Photon Point Research Articles

Low-q2Electron Scattering from the 15.109-MeV State ofC12and the Conserved-Vector-Current Test

High-precision electron scattering measurements from the 15.109-MeV ${1}^{+}$ state in $^{12}\mathrm{C}$ are made at $\ensuremath{\theta}=75 \mathrm{and} 110\ifmmode^\circ\else\textdegree\fi{}$ with $35\ensuremath{\le}E\ensuremath{\le}55$ MeV. From the measurements $B(M1)$ is extrapolated to the photon point and the radiative width is determined, ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}=37.0\ifmmode\pm\else\textpm\fi{}1.1$ eV. The corresponding weak magnetism results for $\ensuremath{\beta}$ decay and $\ensuremath{\mu}$ capture are given.

Specific absorbed fractions for photon point sources within a scattering medium

Dose distributions from point gamma -ray sources within bound and unbound tissue-like absorbers were obtained by means of Monte Carlo calculations. Results are presented for source energies ranging from 30 to 2750 keV. These results are compared with approximate dose distributions utilizing an 'effective' absorption coefficient and with moment method calculations of the dose distribution within an infinite water phantom. Boundary effects were evaluated by comparing the dose in spheres of radii 10, 20, 30 and 40 cm with the dose in an unbounded absorber. In some cases, the introduction of a non-reflecting boundary reduces the dose at the boundary by nearly a factor of two. However, boundary effects are shown to be unimportant at distances greater than one mean free path from a non-reflecting interface.

Coulomb Distortion Effects in Large-AngleM1Electroexcitation

A reanalysis of inelastic electron-scattering measurements from giant $M1$ states in $^{28}\mathrm{Si}$ and $^{12}\mathrm{C}$ and in $^{26}\mathrm{Mg}$ is made using Coulomb-distortion corrections in place of the plane-wave Born-approximation analysis. It is shown that the corrections even for light nuclei can reduce the nuclear form factors for $M1$ transitions outside the experimental error quoted in the plane-wave Born approximation analysis of electron scattering. This reduction in $B(M1, q)$ is magnified at the photon point.

Transverse form factors of excited states in 16O

Abstract : Experimental results are reported about the electromagnetic properties of excited states below the giant resonance' in O16 using 180 deg inelastic scattering of electrons with incident energies of 43, 59 and 69 MeV. A comparison is made with the transverse form factors for inelastic electron scattering from 1, T = 1 states, calculated by Lewis, and from 2, T = 1 states calculated by deForest on the basis of the particle-hole model of the nucleus. Combined with known photon absorption cross sections, the interpretation of all the available data for the 13 MeV level required a 1 state to account for the photon point and the 2 state for the high q points. For the level at 17 MeV the theory is about a factor of 2 higher than the electron scattering results. The peak observed at 20.2 MeV has a transverse form factor with a q-dependence that follows within a factor of 2 the theoretical results for the strong 2 state calculated by deForest. Properties of levels at 11.00 and 12.0 MeV excitation are also discussed. (Author)