Autoionization cross section of potassium atom excited by electron impact

The autoionization cross section of potassium atoms excited by electron impact is measured in the energy range from the first autoionization threshold at 18.72 eV to 202 eV. The data are obtained by deter-mining the total intensity of electron spectra resulting from the decay of the 3p ⁵ n ₁ l ₁ n ₂ l ₂ autoionizing states. The cross section has two maxima, 1.8 × 10^?16 and 2.2 × 10^?16 cm², at 21 and 32 eV, respectively. The excitation dynamics of autoionization states suggests that the first maximum is associated with the resonance character of the near-threshold excitation. The second maximum, as well as the behavior of the cross section at energies above 50 eV, reflects the dynamics of electron excitation of quartet and doublet autoionizing states. The measured autoionization cross section is compared with known data for the total single ionization cross section of potassium atom by electron impact. The relative contribution of the autoionization cross section to the total single ionization cross section is found to reach 30% at 32 eV.     

The energy dependence of nuclear reaction cross sections

The reaction cross section σ_R^pA(E) for proton-nucleus collisions varies with energy as the total cross section σ_t^pN(E) does for proton-nucleon scattering in the energy regime 100 MeV ? E ?400 GeV. We propose several empirical relations, and test them by a χ² analysis of various data. Within the framework of Glauber theory, the parameters in the relations can be linked to the cross section for a single inelastic collision.     

The nonelastic projectile break-up cross section from particle-gamma coincidence measurements for the 6li + 40ca reaction at 156 mev

The cross sections for nonelastic break-up modes have been studied for the ⁶Li + ⁴⁰Ca reaction at E_Li = 156 MeV. Gamma-ray spectra from target-like residual nuclei were measured in coinci- dence with beam-velocity projectile fragments and a value for the nonelastic break-up cross section σ^b.u_non = 582 ± 110 mb has been found. Together with results of inclusive charged-particle measure- ments we infer for the total break-up cross section σ^b.u_tot = 930 ± 115 mb comprising about 50% of the total reaction cross section. The nonelastic contribution of the break-up reaction appears to be less than predicted by the DWBA break-up theory. This result is directly evident from the differential cross sections by comparing inclusive and exclusive results.     

Schwingungsanregung von H2-Molekülen durch Zentralstoß mit Li+-Ionen

An apparatus is described for measuring the inelastic differential cross section for vibrational excitation in collisions of diatomic molecules with monoenergetic ions at laboratory energies between 10 and 50 eV. The method consists of measuring the time of flight of single ions with a time amplitude converter and displaying the results on a 100 channel pulse height analyzer. From the shift in the time of flight relative to that expected for elastic scattering the final state of the molecule excited in a single collision is identified. By studying only central collisions with almost zero impact parameter rotational excitation is strongly suppressed. Measured times of flight after collisions of monoenergetic Li⁺ ions with H₂ show that with increasing energy the most probable vibrational quantum jump increases from 0→1 to 0→2,0→3 etc. Contrary to the usual assumption of a small steric factor for vibrational excitation the results show that the inelastic cross section is larger than the elastic cross section. Using reported potential parameters the energy dependence of the most probable excited state is compared with the calculations of Secrest and Johnson for a one-dimensional collinear collision. The satisfactory agreement suggests that the steric factor is close to 1. From measurements at different scattering angles at 10 eV the integral inelastic cross section is found to be about 0.2 Ų corresponding to a differential cross section of 0.4 Ų/sr. Measured values of integral and differential total cross sections for Li⁺-He andLi⁺-H₂ are reported and compared with theory. Direct dissociation of D₂ by Li⁺ in the energy range from 25 to 55 eV was not observed, yielding an upper limit for the cross section of 4 · 10^?4 Ų/sr.     

Absorption of massless scalar wave from Schwarzschild black hole surrounded by quintessence

By using the partial wave method, we investigate the absorption of massless scalar wave from Schwarzschild black hole surrounded by the quintessence. We obtained the expression of absorption cross section
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Then we numerically carry out the absorption cross section and we find that the larger angular momentum quantum number l is, the smaller the corresponding maximum value of partial absorption cross section is, and that the total absorption cross section tends to geometric-optical limit σ_abs^hf≈ π b_c². We also find that higher value of ω_q (state parameter of the quintessence) corresponds the higher value of absorption cross section σ_abs.     

Cross section of the reaction 6Li(p, γ)7Be

The cross section of the reaction ⁶Li(p, γ)⁷Be has been measured using Ge(Li) γ-ray spectrometers for proton bombarding energies E_p from 200 keV to 1200 keV. At E_p = 800 keV, the total (p, γ) integrated cross section is found to be 3.1 ± 0.4 μb. The cross section adopted from consideration of this and previous measurements is in good agreement with that predicted from the known thermal neutron cross section for ⁶Li(n, γ)⁷Li on the assumption that properties of mirror direct capture reactions can be well described by optical potentials that use the same parmeter values for the two reactions.     

Three-body calculation of neutron-deuteron elastic scattering in the energy region from 2.5 MeV up to 50 MeV

The three-body Faddeev equations for neutron-deuteron scattering are solved in the energy region from 2.5 MeV to 50 MeV of the incident neutron energy with small energy steps. Higher-rank separable potentials are used in the¹ s ₀ wave and in the³ s ₁—³ d ₁ waves, while rank-1 separable potentials are used in¹ p ₁,³ p _0,1,2 ¹ d ₂ ³ d _2,3 waves. The calculation is compared with experiments for the total cross section, the total break-up cross section, the differential cross section and the analyzing power of neutron-deuteron scattering. The improvements in the agreement as compared to previous calculations are impressive in many cases. Especially, the calculated total cross section agrees with the experiment below 30 MeV within the error bars, which are as small as 1%. A discussion on the numerical accuracy is given. General aspects of the calculated cross section are discussed. It is pointed out that thes-wave asymptotic normalization of the deuteron wave function (A _s ) is important.     

Formation of higher-order fullerene dianions in collisions with Na atoms

We have measured electron capture cross sections in collisions between higher order fullerene anions C_n ^- (n=76, 78, 82, 84, 86, 90 and 96) and Na atoms. The ions were produced in an electrospray ion source (ESI) and accelerated to an energy of 50 keV. The measured cross section for dianion formation is three times larger for C₉₆ than that for C₆₀. The latter cross section was earlier found to be 36 ?². The dramatic increase of the cross section with fullerene size is explained by means of the curve crossing model for electron transfer.     

Charge exchange cross sections for He+ incident on Cs

The total charge-exchange cross section, σ₊₀, for He⁺ incident on Cs vapor has been measured in the energy range 0.5 to 41 keV. The cross section falls from (1664 ± 100) × 10^?17 cm² at 1.4 keV to (224 ± 20) × 10^-17 cm² at 41 keV. These measurements are compared with previous measurements and with theoretical calculations of this cross section.     

Direct Measurement of 12C?+?4 He Fusion Cross Section Near Stellar energy

The reaction ¹²C?+?⁴He ?? ¹⁶O?+??? at E _cm?= 0.3?MeV plays an important role in stellar evolution, but the reaction cross section has not been measured yet. Recently we succeeded to measure total cross section of the reaction down to E _cm?= 1.5?MeV at Kyushu University. We have a plan to measure the cross section down to 0.7?MeV in several years, and to extrapolate the results to 0.3?MeV.     

A reassessment of the O(αs2) three-jet cross section for e+e− annihilation

Results of a new evaluation of the O(α_s²) dressed three-jet cross section for e⁺e^? annihilation are summarized. For vanishing cutoffs, the different results in published three-jet cross section formulae are due to differing definitions of resolvable four-jet events. Subleading terms which were ignored in previous calculations are evaluated and found to be sizeable in the phase space region where three-jet events become more two-jet-like. A simple calculation demonstrates that α_s values determined according to the three-jet cross section formulae of Gutbrod, Kramer and Schierholz are systematically too large.     

Direct and resonant capture observed in the 3H(τ,γ)6 Li reaction

A direct capture model is used to calculate the ³H(τ, γ)⁶ Li cross section. The result for the ground-state cross section is in very good agreement with the data. The calculation for the cross section for the first excited state is in good agreement with the shape and angular dependence of the measured cross section at lower energies. Above E_τ=10 MeV a large discrepancy indicates a non-direct contribution. This is interpreted as a resonance in the compound nucleus ⁶Li with a configuration other than ${}^3\text{He}\text{+}{}^3\text{H}$.     

A new optical method of measuring electron impact excitation cross section of atoms: Cross section of the metastable 6s6p P0 level of Hg

We report a new method that is potentially applicable to the measurement of electron impact excitation cross section of any atoms. Measurement of the cross section of the metastable 6s6p ³P₀ level of mercury is conducted to demonstrate the method, which involves using cavity ringdown spectroscopy to determine the absolute number density of mercury atoms in the 6s6p ³P₀ energy level. The measured cross section is 1.7×¹⁰−17 cm² and in agreement with the literature values. Compared with the optical methods that have been used during the last three decades, this new approach not only serves as an alternative optical method, but also is applicable to the atoms under both high and low pressure conditions.     

The photoproton reaction of 25Mg

The proton yields from the ²⁵Mg(e, p) reaction have been measured for E_p > 3 MeV, at θ = 90°, using an enriched ²⁵Mg sample in the electron energy range 15–28 MeV. Partial photoproton cross sections to the ground and excited states in ²⁴Na have been deduced and a lower limit is placed on the ²⁵Mg(γ, np) cross section. The derived photoproton cross section combined with existing photoneutron data allows the ²⁵Mg absorption cross section to be estimated. Configuration splitting of the ²⁵Mg GDR is confirmed, and the effects of isospin splitting are considered.     

The reactions of 12C with 12C AT 293 MeV

Energy spectra, angular distributions, and elemental yield distributions have been measured for products Z = 1?9 produced in the reactions of ¹²C on ¹²C. A total reaction cross section 1170_?100⁺¹⁷⁰ mb was determined from the measured elemental cross sections and the principle of charge conservation. This total reaction cross section is about 250 mb less than the geometric cross section and agrees with the Glauber-model calculations of DeVries and Peng. The experimental energy spectra, angular distributions, and yield distributions were compared with those from model calculations for the statistical decay of the products of fusion and of incomplete fusion reactions. For both types of calculations, a modified version of the code LILITA was used. By comparing the data to model calculations, an upper limit of 75 mb for the fusion cross section was determined. That limit corresponds to an upper limit of L_crit for fusion of 10? in the sharp-cutoff approximation. The dominant reaction mechanisms appear to be incomplete fusion processes.     

Fragmentation of the total cross section in the reaction16O+208Pb

The fragmentation of the total reaction cross section was investigated for¹⁶O +²⁰⁸Pb atE _c.m.=84 MeV andE _c.m.=92 MeV. Total cross sections for the inelastic, transfer and fission channels were measured. The sum of the inelastic and transfer channels accounts for 30% of the total reaction cross section; the residual strength is found in a compoundfission process.     

The holographic bubble chamber experiment and the determination of the effective charmed quark mass and theK-factor for hadronic charm production

In the first holographic bubble chamber experiment — the HOBC experiment — we have accumulated a total of 40000 holograms with particle interactions. We have determined the total charm pair cross section inpN collisions to be 23.3 _?7.7 ⁺¹⁰ μb and 3.6 _?1.7 ^+2.3 μb for 360 and 200 GeV/c incident protons respectively. We have assumed a linear dependence of the cross section on the atomic number of the target. This experiment has demonstrated the feasibility of holographic recording in small bubble chambers. Assuming that the charm cross section can be described by the standard QCD factorized expression with gluon fusion and quark-antiquark annihilation, we have used our measured charm cross sections with other measurements to determine the effective charmed quark mass to be 1.8 _?0.35 ^+0.25 GeV/c². TheK factor, which describes the importance of the higher order corrections, is calculated to be 9.8 _?6.9 ^+12.5 (See noted added in proof.)     

A reassessment of the O(αs) three-jet cross section for ee annihilation

Results of a new evaluation of the O(α_s²) dressed three-jet cross section for e⁺e⁻ annihilation are summarized. For vanishing cutoffs, the different results in published three-jet cross section formulae are due to differing definitions of resolvable four-jet events. Subleading terms which were ignored in previous calculations are evaluated and found to be sizeable in the phase space region where three-jet events become more two-jet-like. A simple calculation demonstrates that α_s values determined according to the three-jet cross section formulae of Gutbrod, Kramer and Schierholz are systematically too large.     

Evidence for multiple states of hydrogen on palladium

Adsorption of hydrogen on polycrystalline palladium has been investigated using ESD techniques. Although a single thermal desorption peak is observed for H₂ and Pd, total ESD cross section measurements suggest the existence of four distinct sources for desorbing H⁺ and H^? species. The very large cross section associated with the H^? signal along with its behavior during sample heating suggests the possible existence of a molecular precursor state.     

Giant resonances of endohedral atoms

It is demonstrated for the first time that the effect of a fullerene shell on the photoionization of a “caged” atom in an endohedral can result in the formation of giant endohedral resonances or GER. This is illustrated by the concrete case of the Xe@C₆₀ photoionization cross section that, at 17 eV, exhibits a powerful resonance with total oscillator strengths of about 25. The prominent modification of the 5p ⁶ electron photoionization cross section of Xe@C₆₀ takes place due to the strong fullerene shell polarization under the action of the incoming electromagnetic wave and the oscillation of this cross section due to the reflection of the photoelectron from Xe by the C₆₀. These two factors transform the smoothly decreasing 5p ⁶ cross section of Xe into a rather complex curve with a powerful maximum for Xe@C₆₀, with the oscillator strength of it being equal to 25. We also present the results for the dipole angular anisotropy parameter that is strongly affected by the reflection of the photoelectron waves, but not modified by C₆₀ polarization. The text was submitted by the authors in English.