K-shell ionization of Si,Ti, Cu and Ag for incident protons,4He and14N ions in the energy range of 0.17–2.0 MeV/amu

K-shell X-ray production cross sections of Si, Ti, Cu and Ag were measured for incident protons,⁴He and¹⁴N ions in the energy range of 0.17≦E ₁/A ₁≦2 MeV/amu. The experimental ionization cross sections are compared with calculations according to the simple Plane Wave Born Approximation (PWBA) theory as well as the corrected PWBA model (PWBABC). Strong deviations of the experimental cross sections from theZ ₂ ¹ scaling are observed and discussed quantitatively.     

Search for the density effect in inner-shell lonization by ultra relativistic electron impact

We have extended the measurements ofK-andL-shell ionization cross sections by electron impact into the ultra relativistic energy region, 0.9≦E≦2.0 GeV, in order to search for a saturation of the cross section. This phenomenon, which is due to the polarization of the target medium, is called density effect. It is predicted to occur at several hundred MeV impact energy and preferentially for lowZ target elements. Theoretical calculations are presented, based on the one-photon-exchange approximation. The absolute measurements of theK-andL-shell cross sections for Ni(K), Cu(K), Ag(K, L) and Au(L) performed at the 2.5 GeV electron synchrotron of the Bonn University, however, exhibit that the cross sections show no saturation but are still increasing. Furthermore, from theK X-ray yields, obtained at 0.9 and 2.0 GeV by bombarding the lowZ elements S, Ca, Mn, Ni and Ge, we obtain for the corresponding cross section ratio σ _K (2GeV)/σ _K (0.9GeV)=1.08±0.01 on the average. TheK X-ray yield of a composite Ca — Mn target amounts to $$[\sigma _K (Ca;2.0GeV)/\sigma _K (Mn;2.0GeV)]/[\sigma _K (Ca;0.9GeV/\sigma _K (Mn;0.9GeV)] = 0.99 \pm 0.02.$$ . All three results are in disagreement with theory. This severe discrepancy is discussed but the origin for it is not yet understood.     

Inner-shell ionization ofZ=25–32 elements by 5-48 MeV32S ions

TheK-shell ionization cross sections of Mn, Ni, Cu, Zn and Ge under³²S bombardment have been measured in the energy range from 5 to 48 MeV. The cross sections are compared with available theories based on a direct Coulomb ionization mechanism and with the predictions of theK-vacancy sharing process. This last process can reasonably account for the measured cross sections at high bombarding energies. The energy shifts of theK _α- andK _β-lines and theK _α/K _β-intensity ratios have also been measured. This information is used to deduce the defect configuration of the atoms. The mechanisms responsible for the multiple vacancy production are discussed.     

K-shell X-ray production for fluorine ions on target elements Ti to La

The production of target atomK-shell X-rays has been studied for 2 to 28 MeV fluorine ions incident on thin solid targets of 14 elements with atomic numbers Z₂=22 to 57. Total X-ray production cross sections, energy shifts ofK _α andK _β lines andK _α/K _β intensity ratios were measured with a Si(Li) detector. The results of cross section measurements are compared with theoretical predictions of inner shell ionization. In most cases, satisfactory agreement between measured cross sections and theoretical Coulomb ionization cross sections, corrected for the perturbation of the target atom by the projectile charge and for relativistic effects, was obtained.     

The structure of25Mg

Gamma-decay modes and spin(-parity) assignments of levels in²⁵Mg have been systematically investigated up to 10 MeV excitation energy by particle-γ-ray angularcorrelation measurements with the²⁴Mg(d, pγ) reaction at 6.5 MeV bombarding energy and with the²²Ne(α,nγ) reaction at 11.8, 12.5, 14.4 and 15.5 MeV bombarding energy. A level scheme has been established which is comprehensive up to 8.3 MeV excitation energy forI≦9/2 and up to 10 MeV for 9/2O d _5/2 — 1s _1/2-O d _3/2 shell and the unifieds-d shell Hamiltonian. The agreement is good to excellent. The first intruder states are located near 6.8 MeV excitation energy. The collective properties of²⁵Mg beyond the well established rotational bands are investigated using both the new experimental information and theB(E2)'s obtained from the shell model. The spectrum of²⁵Mg is completely rotational for the first five to six MeV above the yrast line. Shell modelB (M 1)'s reflect the Nilsson model structure of²⁵Mg in great detail. The prospectiveI ^π=9/2^?, 13/2^?, and 15/2^? members of the established negative-parity,K=1/2 band are found in levels atE _x=7801, 9410, and 8896 keV.     

Measurements ofK-shell ionization with132Xe and208Pb projectiles in the energy range of 1.4–5.9 MeV/u

Projectile and targetK-shell ionization cross sections induced by 3.6-, 4.7-, and 5.9 MeV/u¹³²Xe ions and 1.4-, 3.6-, 4.7-, and 5.9 MeV/u²⁰⁸Pb ions from the UNILAC in thin solid targets between C and U are measured. The cross sections are discussed in terms of the molecular model of innershell vacancy production in heavy ion-atom collisions. The sharing of 2p _1/2σ vacancies between theK shells of the two collision partners in these very heavy ion-atom collisions is found to deviate from the Meyerhof-Demkov formula forR≦10^?2. The measured ionization cross sections are compared with theoretical calculations for 1sσ and 2p _1/2σ excitation cross sections. AZ _UA=Z₁+Z ₂ dependence is found independent ofZ ₁/Z ₂. Outer-shell vacancy configurations measured in these close encounters are reported.     

Oxygen inducedK-shell ionization of selected elements from sulphur to bromine

K-shell X-ray production cross sections for oxygen ions on thin solid targets of 13 selected elements with atomic numbers between 16 and 35 were measured by a Si(Li) detector at incident ion energies from 7 to 24 MeV. Ionization cross sections are compared with calculations assuming Coulomb-ionization. Best agreement is found with theoretical cross sections that include corrections for binding energy and Coulomb deflection effects. Energy shifts ofK _α andK _β X-rays andK _α /K _β intensity ratios were also measured and are used to deduce information about outer shell ionization.     

Study of high energetic electrons emitted during heavy ion collisions

Double differential cross sectionsd ² σ/dΩdE were measured for high energetic electrons emitted in heavy ion collisions. Electrons were detected in the energy range of 60 keV-500 keV for various target projectile combinations 66≦Z _u =Z _t +Z _p ≦145 and projectile velocities between 7 % and 10 % of the speed of light. Clear evidence was found that these electrons stem from the united atom formed during the collision. Slope and height of the spectra are discussed with respect to the momentum distribution of strongly bound states (i.e. theL-shell) at momenta far above the mean value. In addition for the systems S, Ni, Br→Pb electrons were detected in coincidence withK x-rays of Pb. By this method the contribution of theK-shell of the combined system to the total spectrum could be separated. Binding energies of theK-shell were estimated by a slope comparison between the coincident and single spectrum. The resulting values are close to the united atom limit.     

Study of the heavy products from84Kr+238U collisions at 522 MeV

Angular distributions and integral cross sections for heavy reaction products from⁸⁴Kr +²³⁸U collisions at 522 MeV were measured using catcher foil techniques and off-line X-ray identification of individual reaction product isotopes. There is no evidence for a fission-fusion mechanism being responsible for the formation of the “gold finger”. The data show that usual deep inelastic collisions account for the formation of all products with 70≦Z≦86. Compared to existing data atE≦605 MeV, the deduced mass distribution indicates reduced fission probabilities forZ≧80 fragments at 522 MeV. This is consistent with the expected dependence of fission probability on excitation energy and especially on angular momentum.     

Studies on strongly damped components in relatively light heavy ion reaction systems

Strongly damped components have been studied in relatively light heavy ion reaction systems;²⁰Ne(E _lab=93, 120 and 146MeV)+⁵⁰Cr,²⁰Ne(E _lab=146MeV)+⁵⁴Cr and²⁰Ne(E _lab=146MeV)+⁹²Mo,¹⁰⁰Mo. The kinetic energy, angular and charge distributions have been observed for those products. The yields of symmetric-mass-splitting products for²⁰Ne+⁵⁰Cr were found about three times larger than those for²⁰Ne+⁵⁴Cr. There was also observed a similar difference in the cross sections of the symmetric-mass-splitting products between²⁰Ne+⁹²Mo and²⁰Ne+¹⁰⁰Mo reactions. In order to explain the bombarding energy dependence of the cross sections of symmetric-mass-splitting products by the transport theory, it was found necessary to assume that the mean life of the composite nucleus was dependent on the bombarding energy. However, the target isotope dependence of the cross sections could not be explained by such an assumption. They could be partly explained by fission calculations.     

Atomic number dependence ofL-shell vacancy rearrangement probabilities onKα X-ray satellites induced by 6 MeV/amu N4+ impacts

L-shell vacancy rearrangement probabilities, \(\tilde f\) 's, prior toKα X-ray emission andL-shell widths were determined from intensity distributions of theKα satellite structures. Characteristic X-rays were induced by 6 MeV/amu N⁴⁺ impacts on atoms with various chemical compositions and with different bonding structures, whose atomic numbers range from 9 to 30. In the region where target atomic numberZ ₂≦12, the experimentally deduced \(\tilde f\) values exceed theoretical ones to large extent. On the other hand, the theoretical \(\tilde f\) values give upper limits to the experimental ones in the regionZ ₂≧13. No significant chemical effect could be found in \(\tilde f\) values for all the atoms investigated except forF.     

Eigenvalues of the Faddeev equation kernel for a system of three spinless particles

For a system of three spinless particles interacting via separable Yamaguchi potential the possibility of the existence of three-particle resonances is studied. To this end, the eigenvaluesλ _i ^L (E ₃) of the Faddeev equation kernel have been calculated in the c.m.-energy region ?30 MeV≦E ₃≦15 MeV for total momentum statesL=0 andL=1. It is shown that in the investigated energy range there are no resonances.     

Inner-shell ionization ofZ=25–32 elements by 5-48 MeV32S ions

TheK-shell ionization cross sections of Mn, Ni, Cu, Zn and Ge under³²S bombardment have been measured in the energy range from 5 to 48 MeV. The cross sections are compared with available theories based on a direct Coulomb ionization mechanism and with the predictions of theK-vacancy sharing process. This last process can reasonably account for the measured cross sections at high bombarding energies. The energy shifts of theK - andK -lines and theK /K -intensity ratios have also been measured. This information is used to deduce the defect configuration of the atoms. The mechanisms responsible for the multiple vacancy production are discussed.     

Investigation of large angle structure in α-scattering from calcium isotopes betweenE α=36–61 MeV

Elasticα-scattering angular distributions have been measured atE _α=36.2 MeV, 39.6 MeV, 42.6 MeV, 49.5 MeV, 61.0 MeV for⁴⁰Ca and atE _α=36.2 MeV, 42.6 MeV, 49.5 MeV and 61.0 MeV for⁴⁴Ca, respectively. At backward angles the data display an oscillatory structure forE _α<50 MeV and more smoothly decreasing slopes atE _α =61.0 MeV resembling the data obtained at higher energies. The⁴⁰Ca data belowE _α =50 MeV show the well known backward enhancement, which at 42.6 MeV and 49.5 MeV can be fitted by aP ₁₄ ² and aP ₁₆ ² respectively. Together with previous data,P _L ²-structures have now been observed for allL-values betweenL=8 andL=16. The slope of the curveL(L+1) versus excitation energy is slightly smaller forL>12 than forL<12. Optical model analyses (within a Woods-Saxon-folding model) lead to large differences between the⁴⁴Ca and⁴⁰Ca parameters. Furthermore, in our parametrization, the⁴⁰Ca real potential depth shows dramatic changes with energy. This feature seems outside the domain of the optical model and requires consideration of additional effects (e.g. antisymmetrization) not included in the standard optical model. Present microscopic calculations on the basis of the Resonating Group Method are discussed in connection with the characteristic features ofα-scattering from⁴⁰Ca.     

On the effect of off-shell wavefunctions onK andL shell charge transfer in fast,asymmetric collisions

Within the semiclassical strong potential Born approximation (SPB) we have calculated the electron capture from theK andL shell of a heavy target atom by protons using two different peaking approximations. Both total capture cross sections and impact parameter distributions are compared with the impulse approximation (IA) and in the case of transfer from the ArK-shell also with an exact evaluation of the SPB and with experimental data. While for theK shell, all theories give a similar impact-parameter dependence, there is a substantial difference between IA and SPB results for the 2s subshell.     

Collective mass parameters and linear response techniques in three-dimensional grids

The²⁴Mg(α,γ ₀)²⁸Si capture reaction has been studied for bombarding energies 4.4 ≦E _α ≦9.6 MeV. Through angular distributions taken in steps of 60 keV the groundstate yield has been decomposed into its contributingE1 andE2 components. Excitation energies and widths of several narrow 1^? and 2⁺ levels were determined. Significant deviations of the phase factor cosδ from the statistical expectation value were analysed in terms of a two-state interfering process and yielded as much as (40 ±10)% semidirect contributions to the α-capture reaction.     

Sub-Coulomb transfer and fission in collisions of129Xe,132Xe and136Xe with238U

Integral cross sections for fission and for one- and two-neutron transfer reactions in the system¹³²Xe+²³⁸U were measured radiochemically in the energy range 0.7≦E/E _Coul≦1. The excitation functions for fission and transfer are found to be essentially parallel below 0.85×E _Coul. Even at the lowest energies the transfer cross sections exceed the fission cross section by more than one order of magnitude. With the other projectiles¹²⁹Xe and¹³⁶Xe different transfer cross sections illustrating their sensitivity for the ground stateQ-values,Q _gg , are observed while the fission cross sections are the same as in the¹³²Xe +²³⁸U reaction. The fission data are interpreted in terms of a continuous transition between Coulomb fission and several transfer-induced fission processes.     

The 56Fe(α, γ)60Ni reaction cross section

The yield of 1.332 MeV γ-rays from the reaction ⁵⁶Fe(α, γ)⁶⁰Ni has been measured as a function of α-particle bombarding energy in the range 4.2–7.1 MeV. This energy region includes the (α, n) threshold at E_α = 5.46 MeV. The energy dependence of this γ-ray cross section, as well as the (α, nγ) cross section, is compared with statistical model calculations. Good agreement is achieved between these data and calculations using global optical model parameters to determine the transmission functions. In particular, the pronounced threshold effect in the (α, γ) yield, at the opening of the (α, n) channel, is well represented.     

Directional transport equations for plasmas

The yields of the reactions NUCLEUS (γ,yp xn)²⁴Na have been measured for eleven elements with 13≦Z≦29 at maximum bremsstrahlung energies 100 MeV≦E _{γ max}≦ 1000 MeV. An exponential decrease with increasingZ of the mean cross section calculated from the yield data has been obtained. ThisZ-dependence fits well to the systematics of spallation product cross-sections.     

70Ge(α, γ)74Se cross section measurements at energies of astrophysical interest

The cross section of the reaction⁷⁰Ge(α, γ)⁷⁴Se has been measured over the bombarding energy range of 5.05 MeV <E _α < 7.80 MeV using single and coincidence gamma spectroscopy techniques. The experimental S-factor values are in agreement with theoretical statistical-model calculations. Reaction rates for the⁷⁰Ge(α, γ)⁷⁴Se and the inverse (γ, α) reactions have been determined for appropriate temperatures.