Precision spectroscopy of pionic 1s states of Sn nuclei and evidence for partial restoration of chiral symmetry in the nuclear medium

Deeply bound 1s states of #pi#"- in "1"1"5","1"1"9","1"2"3Sn were preferentially observed using the Sn(d, "3He) pion-transfer reaction under the recoil-free condition. The 1s binding energies and widths were precisely determined, and were used to deduce the isovector parameter of the s-wave pion-nucleus potential to be b_1 = -0.115 #+-# 0.005 m_#pi#"-"1. The observed enhancement of b_1 over the free #pi#N value indicates a reduction of the chiral order parameter, f #pi#"*(#rho#)"2/f_#pi#"2 = 0.65 #+-# 0.05, at the normal nuclear density, #rho# = #rho#_0. (orig.)SIGLEAvailable from TIB Hannover: RO 801(2002-31) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Half-life measurements of bare, mass-resolved isomers in a storage-cooler ring

Secondary beams from fragmentation of "5"8Ni have been produced with energies of 200-220 A.MeV, separated with the fragment separator FRS and injected into the storage-cooler ring ESR for half-life measurements. The relative momentum spread #DELTA#p/p#approx#1.10"-"6 (FWHM) which we achieved allowed us to resolve the ground and isomeric states of cooled "5"2Mn and "5"3Fe nuclei in the measured mass spectra. The circulating beams were fully ionized which rendered possible, for the first time, to measure pure #beta#"+ branches for "5"2"gFe and "5"3"gFe and the sum of pure #beta#"+ and #gamma# branches in the decay of the isomers "5"2"mMn and "5"3"mFe. (orig.)15 refs.Available from TIB Hannover: RO 801(95-53) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Study of the nucleon density distribution of "6He and "8He by proton elastic scattering in inverse kinematics

Nuclear matter distributions of the neutron-rich nuclei "6He and "8He were studied via proton-nucleus scattering in inverse kinematics using the recoil detector IKAR. The differential cross sections for p"4He, p"6He and p"8He elastic scattering were measured with an uncertainty of #+-#2% for the absolute normalization for proton recoil energies from 1 to 20 MeV. The experimental techniques and the data analysis are described and first Glauber calculations presented. Data analysis is still in progress so only preliminary results are given. (orig.)Available from TIB Hannover: RO 801(94-43) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Evidence for a neutron skin in "2"0N

Nuclear interaction and charge-changing cross sections were measured for 950.A MeV "2"0N, "2"0O, "2"0F, "2"0Ne, "2"0Na and "2"0Mg beams incident on a carbon target. The experimental results are compared to other data, in particular to those obtained for stable nuclei. Root mean square nuclear matter radii and upper limits of root mean square proton radii are derived from the experimental data. Evidence is presented for the existence of a neutron skin in "2"0N. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Nucleon distributions of "6He and "8He from intermediate-energy proton elastic scattering in inverse kinematics

Nuclear matter density distributions of "4He and the neutron-rich nuclei "6He and "8He were studied via intermediate-energy proton nucleus scattering in inverse kinematics using the recoil detector IKAR. For these nuclei, differential cross sections for elastic scattering at low momentum transfer were measured with an accuracy of 2% on absolute normalization. The experimental method and the procedure of data analysis are described. Phenomenological and microscopically calculated nuclear matter distributions were related to the measured cross sections with the aid of the Glauber multiple scattering theory. (orig.)13 refs.Available from TIB Hannover: RO 801(95-33) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Invariant mass spectrum and #alpha# - n correlation function studied in the fragmentation of "6He on a carbon target

Momentum distributions and invariant mass spectra from the breakup of "6He ions with an energy of 250 MeV/u interacting with a carbon target have been studied. The data were used to extract information about the reaction mechanism which is influenced by the structure of "6He. It is found that the dominant reaction mechanism is a two-step process: knock out of one neutron followed by the decay of the "5He resonance. The shape of the (#alpha#+n) two-body invariant mass spectrum is interpreted as mainly reflecting the "5He ground state which is a J "#pi# =3/2"- resonance. However, no evidence for correlations between #alpha# particles and neutrons is observed in the momentum widths of the distributions. It is demonstrated that a combined analysis of the two-body invariant mass spectrum and an appropriate correlation function may be used to determine the properties of the intermediate resonance. (orig.)Available from TIB Hannover: RO 801(97-61) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Large spin alignment of the unbound "5He fragment after fragmentation of 240 MeV/u"6He

Peripheral fragmentation of a 240 MeV/u beam of the halo nucleus "6He incident on carbon target has been studied in a kinematically complete experiment. It is found that one-neutron stripping to the unbound nucleus "5He is the dominant fragmentation mechanism and that it leads to a spin alignment of "5He in a plane perpendicular to the "5He momentum vector. This is expected to be a common feature for all neutron halo nuclei. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman