Narrow Momentum Distribution Research Articles

New results on the halo structure of [formula omitted

The longitudinal momentum distribution of 7 Be fragments after fragmentation of 8 B and the one-proton removal cross section ( σ −1 p ) in a carbon target were measured at 1440 MeV/u with the fragment separator FRS used as an energy-loss spectrometer. The results show a narrow momentum distribution with a FWHM value of 91±5 MeV/c and a large cross-section, σ −1 p = 98±6 mb. Both these results support the interpretation of a spatially extended proton orbit forming a halo in the 8 B ground state. The momentum distribution and the one-proton removal cross section are shown to be reproduced with a three-body wave function for 8 B where the target is treated as a black disc in the breakup process.

Experiments with radioactive beams

Examples of recent experiments with radioactive beams at intermediate beam energies are given. The neutron halos encountered near the drip line are of an extreme single-particle nature, loosely bound and spatially extended. They are characterized by large electric-dipole strength at low energies that essentially exhausts the relevant cluster sum rules. Other characteristic features are the breakup by shake-off and diffraction dissociation, and the narrow momentum distributions observed for the projectile residue. Finally, some preliminary results on the spectroscopy of single-particle halo and core states by stripping reactions are reported.

Positron annihilation investigation of porous silicon heat treated to 1000 °C

Positron lifetime and Doppler broadening spectroscopies were applied to investigate a porous silicon film subjected to heat treatment in an argon atmosphere. Heating between 300 and 500 °C increased the mass of the film by 17% due to oxygen uptake and the concentration of open volume defects associated with the formation of an oxide layer on the silicon nanocrystallites increased by a factor of 3. Between 600 and 1000 °C their concentration decreased gradually to 1/2 the original concentration. Doppler broadening results indicate two distinct electron momentum distributions, one arising from open volume defects and one from pickoff annihilation of positronium at the pore walls caused by electrons with an unexpectedly narrow momentum distribution.

Experiments with radioactive beams

Examples of recent experiments with radioactive beams at intermediate beam energies are given. The neutron halos encountered near the drip line are of an extreme single-particle nature, loosely bound and spatially extended. They are characterized by large electric-dipole strength at low energies that essentially exhausts the relevant cluster sum rules. Other characteristic features are the breakup by shake-off and diffraction dissociation, and the narrow momentum distributions observed for the projectile residue. Finally, some preliminary results on the spectroscopy of single-particle halo and core states by stripping reactions are reported.

Momentum distribution of 7Be from ( 8B, 7Be) reaction within the Glauber model

The longitudinal momentum distribution of 7Be from the breakup reaction of 8B on a 12C target is calculated within the Glauber model. If we take into account the core absorption effect, then both the interaction cross section and narrow momentum distribution are explained consistently.

Interaction cross section and interaction radius of the 8B nucleus

The interaction cross section ( σ I) was re-measured by a transmission-type measurement for 5 8B 3 at 790 A·MeV on a C target confirming the previously reported value. 8B, although it has a very small proton separation energy 0.137 MeV, shows no remarkable enhancement of the σ I expected from a possible proton halo, as suggested from studies of the quadrupole moment and other recent data such as the reaction cross section at low energies. The root-mean-square (RMS) radius of the nucleon distribution has been deduced using the Glauber model. The relation between the halo tail and the separation energy is discussed on the mirror nuclei 8B and 8Li. It was also found that the previously reported narrow momentum distribution of 7Be from the fragmentation of 8B is well reproduced by the presently determined density distribution.

Pulsed sub-recoil laser cooling of atoms

In this paper we propose a new and simple velocity selective method, which combines the velocity selective coherent population trapping of atoms in a light field and the kinetic energy coupling between the dark state and coupled state(s) during free flight, in order to reach a very narrow momentum distribution in a short period of time. This technique combined with force-assisted velocity selective coherent population trapping can produce very efficient cooling and trapping. It can also be used to overcome the cooling limit caused by the leakage of the dark state.

Momentum distributions for 12,14Be fragmentation.

Data on the fragmentation of [sup 12,14]Be on [sup 12]C at 56 and 65 MeV per nucleon have been obtained. The [sup 12]Be fragments from the breakup of [sup 14]Be display both a narrow longitudinal momentum distribution and a distinctive angular distribution that is consistent with an extended neutron halo'' in this nucleus. This is the first experiment in which both longitudinal and transverse fragment momentum distributions of exotic nuclei have been simultaneously measured.