Dirac-Fock studies of some electronic properties of actinide ions

Results of accurate Dirac-Fock studies of some U, Np, Pu and Am ions are reported; these include one-electron eigen-values, spin-orbit splittings, 〈rⁿ〉 values for the 5f electrons, Slater F^k and G^k integrals, Mössbauer isomer shift electronic densities and the 〈j_i〉 integrals needed for neutron magnetic form factors.     

Temperature quenching of luminescence for linear and derivative nuclear operators

An earlier study of the thermal quenching of luminescence using the single-configurational-coordinate model is extended from Condon-approximation overlap integrals 〈u_n|v_m〉² to the linear and derivative integrals 〈u_n|z_v|v_m〉² and 〈u_n|?/?z_v|v_m〉². For non-radiative transitions, the thermally weighted nuclear factor in the transition rate is, for the linear and derivative integrals, the corresponding factor for 〈u_n|v_m〉² integrals multiplied by 2E_Xv/?ω_v and $\text{2[E}{}_{\mathrm{Xv}}\text{- E}{}_{\mathrm{p}}{}_{\mathrm{U}}\text{(T)]/}\text{h}\text{?}\text{ω}{}_{\mathrm{v}}$, respectively. E_Xv is the energy of the crossover above the initial- v-parabola minimum, and E_pU(T) is the single activation energy fitted to the nuclear factor's temperature dependence for 〈u_n|v_m〉² integrals. These multiplying factors are exact for equal parabola force constants and good approximations for unequal force constants. These multiplying factors will be difficult to distinguish experimentally. The more important considerations for fitting the model to thermal-quenching data are the parabola placement and the Condon-approximation integrals described previously.     

Range-energy relation of electrons in a KCl crystal

The range of electron in KCl 〈100〉 and KCl 〈110〉 crystals in the energy between 30 and 60 keV have been experimentally determined. The data fit an equation of the type, R = kEⁿ. The values of k and n exhibit crystalline orientation dependence.     

Franck-Condon factors and R-centroids for the BΣ → AΠ band system of CN

Franck-Condon factors and R-centroids for the transition from the B²Σ electronic state of CN to the A²Π state have been calculated. The validity of the Morse potential energy function for this system has been studied by using the calculated values of α_e. Also, the ratios 〈rⁿ〉/〈rⁿ⁻¹〉 have been obtained to check the applicabili ty of the R-centroid approximation.     

Characteristics of π−-meson multiplicity distributions in central collisions of12C and16O with nuclei at a momentum of 4.5 GeV/c per incident nucleon

Multiplicities of π^?-mesons from central collisions of¹²C and¹⁶O(4.5 GeV/c/n momentum) with several target nuclei were studied in a streamer chamber experiment. The parameter η=(〈n _? ² 〉?〈n_?〉²)/〈n_?〉 was determined for several samples of events characterized by different values of Θ _ch — the “vetoangle” for emission of the projectile charged fragments. The value of η is shown to decrease when the projectile mass number increases from 12 to 16 and to decrease significantly when Θ _ch increases from 0° to 4°, whereas it remains nearly constant when Θ _ch increases further to 14°. The results are compared with predictions of some theoretical models.     

Mass asymmetry dependence of angular distribution in237Np(α29 and 44 MeV,f): single particle effect

Angular distributions of fission products have been measured as a function of mass asymmetry in the odd-Z ²³⁷Np(α_{29 and 44 MeV},f) system using a recoil-catcher technique and off-line gamma spectrometry. Higher angular anisotropies were observed for the asymmetric mode products compared to the symmetric mode products at both energies. Average anisotropies for individual modes are lower than those for neighbouring even-even fissioning nucleus²⁴²Pu due to odd-nucleon spin effect. Present data have been analysed according to the transition state model assuming two modes of fission with characteristic saddle-shapes, barriers and multichance fission probabilities. It is seen that angular distributions for the symmetric and asymmetric modes are decided at and well past the corresponding saddle points respectively. Odd-nucleon spin contribution (〈k ²〉) to the tilting mode variance have been deduced. For (²⁴¹)Am fission, 〈k ²〉 values for the asymmetric and symmetric modes are ≤ 14 and > 14 ?² respectively. The 〈k ²〉 value averaged over several nuclei from preactinide (²⁰¹Ti) to actinide (²⁴⁸Cf) is 11.5 ± 4.2 ?². Average 〈k ²〉 value is in close agreement with the theoretical estimate.     

Remarks on the charged multiplicity of hadronic Z0(91) decays

The charged multiplicity distribution of hadronic decays of Z ⁰ from LEP and those of inclusive $e^{+}+e^{-}?ghtarrow h{?erline h} at E_{? cm}=14 {? to} 60 {? GeV}$ at E _cm = 14 to 61 GeV are analyzed using a Poisson-type distribution for photon statistics, due to Scully-Lamb. Its two parameters are expressed in terms of 〈n〉 and f ₂ = 〈n(n ? 1)〉 ? 〈n〉² of the data in order to perform no-free-parameter fits. It is found that f₂ behaves like $E_{? cm}^{a}$ with a = 2.01 ± 0.11, whereas C ₂ = 〈n ²〉/〈n〉² ～ E _cm with ΔC ₂/ΔE _cm = (1.81 ± 0.14)·10^?3.     

Study of the effective transverse momentum of partons in the proton using prompt photons in photoproduction at HERA

The photoproduction of prompt photons, together with an accompanying jet, has been measured with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb⁻¹. A study of the effective transverse momentum, 〈k_T〉, of partons in the proton, as modelled within the framework of the PYTHIA Monte Carlo, gives a value of 〈k_T〉=1.69±0.18^+0.18_−0.20 GeV for the γp centre-of-mass energy range 134<W<251 GeV. This result is in agreement with the previously observed trend in hadron–hadron scattering for 〈k_T〉 to rise with interaction energy.     

Excitation dynamics during the multiphoton absorption in SF6+buffer-gas mixtures

A detailed analysis of the total average number of absorbed photons 〈n〉_total during Infrared multiphoton absorption processes in mixtures of SF₆-Ar, N₂ and CH₄ buffer gases is presented. The results for 〈n〉_total are deduced using pulsed photoacoustic technique in collisional regime. Complete analysis is based on the theoretical generalized coupled two-level model (GCT) and its application to different gas mixtures. Evaluation of partial 〈n〉_coll. values is presented too, obtained using the results from time-resolved optoacoustic (TROA) and time-resolved absorption (TRA) methods for V-T relaxation times (τ_V-T) and the saturable absorber (SA) method for R,R-T relaxation times (τ_rot.-rel.), and applying them directly to the GCT model. All methods (TROA and SA) and the GCT model use the same photoacoustic results from our experiment under identical experimental conditions.     

Mössbaueruntersuchungen an195Pt und201Hg

Using the Mössbauer technique the magnetic hyperfine splitting of the 130 keV transition in¹⁹⁵Pt has been observed in a Pt-Fe alloy. The derived magnetic moment is μ₁₃₀=(0.81 _?0.25 ^+0.13 μ _k . Isomershift measurements with the 130 keV and the 99 keV transitions in alloys yielded Δ〈r ²〉₁₃₀/Δ〈r ²〉₉₉=1.5±0.2 for the ratio of the changes in the mean square charge radius of the two excited states. From isomershifts of the 99 keV transition in compounds an estimate of Δ〈r ²〉₉₉/〈r ²〉=?(1.6 _?0.9 ^+4.4 ) · 10^?4 is made for the change in radius of the first excited state. The linewidth of the Mössbauer spectrum of the 32.2 keV transition in²⁰¹Hg gives a lower limit of 0.1 ns for the half-life of the second excited state. The results are compared with values for other nuclides in this mass region.     

Ground state properties of CsCoCl3

The electronic spectra of CsCoCl₃ are fit to a Hamiltonian that includes terms for interelectron repulsion, octahedral and trigonal crystal fields, and spin-orbit coupling. The fit adequately accounts for both the optical spectrum and the electronic Raman spectrum. The fitted parameters give empirical estimates of the radial expectation values 〈r^?1〉 and 〈r^?3〉 as well as the charge on the cobalt. The ground state wave functions generated from the fit are used to calculate the following properties: parallel and perpendicular g factors, Co hyperfine field, ⁵⁹Co quadrupole splitting, anisotropy of magnetic exchange, the magnetic moment of Co²⁺, and the spin flop field. The agreement between calculated values and observed values for this variety of independently obtained properties is reasonable in all cases.     

Neutral-pion correlations. Test of production models

The observed increase of the average number of neutral pions, 〈n_o〉_n?, as a function of the number of charged pions produced in high-energy experiments, can be accounted for by several theoretical models. We analyze the basic trends of the models and find that in the region where 〈n_o〉_n? increases, the π⁰ multiplicity distribution is mainly determined by the isospin properties of the pion clusters and is insensitive to the overall multiplicity distribution. We calculate the values of f_2,n?⁰, the correlation parameter of two π⁰ for a given number of π^?, and show how its measurement can provide a clear test of the different production models.     

Transverse momentum in Drell-Yan processes

We study the transverse momentum distribution of muon pairs from Drell-Yan processes in QCD. In particular the dependence of 〈k_⊥²〉 on Q² is considered. QCD predicts an approximately linear rise of 〈k_⊥²〉 with S or Q² only at fixed τ = Q²/S. The slope as a function of τ is quantitatively studied for P$\text{P}$ and P-nucleus scattering. The most recent data showing a rather flat 〈k_⊥²〉 in Q² at fixed S are found to be consistent with QCD.     

New bounds for dilepton production from heavy neutral leptons

Bounds on 〈E_?ⁿ〉/〈E₊ⁿ〈, 〉E₊E_?〈/〉E₂²〈 and 〈E₊E_?〉/〈E₊〉〈E_?〉 are direved for the processes ν_μN → μ^?μ⁺(e⁺) + X and μN → μ^?μ⁺ + X if dileptons are mediated by a $\text{spin}\text{-}\text{1}\text{2}$ heavy neutral lepton L₀. The bounds are shown to be independent of the production mechanism and mass of L₀. Useful conditional bounds are obtained relating the bounded quantities, which give information about the structure of the weak current responsible for L₀ decay.     

Partial virial theorems for atomic-molecular systems

New virial relations for three-and four-particle atomic-molecular systems are proposed. Using operators of extension or squeezing of interparticle distances, it is shown that, for all pairs of j and k particles in S states of these systems, the following partial virial relations are valid: 〈2T _jk 〉+〈 V _jk 〉=0, where 〈V _jk 〉 is the average Coulomb interaction energy for a pair of particles and 〈T _jk 〉 is a part of the average kinetic energy of the system. There are three and six such relations for three-and four-particle systems, respectively. The conventional virial theorem (〈 2T〉+〈V〉=0) for the average total kinetic and potential energies of the system (〈 T〉 and 〈V〉, respectively) corresponds to the summation of partial virial relations over all pairs of particles. It is shown by an example of variational calculations of the helium atom ⁴He²⁺ e ^? e ^? and the helium muon-electron mesoatom ⁴He²⁺μ^? e ^? that partial virial relations are a highly sensitive indicator of the accuracy of wave functions.     

Uncorrelated-jet-model predictions for the multiplicity distribution of π− mesons produced in high-energy annihilations p¯p → pions

The uncorrelated jet model is used to obtain a grand partition function for the pions produced in the process $\overline{p}p$ → pions. The grand partition function is evaluated asymptotically for large energies. It is used to relate the correlation parameter f₂ = 〈n_?²〉 ? 〈n_?〉² ? 〈n_?〉 to the average multiplicity of negative pions 〈n_?〉. The results are consistent with the presently available experimental data, though data at higher energies are necessary to draw physically interesting conclusions.     

π0 Multiplicities in π+;p interactions at 10.5 GeVc

Measurement of the π⁰ multiplicity cross sections are reported for n₀ ? 6, where n⁰ is the number of produced π⁰ particles, and for N ? 8, where N is the number of charged particles. The inclusive π⁰ cross section is 29 ± 3 mb. Values for the correlation parameters, 〈n₀〉 and 〈n₀(n₀ ? 1)〉², are also presented.     

General features ofK + d interactions at 70 GeV/c

We have studied 70 GeV/cK ⁺ d interactions from about 10 K events. The inelastic cross-section for three or more prongs is found to be (28.9±0.4) mb. From odd-and even-prong topologies we have extracted topological break-up ofK ⁺ n interactions by taking into account spectator corrections, rescattering effects and Glauber screening. The rescattering fraction is found to be 0.06±0.01 which is substantially different from pion and proton interactions. Combining ourK ⁺ n data with other existing π^± n andp ^±n we find〈n _ch 〉 ^ph ?〈n _ch 〉 ^hn =0.33±0.04 andD/〈n _ch 〉=0.529±0.003.