Abstract
The radioactivity of the α particle is among the most compelling evidence for the existence of cluster structures in atomic nuclei. During the decay process, a pre-existing α particle tunnels through the potential barrier formed by the residual nucleus1,2. The degree of preformation of the α particle, a strongly bound system of two protons and two neutrons, is extracted from the data by dividing the α-decay probability by the barrier penetrability for a given particle energy. The preformation probability changes rapidly near nuclear shell closures, which is direct evidence that clustering is connected to nuclear structure3. Enhanced preformation was observed in the lightest α-particle emitters, spherical tellurium and xenon isotopes decaying to magic isotopes of tin. Here we show the most extreme case of α-particle preformation from the measurement of the decay of tellurium-104 (104Te). With a half-life of \(7.{2}_{-1.5}^{+2.3}\,{\rm{ns}}\), 104Te is the fastest ground-state α-emitting nucleus known so far. The deduced preformation demonstrates that the enhancement is greater for 104Te than for any other nucleus. One nuclear model that can explain our observation postulates that the α particle can exist only in the low-nuclear-matter-density regions on the surface of the nucleus. The uniquely high preformation for 104Te is attributed to its relation to doubly magic tin-100 (100Sn), creating conditions conducive to form an α particle.
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Data availability
The data used in this work originate from experiment 168 at RIKEN RIBF. The raw data are available on request.
Code availability
The code used to analyse the data is available on reasonable request.
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Acknowledgements
We would like to extend our gratitude to the entire RIBF operations team. Also, we would like to thank T. Papenbrock and K. L. Jones for helpful discussions. The material is based on work supported in part by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under contract nos. DE-FG02-96ER40983 (UTK) and DE-AC05-00OR22725 (ORNL), the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344 and the Polish National Science Center under grant no. 2020/39/B/ST2/02346 and contract no. UMO-2019/33/B/ST2/02908. This work was also sponsored by JSPS KAKENHI grant nos. 25H01273 and 24K0655, the RIKEN programme RiNA-Net, the Stewardship Science Academic Alliances programme through DOE awards no. DE-NA0003899 (UTK), the National Science Foundation NSF-MRI-1919735 (UTK), the Spanish MCIN/AEI/10.13039/501100011033 under grants TED2021-130592B-I00 (PROTOTWIN) and PID2021-126998OB-I00 (FASCINA) and supported by BMBF under Verbundprojekt 05P2021 (ErUM-FSP T07) grant 05P21PKFN1. A.E. was supported by the DFG under grant number JO 391/20-1. A.A. acknowledges support from the Polish National Agency for Academic Exchange (NAWA) under the STER Programme - Internationalisation of Doctoral Schools, project ‘International Doctoral Program at NCBJ & IChTJ’ (project no. BPI/STE/2021/1/00033/U/00001). This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (https://www.energy.gov/doe-public-access-plan).
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R.G. and K.P.R. were the lead and co-spokesperson for the experiment, respectively. The design and installation was led by R.G., T.T.K. and I.C., with further contributions from R.Y. and D.H. Supplemental equipment was provided by J.M.A., R.Y. and S.N. The data acquisition system and software was maintained by T.T.K., I.C., R.Y., Z.Y.X., T.J.R. and R.G. Online data monitoring and operation of the experiment was performed by I.C., R.G., T.T.K., K.P.R., S.N., R.Y., N.F., N.K., S.G., C.M., N.B., P.B., A.E., J.F., G.G.d.L., S.H., D.H., N.I., K.K., A.K., K.N., V.P., T.J.R., A.S. and Z.Y.X. The beam transportation was led by N.F., S.M., Y.S., H. Suzuki, H.T., Y.T. and M.Y. The offline analysis was led by I.C., with contributions from R.Y., Z.Y.X., A.A. and B.K. The manuscript was written by I.C. and R.G. All authors have read and commented on the manuscript.
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Extended data figures and tables
Extended Data Fig. 1 Experimental detector set-up.
The implantation set-up used to stop the energetic ion beam and measure the subsequent decays. For illustrative purposes, some of the outside LaBr3 detectors are transparent glass to view the implantation configuration. In the figure, the radioactive ion beam comes from the bottom left to implant into the LYSO, depicted as the orange square.
Extended Data Fig. 2 Digital signal deconvolution.
a–c, Fits of a single peak (a), a pile-up event with an 8-ns time difference (b) and a pile-up event with an 18-ns time difference (c). The pink curve is the total fit of the black experimental points and the blue and green lines represent the decomposition in terms of the first and second decays, respectively.
Extended Data Fig. 3 Measured energy response of 108Xe and 104Te decays.
Light yield measurements for the decay chain of 108Xe (black) through 104Te (red). Each point is marked with error from the resolution of the detector plus the error resulting from the trace deconvolution. Variations according to these uncertainties are incorporated as the systematic errors.
Extended Data Fig. 4 Calibration from measured light to α energy.
Calibration from light yield to α-decay energy using neighbouring α-emitters near 100Sn and a 210Po check source for the highest energy point. The measured light yields for 108Xe and 104Te are shown by the blue and red points, respectively. The green band represents the error in the fit, which is propagated into the error in the α energy.
Extended Data Fig. 5 Reduced width calculations for Po isotopes.
Comparison of reported reduced widths from Rasmussen3 (red diamonds) with those calculated for this work (black circles).
Extended Data Fig. 6 Error distributions for 104Te reduced width.
a–d, Using the decay energy (a) and half-life (d) distributions, an input distribution (c) is propagated into the reduced width calculations. The resulting error distribution for the reduced width is shown in b.
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Cox, I., Grzywacz, R., King, T.T. et al. Direct observation of the superallowed α-decay of 104Te. Nature (2026). https://doi.org/10.1038/s41586-026-10581-w
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DOI: https://doi.org/10.1038/s41586-026-10581-w
