Search

The influence of the neutron richness on binary decays is investigated in 78,82Kr+40Ca reactions at 5.5 MeV/A incident energy. Kinetic energy distributions and angular distributions of fragments with atomic number 6≤Z≤28 were measured using the 4π-INDRA array. Global features are compatible with an emission from a long-lived system. The yields around the symmetric splitting are about 30% smaller for the neutron rich system. The persistence of strong structural effects is evidenced from elemental cross-sections of the light fragments. The cross-sections for odd-Z fragments are higher for the neutron rich CN while cross-sections for even-Z fragments are higher for the neutron poor CN. Calculations assuming two different potential energy surfaces are presented

Polarization observables in nuclear reactions with stable beams have provided important information concerning structural properties of nuclei and reaction mechanisms and hold great promise in the context of exotic nuclei. We report on the development of a polarized target based on plastic foils of 20–200 μm thickness to be used with radioactive ion beams. The operation of such a target requires a moderately high magnetic field and very low temperatures. The plastic foil is placed inside a chamber attached to the mixing chamber of a 3He–4He dilution refrigerator. Cooling of the foil is achieved via a superfluid film of 4He that can be supplied through two capillaries. The chamber has two thin, highly uniform silicon nitride windows. An NMR coil is attached to the target to monitor the polarization. Results of a first test to characterize the target system, using the elastic scattering of 38 MeV 12C by protons in inverse kinematics are presented.

A renewed interest in Accelerator Mass Spectrometry (AMS) from nuclear physics laboratories is emerging in connection with Radioactive Ion Beams (RIBs). At the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory (ORNL) we are exploring the AMS capabilities of the 25-MV tandem accelerator. Behind this effort is the realization that two fields of research – AMS and RIBs – complement each other in techniques. Development of effective and efficient beam purification techniques is of common interest to both AMS and the RIB program. Two main characteristics of the 25-MV tandem provide unique opportunities for performing the highest sensitivity measurements of AMS; namely (i) the highest operating voltage in the world, and (ii) a folded geometry which involves a 180° magnet in the terminal. For the RIB program, we have used AMS techniques to improve the sensitivity of detection of some radioactive species in the measurement of unknown masses of n-rich nuclei. For AMS, we have concentrated in exploring two important isotopes, 14C and 36Cl, for applications that require the highest sensitivity. We have successfully measured 36Cl/Cl ratios as low as a few times 10−16 in seawater samples demonstrating that our setup has the highest sensitivity for this isotope and proving that 36Cl can be measured at the levels required for a tracer in oceanography.

Neutron-rich radioactive ion beams available from the HRIBF allow a variety of measurements around the 132Sn region, including Coulomb excitation and single-nucleon transfer. The B(E2;0+ → 2+) values for first 2+ excited states of even-even neutron-rich 132-136Te and 126-130Sn have been measured by Coulomb excitation in inverse kinematics. Neutron transfer onto a 134Te beam from 9Be and 13C targets, to populate single-particle states in 135Te, has also been studied. Gamma rays from the 13C(134Te, 12C) reaction were used to identify the νi13/2 state in 135Te, 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.

The rates of the 18 F( p , α ) 15 O and 18 F( p , γ ) 19 Ne reactions in astrophysical environments depend on the properties of 19 Ne levels above the 18 F + p threshold. There are at least 8 levels in the mirror nucleus 19 F for which analogs have not been observed in 19 Ne in the excitation energy range E x = 6.4 – 7.6 MeV . These levels may significantly enhance the 18 F + p reaction rates, and thus we have made a search for these levels by measuring the 1 H( 18 F, p ) 18 F excitation function over the energy range E c . m . = 0.3 - 1.3 MeV . We have identified and measured the properties of a newly observed level at E x = 7.420 ± 0.014 MeV , which is most likely the mirror to the J π = 7 2 + 19 F level at 7.56 MeV. We have additionally found a significant discrepancy with a recent compilation for the properties of a 19 Ne state at E x = 7.5 MeV and set upper limits on the proton widths of missing levels.

Neutron-rich radioactive ion beams available from the HRIBF allow a variety of measurements around the 132Sn region, including Coulomb excitation, fusion-evaporation, and neutron transfer. The B ( E 2 ; 0 + → 2 + ) value for first 2+ excited states of even-even neutron-rich 132–136Te and 126–134Sn 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 134Te beam, from 9Be and 13C targets to populate single-particle states in 135Te, has also been studied. Gamma rays from the 13C(134Te, 12C) reaction were used to identify the ν i 13 / 2 state in 135Te, at an energy of 2109 keV. These and other results, and plans for future experiments with these neutron-rich beams, are presented.

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

The rates of the 18 F( p , α ) 15 O and 18 F( p , γ) 19 Ne reactions at T = 0.1 – 0.4 GK are necessary to understand the emission of positron-annihilation gamma rays expected from novae. Observations of such gamma rays by space-based telescopes would provide direct tests of nova models. These rates, however, are uncertain because of the unknown level structure of 19 Ne above the 18 F+ p threshold. Missing levels in 19 Ne were searched for by stopping a 24-MeV 18 F beam in a thick polypropylene target, and scattered protons were detected in a silicon-strip detector. The 18 F( p , p ) 18 F excitation function has been measured from E c.m. = 0.3 - 1.3 MeV covering most energies of astrophysical interest, and a significant discrepancy was observed with a recent compilation of 19 Ne resonance parameters.

Neutron-rich radioactive ion beams available from the HRIBF allow a variety of exciting measurements around the 132 Sn region, including Coulomb excitation, fusion-evaporation, and neutron transfer. The B ( E 2 ; 0 + → 2 + ) value for first 2 + excited states of neutron-rich 132,134,136 Te and 126,128,130,132,134 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. Results, and plans for future experiments with these neutron-rich beams, are presented.

Evaporation residue cross sections have been measured with neutron-rich radioactive 132 Sn beams on 64 Ni in the vicinity of the Coulomb barrier. The average beam intensity was 2 × 10 4 particles per second and the smallest cross section measured was less than 5 mb. Large sub-barrier fusion enhancement was observed. The measurement is compared to coupled-channel calculations taking into account inelastic excitation and nucleon transfer.

Evaporation residue cross sections have been measured using neutron-rich radioactive 132Sn beams incident on a 64Ni target in the vicinity of the Coulomb barrier. This is the first experiment using accelerated 132Sn beams to study nuclear reaction mechanisms. The average beam intensity was 2x 104 particles per second and the smallest cross section measured was less than 5 mb. A large sub-barrier fusion enhancement was observed compared to evaporation residue cross sections for 64Ni on stable even Sn isotopes. The enhancement cannot be accounted for by a simple barrier shift due to the change in nuclear sizes. Coupled-channel calculations including inelastic excitation underpredict the measured cross sections below the barrier. The presence of several neutron transfer channels with large positive Q values suggests that multinucleon transfer may play an important role in enhancing the fusion of 132Sn and 64Ni.

The cross section, kinetic energy distribution and angular distribution of frag- ments with atomic number 3 Z 28 emitted in the reaction 78 Kr + 40 Ca at the bombard- ing energy of 5.5 MeV/nucleon and coincidence between light charged particles and frag- ments were measured by means of the 4 -INDRA array to study the decay mechanism of medium mass excited nucleus. Global features indicate a high degree of relaxation and are compatible with a binary fission from compound nucleus. The mean value of the kinetic energy distributions of fragments indicates dominance of Coulomb interaction, while the width of the distribution signals large fluctuations. Inclusive cross-section distributions of fragments with charge 3 Z 28 are bell-shaped and a strong even-odd-staggering (o-e- s) is observed for 3 Z 12. Coincidence measurements suggest that the light partners in very asymmetric fission are emitted at excitation energies below the particle emission thresholds. Data were confronted to the predictions of statistical model describing the decay of compound nuclei by emission of light particles and fragments. Calculations as- suming spherical fission fragments and finite-range liquid drop fission barriers are not able to explain the experimental features. Attempts have been made to improve the agreement with experimental data. The analysis indicates the strong influence of the shape parame- terization of the potential energy surface in describing the fission process of intermediate mass compound nuclei.

Radioactive ion beams of ${}^{17}\mathrm{F}$ were used to study several resonance states in ${}^{18}\mathrm{Ne}$. Clear evidence for simultaneous two-proton emission from the 6.15 MeV state $({J}^{\ensuremath{\pi}}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1}^{\ensuremath{-}})$ in ${}^{18}\mathrm{Ne}$ has been observed with the reaction ${}^{17}\mathrm{F}{+}^{1}\mathrm{H}$. Because of limited angular coverage, the data did not differentiate between the two possible mechanisms of simultaneous decay, diproton ${(}^{2}\mathrm{He})$ emission or direct three-body decay. The two-proton partial width was found to be $21\ifmmode\pm\else\textpm\fi{}3\mathrm{eV}$ assuming ${}^{2}\mathrm{He}$ emission and $57\ifmmode\pm\else\textpm\fi{}6\mathrm{eV}$ assuming three-body decay. The total width of the ${1}^{\ensuremath{-}}$ state was measured to be $50\ifmmode\pm\else\textpm\fi{}5\mathrm{keV}$. Several additional resonances that decay by single proton emission were also studied.

The time delays in fission induced by bombardment of W with 180 MeV $^{32}\mathrm{S}$, $240\text{\ensuremath{-}}255$ MeV $^{48}\mathrm{Ti}$, $330\text{\ensuremath{-}}375$ MeV $^{58}\mathrm{Ni}$, and 390 MeV $^{74}\mathrm{Ge}$ have been measured by observation of crystal blocking. Nearly all results are consistent with exponential decay with lifetimes of order ${10}^{\ensuremath{-}18}$ s which depend weakly on the atomic number of the composite nucleus. This is inconsistent with the Bohr-Wheeler model of fission from a compound nucleus in statistical equilibrium at each stage in a neutron evaporation cascade and supports a picture of strongly damped quasifission. A simple diffusion model with one-body dissipation reproduces roughly the observed time scale and the exponential decay. It suggests that the outer fission barrier could play a significant role in the observed, very slow decays.

none 25 none J. P. WIELECZKO; E. BONNET; J. GOMEZ DEL CAMPO; M. LA COMMARA; M. VIGILANTE; J. D. FRANKLAND; A. CHBIHI; E. ROSATO; G. SPADACCINI; A. GALINDO-URIBARRI; D. SHAPIRA; C. BECK; B. BORDERIE; R. BOUGAULT; R. DAYRAS; G. DE ANGELIS; P. LAUTESSE; N. LE NEINDRE; D'ONOFRIO A; M. PARLOG; D. PIERROUTSAKOU; F. REJMUND; M. F. RIVET; M. ROMOLI; AND R. ROYL J. P., Wieleczko; E., Bonnet; J., GOMEZ DEL CAMPO; M., LA COMMARA; M., Vigilante; J. D., Frankland; A., Chbihi; E., Rosato; G., Spadaccini; A., GALINDO URIBARRI; D., Shapira; C., Beck; B., Borderie; R., Bougault; R., Dayras; G., DE ANGELIS; P., Lautesse; N., LE NEINDRE; D'Onofrio, Antonio; M., Parlog; D., Pierroutsakou; F., Rejmund; M. F., Rivet; M., Romoli; AND R., Royl

A fast and efficient method to study (p,p) and (p,α) resonances with radioactive beams in inverse kinematics is described. It is based on the use of thick targets and large area double-sided silicon strip detectors (DSSDs) to detect the recoiling light-charged particles and to determine precisely their scattering angle. The first nuclear physics experiments with the technique have been performed recently at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge with stable beams of 17 O and radioactive beams of 17 F . The high-quality resonance measurements obtained demonstrate the capabilities of the technique. Pure 17 F beams from HRIBF were produced by fully stripping the ions and separating the interfering and more abundant 17 O ions by the beam transport system. The removal of interfering isobars is one of the various common challenges to both accelerator mass spectrometry (AMS) and radioactive ion beam (RIB) production. Experiments done with RIBs will benefit from the use of the most efficient techniques for production, isobar separation, transport and detection.

The breakup of radioactive 17 F into a proton and 16 O was measured by bombarding 208 Pb with 170 MeV 17 F. The angular correlations of the fragments and the energy distributions of the protons suggest that the dominant breakup mechanism is a direct process in which a proton is excited into the low energy continuum above the breakup threshold. The breakup cross section measured near the grazing angle is 6.6±0.7 mb/sr for analysis with postacceleration considered and 3.9±0.4 mb/sr without postacceleration. This cross section is small compared to the fusion cross section at energies near the Coulomb barrier, so the breakup can have little influence on the fusion process.

The production of very neutron-deficient isotopes near 100Sn has been investigated by using on-line mass separation of evaporation residues produced by heavy-ion induced complete-fusion reactions. We measured the cross sections for 99Cd, 100In, 101Sn and 102In via 58Ni+58Ni fusion reactions followed by cluster emission, and via 58Ni+50Cr fusion reactions accompanied by evaporation of protons, neutrons or α particles. Both types of reactions yield similar cross sections for the production of exotic nuclei near 100Sn. The data are discussed in comparison with results obtained from statistical-model calculations.

A focal plane detector has been constructed for detecting fusion residues in a gas-filled Enge split-pole spectrograph. It provides position, timing and energy for particle identification. With a timing channel plate detector in the target chamber, the particle time-of-flight can be measured. This detector system is particularly suitable for studying fusion–evaporation reactions in inverse kinematics.

Intermediate mass fragments (IMF) and light particles emitted from the Ni-58 + Ni-58 reaction at a beam energy of 375 MeV have been studied. The fragments and light particles were measured in coincidence with 4 pi gamma-ray spectrometer. The Z=6 (C) kinetic energy spectra and the distribution of the final nuclei in coincidence with the emitted C are well described by Hauser-Feshbach calculations extended to many channels. A detailed study of C-Psi and 3 alpha-gamma correlations indicate a strong selectivity of the IMF decay. Our results indicate that the IMF can populate nuclei that are not accessible via multiple light particle (Z

Measurements of energy spectra for protons, deuterons, tritons, and {alpha} particles in coincidence with heavy evaporation residues were made with a large logarithmic detector array which covered the angular range of 3{degree} to 24{degree}. We performed detailed comparisons with statistical calculations which model the evaporative decay of a compound nucleus formed in the collisions. We found out that it was possible to account for the observed energy spectra of the light particles and their relative yields if one assumes initial evaporation from a highly deformed composite system (dinuclear) which at a later stage in the cascade relaxes into a normal compound nucleus. {copyright} {ital 1997} {ital The American Physical Society}

A first-principles calculation of the resonant-coherent excitation of planar-channeled hydrogenic ions is presented. The interplay between coherent interaction with the periodic crystal lattice potential and inelastic electron-electron collisions is shown to be crucial in both intraionic transitions and electron loss from the ion. The magnitude of resonant-coherent excitation is predicted to oscillate with the amplitude of the oscillations of the ion trajectory. Good agreement is found with experiments.

Triple (p-p-fragment) coincidences from the $^{58}\mathrm{Ni}$${+}^{58}$Ni reaction at 850 MeV have been measured. By detecting the source of the emitted particles we were able to study the directional dependence of the p-p correlation function. From this dependence both the source size (${\mathit{r}}_{0}$) and the particle emission time (\ensuremath{\tau}) have been extracted. The extracted p-p correlation functions could be fitted with source size and lifetime in the range of 3.${3}_{\mathrm{\ensuremath{-}}0.7}^{+1.3}$ fm and 3.${2}_{\mathrm{\ensuremath{-}}2.2}^{+1.3}$\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}22}$ s, respectively.

The inclusive single photon spectrum has been measured in the p T range from a few MeV/ c up to approximately 1 GeV/ c at several rapidities in the interval from −2.1 y cm c proton-beryllium and proton-tungsten collisions at the Brookhaven AGS. The measured photon distributions are compared with the expected distribution of photons from π 0 decays and hadronic bremsstrahlung in a search for new sources of “soft” photons at low transverse momentum.

Decay modes of excited nuclei are studied in 78,82 Kr + 40 Ca reactions at 5.5 MeV/nucleon by means of light-charged particles measured in coincidence with intermediate mass fragments and fission-like fragments. Inclusive cross-section distributions of fragments with charge 3 ≤ Z ≤ 28 are bell-shaped and a strong oddeven-staggering (o-e-s) is observed for 3 ≤ Z ≤ 12. Coincidence measurements suggest that the light partners in very asymmetric fission are emitted at excitation energies below the particle emission thresholds. Data were confronted to the predictions of statistical models describing the decay of compound nuclei by emission of light particles and fragments. Comparison with models suggests that the o-e-s of the light-fragment yields is mainly due to the successive steps of compound nucleus disintegration.

Decay modes of excited nuclei are investigated in {sup 78,82}Kr+{sup 40}Ca reactions at 5.5 MeV/nucleon. Charged products were measured by means of the 4{pi} INDRA array. Kinetic-energy spectra and angular distributions of fragments with atomic number 3 {le} Z {le} 28 indicate a high degree of relaxation and are compatible with a fissionlike phenomenon. Persistence of structure effects is evidenced from elemental cross sections ({sigma}{sub Z}) as well as a strong odd-even staggering (o-e-s) of the light-fragment yields. The magnitude of the staggering does not significantly depend on the neutron content of the emitting system. Fragment-particle coincidences suggest that the light partners in very asymmetric fission are emitted either cold or at excitation energies below the particle emission thresholds. The evaporation residue cross section of the {sup 78}Kr+{sup 40}Ca reaction is slightly higher than the one measured in the {sup 82}Kr+{sup 40}Ca reaction. The fissionlike component is larger by {approx}25% for the reaction having the lowest neutron-to-proton ratio. These experimental features are confronted to the predictions of theoretical models. The Hauser-Feshbach approach including the emission of fragments up to Z = 14 in their ground states as well as excited states does not account for the main features of {sigma}{submore » Z}. For both reactions, the transition-state formalism reasonably reproduces the Z distribution of the fragments with charge 12 {le} Z {le} 28. However, this model strongly overestimates the light-fragment cross sections and does not explain the o-e-s of the yields for 6 {le} Z {le} 10. The shape of the whole Z distribution and the o-e-s of the light-fragment yields are satisfactorily reproduced within the dinuclear system framework which treats the competition among evaporation, fusion-fission, and quasifission processes. The model suggests that heavy fragments come mainly from quasifission while light fragments are predominantly populated by fusion. An underestimation of the cross sections for 16 {le} Z {le} 22 could signal a mechanism in addition to the capture process.« less

Mass and charge distributions for heavy residues in the reaction 20 Ne + 60 Ni at 50 MeV/nucleon were measured by in-beam and off-line γ-ray spectrometry. The stacked foil method was used to obtain information about the distribution of the velocity component parallel to the beam direction for target-like residues. The comparison of the data to the predictions of a participant-spectator model indicates that an 8% width for the dissipated energy distribution accounts for the observed projected ranges.

The elastic angular distributions for [sup 58]Ni+[sup 27]Al have been measured at five energies from [ital E][sub c.m.]=48.8 to 69.5 MeV. The optical model analysis assumes both phenomenological and folding model potentials. Regions of sensitivity, where the potential is well determined, are found to be different for the real and the imaginary parts, and to vary with energy. The values of the real potential in the surface are weakly dependent on energy.

Complex fragments have been detected in singles and in γ-particle coincidence measurements for the 19 F + 64 Ni system, at 118 MeV incident energy. Cross sections for the excited states of the complex fragments were measured detecting the characteristic γ-transitions deexciting these states. The measurement of cross sections for the population of the ground and excited states of 18 O and 13 C, as well as of the production cross sections of heavy residues in coincidence with these ejectiles, as a function of the total dissipated energy, indicate an evolution of energy sharing, with increasing mass transfer, from equipartition to thermal equilibrium.

We have used the 90,92,94,96 Zr( 6 Li, 6 Li) reaction at E = 70 MeV to deduce the ratio of M n M p for transitions to the first 2 + and 3 − excited states. For the first 2 + state, we find M n M p increases from less than N Z to greater than N Z going from 90 Zr to 96 Zr. However, for the 3 − state we find that M n M p is significantly smaller than N Z for all four isotopes, a result which is in sharp disagreement with previous work. We find that our measured values of M n M p are well reproduced by random-phase-approximation calculations including pairing.

X-rays generated by fully stripped titanium ions channeled along the 〈100〉 axis of a thin gold single crystal have been measured in coincidence with charge-changed ions as a function of ion energy loss. X-rays from the process of radiative electron capture are used to derive mean target electron densities for three values of mean energy loss. These densities are compared with densities calculated from a free-electron gas model for stopping. The results are used in a model calculation for Lyman series X-ray emission yields which includes effects of strong competition from secondary electron impact excitation and ionization of excited-state hydrogenic ions formed by electron capture in the crystal.

Exclusive {ital p}-{ital p} correlations from the {sup 58}Ni+{sup 58}Ni reaction at 850 MeV incident energy have been measured. The enhancement in the {ital p}-{ital p} correlation function observed for small values of {Delta}{ital p} with a gate on {ital v}{sub rel} is satisfactorily explained by stochastic proton emission followed by the {ital p}-{ital p} final-state interaction. A strong dependence of the {ital p}-{ital p} correlation function on the relative angle between the two-proton c.m. and the fragment velocities has been found. Also a dependence of the {ital p}-{ital p} correlation function on the {Delta}{bold p} orientation with respect to the plane defined by the two-proton c.m. and the fragment velocities has been observed. This latter behavior has been attributed to angular momentum effects.

The back-angle yields of the oxygen and carbon particles from the {sup 31}P+{sup 16}O reaction have been measured at {ital E}{sub lab}({sup 31}P)=135.6 MeV by using reverse kinematics. Comparison with similar data for the {sup 35}Cl+{sup 12}C reaction forming the same compound nucleus at the same excitation energy and with a very similar spin distribution shows very small entrance-channel dependence of back-angle yields. These results are in contrast to a similar study of the reactions {sup 28}Si+{sup 12}C and {sup 24}Mg+{sup 16}O. It is evident that the oxygen and carbon yields from the {sup 31}P+{sup 16}O and {sup 35}Cl+{sup 12}C reactions have a predominantly compound nucleus origin in contrast to those from the {sup 28}Si+{sup 12}C and {sup 24}Mg+{sup 16}O reactions. Possible connection of this nonequilibrium entrance channel dependence with the presence of nuclear molecular resonances is discussed.

Cross sections for emission of complex fragments ({ital Z}{gt}2) in their ground and excited states are presented for the reaction {sup 58}Ni+{sup 58}Ni at a bombarding energy of 630 MeV. Measurements of energy spectra, angular distributions, and angle-integrated cross sections were made for fragments of {ital Z}=4 to 20. {gamma} rays emitted in coincidence with the fragments were measured in a 4{pi} geometry using 62 NaI detectors and 8 Compton-suppressed germanium detectors. Data presented are mostly for the cross sections extracted by {gamma}-ray techniques. A simple statistical approach to associate the ratio of cross sections for excited states and ground states to the temperature of the emitter fails to give the expected temperatures. However, it is shown that this is mostly due to the fact that the fragments that {gamma} decay are secondary fragments produced by particle decay of the primary fragments. A Hauser-Feshbach analysis accounts well for the fragment cross sections, energy spectra, and extracted temperatures, provided that evaporation from the primary fragments is included.

Dielectronic excitation of H-like S, Ca and Ti is shown to occur in the dense electron gas of a crystal channel. Cross sections for collisional ionization of the short lived excited states can then be determined. Ionic excitation can also be achieved by resonant coherent excitation in which case specific m states can be excited for further study.

The excitation and electromagnetic decay of the giant resonance region (8--15 MeV) in {sup 208}Pb have been measured with the {sup 208}Pb({sup 17}O,{sup 17}O{prime}) reaction at 84 MeV/nucleon. The study of coincidences between scattered {sup 17}O ions and photon decays to the {sup 208}Pb ground state, including angular correlations, serves to isolate the isovector giant dipole resonance and enable us to investigate the mechanisms of its excitation and decay in detail. The angular correlations and yields are accounted for quantitatively by a pure Coulomb excitation model of the reaction process. The distribution in energy of the ground-state photon decay cross section is well described by an approximate application of the multistep theory of nuclear reactions. The photon coincidence measurements enable us to extract the differential cross sections for the 10.6-MeV giant quadrupole and 13.9-MeV monopole resonances with low uncertainty. An analysis of the Coulomb-nuclear interference for the 10.6-MeV excitation indicates that the ratio of neutron to proton matrix elements, {ital M}{sub {ital n}}/{ital M}{sub {ital p}}, is 1.7{plus minus}0.4, consistent with a predominantly isoscalar character for the giant quadrupole resonance.