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On the basis of the phenomenological non-relativistic quark model, we have obtained the ground-state masses of the light pseudo-scalar and vector mesons. The full Hamiltonian used in the investigation includes the kinetic energy, the confinement potential, the one-gluon-exchange potential and the instanton-induced quark–antiquark interaction. A good agreement is obtained with the experimental masses. The η–η′ splitting is explained. The limitation of the perturbative treatment for estimating the π–ρ splitting using OGEP is also pointed out.

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X‐ray mass attentuation coefficients for the elements aluminium, copper, molybdenum and tantalum, the materials nylon, PTFE and lucite and the compounds magnesium sulphate, calcium sulphate chromium(III) acetate, cobalt acetate and zinc sulphate were measured using 6.46 keV photons from a 57Co source and adopting a novel method employing a proportional counter spectrometer. For the elements and materials the close agreement of the measured μ/ρ values with the theoretical values indicates the suitability of the proposed method for studying the validity of the mixture rule in the case of compounds. For magnesium sulphate, calcium sulphate, cobalt acetate and zinc sulphate the measured μ/ρ values agree within 1% with the theoretically estimated values, indicating the validity of the mixture rule. However, with chromium(III) acetate, where the chromium K‐edge is less than the incident photon energy by only about 471 eV, the measured μ/ρ value shows a deviation of about – 11%. This is attributed to the effects of EXAFS and to the effects of the chemical environment on the μ/ρ value, which result in an uncertainty in the value of μ/ρ to be used when applying the mixture rule.

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