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Producing positronium (Ps) in the metastable 2 3 S state is of interest for various applications in fundamental physics. We report here on an experiment in which Ps atoms are produced in this long-lived state by spontaneous radiative decay of Ps excited to the 3 3 P level manifold. The Ps cloud excitation is obtained with a UV laser pulse in an experimental vacuum chamber in presence of guiding magnetic field of 25 mT and an average electric field of 300 V cm −1 . The evidence of the 2 3 S state production is obtained to the 3.6σ level of statistical significance using a novel analysis technique of the single-shot positronium annihilation lifetime spectra. The dynamic of the Ps population on the involved levels has been studied with a rate equation model.

proton minibeam radiation therapy (pMBRt) is a novel dose delivery method based on spatial dose fractionation. pMBRT has been shown to be promising in terms of reduced side effects and superior tumour control in high-grade glioma-bearing rats compared to standard irradiation. These findings, together with the recent optimized implementation of pMBRt in a clinical pencil beam scanning system, have triggered reflection on the possible application to patient treatments. In this context, the present study was designed to conduct a first theoretical investigation of the clinical potential of this technique. for this purpose, a dedicated dose engine was developed and used to evaluate two clinically relevant patient treatment plans (high-grade glioma and meningioma). treatment plans were compared with standard proton therapy plans assessed by means of a commercial treatment planning system (ecLipSe-Varian Medical systems) and Monte carlo simulations. A multislit brass collimator consisting of 0.4 mm wide slits separated by a centre-to-centre distance of 4 or 6 mm was placed between the nozzle and the patient to shape the planar minibeams. for each plan, spread-out Bragg peaks and homogeneous dose distributions (±7% dose variations) can be obtained in target volumes. The Peak-to-Valley Dose Ratios (PVDR) were evaluated between 9.2 and 12.8 at a depth of 20 mm for meningioma and glioma, respectively. Dose volume histograms (DVHs) for target volumes and organs at risk were quantitatively compared, resulting in a slightly better target homogeneity with standard pt than with pMBRt plans, but similar DVHs for deep-seated organs-at-risk and lower average dose for shallow organs. The proposed delivery method evaluated in this work opens the way to an effective treatment for radioresistant tumours and will support the design of future clinical research.