Population Of Final States Research Articles

Selective Final-State Population in Electron Capture by Low-Energy Highly Charged Projectiles Studied by Energy-Gain Spectroscopy

Energy-gain spectra and total cross sections have been measured for projectiles of 492-eV ${\mathrm{Ne}}^{+10}$ and 443-eV ${\mathrm{Ne}}^{+9}$ capturing electrons from rare-gas targets. For each collision system a single, or at most two, principal quantum numbers on the projectile are found to be populated. The effective electron-transfer probabilities are found to be quite dependent upon the collision system.

Satellite structure in the argon 2s photoelectron spectrum

The argon 2s photoelectron satellite spectrum has been calculated for high incident photon energy using correlated final ion state wavefunctions determined with a configuration interaction technique. The contributions to the lower kinetic energy satellite structure, which are predicted to amount to 10.3% of the main line intensity, correspond to the population of (2s3p)np and (2s3s)ns final states. Satellites with a total intensity of 1.4% relative to the main line are also predicted to occur at higher kinetic energy, corresponding to the population of mainly (2p3p)nd and (2p3s)np final states. The theoretical findings are compared with the available experimental data.

Photoemission from the f 12 and f 13 configurations

It is shown that fractional parentage coefficients calculated in intermediate coupling provide a quantitative representation of the final-state population produced by photoemission from 4f 13. Calculations in LS coupling show significant deviations for both 4f 12 and 4f 13.

16O, 24, 26Mg, 28Si, 32S, 40Ca(α, 12C) and multi-α-cluster transfer reactions

The (α, 12C) reaction has been studied on a variety of nuclei, A = 16 to 40, at E α = 90.3 MeV. The data indicate a rapid fall-off of cross sections with increasing target mass, approximately as A t −5 ± 1. This and other systematics are used to estimate cross sections for multi-α-cluster transfer reactions in heavy nuclei and suggest σ T < 10 −34 cm 2 consistent with present experimental limits. The data for 24Mg(α, 12C) 16O has been studied in more detail and indicates a selective population of final states including 16O g.s., with oscillatory angular distributions in some instances. Finite-range distorted-wave Born approximation calculations for direct 8Be pickup have been performed utilizing cluster overlap amplitudes obtained with zero-order SU(3) wave functions. The calculations are in qualitative, and often quantitative, agreement with shapes and absolute magnitudes of the measured angular distributions although the cross sections for certain α-cluster states (2 +, E x ≈ 7 MeV; 4 +, E x ≈ 10.3 MeV) are greatly overestimated with this model. Other more complicated mechanisms, such as successive α-transfer, cannot be excluded. The systematics of the calculated 8Be cluster overlaps and the calculated and measured (α, 12C) cross sections are investigated, and implications for multi-α-cluster transfer reactions are discussed.

Total and partial cross sections for charge transfer in collisions of multicharged ions with atomic hydrogen

The total cross sections for charge transfer in ${\mathrm{Ne}}^{10+}$ + H, ${\mathrm{Si}}^{14+}$ + H, and ${\mathrm{Ca}}^{20+}$ + H collisions are calculated for ion impact energies of 0.025-2000, 0.025-5000, and 0.1-10 keV/amu, respectively, by means of a unitarized-distorted-wave-approximation method. A scaling rule is derived from the results to predict cross section data. The partial cross sections for electron transfer into the individual orbitals around the projectiles are also investigated. The results show that the most probable principal quantum number of the final state is almost independent to impact energy below 100 keV/amu, while with increasing impact energy above 100 keV/amu it decreases considerably. The strong effects of level crossing and momentum transfer are confirmed to appear in the distributions of final-state population over angular momentum quantum number.

Multipolarities of γ-rays from 92, 94Nb and 94,95,96,97,98Tc

92, 94Nb and 94, 96, 98Tc have been produced by the (p, n) reaction at proton energies on and near the d 5 2 isobaric analog resonance. 95,97Tc have been produced by the (p, γ) reaction below the (p, n) threshold. Internal conversion electrons due to the decay of their excited states were detected on-line with a mini-orange spectrometer which is optimized for the energy range 50 to 500 keV. Gamma rays from these nuclei were detected with a thin Ge(Li) detector. Isomeric-delayed internal conversion electrons and γ-rays were observed, using a nanosecond-pulsed beam. The internal conversion coefficients for 55 transitions in these nuclei have been determined and their multipolarities deduced. The multipolarity of the transitions in these nuclei is predominantly M1. Negative parities have been assigned through use of the d 5 2 isobaric analog resonance enhancements of the population of negative-parity final states. The systematic behavior of the 2 −, 3 − doublet and of the g 9 2 ⊗ d 5 2 multiplet in these nuclei is discussed.

Systematic trends in the inelastic cross sections and form factors for nl→n'l' direct collisional transitions

Certain theoretical predictions are presented for the preferential population of final states with angular momentum l' in collisions involving an initially excited atom. Varying l', the authors find that the maxima of both the inelastic form factors and cross sections for the nl to n'l' transitions in hydrogen, induced by collision with electrons and heavy particles, in general oscillate on a background which rises as l' is increased, until they both attain a pronounced peak at a unique value l'max which is strongly dependent on only the initial principal quantum number n and which is fairly insensitive to changes in l and n'. An expression for l'max is derived. For l'>l'max, the form factors and associated cross sections exhibit a dramatic decline, resulting in negligible population of those states. The predictions differ from those suggested by the Bethe high-energy asymptotic limit which favours dipole transitions, and assume significance in situations where excited states are important.

(α,He2) Reaction as a Spectroscopic Tool for Investigating High-Spin States

A $^{2}\mathrm{He}$ detection system has been developed and used to investigate the ($\ensuremath{\alpha},^{2}\mathrm{He}$) reaction at 65 MeV on $^{12}\mathrm{C}$, $^{13}\mathrm{C}$, and $^{16}\mathrm{O}$ targets. Extreme spectroscopic selectivity with preferential population of final states with ${({d}_{\frac{5}{2}})}_{{4}^{+}}^{2}$ character was observed. Applications of this experimental technique to the detection of other unbound reaction products are proposed.

The study of (d, t) and (d, 3He) reactions in several 1p shell nuclei using vector-polarized beams

Cross-section and vector analyzing power angular distributions using 15 MeV deuterons were taken over an angular range of θ 1ab = 20–100° for the 10B(d, t) 9B g.s.and 2.36 Mev state, 10B(d, 3He) 9Be g.s. and 2.43 Mev state, 13C(d, t) 12C g.s., 14N(d, t) 13N g.s., and 14N(d, 3He) 13C g.s. reactions, and vector analyzing power data alone were taken for the 16O(d, t) 15O g.s. and 16O(d, 3He) 15N g.s. reactions. Beams of vector-polarized deuterons were used for the vector analyzing power determinations. A comparison is made of the results for (d, t) and (d, 3He) reactions leading to mirror states when the self-conjugate targets 10B and 14N are used. The reactions provide evidence for a j-dependence of the vector analyzing power for l = 1 transfers in 1p shell nuclei. When the reactions involve a j-value admixture, the vector analyzing powers are used to attempt to determine percentage admixtures involved in the population of several final states.

Secondary-electron emission spectroscopy and the observation of high-energy excited states in graphite: Theory and experiment

Fine structure in the energy distribution of secondary electrons back-scattered from a graphite crystal surface is resolved and shown to be consequence of inelastic electron-electron scattering in which the dominant process is the population of final states above the vacuum level by electron-hole pair production via screened-Coulombic interaction between the incident primary electrons and the valence electrons in the solid. The scattering theory of Kane is applicable and emphasizes that features due to one-electron density of final states should be resolvable in experimental secondary-electron-emission spectra of crystals. Experimental results are presented, which provide strong support for this view. Previous measurements on graphite have been extended and weak secondary-electron-emission structure, resolved in the second derivative of the energy-distribution spectrum, is reported for kinetic energies, $10\ensuremath{\lesssim}{E}_{\mathrm{kin}}\ensuremath{\lesssim}40$ eV. Maxima are observed at 16.2, 22.2, 29.2, 31.2, 36.2, and 40.7 \ifmmode\pm\else\textpm\fi{} 0.5 eV above the Fermi energy. Details are presented of a first-principles high-energy band-structure calculation of graphite extending over a 80-eV energy range. The observed spectral features correlate closely with final-density-of-states maxima as predicted by the theory.

Photodisintegration of 13C

The nucleon decay of the photoresonance in 13C is analyzed using bound-state shell model and R-matrix theory. Total and partial photo cross sections, branching ratios, final state population, and nucleon emission spectra are considered and compared with available data.

An Interpretation of De-excitation Gamma Ray Measurements Following the Photodisintegration of 12C, 16O, and 40Ca

The relative populations of final states in photonuclear reactions for 12C, 160, and 40Ca are examined in the light of information on the known major configurations present in the wavefunctions of those final states, with the assumption that the nucleon excited in the radiation absorption process is in fact the one emitted. This assumption is investigated and found to be reasonable for 12C and 160 but not for 40Ca. The data on relative populations of final states are interpreted to give information on the relative strengths of configurations in the wavefunctions of the ground states of the three nuclei.

Four-nucleon transfer reaction induced by 10B on 12C

Abstract The four-nucleon transfer reaction induced by 10 B on 12 C has been studied above the Coulomb barrier. The population of final states of 16 O is less selective than in other four-nucleon transfer reactions induced by 6 Li, 7 Li, or 16 O. This fact as well as the structureless angular distributions can be explained by the complexity of the structure of the ground state of 10 B, which has large components with a lower degree of symmetry than the α-particle.