The Temperature Dependence to 1550°C of the Effective Resonance Integral of Thorium Oxide Rods

The temperature dependence of the thorium-oxide resonance integral has been measured over a wide (20 to 1550 °C) temperature range. The activation method was used; the 310 keV γ ray from the decay of ²³³Pa was measured with a multichannel pulse-height analyzer. Measurements were performed on ThO₂ rods of 0.490− and 0.353−in. diam. (surface-to-mass ratio = 0.340 and 0.465 cm²/g, respectively). The temperature dependence of the thorium-oxide resonance integral was found not to be a linear function of either (t − t₀) or (√T − √T₀), where t and T and centigrade and Kelvin temperature, and t₀ and T₀ are 20°C, and 293°K, respectively. Thus the familiar forms of the temperature dependence of the effective resonance integral, namely RI(T)/RI(T₀) = 1 + α (t − t₀) = 1 + β × (√T − √T_o) are not appropriate representations of the data. The Doppler coefficient in a 1/E spectrum is defined by α₀ = [1/RI(T)] [dRI(T)/ dT] where RI(T) is the effective resonance integral of the sample excluding the 1/v contribution, and T is the temperature of the sample. It has been found that α₀ = [(0.16 ± 0.01)/T] yields a good fit to the experimental data of both sample sizes. It follows that RI(T) = RI(T₀) (T/T₀)^{(0.16 ± 0.01)}.