A large-area scintillating fibre detector for relativistic heavy ions Cub, J; Stengel, G; Grünschloß, A ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
1998, 1998-01-00, Letnik:
402, Številka:
1
Journal Article
Recenzirano
A scintillating fibre detector for relativistic heavy ions with an active area of 50 × 50 cm
2 has been developed and was tested with various ion beams (1 ≤
Z ≤ 92). At count rates of up to 10
5 ...particles/s, the position resolution was found to be determined by the fibre width of 1 mm; depending on the nuclear charge of the beam, efficiencies between 89% and 100% and time resolutions between 800 and 200 ps (FWHM) were obtained.
The Coulomb Dissociation (CD) cross sections of the stable isotopes 92,94,100Mo and of the unstable isotope 93Mo were measured at the LAND R3B setup at GSI Helmholtzzentrum für Schwerionenforschung ...in Darmstadt, Germany. Experimental data on these isotopes may help to explain the problem of the underproduction of 92,94Mo and 96,98Ru in the models of p-process nucleosynthesis. The CD cross sections obtained for the stable Mo isotopes are in good agreement with experiments performed with real photons, thus validating the method of Coulomb Dissociation. The result for the reaction 93Mo(γ,n) is especially important since the corresponding cross section has not been measured before. A preliminary integral Coulomb Dissociation cross section of the 94Mo(γ,n) reaction is presented. Further analysis will complete the experimental database for the (γ,n) production chain of the p-isotopes of molybdenum.
Dissociation of a 227 MeV/u
8He beam in a lead target has been studied in a kinematically complete experiment. The results are compared with similar data from the well-known halo nucleus
6He. ...Coulomb–nuclear interference in the inelastic channel gives evidence for a
I
π
=1
− resonance in
8He at
E
x=4.15 MeV. The deduced
B(E1) value of 0.38±0.07
e
2
fm
2
indicates a uniform distribution of the four neutrons around the
α-particle core.
The neutron-rich isotopes
129–133Sn were studied in a Coulomb excitation experiment at about 500 AMeV using the FRS-LAND setup at GSI. From the exclusive measurement of all projectile-like particles ...following the excitation and decay of the projectile in a high-Z target, the energy differential cross section can be extracted. At these beam energies dipole transitions are dominating, and within the semi-classical approach the Coulomb excitation cross sections can be transformed into photoabsorption cross sections.
In contrast to stable Sn nuclei, a substantial fraction of dipole strength is observed at energies below the giant dipole resonance (GDR). For
130Sn and
132Sn this strength is located in a peak-like structure around 10 MeV excitation energy and exhibits a few percent of the Thomas-Reiche Kuhn (TRK) sum-rule strength. Several calculations predict the appearance of dipole strength at low excitation energies in neutron-rich nuclei. This low-lying strength is often referred to as pygmy dipole resonance (PDR) and, in a macroscopic picture, is discussed in terms of a collective oscillation of excess neutrons versus the core nucleons. Moreover, a sharp rise is observed at the neutron separation threshold around 5 MeV for the odd isotopes. A possible contribution of 'threshold strength', which can be described within the direct-breakup model is discussed. The results for the neutron-rich Sn isotopes are confronted with results on stable nuclei investigated in experiments using real photons.
Transverse and longitudinal momentum distributions of Li-9 fragments from Li-11 break-up reactions in C, Al and Pb targets have been measured at 280 MeV/u. The two-neutron removal cross-section was ...measured to be sigma(-2n), = 0.26 +/- 0.02 b for the carbon target, sigma(-2n) = 0.47 +/- 0.08 b for the aluminum target and sigma(-2n), = 1.9 +/- 0.4 b for the lead target. No significant difference is observed between the narrow widths (FWHM approximate to 47 MeV/c) of the transverse and longitudinal momentum distributions of the Li-9 fragments. The physical implications of this are discussed.
Development of a fast pad readout system for the HADES shower detector Bałanda, A; Dębowski, M; Jaskuła, M ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/1998, Letnik:
417, Številka:
2
Journal Article
Recenzirano
The paper presents the readout system for the 18432 channels of the HADES shower detector. The readout system consists of an analog front-end ASIC for the readout of the pad multiwire chamber, a ...readout controller board, the so-called readout board for collection and digitization of the analog information from the ASIC and an optical link system for the data transfer. The readout system is designed to cope with event rate of 10
5
events/s and a data transfer rate of 1.9
Gbyte/s. Utilizing a multistage fast multiplexing system, the cost per channel is kept on the level of $5. Recent results from a test experiment confirm the intended performance of the readout system.
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