Z1 and Z2 variations in the stopping powers of Z1=10 to 18 ions deduced from Dsam lifetime measurements

From lifetime measurements of the ²²Ne(3.26 MeV), ¹³P(2.23 MeV) levels and published data, deviations from theory of the stopping powers for Ne and other ions in many materials have been deduced; they correlate strongly with electron densities deduced from positron lifetimes. The data also indicate that Z₁ deviations for s-d shell nuclei are Z₂ dependent.     

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.     

‘Slow’ residues observed in the reaction20Ne+208Pb at E/A=8.6, 11.4 and 15.0 MeV/u

Velocity distributions of heavy residuesA _Res>A _tar,Z _Res>Z _tar identified by means ofα spectroscopy, have been investigated at the velocity filter SHIP in reactions²⁰Ne+²⁰⁸Pb at projectile energies E/A=8.6, 11.4 and 15.0 MeV/u. Besides products from complete or nearly complete fusion, characterized by velocity distributions peaking atν/ν _CN?0.8–1.0, heavy residues with mean velocities of about half of the compound nucleus velocity were observed. The Z-distribution of this component was found to peak atZ=87. It is interpreted as residues from fusion of target nuclei with projectile fragments produced by nearly symmetric break-up. The experimental results were compared with predictions of theoretical models: cross sections for incomplete fusion were calculated using the sum-rule model of Wilcynski et al., while residue cross sections were calculated using the evaporation code HIVAP. A fair agreement between experimental and calculated mass distributions of heavy residues and transferred projectile fragments is achieved if an energy dissipation of ?23% (at E/A=8.6 MeV/u) and ?8% (at E/A=11.4 MeV/u) of the incident projectile energy is introduced. The observed peak of theZ-distribution atZ=87 is predominantly effected due to a higher fission probability of products withZ>87 during the deexcitation process and experimental limitations in the identification of products withZ≦86 by means of a spectroscopy, which cause a decrease of the observed production rates towards lowerZ.     

Asymmetry of bremsstrahlung by moderately relativistic polarized electrons

The asymmetry of bremsstrahlung by transversely polarized electrons using Sommerfeld–Maue wave functions has been calculated. In order to simplify the final formula the relativistic approximation has been used. The results obtained show a linear dependence of the asymmetry on the atomic number Z for the range 4≤Z≤26. It is shown that the approach developed gives the zeroth asymmetry for ultrarelativistic energies as expected but for initial electron energies ～5 MeV the asymmetry may achieve a magnitude ～8% (for Z=26). Polarimetry of electrons with energy higher than 1 MeV (where conventional Mott polarimeters have large experimental difficulties) may be carried out using the bremsstrahlung process providing a reasonable asymmetry and high cross section.     

Is the Kβ/Kα x-ray intensity ratio dependent upon the energy of an inducing proton?

K_β/K_αX-ray intensity ratios have been measured for various elements between Z = 29 and Z = 79 for incident proton energies of 23.6, 32.1 and 43.6 MeV. The results yield no evidence for a variation in ratio with particle energy.     

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.     

Study of three-nucleon mechanisms in the photodisintegration of 3He

The cross section of the ³He(γ,pp)n reaction has been measured for the first time over a wide photon energy and proton angular range (200 MeV ≤ E_γ ≤ 800 MeV; 20° ≤ ϑ_p^lab ≤ 160°) using the large acceptance detector DAPHNE at the tagged photon facility of the MAMI microtron in Mainz. The wide kinematical coverage of the measurement has allowed a detailed analysis of three-nucleon absorption mechanisms. A model developed by Laget explains the main characteristics of the data in the Δ resonance region.     

Role of pairing degrees of freedom and higher multipolarity deformations in spontaneous fission process

Spontaneous fission (T_sf) and alpha-decay half-lives (T_α) of the heaviest nuclei with atomic number 100 ≤ Z ≤ 114 are calculated on the basis of the deformed Woods-Saxon potential. The calculations of (T_sf) are performed by the WKB approximation, in the multi-dimensional dynamical-programing method (MDP).We have examined three different effects: the effect of higher even-multipolarity shape parameters (β₆ and β₈), the role of reflection-asymmetry (β₃ and β₅) and the influence of pairing degrees of freedom (Δ_p and Δ_n).Alpha-decay half-lives (T_α) have been calculated by the Viola-Seaborg (V-S) formula with the parameters modified to the latest experimental data.     

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.     

Highly excited “nuclear molecules”: A way to explain the fluctuations in DBHIC excitation functions. Study of the28Si +28Si colliding system at 5.3 MeV ·A

The properties of the strong fluctuations observed in the excitation functions of Dissipative Binary Heavy Ion Collisions (DBHIC) have been studied for the system²⁸Si+²⁸Si in the energy range 150 MeV ≤E _lab ≤ 156 MeV with 150 keV step laboratory incident energy, by angular distributions and excitation functions measurements. Experimental results are compared to the the recently developed Partially Overlapping Molecular Level Model (POMLM). The parameters of the model have been determined with reasonable accuracy by describing all the quantities characterizing the fluctuations in the excitation functions i.e.: Average Angular Distributions, Energy Autocorrelation Functions, Variances, Angular Correlation Coefficients. The results of the analysis strongly support the idea of a process proceeding through the formation of an highly excited “nuclear molecule”. Experimental data collected at the most forward angles show the effects of strong excitation of a few final channels.     

Untersuchungen zur Struktur des Kerns23Ne

Low-lying states of²³Ne up to about 3 MeV excitation energy have been investigated by studying the reactions²²Ne(d, p)²³Ne (E _d =4–6 MeV) and²³Na(n, p γ)²³Ne(E _n=8–9 MeV). From the (d, p) data,l-values and spectroscopic factors for the transferred neutron have been extracted by DWBA analyses. From the (n, p γ) data,γ-ray branchings and possible spin assignments have been derived. The results are used to discuss the applicability of the Nilsson model and the excited core model to the nucleus²³Ne.     

Dynamical intermediate-mass fragment production in197Au+197Au collisions at energies ≤15 MeV/u

We present radiochemical data on the production of intermediate-mass fragments (IMF, 11≤Z<≈25) in collisions of¹⁹⁷Au+¹⁹⁷Au at 9, 11, 13 and 15 MeV/u. We demonstrate that the IMFs are produced in two-step reactions: Highly excited heavy nuclei are formed in a binary deep-inelastic reaction, and the IMFs originate from fast mass-asymmetric sequential fission of these primary reaction products.     

Calculated beta-ray spectra from decay of fission products produced by thermal-neutron fission of 235U

Beta-ray spectra from decay of fission products created by thermal-neutron fission of ²³⁵U have been calculated using summation techniques and using an independently created beta-ray data file. The calculated beta-ray spectra are in very good agreement for E_β ? 1 to 8 MeV with recently measured specta of beta rays for two very different exposure and counting time conditions: (a) an “instantaneous” spectrum following a 1.5 day exposure, and (b) an 8 s counting-time spectrum obtained 1.7 s following a 1 s exposure of ²³⁵U by thermal neutrons.     

Excitation of the giant dipole resonance in the scattering of isoscalar projectiles

The excitation of the giant dipole resonance in nuclei with N > Z by isoscalar projectiles α and d is discussed within a simple collective model for isoscalar dipole excitations. Calculations have been performed for ²⁰⁸Pb; they are compared to recent data on the excitation of the new giant resonance at E_x = 13.8 MeV. For α scattering the effect of dipole excitation is quite weak but significant contributions are obtained for d scattering.     

High-spin states in the single-closed-shell nucleus 142Nd

The excited states of ¹⁴²₆₀Nd₈₂ have been studied using the ¹⁴⁰Ce(α, 2nγ)¹⁴²Nd and ¹⁴²Ce(α, 4γ)¹⁴²Nd reactions. Singles γ-ray, γ-γ coincidence spectra and angular distributions of γ-rays with respect to the beam direction have been measured. Excited states up to 6.7 MeV with spin values up to 14 are populated. The energy spacings between the lower excited states with spin values up to 8 are similar to those found in the lighter N = 82, even-Z isotones. The majority of the observed states with spin values up to 10 can be explained as two-quasiparticle states. Several of the highest-spin states can be explained qualitatively as fourquasiparticle states. Strong population of the highest excited states (at about 5.7 MeV) is noted, like in other N = 82 isotones. The observed levels in ¹⁴²Nd are compared with the shell model predictions using a simple δ-force interaction between two nucleons.     

Lifetime measurements of spherical and deformed states in 1f7/2 nuclei

Lifetimes have been determined using the Doppler Shift Attenuation Method in the N ≈ Z nuclei ⁴⁶V and ⁴⁸V, populated with the reaction ²⁸Si on ²⁴Mg at 115 MeV and ²⁴Mg on ²⁸Si at 100 MeV using Au and Pb backed targets. The coexistence of spherical and deformed states in the middle of the 1f_7/2 shell is discussed. The B(E2) and B(M1) reduced rates agree very well with large scale shell model predictions.     

Levels in104Ru populated by the β−-decay of104Tc

Theβ ^? — andγ-activities of 18.4 min¹⁰⁴Tc have been studied with singles and coincidence measurements. Sources were prepared by chemical separation of technetium from the fission products of thermal-neutron-induced fission of²³⁵U. A revised level scheme of¹⁰⁴Ru up to an excitation energy of 4.26 MeV is proposed. Fromβ-γ coincidence measurements, aQ _β-value of 5.62±0.07 MeV has been obtained.