The population of evaporation residue entry states in the decay of the compound nucleus Er*(54 MeV) is investigated in a cross-bombardment employing the re­ actions 1 6 0 + 1 4 Nd and ^Ni + ^Zr. Evaporation residue cross sections and entry state 7-ray fold distributions of the dominant exit channels were obtained for each reaction, using a 4π 7-ray detection system. An entrance-channel dependence of the 7-ray fold distributions of the xn products is observed. This effect is described successfully by the statistical model making use of compound nucleus angular mo­ mentum distributions obtained with a fusion model that provides a good description of the bombarding energy dependence of fusion data for both reactions. In accor­ dance with recent findings on the decay of Yb*, it is suggested that the observed differences in the population of the dominant exit channels originate from the pri­ mary spin distributions rather than a possible dependence of the compound nucleus decay on the formation mode.

The population of evaporation residue entry states in the decay of the compound nucleus Er*(54 MeV) is investigated in a cross-bombardment employing the re­ actions 1 6 0 + 1 4 Nd and ^Ni + ^Zr. Evaporation residue cross sections and entry state 7-ray fold distributions of the dominant exit channels were obtained for each reaction, using a 4π 7-ray detection system. An entrance-channel dependence of the 7-ray fold distributions of the xn products is observed. This effect is described successfully by the statistical model making use of compound nucleus angular mo­ mentum distributions obtained with a fusion model that provides a good description of the bombarding energy dependence of fusion data for both reactions. In accor­ dance with recent findings on the decay of Yb*, it is suggested that the observed differences in the population of the dominant exit channels originate from the pri­ mary spin distributions rather than a possible dependence of the compound nucleus decay on the formation mode.

We have investigated the El strength function of llBe by Coulomb excitiA ation and measurement of the subsequent projectile photon decay. The photons were measured in a wall of BaF'2 detectors. We have used the virtual photon method to extract the photabsorption cross section and hence the dipole strength function. We compare our findings with sum rule predictions. This is a f is t example of techniques we will extend to heavier mass nuclei.

Neutron-rich radioactive ion beams available from the HRIBF allow a variety of measurements around the (132)Sn region, including Coulomb excitation, fusion-evaporation, and neutron transfer. The B(E2; 0(+) -> 2(+)) value for first 2(+) excited states of even-even neutron-rich (132-136)Te and (126-134) Sn have been measured by Coulomb excitation in inverse kinematics. The results are discussed in terms of the shell model and the quasiparticle random phase approximation. Neutron transfer onto a (134)Te beam, from (9)Be and (13)C targets to populate single-particle states in (135)Te, has also been studied. Gamma rays from the (13)C((134) Te, (12)C) reaction were used to identify the vi(13/2) state in (135)Te, at an energy of 2109 keV. These and other results, and plans for future experiments with these neutron-rich beams, are presented.

We describe an experiment optimized to determine the transition probabilities for excitation of the first excited 2+ state in 132Sn. The large excitation energy (4.04 MeV) and consequent small excitation cross-section, together with the modest beam intensity available makes this a challenging experiment. The preliminary result is B(E2; 0+ → 2+) = 0.11 ± 0.03e 2 b 2. The high efficiency and generalized nature of the setup enabled us to also measure the first 2+ state in the two-neutron nucleus 134Sn. We have determined a value of B(E2; 0+ → 2+) = 0.029 ± 0.005e 2 b 2 which shows no sign of the asymmetry with respect to the N = 82 shell closure exhibited by the Te isotopes.

Exclusive measurements of high energy γ-rays in the decay of164Er, formed in the reaction40Ar+124Sn, have been performed to study angular momentum dependence of the giant dipole resonance (GDR) strength function. The γ-ray spectra were measured in coincidence with A=160 evaporation residues (4n channel at Ebeam = 163 MeV and 187 MeV. A statistical model analysis, incorporating a two-component GDR strength function, shows increase in the GDR width as the average spin of the compound nucleus increases from 26ħ, (at 163 MeV to 54ħ (at 187 MeV). This is consistent with the predictions of a thermal shape fluctuation model.

We have measured the B(E2;0(+) --> 2(+)) for the first excited 2(+) states in the double-closed shell nucleus Sn-132 and the two-neutron nucleus Sn-134. The results, based on a preliminary analysis are shown in Fig. 1 along with measurements on the stable Sn isotopes, and earlier results on Sn-126,Sn-128,Sn-130 [1]. The experimental setup developed for the Sn-132,Sn-134 measurements was also employed in a successful measurement of B(E2;0(+) --> 2(+)) for the closed-neutron-shell nucleus Ge-82.

The availability of fast radioactive beams offers the possibility for studies of E1-strength in projectiles via Coulomb excitation. Theoretical calculations predict that a significant fraction of this strength is shifted towards lower excitation energies in neutron-rich systems (e.g., [1]). At the NSCL, virtual photon scattering was used to probe the discrete structure of both O-18 and O-20 for levels in the region between 1 and 8 MeV Two 1(-) levels at 5.35(10) and 6.85(5) MeV were observed for the first time in O-20 [2]. The observed gamma-ray spectrum for O-20 is, in fact, dominated by transitions resulting from E1 excitations to these states. The extracted B(E1) up arrow values of similar to0.062(16) e(2)fm(2) and 0.035(9) e(2)fm(2) for the 5.35 and 6.85 MeV levels, respectively, are larger than shell model calculations predict [3, 4]. Such large dipole strengths are not observed for low-lying 1(-) states in 180, indicating a shift of dipole strength towards lower energies as one approaches the neutron drip-line.

Intermediate energy Coulomb excitation at 100 MeV/nucleon was used to probe the low-lying level structure of both O-18 and O-20 in the region between 1 and 8 MeV. Discrete 1(-) states with energies of 5.35(10) and 6.85(5) MeV were observed in O-20. The strong direct excitation and subsequent gamma-ray decay of these states, along with B(Elambda) predictions for O-18,O-20 levels in this energy region, established their dipole character. The extracted B(E1)up arrow values of 0.062(16)e(2) fm(2) and 0.035(9)e(2) fm(2) for the 5.35- and 6.85-MeV states, respectively, are significantly larger than shell model calculations, though modification of the single-particle energies, in particular, the p-sd shell gap, improves the agreement. The summed B(E1)up arrow value for these levels (in Weisskopf units) is consistent with that for other nuclei that have been discussed recently in the literature as potential Pygmy dipole resonance hosts.

Intermediate energy Coulomb excitation at 100 MeV/nucleon was used to probe the low-lying level structure of both ${}^{18}\mathrm{O}$ and ${}^{20}\mathrm{O}$ in the region between 1 and 8 MeV. Discrete ${1}^{\ensuremath{-}}$ states with energies of 5.35(10) and 6.85(5) MeV were observed in ${}^{20}\mathrm{O}.$ The strong direct excitation and subsequent $\ensuremath{\gamma}$-ray decay of these states, along with $B(E\ensuremath{\lambda})$ predictions for ${}^{18,20}\mathrm{O}$ levels in this energy region, established their dipole character. The extracted $B(E1)\ensuremath{\uparrow}$ values of ${0.062(16)e}^{2}{\mathrm{fm}}^{2}$ and ${0.035(9)e}^{2}{\mathrm{fm}}^{2}$ for the 5.35- and 6.85-MeV states, respectively, are significantly larger than shell model calculations, though modification of the single-particle energies, in particular, the $p\ensuremath{-}\mathrm{sd}$ shell gap, improves the agreement. The summed $B(E1)\ensuremath{\uparrow}$ value for these levels (in Weisskopf units) is consistent with that for other nuclei that have been discussed recently in the literature as potential Pygmy dipole resonance hosts.

The time scales for nuclear fission have been explored using both pre-and postfission neutrons and GDR gamma rays. Four systems were investigated: 133-MeV 16 O + 176 Yb and 208 Pb and 104-MeV 4 He + 188 Os and 209 Bi. Fission fragments were measured in coincidence with PPACs. The neutrons were detected using eight detectors from the DEMON array, while gamma rays were measured using the US BaF2 array. The pre-and postfission gamma rays were determined using moving source fits parallel and perpendicular to the fission fragment emission directions. The time scales for fission for the neutrons were determined using the neutron clock technique. The gamma-ray data were fitted using a statistical model calculation based on the code CASCADE. The results of the fits from both data types were used to extract nuclear friction coefficients, γ , and fission time scales. The γ values ranged from 7 to 20, while the fission times were (31–105)×10 −21 s.

The spectra of high-energy γ rays emitted by the Giant Dipole Resonance (GDR) built on moderately excited states associated with the evaporation of 0, 1 and 2 nucleons were measured in the 90Zr+89Y symmetric fusion reaction. The radiative fusion data suggest statistical emission from the compound nucleus. In addition, the analysis of the high-energy γ-ray spectra associated with the different evaporation channels at the present temperature of 0.7 MeV and spin range 15–20 ℏ show a fairly narrow width of 5.0±0.35 MeV. This value is smaller than what would be expected in a nucleus where shell effects do not play a role.

Angular distributions of fluorine and oxygen produced from 170 MeV 17^F incident on 208^Pb were measured. The elastic scattering data are in good agreement with optical model calculations using a double-folding potential and parameters similar to those obtained from 16^O+208^Pb. A large yield of oxygen was observed near \theta_lab=36 deg. It is reproduced fairly well by a calculation of the (17^F,16^O) breakup, which is dominated by one-proton stripping reactions. The discrepancy between our previous coincidence measurement and theoretical predictions was resolved by including core absorption in the present calculation.

Projectile photon coincidences were measured for the scattering of an 80 MeV/nucleon 64Zn beam from *‘*Pb and *“Bi targets at the GANIL heavy ion accelerator facility. Projectile-like particles between 0.5” and 4.5“ relative to the incident beam direction were detected in the SPEG energy loss spectrometer where their momentum, charge, and mass were determined. Photons were detected in the BaF2 scintillation detector array TAPS. Light charged particles produced in the reaction were detected in the KVI Forward Wall. The analysis of the data acquired in this experiment is focused on three different phenomena: (1) the two phonon giant dipole resonance, (2) time dependence of the decay of the one phonon giant dipole resonance, and (3) giant resonance strength in projectile nuclei.

A program to study resonant states in light nuclei with radioactive ion beams in inverse kinematics and using thick targets together with double-sided silicon strip detectors (DSSDs) has been started at the Holifield Radioactive Ion Beam Facility (HRIBF). This program has led to the discovery of the simultaneous two-proton decay from states in Ne-18 populated by F-17 + p. Results from our search for this long sought decay mode will be presented.

The investigation of collective modes in unstable nuclei has recently become an important topic in the study of exotic nuclei. The isovector giant dipole resonance (GDR) is one of the most important and easily accessible of these collective modes. Theoretical calculations predict that GDR strength in neutronrich nuclei will shift towards lower excitation energies as one probes closer to the neutron dripline [1,2]. As