Tea in the Atrium Room: 307

Colloquium Room: 307 Title: Direct Observation of the Superallowed α Decay of ¹⁰⁴Te Abstract: Sixty years ago it was predicted that the α decay of nuclei just above doubly magic ¹⁰⁰Sn would be unusually fast ("superallowed" ) [1] because the emitted α particle and the ¹⁰⁰Sn core form an exceptionally favorable molecule-like configuration. The groundwork was laid by the discovery of the ¹⁰⁹Xe → ¹⁰⁵Te → ¹⁰¹Sn α-decay chain [2] and its subsequent measurement [3], and then by the first observation of the ¹⁰⁸Xe → ¹⁰⁴Te → ¹⁰⁰Sn chain feeding doubly magic ¹⁰⁰Sn [4]. The ¹⁰⁴Te itself α-decays directly into doubly magic ¹⁰⁰Sn. This nucleus is extremely difficult to synthesize, and its decay is so fast that it eluded measurement for decades. I will describe the experiment yielding the first direct measurement of the ¹⁰⁴Te lifetime [5]. A novel recoil-decay scintillation detector [6] and advances in understanding scintillator light collection [7] enabled this first direct measurement of the ¹⁰⁴Te lifetime. The decay turns out to be even more enhanced than theory predicted, raising a basic question about how and where an α particle assembles inside a nucleus before it escapes, a question that reaches from nuclear structure to the physics of clustering in dense matter. **References** [1] R. Macfarlane and A. Siivola, Physical Review Letters 14, 114 (1965). [2] S. N. Liddick et al., Phys. Rev. Lett. 97, 082501 (2006). [3] I. G. Darby et al., Phys. Rev. Lett. 105, 162502 (2010). [4] K. Auranen et al., Phys. Rev. Lett. 121, 182501 (2018). [5] I. Cox et al. Nature volume 654, 52–56 (2026). [6] Y. Xiao et al., Phys. Rev. C 100, 034315 (2019). [7] B. Kreider et al., Nucl. Instr. Meth. A 1085, 171298 (2026).