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.     

The mechanism of the 7Li(d, 2α)n reaction from Ed = 3 to 15 MeV

The ⁷Li(d, 2α)n reaction proceeds almost entirely through excitation and sequential decay of the 16.63 and 16.92 MeV levels in ⁸Be, for incident energies 1 to 13 MeV above their threshold. The energy dependence for forming these levels with the neutron emitted at 0° is approximately that predicted assuming the neutron is a spectator from the incident deuteron. None of the individual spectra, the angular dependence of the cross section at fixed E_d, or the bombarding-energy-dependence of the cross section for forming the levels is consistent with the involvement of a spectator neutron from the ⁷Li target.     

Direct pair production by positive and negative electrons in a hydrogen bubble chamber

The production of electron pairs by negative and positive electrons in the energy region 0.65 – 5.8 GeV has been investigated in the DESY 81-cm hydrogen bubble chamber. The effective cross section σ = 0.62 ± 0.04 mb averaged over the energy spectrum of incident electrons is found to be in good agreement with the predictions of quantum electrodynamics. The energy distribution of created pairs as well as the dependence of the total cross section on energy are best represented by the expression of Murota, Ueda and Tanaka with the constant c = 0.66 ± _0.17^0.24 and by Bhabhá's formula with the constants c₁ = 1 and c₂ = 2.8 ± _0.7^0.9. The contribution of the interference term between space-like and time-like Feynman diagrams to the cross section is estimated to be less than about 10% and to fall off with an increase of the incident energy.     

Comparison between bremsstrahlung cross section measurements at the short wavelenght limit and theoretical results

Recent precise measurements of the electron bremsstrahlung cross section d²σ/dk dΩ_k at the short wavelength limit for an incident electron energy of 1.84 MeV important discrepancies between experimental results and earlier theoretical calculations. A new exact theoretical result, for a point Coulomb potential is presented: descrepancies with experimental results remain.     

Induced decay of positronium and grasers

The differential cross section and the total cross section for the stimulated decay of positronium by an incident photon of frequencyΩ is calculated as a function of the dimensionless variableξ=hΩ/mc ². Forξ?1 the total cross section is found to decrease asξ ^?2. We also look at the particular case of positronium in a black-body radiation field. Expressions for the number of induced annihilations per second as functions of the dimensionless ratiomc ²/kT and the number of positronium atoms are obtained. It is found that this rate is proportional to (kT/mc ²)² forkT?mc ² and to (kT/mc ²)ln(kT/mc ²) forkT?mc ². The possibility of utilizing induced two-photon decay of positronium as a γ-ray laser at the wavelength λ _C /2 is examined, where λ _C is the Compton wavelength.     

A comparison of the production of K (890) in Kp and Kp interactions

Results are presented on an analysis of the reaction K⁺p → K^∗+ (890) p at 16 GeV/c and compared with data at lower incident momenta and with corresponding results for the reaction K⁻p → K^∗− (890) p. It is found for both reactions that the energy dependence of the cross section exhibits a simple (p⁻ⁿ_lab behaviour.     

Production of high transverse momentum prompt photons and neutral pions in proton-proton interactions at 280 GeV/c

The inclusive cross sections for production of prompt photons and π⁰ s by 280 GeV/c protons incident on a liquid hydrogen target, have been measured forp _T in the range 4.0 to 6.5 GeV/c and for |x _F |<0.45. A quantitative comparison of the prompt photon cross section with next-to-leading order QCD predictions using Duke and Owens structure functions is performed. Phenomenological fits to the π⁰ and prompt photon cross sections are given.     

Measurement of the inclusive charged-current cross section for neutrino and antineutrino scattering on isoscalar nucleons

This paper reports on measurements of the total cross section for the inclusive reaction v_μ+N , as a function of incident energy. Neutrinos and antineutrinos with energy in the range 30–300 GeV were produced in the 1982 Fermilab narrow-band neutrino beamline. A total of 35 000 neutrino and 7000 antineutrino interactions were recorded in the CCFR detector located in LabE. The incident neutrino flux was determined by methods similar to those used in previous experiments. The rate of increase with energy of the total cross section (σ/E _v) in the range 30 to 75 GeV was determined to be 0.659±0.005(stat)±0.039(syst)×10^?38 cm²/GeV and 0.307±0.008(stat)±0.020(syst)×10^?38 cm²/GeV for incident neutrinos and antineutrinos, respectively. The 5.9% systematic errors are due primarily to uncertainties in the flux intensity measurement. The energy dependence of the cross section in the regionE _ν=100–300 GeV was found to be linear, as determined by relative normalization techniques. A weighted average of our previous and present measurement for the total ν-N cross section yields: $$\begin{gathered} \sigma (vN) = 0.666 \pm 0.020(statistical \hfill \\ + systematic)E_v 10^{ - 38} cm^2 ; \hfill \\ \sigma (\bar vN) = 0.324 \pm 0.014(statistical \hfill \\ + systematic)E_v 10^{ - 38} cm^2 ; \hfill \\ \end{gathered} $$ .     

Analyzing power fluctuations in nuclear reactions

The joint analysis of differential analyzing power (AP) and differential cross section in the nuclear reactions of +J ₁→J ₂ +J ₃ type in the region of strongly overlapping resonances are presented. Consideration is valid in the absence of the channel-channel compound nuclear correlations. The fluctuations of AP and cross section are proved to be statistically correlated, the greater the direct contribution to the reaction cross section the stronger this correlation. For the purely statistical reactions the correlation is absent. It is shown that the joint investigation of the AP and cross section fluctuations gives possibility to extract the direct reaction AP and the separate the direct and compound nucleus contributions into the reaction cross section. In particular it can be done by means of the statistical correlation (SC) analysis. Furthermore, the SC analysis may serve as a test for revealing the intermediate structure involved in the reaction. Finally, the joint study of differential AP and differential cross section may be used to determine the spins of nuclear levels and polarization of incident beam. The results are employed to separate the compound and direct contributions in the inelastic scattering of polarized protons on²⁸Si. Comparison with experiment quantitatively supports the existence of the SC between the fluctuations of AP and cross section. Possible extension of the SC analysis to the case of the presence of channel-channel compound nuclear correlations are discussed.     

Heavy ion induced transfer reactions on 148Nd

Transfer reactions induced by ¹⁶O and ¹⁸O beams on ¹⁴⁸Nd were measured with a time-of-flight setup at 72 MeV incident energy. The angular distributions are bell shapes having their maxima at angles somewhat below the grazing angle. The excitation in the final nuclei takes place (if possible) near the optimum Q-value and is spread over 5 MeV for the one-particle transfer reactions and up to 10 MeV for the multiparticle transfers. The cross sections for the individual channels are explained mostly by Q-window considerations. In spite of the differences in the individual channels the total transfer cross section integrated over excitation energy, angle, and all channels turns out to be the same same for both ¹⁶O and ¹⁸O beams. This cross section amounts to 20 % of the total reaction cross section and nicely fills the gap between the measured fusion cross section and the total reaction cross section obtained from optical model calculations based on elastic scattering data.     

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.     

Direct and compound nuclear contributions to the 13C(6Li,t) reaction at Elab = 25 MeV

The reaction ¹³C(⁶Li, t)¹⁶O has been studied in the incident energy range 24–26 MeV. Complete angular distributions have been measured at E_⁶Li, = 25 MeV in the angular range θ_lab = 8°–172°, with the reaction ⁶Li(¹³C, t)⁶O being used for the backward angle measurements. Cross sections for evaporation residues from the fusion of the ⁶Li + ¹³C system have been measured in the incident ⁶Li energy range 9.2–35.1 MeV. Compound nuclear contributions to the transfer cross sections have been calculated using the Hauser-Feshbach statistical theory with the assumption that the compound-nucleus formation cross section is equal to the measured fusion cross section. By comparison of the compound nuclear calculations with backward angle data it is found that the sharp cutoff approximation commonly used to represent the initial angular momentum distribution of the compound nucleus is not adequate for the ¹³C(⁶Li, t)¹⁶O reaction. Good fits to the backward angle data can be obtained by using a smooth cutoff approximation. The forward angle cross sections have been compared with exact finite-range distorted-wave Born approximation calculations to extract transferred angular momenta and spectroscopic strengths. The present results differ from those of an earlier study. These differences are due to the inclusion of forward angle data in the present study.     

One-neutron transfer contribution to the elastic 32 S+ 32S scattering at Einc = 91.3 MeV

The elastic scattering differential cross section for ³²S incident on ³³S at E_inc = 91.3 MeV has been measured. The observed backward oscillations are successfully described by explicit inclusion of a parity-dependent term in the real potential for the optical-model calculations of the elastic scattering. To investigate possible sources of the parity-dependent term, the backward oscillations were also interpreted as being produced by the interference between the elastic amplitude and the one-neutron elastic one-step transfer process.     

Nucleon transfer reactions to rotational states induced by206, 208Pb projectiles

In a systematic study of nucleon transfer reactions accompanied by Coulomb excitation we have bombarded¹⁵²Sm,¹⁶⁰Gd and²³²Th with^{206, 208}pb beams at incident energies close to the Coulomb barrier. Particle-gamma coincidence techniques were used to identify excited states of reaction products populated through inelastic scattering and in nucleon transfer reactions. One-neutron stripping and pick-up reactions on¹⁵²Sm were observed leading to known states of the rotation alignedi _13/2-bands in¹⁵³Sm and¹⁵¹Sm. In the¹⁶⁰Gd+^{206, 208}Pb systems no significant population of low lying states of product nuclei was found in the nucleon-transfer channels. Large cross sections were observed for one- and two-neutron pick-up from²³²Th at an incident energy of 6.4 MeV/u. Around the grazing angle they are of the same order of magnitude as the cross section measured for inelastic scattering. The results are analyzed in the framework of semiclassical models.     

Estimate ofd′- production in protonproton collisions

An estimate of the cross section for the production of a narrow isosinglet 0^?-dibaryon (d′) resonance inpp-collisions is given. This cross section is shown to be in the range of a fewμb at incident energies close to threshold. The resonance parameters used are those obtained from a recent analysis of pionic double charge exchange data which at low pion energies clearly exhibit features in accordance with the existence ofd′.     

Universality of the rate of growth of all hadron-nucleon total cross sections in the range 10 to 1500 GeV/c

The energy dependence of total cross section of hadron-nucleon collisions has been studied in terms of two components: the first component decreases with increasing energy of the incident hadron whereas the second component increases like ln s. The coefficient of ln s is found to be the same within 5% for p^±p, π^±p and K^±p collisions. The rate of growth of the rising component i.e., dσ /d(ln,s), of inelastic cross sections, deduced from σ_tot and σ_el, of pp and πp are found to be the same within 1.5 standard deviations; an attempt has been made to understand this near equality from factorization of the pomeron.     

Absolute cross sections of electron attachment to molecular clusters: Part I. Formation of (CO2) N −

A procedure of determining absolute cross section σ^? of electron attachment to (CO₂)_N clusters at pair collisions in crossed beams is suggested. The cross section is measured as a function of energy (E = 0.1–50 eV) and of cluster mean size N in a beam $(\bar N = 2 - 4000 molecules)$ . It is found that, even at $\bar N > 200$ and E ≤ 3 eV, σ^? is equal to, or larger than, 7 × 10^?13 cm², i.e., by more than one order of magnitude exceeds the maximal cross section of CO₂ ionization by electron impact. The dependences σ^? $(\bar N,E)$ have two wide continua at E ≤ 5.2 eV and E ≥ 6.9 eV, which correlate well with known functions of CO₂ electron-impact-induced excitation. These continua are attributed largely to formation of (CO₂) _N ^? ions during electron thermalization and solvation in the clusters. At E → 0, the polarization capture of an incident electron by the cluster leads to a sharp increase in cross section σ^?(E). From the dependences σ^? $(\bar N,E)$ measured, the thermalization and sovation probabilities for electrons with E ≤ 0.8 eV and the rate of electron energy loss in the cluster are found.     

The differential cross section and polarization quantities in the 4He(d,p)n4He and 2H(α, n)p4He reactions

The differential cross section and the polarization quantities (T₁₁, T₂₀, T₂₁, T₂₂, P_γ') in the deuteron breakup reaction by an α-particle are calculated in the framework of the recently developed three-body model. All values are discussed under the incomplete kinematical condition. All polarization quantities are caused by the difference of the potential between $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ waves of the N-α interaction. Results of the calculation are compared with the available measurement of (i) the differential cross section and the deuteron vector analysing power in the ⁴He($\text{d}$, p)n⁴He reaction and (ii) the differential cross section and neutron polarization in the ²H(α, $\text{n}$)p⁴He reaction. The agreement with experiment is very satisfactory in each case. Among the tensor analysing powers of the deuteron the absolute value of T₂₀ is very large. Observables at the FSI peak corresponding to ⁵He_g.s. are discussed systematically in the energy region of 5.4–20 MeV of the incident deuteron in the ⁴He(d, p)n⁴He reaction. Although the differential cross section is not sensitive to the energy of the three-body resonance, the polarization quantities T₁₁, T₂₀, P_γ' are quite sensitive to it.     

Pion electroproduction in the 3He(e,é π+)3H reaction at intermediate energies

The differential coincident pion electroproduction cross section in the ³He(e,é π⁺)³H reaction has been measured with high resolution with the three-spectrometer set-up at the Mainz Microtron (MAMI) electron accelerator. Measurements were performed at the four incident energies E₀ = 855, 675, 600, and 555 MeV at fixed four-momentum transfer Q² = 0.045 GeV², with the pions detected in parallel kinematics. This enables a separation of the measured cross section into the transverse and longitudinal structure functions by means of the Rosenbluth method. The experimental data are compared to model calculations, in which the elementary pion production amplitude includes the standard Born-amplitudes and also delta and higher resonance terms. Three-body Fadeev wave functions are used and the final state interaction of the outgoing pion is taken into account. The calculation describes the data only after medium modifications of the delta and of the pion are included.     

Calculations of inelastic cross sections for rotational excitation

Cross sections for scattering of N₂ (j=0) molecules on He atoms have been calculated for relative energies below 5 · 10^?3 eV (58 °K). The time independent scattering formalism ofArthurs andDalgarno was used together with an assumed Lennard-Jones type potential with anisotropicP ₂(cos?) terms in the attractive and repulsive parts. The resulting system of coupled differential equations was solved in the distorted wave and close coupling approximations for the differential and integral cross sections for elastic and inelastic (j=0→j=2) scattering. In the integral inelastic cross section several sharp resonances were found to contribute 40% to the cross section at energies below 40 °K. The resonance peaks are attributed to orbiting or short-lived compound states since they are also observed in the elastic cross section at energies which are lower by the excitation energy of 1.5 · 10^?3 eV. Finally, the effect of varying the potential parameters on the integral inelastic cross section was studied at 50 °K and a rough formula for the cross section as a function of the parameters is obtained. The formula shows that a certain ratio of repulsive and attractive anisotropies leads to a small inelastic cross section indicating a mutual cancellation.