D. J. Vieira

The GSI projectile fragment separator (FRS): A Versatile magnetic system for relativistic heavy ions

The projectile fragment separator FRS designed for research and applied studies with relativistic heavy ions was installed at GSI as a part of the new high-energy SIS/ESR accelerator facility. This high-resolution forward spectrometer has been successfully used in first atomic and nuclear physics experiments using neon, argon, krypton, xenon, and gold beams in the energy range from 500 to 2000 MeV/u. For the first time relativistic xenon and gold fragments have been isotopically separated. In this contribution we describe first experiments characterizing the performance of this spectrometer.

Distribution of Ir and Pt isotopes produced as fragments of 1 A GeV 197Au projectiles: a thermometer for peripheral nuclear collisions

Abstract Cross sections of iridium and platinum isotopes have been measured, which were produced as fragments from 197 Au projectiles interacting with aluminum target nuclei at 1 A GeV. The fragments were identified by a kinematic analysis ( ΔE − Bρ -time-of-flight) and by an ion-optical separation at the projectile-fragment separator FRS at GSI. Indications are found for high excitation energies and weak proton-neutron correlations in the peripheral nuclear-collision process.

Direct mass measurements of the neutron-rich isotopes of fluorine through chlorine

Abstract The masses of 34 neutron-rich isotopes of fluorine through chlorine are reported. These measurements more fully delineate the mass surface in the region of deformed nuclei centered around 31 Na and, in addition, provide the first mass values of several silicon through sulfur nuclei. We compare our data to recent shell model and mass model calculations

Optical design of the TOFI (time-of-flight isochronous)spectrometer for mass measurements of exotic nuclei

Abstract The design of a novel recoil time-of-flight isochronous spectrometer for systematic mass measurements of nuclei which lie far from the valley of β-stability is described. Using a four identical cell approach, optical aberrations of the spectrometer are minimized resulting in a calculated flight-time mass resolving power of m Δm = 2000 . With the spectrometer designed for a solid angle acceptance of μ = 2.8 msr and a momentum over charge acceptance of ( Δp ze )/( p ze ) = ± 2% , use of the high intensity proton beam at LAMPF will facilitate good statistics experiments yielding new direct mass measurements with uncertainties of 30 keV to 1 MeV (depending on production rates) for nuclei with A

Background identification and suppression for the measurement of (n,γ) reactions with the DANCE array at LANSCE

Abstract In the commissioning phase of the DANCE project (Detector for Advanced Neutron Capture Experiments) measurements have been performed with special emphasis on the identification and suppression of possible backgrounds for the planned (n,γ) experiments. This report describes several background sources, observed in the experiment or anticipated from simulations, which will need to be suppressed in this and in similar detectors that are planned at other facilities. First successes are documented in the suppression of background from scattered neutrons captured in the detector as well as from the internal radiation. Experimental results and simulations using the GEANT code are compared.

Longitudinal momenta and production cross-sections of isotopes formed by fragmentation of a 500 A×MeV86Kr beam

Abstract At the projectile-fragment separator FRS at GSI, longitudinal momentum distributions and production cross-sections were investigated for reactions between a 500 A× MeV 86 Kr beam and beryllium, copper and tantalum targets. Fragments in a wide A Z range were studied. For fragments close to the projectile the measured longitudinal momentum distributions agree qualitatively with a semi-empirical parametrization. Deviations from this simple picture are found, however, for the momentum widths of light fragments and for the momentum transfer to those fragments that differ in their A Z ratio from the most probable value. The experimental data on production cross-sections are used for testing the predictions obtained from a semi-empirical parametrization, a geometrical abrasion model and an intranuclear-cascade model. The cross-section for the formation of the doubly magic nucleus 78Ni in 86Kr fragmentation is estimated to be 17 pb.

New neutron-rich isotopes in the scandium-to-nickel region, produced by fragmentation of a 500 MeV/u86Kr beam

We have measured production cross-sections of the new neutron-rich isotopes58Ti,61V,63Cr,66Mn,69Fe,71Co and neighbouring isotopes that have been identified as projectile fragments from reactions between a 500 MeV/u86Kr beam and a beryllium target. The isotope identification was performed with the zero-degree magnetic spectrometer FRS at GSI, using in addition time-of-flight and energy-loss measurements. The experimental production cross-sections for the new nuclides and neighbouring isotopes are compared with an empirical parametrization. The resulting prospects for reaching even more neutron-rich isotopes, such as the doubly-magic nuclide78Ni, are discussed.

The Time-of-Flight Isochronous (TOFI) spectrometer for direct mass measurements of exotic light nuclei

Abstract A new type of time-of-flight recoil spectrometer designed to measure the masses of neutron-rich light nuclei has recently been completed at LAMPF. The spectrometer relies on an isochronous design that directly correlates an ions time-of-flight through the spectrometer with its mass-to-charge ratio. Additional measurements of the ions velocity and energy enable the charge state of the recoil to be uniquely defined and thus permit precision mass measurements given sufficient statistics. The performance of the spectrometer has been investigated in both off-line (using alpha sources) and on-line tests. The design resolution of ΔM/M = 1 2000 (fwhm) has been achieved. Initial performance results of the spectrometer are described with emphasis placed on the techniques used to achieve the overall high mass resolution and large solid angle/momentum acceptance.

Large-area fast-timing detectors developed for the TOFI spectrometer

Large-area fast-timing detectors have been developed for use in the TOFI spectrometer. A gridless detector was constructed in which secondary electrons emitted from a thin ( ∼ 80 μg/cm2 ) target foil were transported isochronously to microchannel plate electron multipliers by crossed electric and magnetic fields. A novel convex anode was designed to reduce the time dispersion caused by the position at which the secondary electrons were collected. Timing performance for aluminium oxide target foils was found to be superiors to that of carbon foils. Intrinsic timing resolutions of 68 and 109 ps fwhm have been measured for 5.4 MeV alpha particles from a thin 241Am source for two different detectors with active areas of 270 and 1000 mm2, respectively. Detection efficiencies in excess of 75% for alpha particles were measured.

Acquisition-analysis system for the DANCE (detector for advanced neutron capture experiments) BaF/sub 2/ gamma-ray calorimeter

The DANCE detector is a segmented 4/spl pi/ gamma-ray calorimeter for measuring (n, /spl gamma/) and (n,fission) cross-sections of stable and long-lived radioactive isotopes. DANCE uses waveform digitization to acquire the basic gamma-ray data, which maximizes the information available for event reconstruction, but has necessitated the development of several techniques for handling the resulting high data rates. This paper describes the basic experimental requirements for acquisition and analysis and how we have satisfied these requirements primarily by extending existing acquisition and analysis frameworks.