The sub-barrier fusion of40Ar with144,148,154Sm

The cross sections for production of evaporation residues (σ _er) and for fusion-fission (σ _ff) have been measured for⁴⁰Ar+^{144, 148, 154}Sm at sub-barrier energies by observation of x-ray emission from radioactive products and by direct,ΔE?E identification of fission fragments, respectively. These isotopes span the transition region from spherical (¹⁴⁴Sm) to strongly deformed (¹⁵⁴Sm) equilibrium shapes. The cross section for fusion,σ _fus=σ _er+σ _ff, is found to vary markedly at low energies with the isotope number and, hence, with the quadrupole collectivity of the target. The thresholds for fusion of¹⁴⁸Sm and¹⁴⁴Sm are, respectively, ～3.5 MeV and ～7 MeV (c.m.) higher than for fusion with¹⁵⁴Sm. These differences and the energy dependence of the fusion cross sections are discussed in terms of the effect of nuclear deformation on heavy-ion fusion. A comparative analysis of results for¹⁶O+Sm and⁴⁰Ar+Sm in terms of static deformation indicates thatσ _fus for the Ar+Sm system at very low energies is enhanced relative to the prediction for a one-dimensional barrier based on a fit toσ _fus for¹⁶O+Sm. This may be an indication that additional degrees of freedom (such as formation of a neck or fragment elongation) may be important for fusion with the larger projectile. At energies above the fusion barrier, values ofσ _fus for^{144, 148}Sm are nearly equal, but are significantly smaller than for¹⁵⁴Sm. This is in contrast to the results of previous experiments with¹⁶O projectiles in whichσ _fus (¹⁶O+¹⁴⁸Sm) andσ _fus (¹⁶O+¹⁵⁴Sm) were nearly equal above the barrier. These differences, observed for^{144, 148}Sm and¹⁵⁴Sm at energies above the barrier may reflect a new mechanism which is not encompassed by a static theory.     

Debye-waller factor for electron scattering by surface atoms

The contribution of anharmonic atomic vibrations to the EXAFS-spectrum is described by the third cumulantσ(³) which contributes with a term proportional tok ³ to the phase in the single scattering plane wave approximation. Due to the lattice expansion and enhancedσ(²) in the surface region we get additional temperature dependent contributions, which are evaluated in a curved wave theory. Transforming this expression into the basic formula we get an additional term proportional tok ³ in the phase of the generalized scattering amplitude. This valueΔα(³) has to be subtracted to get a value forσ(³). Numerical results at the O-K-edge of NiO give a value forΔσ(³) of about 10^?4 ų.     

Experimental and theoretical investigation of fmr in (111) thin garnet films with applied uniaxial stress

Analytical expressions for the resonance field shiftδH caused by an applied stressσ are deduced forH _e ∥ [¯1¯12] in the film plane, taking into account also the quadratic terms (～σ²) besides the dominant linear terms (～σ). The linear part ofδH=f(σ) forH _e andσ lying in the film plane depends only on the relative angle betweenH _e andσ, so that for the measurement of magnetostriction constants it is not necessary to have crystallographically oriented thin films.δH forH _e perpendicular to the film is very sensitive to deviations from the perpendicular direction. Both magnetostriction constants λ₁₁₁ and λ₁₀₀ were evaluated on (111) thin YIG ∶ Mn film.     

Hybrid model analysis of intermediate energy (20<E γ<140 MeV) photonuclear reactions on232Th and235,238U

The hybrid model code ALICE/LIVERMORE 82 (with fission option) has been used in the study of photonuclear reactions on²³²Th and^235,238U (20<E _γ<140 MeV). The total fission probabilitiesP _f were calculated. A model was established for the decay of the fission fragments. This model, together with the code ALICE, allowed the calculation of the cross sectionsσ ⁽ⁱ⁾ for emission of at leasti neutrons, and of the average multiplicity¯v and widthW of the neutron distribution for²³⁸U. The theoretical results forP _f ,σ ⁽ⁱ⁾ ,¯v andW show very good agreement with existing experimental data. It is shown that a comparison of the calculations with the available experimental data does not allow for a discrimination between the various photon absorption mechanisms proposed (single-particle absorption vs. quasi-deuteron mechanism).     

Über die Berechnung der Photoerzeugung von π0 aus Streudaten

The cross section forπ ⁰-production is calculated from the results of the dispersion relation approach ofChew, Goldberger, Low andNambu and compared with the experimental data. The predictions are made using the measured values of all scattering phase shifts. A fit of the theoretical result toσ(90?) between 260 and 370 MeV givesf ²=0,082. There is no systematic deviation from the predictions forσ (90?) up toE _γ =450 MeV. The general behavior of the asymmetry coefficientB is correct. A quantitative comparison which would show the contribution of the unknown electric dipole termN ⁽⁺⁾ ofChew et al. is only reasonable after the calculation ofB and the measurements have been improved.C/A depends strongly on the small phases up to 240 MeV. The effects of the small phases are pretty large forσ(l50?) but there is no discrepancy similar to the results forπ ⁺-production above 290 MeV. The formula for the cross section does not reduce to the results of the phenomenological theories ofBrueckner-Watson, Sachs et al. andFeld, if the simplifications made by these authors are taken into account. The origin of the differences is discussed.     

Cross sections and angular distributions of three-jet final states ine + e − annihilation for heavy quarks

The cross sectionsdσ _U ,dσ _L ,dσ _T anddσ _I fore ⁺ e ^?→q \(\bar q\) g are calculated for heavy quarks, and the resultant angular distribution is discussed.     

The spin cut-off factor for60Co

Nine experimental isomeric cross-section ratios for the reactions⁵⁹Co(n, γ)⁶⁰Co,⁶⁰Ni(n,p)⁶⁰Co, and⁶³Cu(n,α)⁶⁰Co are analysed in terms of statistical theory by means of the method ofHuizenga andVandenbosch. Theγ-cascades are treated by a new model which was recently published. The results confirm the energy dependence of the spin cut-off factor for⁶⁰Coσ～U^1/4 which should not be neglected. As a mean value (σ=4.3±0.3 is obtained forU=B _n =7.5 MeV in good agreement with a nuclear moment of inertia for a rigid sphere.     

Angular momentum dissipation in16O +58Ni collisions investigated by observation of light particles andγ rays

A systematic study of angular momentum dissipation in deep-inelastic heavy ion collisions is carried out by combining two experimental methods: the angular correlation ofα particles and protons in coincidence with deeply inelastic light fragments; and the first two moments of theγ-ray multiplicity. The unified analysis of these data, using a quantum mechanical treatment of the particle anisotropies and statistical decay calculations, yields most probable fragment spinsI ₀=10.8±1.1? and 13.4±1.1? for⁵⁸Ni and⁶²Zn, respectively, close to the sticking limit. For the width of the vector spin distribution assumed in our analysis to be equal in all three directions we obtainσ=3.9±1.3 ? and 2.9±1.8? for⁵⁸Ni and⁶²Zn, respectively. These values correspond to most probable alignment parameters 〈P _zz〉=0.66±0.19 and 0.82±0.17 for⁵⁸Ni and⁶²Zn, respectively. As only very few partial waves of this light system undergo deep-inelastic scattering,σ directly relates to spin fluctuations, and is compared to asymptotic values from transport theories.     

Electroproduction of π+ n, π- p andK + Λ,K + 2211; 0 final states above the resonance region

The reactionsΣ _v p→π⁺ n,K ⁺ Λ,K ⁺ ∑ ⁰ andΣ _v n→π⁺ n were studied at invariant hadronic masses around 2.2. GeV forQ ²=0.06, 0.28, 0.70, and 1.35 GeV². The main results are: At small |t| the π⁺ production is dominated by longitudinally polarized photons and can be described by one pion exchange. At low |t| the transverse (π⁺ n) cross section drops steeply withQ ², but remains roughly constant forQ ²≧0.5 GeV². For |t?≧0.8 GeV², (π⁺ n/dt) is almost independent ofQ ². The integrated cross section (π⁺ n) shows a similarQ ²-dependence asσ _tot (γ _v p) forQ ²≧0.28 GeV². The ratioσ(π^- p)/σ(π⁺ n) atQ ²=0.70 and 1.35 GeV² for |t|≧0.6 GeV² is smaller than in photoproduction and close to 1/4. The ratioσ(K ⁺ ∑ ⁰ decreases steeply withQ ² following roughly the predictions of the quark-parton model.     

InclusiveΔ ++ inpp interactions at ISR energies

Inclusive cross sections forΔ ⁺⁺ production inpp interactions at different ISR energies are presented. The differential cross sectiondσ/dx forΔ ⁺⁺ production is found to be approximately independent of Feynmanx. No strong energy dependence is seen over the ISR energy range. The topological cross sections ofΔ ⁺⁺ at \(\sqrt s = 62\) GeV show an appreciable contribution from non-diffractive production mechanisms. An upper limit for theΔ ⁰ production cross section is determined.     

Zum Kernphotoeffekt am Ar40 und Ar38

Liquid Argon was irradiated with bremsstrahlung from 18 to 31 MeV endpoint energy in steps of 2 MeV. The yields of the reactions Ar⁴⁰(γ, n)+(γ, p) and Ar³⁸(γ, n) were measured by detecting the 269a and the 35d rest activity with a low-level-counter. Cross section curves for the (γ, n)-processes could be found from the yield values, and they allowed together withσ _N, σ(γ, p) andσ(γ, np) a determination ofσ(γ, 2n) and σ_γabs for Ar⁴⁰. The integrated cross section forσ(γ, n) from threshold to 33 MeV yields (200±40) MeVmb for Ar⁴⁰ and (210±40) MeVmb for Ar³⁸, the corresponding value for σ_γabs being (450±60) MeVmb for Ar⁴⁰.     

Nuclear orientation measurements of the magnetic dipole moments of the 11/2− Isomeric states in129Xe,131Xe and133Xe

The low-temperature nuclear orientation technique was used to measure the magnetic moments of¹²⁹ mXe,¹³¹ mXe and¹³³ mXe implanted in iron by isotope separator. The magnitudes of the magnetic dipole moments, extracted from the gamma-ray anisotropy measurements areμ=?0.80(10)μ _N for^129m Xe,μ=?0.80(10)μ _N for¹³¹Xe andμ=?0.87(12)% for¹³³Xe. The results for these 11/2^? isomers agree with theoretical calculations by the spin polarization procedure using wave functions from the pairing-plus-quadrupole model.     

Neutron induced reaction cross-section of115In around 14 MeV

A systematic investigation was carried out on¹¹⁵In to determine the contribution of different reactions to the total non-elastic cross-section in the 13.43 and 14.84 MeV incident neutron energy range. All the major components ofσ _NE were measured with exception of theσ ^g(n, n′) cross section. An analytical expression is recommended to estimate theσ _NE data as a function of mass number at E_n=14.1 MeV. By the knowledge ofσ _NE, the energy dependence ofσ ^g(n, n′) could be deduced. The isomeric cross section ratios both for (n, 2n) and (n, n′) processes were also determined in the given energy range. The present experiment proves the dependence ofσ ^m/(σ ^g+σ ^m) ratio on the spin value (I _m) of the isomeric state in the (n, 2n) reaction. Excitation functions of the (n, 2n), (n, n′) (n, p) and (n∶ p, α) reactions calculated by STAPRE code show good agreement with the experimental results.     

Total cross section for hadron production bye + e − annihilation between 9.4 and 9.5 GeV

The total cross section fore ⁺ e ^? annihilation into hadrons for center of mass energies from 9.4 to 9.5 GeV has been measured with the nonmagnetic DESY-Heidelberg detector at DORIS. A value ofR=σ_had/σ_µµ=3.8±0.7 for the continuum region around the Υ (9.46) resonance has been determined. The ratioΓ _ee Γ _had/Γ _tot of electronic, hadronic and total widths has been reevaluated to be (1.00±0.23) keV for the Υ resonance and (0.37±0.16) keV for the Υ′. In addition, a search for directly produced pohotons from Υ decays of the type Υ→γ+gluon+gluon has been performed. The Υ decay into muon pairs has also been searched for.     

The cross section of14N(n,p)14C at stellar energies and its role as a neutron poison forS-process nucleosynthesis

The absolute average cross section 〈σ〉 of the¹⁴N(n, p)¹⁴C reaction has been measured using neutron spectra that closely resemble Maxwell-Boltzmann distributions with thermal energies of kT=25.0 and 52.4 keV: 〈σ〉=0.81±0.05 and 0.52±0.06 mb, respectively. The resulting reaction rates are nearly the same at T₉=0.29 and 0.61, and their average, N_A〈συ〉=(1.3±0.1)×105 cm³ s^?1 mol^?1, is about a factor of three smaller than the previously adopted values obtained by extrapolation between thermal and higher-energy data. Thus, the¹⁴N(n, p)¹⁴C reaction plays a correspondingly smaller role as a neutron poison fors-process nucleosynthesis.