High-energy photon beam production with laser-Compton backscattering

We have produced a beam of high-energy gamma-rays by Compton backscattering of $\text{1064}\text{nm}$ laser photons from 1 GeV electrons circulating in a storage ring. Measuring the energy spectra of the backscattering photons with an HPGe detector, we have found that the maximum energy of $\text{17.6}\text{MeV}$ and the measured energy spectra show agreement with the simulation calculations, while the detected photon yields were measured at about 4×10³, 2×10³ and $\text{3×10}{}^2\text{photons}\text{s}{}^{\mathrm{-1}}\text{mA}{}^{\mathrm{-1}}\text{W}{}^{\mathrm{-1}}$ for the 20, 10 and $\text{2}\text{mm}\text{φ}$ collimators, respectively. The photon energy widths from the collimators correspond to 6.6–$\text{17.6}\text{MeV}$, 12.4–$\text{17.6}\text{MeV}$ and 17.3–$\text{17.6}\text{MeV}$, respectively. By using these photons, we measured the total nuclear photoabsorption cross-sections in the E1 giant resonance energy region for ${}^{197}\text{Au}$ using the attenuation method and we have demonstrated that the photon attenuation method will be a useful tool for studying photonuclear reactions.     

Distribution coefficients in (YSmLuCa)3(FeGe)5O12 film growth

The composition of bubble garnet films has been analyzed by Inductively Coupled Plasma Emission Spectroscopy (ICP) to determine the distribution coefficients for different growth conditions. Under typical growth conditions, the distribution coefficients, k, of each element are as follows: k^Y = 2.15, k^Sm = 1.56, k^Lu = 1.32, k^Ca = 0.45, k^Fe = 0.98, k^Ge = 1.10. As the supercooling temperature (growth rate) increases, k^Ca, which is the smallest and deviates most from 1.0, changes in the direction approaching 1.0. For charge compensation, k^Ge also increases, consequently, k^Fe must decrease. Also k^Y, which is the largest, $\text{k}{}^{\mathrm{Sm}}\text{k}{}^{\mathrm{Y}}$ and $\text{k}{}^{\mathrm{Lu}}\text{k}{}^{\mathrm{Y}}$ change in the direction approaching 1.0. On the other hand, as the melt parameter R₁ (≡ $\text{Fe}{}_2\text{O}{}_3\text{Σ}\text{Ln}{}_2\text{O}{}_3$) increases, k^Fe decreases, and k^Y, k^Sm and k^Lu increase, whereas $\text{k}{}^{\mathrm{Sm}}\text{k}{}^{\mathrm{Y}}$ and $\text{k}{}^{\mathrm{Lu}}\text{k}{}^{\mathrm{Y}}$ remain constant at 0.73 and 0.61, respectively.     

A method for estimating muon production and penetration through a shield

An approximate expression is derived that describes muon production by high-energy protons and the subsequent attenuation of the muons in a shield. It is shown that the muon flux at x ahead of an interaction by a proton of energy ? GeV and where pions have a path length of Δ m in which to decay, will be given by:

$\text{φ=8.5×10}{}^{\mathrm{?2}}\text{εΔ}\text{x}{}^2\text{e}{}^{\mathrm{<mtext>?(</mtext><mtext>\alpha t</mtext><mtext>\epsilon </mtext><mtext>)</mtext>}}\text{μ/}\text{m}{}^2$

, where t is the shield thickness in m and α is an effective muon energy loss rate which has a value of 22 GeV/m for iron and 7.8 GeV/m for concrete. It is further shown that the effective muon attenuation mean-free path is equivalent to $\text{1}\text{16}$ of the range of a muon with the energy of the interacting proton.The width of the muon beam that passes through the shield is also considered and it is shown that the beam profile approximates a Gaussian distribution with a diameter at half-maximum intensity of:

$\text{d=}\text{4.6x}\text{εαt}\text{m}$

.Calculated muon fluxes are shown to correspond reasonably with those obtained by more sophisticated computer methods for proton energies up to at least 30 GeV and over the entire range of shield thicknesses of interest for radiation safety. Results of measurements of muon levels behind beam dumps under various conditions are presented and are shown to be in reasonable agreement with predictions based on the above model.     

The overall sink strength of an inhomogeneous lossy medium. Part I: self-consistent estimates

Steady-state diffusion in a medium containing a continuous distribution of sinks is considered. The medium comprises a matrix, with sink strength $\text{k}{}_2{}^2$, which contains a random array of identical spherical inclusions, with sink strength $\text{k}{}_1{}^2$. On a macroscopic scale, the medium appears homogeneous, with uniform sink strength $\text{k}\text{?}{}^2$. This work is devoted to the estimation of the overall sink strength $\text{k}\text{?}{}^2$, in terms of $\text{k}{}_1{}^2\text{, k}{}_2{}^2$ and the statistics of the distribution of the inclusions. Part I discusses three distinct schemes of self-consistent type. One is based upon a simple embedding procedure and makes no explicit allowance for spatial correlations. The other two make use, in different ways, of the quasicristalline approximation (QCA). Part II develops variational principles which yield bounds for $\text{k}\text{?}{}^2$. The self-consistent estimates are interpreted relative to the variational formulation and explicit numerical results are presented.