Isomerenverhältnis für die Reaktion51V(α,3n)52g,mMn

The isomeric cross-section ratio has been measured for the reaction⁵¹V(α, 3n)^{52 g,m}Mn between 32 and 51 MeV. The experimental results are compared with statistical-model calculations. In these calculations two models for the gamma cascade have been used: the simple dipole cascade model ofVandenbosch andHuizenga, and alternatively the model ofPönitz which includes quadrupole transitions. With the latter model agreement between theory and experiment could be achieved.     

Neutron polarizabilities investigated by quasifree Compton scattering from the deuteron

Measuring Compton scattered photons and recoil neutrons in coincidence, quasifree Compton scattering by the neutron has been investigated at MAMI (Mainz) at theta(lab)(gamma) = 136 degrees in an energy range from 200 to 400 MeV. From the data a polarizability difference of alpha(n)-beta(n) = 9.8+/-3.6(stat)+2.1-1.1(syst)+/-2.2(model) in units of 10(-4) fm(3) has been determined. In combination with the polarizability sum alpha(n)+beta(n) = 15.2+/-0.5 deduced from photoabsorption data, the first precise results for the neutron electric and magnetic polarizabilities, alpha(n) = 12.5+/-1.8(stat)+1.1-0.6(syst)+/-1.1(model) and beta(n) = 2.7-/+1.8(stat)+0.6-1.1(syst)-/+1.1(model), are obtained.     

Der Zerfall des122Xe (T 1/2=20,l h) und des122J (T 1/2=3,6min)

Theγ spectra emitted in the decay of¹²²Xe and¹²²I have been investigated using Ge(Li) detectors and a Ge(Li)-NaI coincidence apparatus. 14γ transitions with energies between 61.8 and 416.9 keV have been identified in the decay of¹²²Xe, 44 transitions between 564.0 and 3,291.0 keV in the decay of¹²²I. Level schemes having 7 excited levels for¹²²I and 21 excited levels for¹²²Te are proposed.     

Resonance behaviour of a perturbed gamma gamma directional correlation in a magnetic field

Using a gaseous H₂ ⁷⁵Se source at low pressure the perturbed directional correlation of the 121–279 keVγγ cascade of⁷⁵As was measured as a function of an external magnetic field. The anisotropy shows a pronounced resonance behaviour around zero field. This effect may be understood as being due to the hyperfine interaction of the nucleus with the electronic shell of the highly charged ion formed after electron capture. The charge distribution of the As ions was estimated and the spin distribution derived from it. Then a comparison with the theory of Leisi was possible giving a qualitative agreement between theory and experiment.     

Quasi-free \pi^0 photoproduction from the bound nucleon

Differential cross-sections for quasi-free photoproduction from the proton and neutron bound in the deuteron have been measured for MeV at using the Glasgow photon tagger at MAMI, the Mainz 48 cm cm NaI(Tl) photon detector and the Göttingen SENECA recoil detector. For the proton measurements made with both liquid-deuterium and liquid-hydrogen targets allow direct comparison of free photoproduction cross-sections as extracted from the bound-proton data with experimental free cross-sections which are found to be in reasonable agreement below 320 MeV. At higher energies the free cross-sections extracted from quasi-free data are significantly smaller than the experimental free cross-sections and theoretical predictions based on multipole analysis. For the first time, free neutron cross-section have been extracted in the -region. They are also in agreement with the predictions from multipole analysis up to 320 MeV and significantly smaller at higher photon energies.Received: 28 May 2003, Published online: 27 January 2004PACS: 13.60.Le Meson production - 14.20.Dh Protons and neutrons - 25.20.Lj Photoproduction reactionsK. Kossert: Part of the Doctoral Thesis.,Present address: Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-38116 Braunschweig, Germany.Present address F. Wissmann: Physikalisch-Technische Bundesanstalt, Bundesallee 100, D-38116 Braunschweig, Germany. Present address B. Seitz: II. Physikalisches Institut der Universität Gießen, Germany.     

Nuclear photoexcitation and delbrück scattering studied in the energy range 2–8 MeV

Elastic scattering by nuclei in the range of mass numbers between 64 and 238 has been studied with monochromatic photons in the energy range between 2 and 8 MeV. These photons were provided either by a Ti(n,γ) source installed in the tangential through channel of the Grenoble high flux reactor, or by²⁴Na and⁵⁶Co sources produced by deuteron bombardment of Al or Fe at the Göttingen cyclotron. The photoexcitation of 23 nuclear levels has been observed and the decay properties and groundstate widths of the majority of these levels have been determined. For the lead scattering target the coherent elastic differential cross section has been studied in detail. There is evidence that below the photo-neutron threshold the elastic scattering via virtual photoexcitation of the nucleus can be approximated by extrapolating the real part of the Giant Dipole Resonance amplitude along a Lorentzian curve. Coulomb corrections to Delbrück scattering seem to play a small role at 6.5 MeV.     

Elastic scattering of γ-rays from lead for energies from 0.145 to 1.33 MeV

Differential cross sections for elastic scattering of 889 and 1120 keV γ-rays from lead have been measured at angles ranging from 30° to 150°. These results and previously measured differential cross sections at 145, 279, 412, 662 and 1332 keV are compared with theoretical predictions taking into account Rayleigh scattering, nuclear Thomson scattering, and Delbrück scattering. The Rayleigh amplitudes of the K-shell were obtained from the theory of Brown et al., the amplitudes of the other shells from form factors calculated from relativistic HFS wave functions. Discrepancies are found at 145, 889, 1120 and 1332 keV while the experimental data at 279, 412 and 662 keV are in good agreement with the theory. A discussion of possible explanations and consequences is presented.     

Ion molecule collisions investigated via nuclear resonance fluorescence

The method of nuclear resonance fluorescence has been applied to analyse the profileN(E) of the 285 keV gamma line of⁷⁵As after electron capture decay of⁷⁵Se in gaseous⁷⁵SeH₂ sources. The profileN(E) depends on the velocity distribution of the radioactive As ions at the moment of γ-decay and, hence, is strongly dependent on the slowing down mechanism. Investigating sources with pressures of 1.5, 15, and 177 Torr different states of the slowing down process could be studied. A simple model is developed that describes the basic properties of the experimental line profiles.     

Low-energy electric-dipole transition widths predicted by the giant dipole resonance and statistical models

Hindrance factors for electric-dipole transitions are predicted on the basis of the giant dipole resonance and statistical models. Good agreement is obtained with empirical data presented in recent compilations.     

Stopping of slow recoil atoms in gases

Nuclear Resonance Fluorescence spectra contain information on the slowing-down behaviour of recoiling atoms in the energy range pertinent to the specific reaction. On the basis of conventional transport theory, measured spectra for arsenic atoms with energies ?15 eV slowing down in helium are analysed. The assumption of continuous slowing down turns out to be well justified, and the thermal motion of the gas atoms is shown to influence the effective stopping power only slightly. Somewhat surprising in view of uncertainties concerning the charge state of the recoiling atoms, theoretical predictions based on Lenz-Jensen elastic interaction agree well with the measured spectra. At present, the experimental data do not allow direct inversion, but the calculated spectra are shown to depend sensitively on the stopping-power input.