PANDORA: A New Experimental Setup for Measuring in-Plasma Nuclear β-Decays

The abundance of elements in the Cosmos is currently a topic of active investigation. Since the dawn of nuclear astrophysics, various processes have been identified to explain the nucleosynthesis process. Among these, the slow (s-) and rapid (r-) neutron capture processes generate 99% of all elements beyond the iron peak. The corresponding nucleosynthesis models are sensitive to a variety of inputs, such as neutron capture cross sections and β-decay rates. Both theory [1,2] and experiments on fully stripped ions [3] have shown that β-decay lifetimes can change by even orders of magnitude in ionized matter. The PANDORA (Plasmas for Astrophysics, Nuclear Decay Observation and Radiation for Archaeometry) project [4,5] aims at building a first of its kind experimental facility, at INFN-LNS Catania, for probing for the first time the nuclear β-decay rates in hot plasmas. In this facility the plasma will mimic some thermodynamical stellar conditions, especially in terms of temperature and consequent in-plasma charge state distribution. The setup consists of a compact, superconducting B-minimum magnetic trap, where plasmas of various elements can be generated via Electron Cyclotron Resonance and reach densities ne~1011-1013 cm-3, with a “tunable” temperature in the range Te~0.1-30 keV. An array of 14 HpGe detectors will be used for measuring the decay rates, counting the gammas emitted by the de-excitation of the daughter nuclei. The number of decays per unit of time will be monitored simultaneously and mapped to the measurement of thermodynamical plasma parameters, achieved by a multi-diagnostic system (RF interferometers and polarimeters, optical and X-ray spectroscopy, X-ray imaging and space resolved spectroscopy). The facility is now under construction, and first plasma is expected in 2026. The setup enables other astrophysical relevant experiments, such as the first measurement of optical opacities of metallic plasmas resembling plasma ejecta from binary neutron stars coalescence. This study is valuable for constraining the electromagnetic signal arising after the merger, known as kilonovae, and the r-process nucleosynthesis yields occurring in such explosive events [5, and papers therein]. While more than a hundred physics cases have been shortlisted, the first measurements will focus on: 94Nb (t1/2 ~ 2 x104 y), 134Cs (t1/2  ~ 2.06 y), 176Lu (t1/2 ~ 3.76x1010). The facility construction is rapidly progressing, and in the meantime the collaboration has developed a generalized theory of β-decay in LTE and nLTE plasmas, benchmarking models predictions with 7Be, 140Pr, 163Dy, in H- or He-like configurations, which have been already measured in Storage Ring experiments at GSI.

[1] K. Takahashi and K. Yokoi, Nuclear β-decays of highly ionized heavy atoms in stellar interiors. Nuclear Physics A 404(3):578-598 · August 1983. DOI: 10.1016/0375-9474(83)90277-4

[2] K. Takahashi and K. Yokoi, Beta-decay rates of highly ionized heavy atoms in stellar interiors, Atomic Data and Nuclear Data Tables. Volume 36, Issue 3, May 1987, Pages 375-409 DOI: https://doi.org/10.1016/0092-640X(87)90010-6

[3] Y. A. Litvinov and F. Bosch, Beta decay of highly charged ions 2011 Rep. Prog. Phys. 74 016301

[4] D. Mascali et al A Novel Approach to β-Decay: PANDORA, a New Experimental Setup for Future In Plasma Measurements. Universe 2022, 8, 80. https://doi.org/10.3390/universe8020080

[5] Mascali, D., Palmerini, S., Torrisi, G., De Angelis, G., Santonocito, D., Kratz, K.-L., eds. (2023). Nuclear physics and astrophysics in plasma traps. Special-Issue in Frontiers in Physics, Lausanne: Frontiers Media SA. doi: 10.3389/978-2-83251-062-9