Radiative capture of deuterons in154Sm and238U

Angular — and velocity — distributions of electrons emitted near zero degree from projectile ions (H⁺, H ₂ ⁺ , H ₃ ⁺ , He⁺, He⁺⁺ at 1.7 MeV/u) traversing solid carbon foils (2 to 20) μg/cm²) have been measured. The data give clear evidence of production mechanisms which go beyond those reported elsewhere.     

Radiative K- capture in hydrogen

The branching ratios for the decays K^-p → Λγ and K^-p → Σ⁰γ are investigated in a chiral SU(3) version of the cloudy-bag model. The calculated branching ratio for Λγ agrees with the existing experimental data, while the prediction for Σ⁰γ (being only slightly smaller) is well within the range accessible to an experiment currently under way at Brookhaven.     

Radiative muon capture in medium-heavy nuclei

Radiative muon capture in nuclei is thoroughly investigated in view of its sensitivity to the pseudoscalar coupling constant g_P. In the photon energy domain of interest (k ? 60 MeV) the effective one-body hamiltonian in use is shown essentially to hold true, with minor corrections due to the muon propagator in the nuclear field and to the two-step process. The closure approximation is avoided by appropriately integrating the response function calculated in the Fermi gas model, in the energy-momentum transfer plane.Theoretical predictions in medium-heavy nuclei of the high-energy photon spectrum, of photon polarization, and of muon-spin photon angular correlation are given for various values of the pseudoscalar coupling constant.     

Radiative Ml capture in light nuclei

The importance of semi-direct processes in E1 and E2 capture reactions has been well documented. Little is known, however, about M1 capture although a vast body of data indicates a non-statistical nature. We discuss here the importance of the semi-direct M1 process and concentrate in particular on recent experimental results claiming that the M 1 strength in²⁹Si isnearly one order of magnitude smaller than in ²⁸Si, the target nucleus. We use shell model arguments to demonstrate that this reduction is indeed consistent with the semi-direct reaction process and that other mechanisms like2p-2h fragmentation and phonon coupling are not likely to be instrumental in elucidating further the non-statistical nature of the²⁸Si+n reaction.     

Radiative muon capture on hydrogen

The radiative capture of negative muons by protons can be used to measure the weak induced pseudoscalar form factor. Brief arguments why this method is preferable to ordinary muon capture are given followed by a discussion of the experimental difficulties. The solution to these problems as attempted by experiment #452 at TRIUMF is presented together with preliminary results from the first run in August 1990. An outlook on the expected final precision and the experimental schedule is also given. Talk presented by W. Bertl at the Symposium “The Future of Muon Physics” in Heidelberg, Germany, May 7–9, 1991     

Radiative capture of negative pions in deuterium

The transition rate for radiative capture of negative pions in deuterium is calculated with the Hamiltonian deduced from pion photoproduction data and with the transition amplitude obtained on the basis of the soft-pion theory. A large contribution to the physical amplitude from the intermediate states with the ρ-meson and nucleon-antinucleon pairs in the soft-pion approach brings both results into agreement within 5 %.     

Radiative muon capture on nuclei

Radiative muon capture rates of stopped meons, spectra, circular polarisation, and asymmetries of emitted -quanta in¹⁶O and⁴⁰Ca are analysed using the shell-model nuclear wave functions. Calculated characteristics show considerable sensitivity to the value of induced pseudoscalar coupling constantg _p. Where possible we compare the theoretical results with the preliminary experimental data.Dedicated to the 25th anniversary of the Joint Institute for Nuclear Research.On leave of absence fromthe Institute of Nuclear Physics, Czechosl. Acad. Sci., 250 68 e, Czechoslovakia.     

Radiative neutron capture near threshold

The surprisingly large “pair” term corrections to threshold radiative neutron capture, previously calculated by Riska and Brown, and Gari and Huffman, are calculated in a new way in which they appear as relativistic corrections to the impulse approximation arising from the small negative energy components of the wave functions of the two nucleon system. Looking at these corrections from this point of view suggests not only that these small negative energy components are observable in non-relativistic processes, but also that the size of these corrections may ultimately depend on, or give information about, a consistent relativistic treatment of the nuclear force problem.     

Radiative electron capture to the continuum

We have analyzed the process of electron capture to the continuum with photon emission, which is referred to as radiative electron capture (RECC). We have considered different projectiles on He targets, observing the behavior of the differential cross section in the first Born approximation, for asymptotic high velocities. These results have been compared with Dettmann's mechanic electron capture to the continuum (MECC) theory. For He targets we find that the RECC process prevails over MECC when the projectile velocity is greater than 20 au. Furthermore we observed that RECC requires larger velocities to prevail when the target is heavy.     

Measurement of the photon asymmetry in capture of polarized neutrons by deuterons

We have looked for parity violation in neutron capture by deuterons. Parity violation would produce an asymmetric angular distribution of the 6.24 MeV photon about the spin direction of the neutron of the form (1 + A cos θ), where θ is the angle between photon momentum and incident neutron spin. We find A = (4.2 ± 3.8) × 10⁻⁶, where the error is the statistical error of counting. If we include an estimate of systematic errors, the error increases to ± 3.9. In addition there is an overall scale error which can be described by multiplying the result by (1 ± 0.15). The value is one standard deviation larger than predictions based on either Cabbibo or gauge theoretical models, which give values of A between 10⁻⁶ and 10⁻⁷.     

keV Neutron capture cross sections of 134Ba and 136Ba

The neutron capture cross sections of ¹³⁴Ba and ¹³⁶Ba have been measured in the energy region 3 to ¹⁰⁰keV. The following average quantities were deduced from the extracted resonance parameters: 〈D〉 = 127±10eV, 10⁴S₀ = 0.85±0.3, 10⁴S₁ = 0.8, 〈Γ_γ〉 = 120±20 meV for ¹³⁴Ba. Analysis of the ¹³⁶Ba data gave 〈Γ_γ〉 = 125±30meV for s-wave neutrons. The average 30 keV capture cross sections for these two s-process nuclei were found to be $\text{225±35}\text{mb}\text{for}{}^{134}\text{Ba and}\text{61±10}\text{mb}\text{for}{}^{136}\text{Ba}$.     

Parity violation: Radiative pion capture in hydrogen

We investigate radiative pion capture in hydrogen, π^? → nγ, as a means of determining the parity-violating πNN coupling constant ?_π. We include contributions from the lightest baryon resonance [Δ(1232)] and the light vector mesons [ρ, ω, φ]. Our results indicate that, despite their negligible role in parity-conserving amplitudes, the effects of the Δ and ρ may hamper the determination of ?_π.     

Radiative lifetimes of superradiant populated Ba Rydberg levels

Radiative lifetimes of 6s7f¹F₃, as8f¹F₃, and 6s9d¹D₂ Ba Rydberg levels were measured in an atomic beam by time resolved recording of the exponential decay of the fluorescence. The excitation was performed by use of two pulsed dye lasers and a superradiant emission or a superradiant cascade controlled by a cavity.     

Radiative electron capture accompanying resonant nuclear scattering

A quantum mechanical theory for the radiative capture (REC) of a target electron by a heavy, swift projectile is formulated, allowing for resonant nuclear scattering through the use of distorted waves. Calculations are performed for the systems O¹⁶, Ne²⁰→He within the exact strong potential Born theory and the impulse approximation. Similar structures as in the case of Coulomb capture are found in the transition probability.     

Radiative thermal neutron capture by natural sulfur

A high precision study of the gamma ray spectrum following neutron capture by a target of natural sulfur is reported. The energy precision obtained has permitted construction of decay schemes for³³S and³⁵S. In the case of the former isotope a total of 22 levels have been identified while for the latter and much weaker reaction 7 states have been observed. While some transitions attributable to capture by³³S are observed, their weakness prohibited detailed analysis. The neutron separation energies, based upon the¹⁴N(n, γ)¹⁵N standard are found to be 8,641.60 (3) keV and 6,985.84 (5) keV for³³S and³⁵S respectively.