No abstract

No abstract

No abstract

The relaxation losses and the corresponding velocity variations, observed at ultrasonic frequencies in (M2O)0.14(B2O3)0.86 alkali borate glasses (M = Li, K, Cs) between 1.5 and 300 K, have been modelled by an asymmetric double-well potential model having a distribution of both the barrier potential and the asymmetry. It is shown that the relaxation strength C* and the spectral density of asymmetries f0 decreases markedly with decreasing cation size. Below 10 K the sound attenuation is regulated by the phonon-assisted relaxation of tunnelling systems and exhibits a tunnelling strength C, ranging between 10−4 and 10−3. At variance with the behaviour observed for C*, C slightly increases with decreasing cation size and is more than one order of magnitude smaller than C*. It is concluded that, differently from classical relaxing states, tunnelling systems are independent of bond strengths and of structural changes characterizing a glassy network, confirming their inherent universality. Above about 120 K the ultrasonic velocity is mainly regulated by vibrational anharmonicity and shows a nearly linear decrease as the temperature is increased, the slope scaling with the cation size. Taken together, the observations point to the existence of a distinct correlation between anharmonicity and local mobility in the glassy network.

No abstract

No abstract

No abstract

In this study we analyzed the ESR signal of alanine dosimeters with gadolinium exposed to 6 MV linear accelerator photons. We observed that the addition of gadolinium brings about an improvement in the sensitivity to photons because of its high atomic number. The experimental data indicated that the addition of gadolinium increases the sensitivity of the alanine to 6 MV photons. This enhancement was better observed at high gadolinium concentrations for which the tissue equivalence is heavily reduced. However, information about the irradiation setup and of the radiation beam features allows one to correct for this difference. Monte Carlo simulations were carried out to obtain information on the expected effect of the addition of gadolinium on the dose absorbed by the alanine molecules inside the pellets. These results are compared with the experimental values, and the agreement is discussed.