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Experiments for the laser guiding studies has been carried out with the 30-fs 100-TW Ti:sapphire laser pulse interaction with the underdense plasma produced by a long-slab (1.2 times 10 mm2) gas jet and an ablative laser-triggered discharged capillary. Formation of an extremely long plasma channel with a length (~10 mm) 10 times above the Rayleigh length is observed when the laser pulse power is much higher than the critical power for relativistic self-focusing. The long-self-guiding- channel formation is accompanied by the electron acceleration with a low transverse emittance (< 0.87pi mm mrad) and high electric current (~10 nC/shot), as well as the generation of a quasi- monoenergetic electron bunch with an energy of ~80 MeV. In order to continuously elongate the plasma channel, a 4-cm- scale discharged capillary was used. We successfully demonstrated laser-plasma acceleration of high-quality electron beams up to nearly semigigaelectronvolts. Our results exactly verified the prediction of laser wakefield acceleration through a centimeter- scale plasma channel in the "blowout bubble" regime, where a microscale plasma cavity produced through the ultrarelativistic laser-plasma interactions plays an essential role in the self- injection and acceleration of electrons.

The evolution of the giant dipole resonance (GDR) in 120 Sn and 208 Pb nuclei at excitation energies in the range of 30–130 MeV and 40–110 MeV, respectively, were studied by measuring high energy γ rays from the decay of the resonance. The excited states were populated by inelastic scattering of α particles at beam energies of 40 and 50 MeV/nucleon for 120 Sn and 40 MeV/nucleon for 208 Pb. A systematic increase of the resonance width with increasing excitation energy was observed for both nuclei. The observed width evolution was compared to calculations employing a model that adiabatically couples the collective excitation to the nuclear shape, and to a model based on the collisional damping of nucleons. The adiabatic coupling model described the width evolution in both nuclei well, whereas the collisional damping calculation could describe the width evolution only in 208 Pb. Light-particle inelastic scattering populates low angular momentum states in the target nucleus. The observed width increase is therefore interpreted to be predominantly due to fluctuations in the nuclear shape induced by temperature. This interpretation is consistent with the adiabatic model calculations and with recent angular momentum-gated measurements of the GDR in excited Sn isotopes.

The fusion-evaporation reaction {sup 58}Ni({sup 32}S,2{alpha}p) has been used to study the neutron-deficient isotope {sup 81}Y. Multiple particle {gamma}-ray coincidences have been detected by the GAMMASPHERE array combined with the MICROBALL charged-particle detector system. Gamma-ray spectra with an improved resolution have been achieved from an event-by-event determination of the nucleus recoil momentum, thus allowing a precise Doppler-shift correction. In this way a resolution enhancement by a factor 2 was obtained for a 1 MeV {gamma} line. During the analysis an E{sub {gamma}}-E{sub {gamma}} matrix as well as an E{sub {gamma}}-E{sub {gamma}}-E{sub {gamma}} cube have been used to extend the previously known level scheme to higher spin (I{approx}(57)/(2)) and excitation energy (E{sub x}{approx}17MeV). More than 100 new {gamma} rays and 80 new levels have been added to the level scheme and six new bands have been established. The interpretation of these bands in terms of the cranking model and their comparison with similar bands in neighboring nuclei is discussed. {copyright} {ital 1997} {ital The American Physical Society}

High-spin states in Kr-77 were identified via analysis of prompt gamma-gamma coincidences in the Ni-58(Si-29,2 alpha 2p) reaction at 128 MeV at the Gammasphere facility. Evaporation channel selecti ...

We have used the Ca-48+Yb-176 reaction to study the population of high-spin states in neutron-rich nuclei by deep-inelastic reactions. Using Gammasphere, we observed gamma transitions from nuclei s ...

The high-spin structure of odd-odd {sup 86}Nb was studied with the early implementation of GAMMASPHERE using 36 Compton-suppressed Ge detectors and the MICROBALL, a 95-element full-sphere charged-particle detector array. High-spin states were populated using the {sup 58}Ni({sup 32}S,3pn) reaction at 135 MeV with beams from the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. A number of bands were observed up to spins as high as (31{sup {minus}}). The yrast positive-parity band shares many characteristics with the {pi}g{sub 9/2}{circle_times}{nu}g{sub 9/2} bands in other odd-odd f-p-g shell nuclei. These similarities include the behavior of the moments of inertia, the magnitude and phase of the signature splitting and its phase reversal near the 10{sup +} state, and the strong alternations in the B(M1)/B(E2) strengths. The moments of inertia in the lowest pair of negative-parity bands start out with a sharp upbend and then gradually fall back to the rigid-body value. New positive- and negative-parity bands appear in the quasiparticle alignment region and eventually become yrast. Some additional positive-parity states around spin 17{h_bar} are candidates for fully or nearly fully aligned shell-model-like configurations. {copyright} {ital 1997} {ital The American Physical Society}

The high spin states of 87 Nb have been studied by using the 58 Ni (32 S , 3p)87 Nb reaction at beam energy 95–105 MeV and the reaction 58 Ni (35 Cl , 2pα) at 124 MeV. γ-γ coincidence relations, angular distributions of γ-rays, excitation functions and DCO ratios were measured. High spin states in 87 Nb have been established up to spin of 37/2ℏ and excitation energy of 7 MeV. CSM calculation was carried out with parameters of configuration dependence of nuclear shape. The nature and configuration of every band in 87 Nb are discussed.

A 4π multidetector light-charged particle and light fragment detection spectrometer is described. It consists of 95 CsI(T1) scintillators closely packed to cover the angular range 4.0°–172°, arranged in 9 rings with increasing forward segmentation. The device is optimally designed to be used in conjunction with Gammasphere. The scintillator light is collected by silicon photodiodes that provide high quantum efficiency and minimal mass. The signals are processed through a charge sensitive preamplifier followed by a slow shaper. Particle identification for 1,2,3 H, 3,4 He ions and Li, Be and B ions is accomplished by pulse shape discrimination. The geometry, construction, energy calibration, gain stability, associated integrated electronics and the data acquisition system are discussed. The capabilities of this spectrometer as a channel selecting device in conjunction with Gammasphere are discussed. A second version of the device with thicker scintillators, that can stop more energetic charged particles and is useful for reaction mechanism studies, is also described.

The evolution of the giant dipole resonance (GDR) in hot 208Pb nuclei was studied by measuring high energy γ-rays from the decay of the resonance built on excited states. Nuclei in the excitation energy range of 40–110 MeV were populated by inelastic scattering of 40 MeV/nucleon α-particles. The GDR width was observed to increase systematically from 4 MeV at the ground state to ∼8 MeV at the highest excitation energy.

High-spin states in Mo-86 were studied by means of the fusion evaporation reaction Ni-58(S-32,2p2n) Mo-86 at 135 MeV beam energy. Charged-particle-gamma gamma and -gamma gamma gamma coincidences recorded with the early implementation of the GAMMASPHERE array and the MICROBALL charged-particle detection system were used to largely extend the level scheme of the T-tau=1 nucleus Mo-86 to a possible spin of I=24h at 13 MeV excitation energy. The excitation scheme is compared to neighboring nuclei. There is evidence for enhanced shell-model influence in the 4 quasiparticle region (I=12-16h). The observed (pi=+,alpha=0) sequence at spin I greater than or equal to 16 h appears to be associated with a triaxial collective rotational band. This interpretation is supported by calculations within the configuration-dependent shell-correction approach with the cranked Nilsson potential. (Less)

The evolution of the giant dipole resonance (GDR) in hot 120 Sn and 208 Pb nuclei was studied by measuring high energy γ-rays from the decay of the resonance. The excited nuclei were populated by inelastic scattering of α-particles at 40 and 50 MeV/nucleon. The resonance width was observed to increase systematically with excitation energy in both systems. Inelastic scattering populates low angular momentum states in the target. The observed width increase is thus attributed to fluctuations in the nuclear shape induced by temperature.

New experimental data has been obtained for the208Pb(α, α′) reaction induced by 160 MeV alpha particles, for inelastic scattering to forward angles. We use these data to investigate the applicability of the multistep scattering theory of Feshbach, Kerman, and Koonin for describing this reaction. The mechanism we study, following the work of Gadioli et al. [1], is of the incident alpha particle remaining intact throughout the scattering process, exciting nucleon particle-hole pairs through multistep process. We conclude that this mechanism, combined with compound nucleus decay at low emission energies, can account for much of the observed data. However, there are indications that other processes also contribute at energies above the compound nucleus emission regime, and we outline future theoretical analyses that are needed.

The recently discovered superdeformed band in one of the strontium isotopes has been identified as belonging to 83Sr from a study with the Gammasphere array and the Microball charged-particle detector system. From its decay pattern, a spin of (81 ± 2) 2 h is deduced for the highest level of this band. Evidence for very fast transition rates and agreement of the characteristics of this band with the theoretical predictions establish the yrast superdeformed nature of this band in 83Sr.

In-beam [gamma]-ray spectroscopic studies of [sup 182]Hg have revealed five new bands. The 2[sup +] state of the prolate band has been identified at an energy of 548.6 keV and is higher than in [sup 184]Hg. A two parameter band mixing calculation results in an interaction energy of 83 keV between the prolate 2[sup +] and the oblate 2[sup +] states. Several additional new bands are seen including some which are interpreted as quadrupole vibrational bands built on the excited prolate minimum.

Highly fragmented exit channels produced by the decay of excited 24Mg projectiles were detected. The longitudinal velocity spectra of protons and alpha particles from such channels are offset. This offset is consistent with post-breakup Coulomb accelerations from the 197Au target nuclei implying that the protons were emitted within 3 X 10−22 s after the target-projectile separation.

A simple 4 π charged-particle sensitive detector useful for γ-ray spectroscopy is described. The detector is a plastic scintillator tube, which surrounds the target. The tube is segmented into four optically isolated cylindrical arcs. The tube is an efficient charge particle hit detector with a very small photon interaction probability.

High spin states in $^{129}\mathrm{Pr}$ and $^{131}\mathrm{Pr}$ have been investigated using in-beam \ensuremath{\gamma}-ray spectroscopy techniques. The yrast band of $^{129}\mathrm{Pr}$ based on the ${\mathit{h}}_{11/2}$ 3/${2}^{\mathrm{\ensuremath{-}}}$[541] proton configuration was observed from 11/${2}^{\mathrm{\ensuremath{-}}}$ up to 43/${2}^{\mathrm{\ensuremath{-}}}$. The band based on the same configuration and two positive-parity side bands based on the ${\mathit{g}}_{7/2}$ 5/${2}^{+}$[413] proton configuration, were observed in $^{131}\mathrm{Pr}$. The delayed yrast band crossing of $^{129}\mathrm{Pr}$ at \ensuremath{\Elzxh}${\mathrm{\ensuremath{\omega}}}_{\mathit{c}}$=0.37 MeV is interpreted as being due to the alignment of the second and third ${\mathit{h}}_{11/2}^{\mathrm{\ensuremath{-}}}$ protons. The band crossing at \ensuremath{\Elzxh}${\mathrm{\ensuremath{\omega}}}_{\mathit{c}}$=0.26 MeV, with a gain in alignment of about 8\ensuremath{\Elzxh}, based on the ${\mathit{g}}_{7/2}$ 5/${2}^{+}$[413] configuration in $^{131}\mathrm{Pr}$ was attributed to the alignment of two ${\mathit{h}}_{11/2}$ protons. The systematics of the proton alignments in a series of Pr isotopes is discussed.

High spin states in90Tc have been studied via the58Ni (35Cl, 2pn)90Tc reaction at beam energy of 124 MeV. Twenty-six newγ-rays were observed, a new level scheme was established and spins were assigned. Two band-like structures were established up to about 20ħ with an excitation energy of 6–7 MeV. The band (B) shows collective characteristic at high spin. We suggest it to be of a quasi-particle configurationπg9/2⊗vf5/2.

High-spin states in {sup 86}Zr up to 30{sup +} and 27{sup -} were observed via the {sup 58}Ni({sup 32}S,4p) reaction at 135 MeV beam energy using the combined GAMMASPHERE and MICROBALL systems. Calculations performed with the configuration-dependent shell-correction approach show that these states are built from six g{sub 9/2} neutrons and at most four protons excited from the p{sub 1/2},p{sub 3/2},f{sub 5/2} subshells to the g{sub 9/2} subshell at small deformation. The highest observed states at 27{sup -} and 30{sup +} are interpreted as band-terminating states with the latter having the highest spin available in the valence space for {sup 86}Zr. (c) 2000 The American Physical Society.

The potential for using deep inelastic reactions to populate high-spin states in neutron-rich nuclei is studied in a series of experiments using GAMMASPHERE for gamma-ray detection and a silicon st ...