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Reactions of halo states: Coulomb excitations

Description: Coulomb dissociation is a relatively clean probe of the structures of one- and two-nucleon halo nuclei. This is illustrated by the breakup of {sup 11}Be, {sup 8}B and {sup 11}Li and is discussed in terms of first order perturbation theory. First-order dipole transitions usually dominate the Coulomb dissociation but quadrupole transitions are not insignificant for a proton halo (e.g. {sup 8}B). Higher-order processes can also distort the observables, such as the momentum distributions of the fragments and the excitation energy spectrum.
Date: September 1, 1997
Creator: Esbensen, H.
Partner: UNT Libraries Government Documents Department

Momentum distributions in breakup reactions

Description: Measurements of the breakup reactions: {sup 11}Be {yields} {sup 10}Be+n and{sup 8} {yields} {sup 7}Be+p are analyzed in a single-particle description. The signature of various structure properties associated with the valence nucleon axe discussed, as well as the significance of the different reaction mechanisms, namely Coulomb dissociation, stripping and nuclear induced diffraction.
Date: February 1, 1996
Creator: Esbensen, H.
Partner: UNT Libraries Government Documents Department

Recent developments for high-intensity proton linacs

Description: High-intensity proton linacs are being proposed for new projects around the world, especially for tritium production, and for pulsed spallation neutron sources. Typical requirements for these linacs include peak beam current of about 100 mA, and final energies of 1 GeV and higher, APT, a tritium production linac, requires cw operation to obtain sufficient average tritium production linac, requires cw operation to obtain sufficient average beam power, and H{sup +} ion sources appear capable of providing the required current and emittances. The pulsed spallation neutron source requires a linac as an injector to one or more accumulator rings, and favors the use of an H{sup minus} beam to allow charge-exchange injection into the rings. For both applications high availability is demanded; the fraction of scheduled beam time for actual production must be 75% or more. Such a high availability requires low beam-loss to avoid radioactivation of the accelerator, and to allow hands-on maintenance that will keep the mean repair and maintenance times short. To keep the accelerator activation sufficiently low, the beam loss should not exceed about 0.1 to 1.0 nA/m, except perhaps for a few localized places, where special design adaptations could be made. The requirement of such small beam losses at such a high intensity presents a new beam physics challenge. This challenge will require greater understanding of the beam distribution, including the low- density beam halo, which is believed to be responsible for most of the beam losses. Furthermore, it will be necessary to choose the apertures so the beam losses will be acceptably low, and because large aperture size is generally accompanied by an economic penalty resulting from reduced power efficiency, an optimized choice of the aperture will be desirable.
Date: April 1, 1996
Creator: Wangler, T.P.; Garnett, R.W.; Gray, E.R. & Nath, S.
Partner: UNT Libraries Government Documents Department

First in-beam observation of excited states in {sup 156}{sub 72}Hf{sub 84} using the recoul-decay tagging method

Description: Excited states in the proton rich nuclide {sup 156}{sub 72}Hf{sub 84} were observed for the first time using the {sup 102}({sup 58}Ni, 2p2n){sup 156}Hf reaction at 270 MeV. Gamma rays were detected with the AYEBALL array of Compton suppressed Ge detectors, placed in front of the Fragment Mass Analyzer, and were assigned to individual reaction charmers using the Recoil-Decay Tagging Method. Prompt {gamma}-ray cascades were associated with the alpha decay of both the ground state and the 8{sup +} isomeric state in {sup 156}Hf. The level scheme constructed for {sup 156}Hf is compared with level schemes of lighter even-even N=84 isotones and is discussed within the framework of the Shell Model.
Date: December 31, 1996
Creator: Seweryniak, D.; Ahmad, H. & Amro, D.J.
Partner: UNT Libraries Government Documents Department