Multifragment decays of heavy nuclei have been studied at the ALADIN spectrometer system at beam energies between 100 and 1000 MeV per nucleon. The observed fragment distributions signal a ...universality of spectator decays at bombarding energies
E
A
≥ 400
MeV
. The role of the radial flow for the fragmentation process is explored by comparing fragment distributions measured for Au+Au collisions at
E
A
= 100
MeV
in central collisions and at
E
A
= 1000 MeV
in more peripheral reactions. At both energies the maximum multiplicity of intermediate mass fragments (IMFs) normalized to the size of the decaying system is about one IMF per 30 nucleons but the element distributions show significant differences. Within a coalescence picture the suppression of heavy fragments in central collisions at
E
A
= 100 MeV
may be related to a reduction of the density in momentum space which is caused by a large collective expansion velocity component.
A modular 4π counter for β-delayed neutrons Kunze, V; Schmidt-Ott, W.-D; Bosch-Wicke, U ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/1995, Letnik:
361, Številka:
1
Journal Article
Recenzirano
We report on the construction of a detector array for low-energy β-delayed neutrons consisting of sixteen NE 213 scintillation counters. Three pulse-shape discrimination techniques were compared, ...with special emphasis on the discrimination of neutrons from γ-rays in the energy region down to 50 keVee (keV electron equivalent). The efficiency as a function of neutron energy was obtained by comparing the precisely known neutron spectrum from the spontaneous fission of
252Cf and the neutron distribution measured in coincidence with the fission events. The neutron energy was determined with the time-of-flight (TOF) technique. In order to examine the light output function
L(
E
p) for recoil protons, a careful energy calibration was done by fitting the Compton edges from standard γ-ray sources. Neutron efficiencies were also calculated with a Monte Carlo code. Agreement between measured and calculated efficiency curves was observed for two differently shaped detectors and neutron flight paths of 1 and 3 m. This correspondence justifies the efficiency calculation for the 4π array with the source in the center. For neutron energies above 800 keV an error of less than 5% in detection efficiency can be reached.
The accumulation of methylphenobarbital (MPB) and phenobarbital (PB) in plasma in two volunteers who were given continuous once-daily oral doses of MPB for 3 weeks was demonstrated by use of a ...selected ion-monitoring GC/MS assay. It was shown that the PB concentration exceeded the MPB concentration in plasma after about day 4, and that both barbiturates achieved plateau concentrations after about 2 weeks. GC/MS studies on the urine of these volunteers permitted the identification of several new metabolites of MPB. These included 5-ethyl-5-(4-hydroxyphenyl)-1-methylbarbituric acid (p-OH-MPB), and the 3-O-methylcatechols of both MPB and PB. The meta-isomers of hydroxy-MPB and hydroxy-PB were identified in urine extracts, but were shown to be methodological artifacts. Quantitative studies, with use of a HPLC assay, were carried out for p-OH-MPB, PB and p-OH-PB in urine, and it was shown that these three substances collectively accounted for some 50% of the administered dose (greater than 30% as p-OH-MPB).
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