. Simple two-particle wave functions are used for mass-58 states where the nucleons occupy the $2{p}_{\frac{3}{2}}$, $1{f}_{\frac{5}{2}}$, or $2{p}_{\frac{1}{2}}$ orbitals.