The pygmy quadrupole resonance and neutron-skin modes in Sn-124

We present an extensive experimental study of the recently predicted pygmy quadrupole resonance (PQR) in Sn isotopes, where complementary probes were used. In this study, and experiments were performed on 124Sn. In both reactions, states below an excitation energy of 5 MeV were populated. The E2 strength integrated over the full transition densities could be extracted from the experiment, while the experiment at the chosen kinematics strongly favors the excitation of surface modes because of the strong α-particle absorption in the nuclear interior. The excitation of such modes is in accordance with the quadrupole-type oscillation of the neutron skin predicted by a microscopic approach based on self-consistent density functional theory and the quasiparticle-phonon model (QPM). The newly determined γ-decay branching ratios hint at a non-statistical character of the E2 strength, as it has also been recently pointed out for the case of the pygmy dipole resonance (PDR). This allows us to distinguish between PQR-type and multiphonon excitations and, consequently, supports the recent first experimental indications of a PQR in 124Sn

Overtones of isoscalar giant resonances studied in direct particle decay measurements

The isoscalar giant dipole resonance (ISGDR), which is the lowest-energy overtone mode of the isoscalar giant resonances, has been studied in some medium-heavy and heavy nuclei in coincidence measurements. The observation of the direct nucleon decay channels significantly helped to enhance giant resonance strengths with respect to the underlying background and continuum, which gave an indication for the existence of a new mode with L = 2 character, assumingly the overtone of the ISGQR

Direct proton decay of the isoscalar giant dipole resonance

The direct proton decay of the isoscalar giant dipole resonance (ISGDR) has been studied in Pb-208 using the (alpha,alpha' p) reaction at a bombarding energy of 200 MeV Through observation of direct-decay protons from the ISGDR in coincidence with scattered a-particles, the population of proton-hole states in Tl-207 was studied, allowing us to test recently performed continuum-RPA (CRPA) calculations for the ISGDR and thereby to learn about its microscopic structure. The energy and width of the ISGDR were also determined to be 22.1 +/- 0.3 MeV and 3.8 +/- 0.8 MeV, respectively. A new resonance of quadrupole character was observed at E-x = 26.9 +/- 0.7 MeV with a width of 6.0 +/- 1.3 MeV

A new wire chamber front-end system, based on the ASD-8 B chip

The Focal-Plane Polarimeter (FPP) for the Big-Bite Spectrometer van den Berg (Nucl Instr. and Meth. B 99 (1995) 637ff) at the KVI requires the read-out of four large-area MWPCs and two VDCs with 3872 wires in-total. The EUROSUPERNOVA collaboration (SNOVA) developed a digital 16 channel preamplifier front-end board, housing two amplifier-shaper-discriminatorchips ASD-8 B. The main features of this board are a fast single-wire readout, a high integration density, a low power consumption and compatibility to common instrumentation standards;The board represents the first successfully running application of the ASD-8 for wire chamber readout. (C) 1999 Elsevier Science B.V. All rights reserved

A new wire chamber front-end system, based on the ASD-8 B chip.

The Focal-Plane Polarimeter (FPP) for the Big-Bite Spectrometer van den Berg (Nucl Instr. and Meth. B 99 (1995) 637ff) at the KVI requires the read-out of four large-area MWPCs and two VDCs with 3872 wires in-total. The EUROSUPERNOVA collaboration (SNOVA) developed a digital 16 channel preamplifier front-end board, housing two amplifier-shaper-discriminatorchips ASD-8 B. The main features of this board are a fast single-wire readout, a high integration density, a low power consumption and compatibility to common instrumentation standards;The board represents the first successfully running application of the ASD-8 for wire chamber readout. (C) 1999 Elsevier Science B.V. All rights reserved