L. Westerberg

Light output and energy resolution of CsI, YAG, GSO, BGO and LSO scintillators for light ions

The light output and energy resolution for the scintillators CsI(Tl), YAG(Ce), GSO(Ce), BGO and LSO(Ce) have been measured with 1H, 2H and 3He ions in the energy region ∼ 3–20 MeV/nucleon using photodiodes for the light readout. A very good energy resolution of ∼ 0.62% for 45 MeV 3He-particles has been obtained for CsI. The YAG(Ce), GSO(Ce) and LSO(Ce) crystals are non-hygroscopic, have fast decay time as main component and are well suited for experiments with high counting rates and strict timing requirements. The LSO crystal gives the best energy resolution, but reveals strong quenching for heavy ions. The GSO crystal is a good candidate for operation in UHV environment and has high stopping power, short decay time (56 ns) and moderate quenching.

On the use of thin ion implanted Si detectors in heavy ion experiments

Abstract We present test results on the use of thin ion implanted epitaxial Si detectors for registration of low- and medium-energy heavy fragments in nuclear reactions. A linear energy response for very low energy nuclei has been observed. A test of 10 μm + 300 μm telescopes under realistic experimental conditions for heavy ion experiments exhibits the possibilities to use these detectors for the measurements of multifragmentation products.

Thin detectors for the CHICSi /spl Delta/E-E telescope

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.

Hydrogen content and outgassing of air-baked and vacuum-fired stainless steel

Abstract The hydrogen content of stainless steel samples, treated by 400 °C heat treatment for 2, 4, 8, 16 and 24 h in ambient air, was determined by the 1H(15N, αγ)12C nuclear resonance reaction, and a standard extraction method. Two reference samples were also analysed, one virgin sample which was not heat treated at all, and one which had been vacuum fired (950 °C, 1 h). The results show that the heat treatment in ambient air results in an outgassing rate comparable to vacuum fired material although the amount of hydrogen in the samples was only lowered by approximately 50%, by the air baking, compared to a reduction to

Isospin effects on two-particle correlation functions in E/A=61 MeV Ar-36+Sn-112,Sn-124 reactions

Small-angle, two-particle correlation functions have been measured for Ar-36+Sn-112,Sn-124 collisions at E/A=61 MeV. Total momentum gated neutron-proton (np) and proton-proton (pp) correlations are stronger for the Sn-124 target. Some of the correlation functions for particle pairs involving deuterons or tritons (nd, pt, and nt) also show a dependence on the isospin of the emitting source.

CHICSi - a 3pi Multi-detector System for Studying Heavy Ion Interactions Inside a Storage Ring

Abstract CHICSi — a 3π multi-detector system is presented. The setup consists of 576 ultra high vacuum compatible telescopes to study intermediate energy heavy ion as well as proton induced collisions at storage rings operating in slow ramping mode. Primary it will be installed at the gas-jet target station of the CELSIUS facility at The Svedberg Laboratory in Uppsala.

A facility for studies of giant multipole resonances by fast heavy-ion scattering

Abstract A technique to study giant resonances by heavy-ion scattering in the energy range 100 A –470 A MeV using one quadrant of the CELSIUS storage ring as a spectrometer is presented. A test experiment using 250 A MeV 16 O on a 40 Ar target has been performed. The inelastically scattered particles could be separated from the background originating from the beam halo using a focal-plane telescope in coincidence with neutron detectors around the target. The resolution in the excitation-energy spectrum was 3.5±0.5 MeV, mainly determined by the beam size at the target.

CHICSi – a Compact Ultra-High Vacuum Compatible Detector System for Nuclear Reaction Experiments at Storage Rings. I. General Structure, Mechanics and UHV Compatibility

CELSIUS Heavy-Ion Collision Silicon detector system (CHICSi) is a large solid angle, barrel-shaped detector system, housing up to 600 detector telescopes arranged in rotational symmetry around the beam axis. CHICSi measures charged particles and fragments from nuclear reactions. It operates at internal targets of storage rings. In order to optimize space and momentum-space coverage and minimize the low-energy detection limits, CHICSi is designed for use in ultra-high vacuum (UHV, similar to 10(-8) Pa) inside a cluster-jet target chamber. This calls for materials in mechanical support, detectors, Very Large Scale Integrated (VLSI) electronics, connectors, cables and other signal transport devices with very low outgassing. Two auxiliary detector systems, which will operate in coincidence with CHICSi, a heavy-recoil, time-of-flight system (HR-TOF) also placed inside the target chamber and a projectile fragmentation wall (PF-WALL) located outside the chamber, have also been constructed. In total, this combined system registers more than 80% of all charged particles and fragments from typical heavy-ion reactions at energies of a few hundreds of MeV per nucleon

Characterization of nuclear sources via two-neutron intensity interferometry

The neutron energy spectrum and the two-neutron correlation function have been measured for the E/A = 45 MeV Ni + Al reaction in order to assess the space-time characteristics of the neutron emitting source. When comparing the data to a statistical model,

Neutron-proton interferometry in 30A MeV40Ar+197Au collisions

Abstract Neutron-proton correlation functions in 30A MeV 40 Ar + 197 Au , 12 C , CH 2 reactions have been measured. In contrast to the nn and pp correlations, which exhibit the shape expected from quantum symmetrization effects and nuclear+Coulomb (pp) final-state interaction, the np function shows much less correlation strength. This may be due to Coulomb repulsion on the proton and/or to a larger effective spin than expected. Selecting high energy nucleons strengthens both the np and pp correlations.