L. Carlén

Study of the Δ isobar excitation in nuclei with the (3He,t) reaction

Abstract Data for the Δ excitation by the (3He,t) reaction at 2.0 GeV on various nuclei are presented together with results on 12C at 1.5 and 2.3 GeV. The Δ peak position and width are found to be target mass independent. Comparison with the p(3He,t) Δ++ reaction, however, shows a shift of the position in energy of the Δ peak. Implications of these results are discussed.

The p(3He,t)Δ++ reaction

Abstract Data are presented for the p(3He,t)Δ++ reaction at 2.0, 2.3 and 1.5 GeV. The reaction specifically excites the Δ++ with very little yield outside the resonance. The data are analysed as one pion exchange and the hadronic form factor for the 3He−1 system is extracted and compared with the magnetic form factor from electron scattering.

Elastic and inelastic scattering of 1.03 GeV 12C projectiles

Abstract Elastic scattering cross sections of 86 MeV/N 12C ions on 12C, NATCa, 89Y and 208Pb targets has been measured together with inelastic scattering to the 4.4 MeV state of 12C. There is some indication for giant (quadrupole) resonance excitation in 40Ca. Optical model and DWBA analyses are reported. Nuclear transparency effect is discussed.

High-spin spectroscopic study of 167Lu

Abstract Three decay sequences associated with the 7 2 + [404], 9 2 − [514] and 1 2 − [541] Nilsson states of 167 Lu have been established to high spin using the 123 Sb( 48 Ca,4n) 167 Lu reaction. The quasineutron and quasiproton band crossings, the energy signature splittings, and the B (M1)/ B (E2) values are discussed and compared with similar quantities for the lighter lutetium isotopes. Configuration-and isotopic-dependent deformations, reflected in such comparisons, indicate that 167 Lu has a larger and more stable prolate deformation than the lighter isotopes and that the 1 2 − [541] configuration has a larger quadrupole deformation than the 9 2 − [514] configuration. The shift of the AB neutron band crossing occurring in the 1 2 − [541] sequences to a larger rotational frequency cannot be understood in terms only of deformation differences. The configuration and neutron-number dependent shapes are also discussed in a “gauge”-space analysis.

Proton configuration dependence of neutron alignments and transition probabilities in 165Lu

Abstract High-spin states in 165 Lu have been populated in the 153 Eu( 16 O, 4n) reaction. An excitation function measurement was made to assign correct γ-rays to transitions in 165 Lu. A level scheme is constructed from the studies of γγ coincidences, and the measurement of γ-ray angular distributions. Nine decay sequences are assigned to 165 Lu. At low spin, these sequences are identified with the 5 2 + [402], 1 2 + [411], 1 2 − [541], 7 2 + [404] and 9 2 − [514] Nilss determined and the variation in the crossing frequency is discussed. ΔI = 1 transitions observed between the favoured and unfavoured decay sequences of four of the five configurations are also discussed.

Centrality Dependence of Neutral Pion Production in 158A GeV

The production of neutral pions in 158AGeV Pb+Pb collisions has been studied in the WA98 experiment at the CERN SPS. Transverse momentum spectra are studied for the range 0.3 GeV/c<mT-m0<4.0 GeV/c. The results for central collisions are compared to various models. The centrality dependence of the neutral pion spectral shape and yield is investigated. An invariance of the spectral shape and a simple scaling of the yield with the number of participating nucleons is observed for centralities with greater than about 30 participating nucleons which is most naturally explained by assuming an equilibrated system.

^{208}

Abstract An 86 MeV/nucleon 12 C beam has been used to bombard targets of C, Ag and Au. Energy spectra of reaction products with Z = 3−6 and A = 6−12 have been measured at angles between 3° and 20°. A simple fragmentation model, while predicting approximately the gross features of the data, fails to describe the results in detail.

Pb+

Abstract Cross sections for the production of π + and π − have been measured over a wide range of angles for 12 C + 7 Li, 12 C + 12 C and 12 C + 208 Pb collisions at 60 A , 75 A and 85 A MeV. Energy distributions are less steep and absolute yields of pions larger than expected from a straightforward Fermi gas nucleon-nucleon scattering prescription. The apparent velocity of the system in which the π + emission is symmetric, is closer to the nucleus-nucleus c.m. velocity than to the mean speed system. The Coulomb-corrected π − π + ratio is close to unity for 12 C + 12 C. The corresponding ratio for 12 C + 208 Pb is, however, much larger than expected from the neutron excess in 208 Pb only.

^{208}

High-spin states in 177Re have been populated in the 165Ho (16O, 4n)177Re reaction. A level scheme is constructed from the studies of γγ-coincidences, the relative excitation function, and γ-ray angular distribution measurements. Three decay sequences identified with 5/2+[402], 1/2-[541] and 9/2-[514] Nilsson orbitals have been extended up to spin 29/2+, 49/2- and 33/2-, respectively, and a newly observed sequence based on the 1/2+[660] Nilsson orbital is established. The experimental data are discussed within the Woods-Saxon cranking model. Observed shifts in the band crossing frequencies are interpreted theoretically as being caused by different deformation driving forces of quasiparticle orbitals. B(M1)/Q02 ratios are discussed in connection with quasineutron alignment.

Pb Collisions

A pilot series of 10 /spl mu/m to 15 /spl mu/m thin silicon detectors has been made for the /spl Delta/E-E telescopes in the CHICSi detector system. This system will operate at the CELSIUS heavy ion storage ring in Uppsala, Sweden. /spl Delta/E-E telescopes provide isotope identification and energy determination of fragments from nuclear collisions. The thin detectors are made as p-i-n diodes in thin etched membranes in 280 /spl mu/m thick silicon wafers. The membranes are made with anisotropic etching using 25 wt.% tetramethylammonium hydroxide (TMAH) solution. The etch speed of this solution is very uniform across a wafer. As a result detectors with uniform thickness can be produced. The etch depth varies with less than /spl plusmn/0.3 /spl mu/m over a wafer and the surface microroughness is in the range from 2 to 4 nm. Each detector has a 10.0 mm/spl times/10.0 mm active area on a 10.2 mm/spl times/10.2 mm membrane surrounded by a 1.1 mm wide supporting frame. The detectors have leakage currents in the active area of approximately 0.5 nA at 20 V. The breakdown voltage of the detectors is above 100 V. Evaluation experiments with telescopes consisting of a thin detector in combination with a thick detector have shown excellent isotope separation capabilities. Mass separation of /sup 6/Li and /sup 7/Li is clearly observable.