  The transformation between the metallic ($\beta$) and semi-conducting
($\alpha$) allotropes of tin is still not well understood. The phase transition
temperature stated in the literature, 286.2 K, seems to be inconsistent with
recent calorimetric measurements. In this paper, this intriguing aspect has
been explored in Sn and Sn-Cu (alloyed 0.5% Cu by weight) using temperature
resolved synchrotron x-ray diffraction measurements performed at the Indus-2
facility. Additionally, the $\alpha \rightleftharpoons \beta$ Sn transition has
been recorded using in-situ heating/cooling experiments in a scanning electron
microscope. Based on these measurements, a protocol has been suggested to
reduce the formation of $\alpha$-Sn in potentially susceptible systems. This
will be useful in experiments like TIN.TIN (The INdia-based TIN detector),
which proposes to employ ~100 - 1000 kg of superconducting tin-based detectors
to search for neutrinoless double beta decay in the isotope $^{124}$Sn.
