High-yield thermalized positronium at room temperature emitted by morphologically tuned nanochanneled silicon targets

Abstract

Nanochanneled silicon targets with high positron/positronium (Ps) conversion rate and efficient Ps cooling were produced. Morphological parameters of the nanochannels, such as their diameter and length, were adjusted to get a large fraction of thermalized Ps at room temperature being emitted into vacuum. Ps cooling measurements were conducted combining single-shot positron annihilation lifetime spectroscopy and Doppler spectroscopy of the 13S → 23P transition. 2γ–3γ annihilation ratio measurements were also performed to estimate the positron/Ps conversion efficiency. In a converter with nanochannel diameter of 7–10 nm and depth of 3.89 μm, ∼28% of implanted positrons with an energy of 3.3 keV was found to be emitted as Ps with a transverse kinetic energy of 11 ± 2 meV. The reduction of the nanochannels depth to 1.13 μm, without changing the nanochannel diameter, was found to result in a less efficient cooling, highlighting the presence of Ps reflection from the bottom end of nanochannels.

J-PET detection modules based on plastic scintillators for performing studies with positron and positronium beams

“…In the future, the continuous beam will be injected into a Surko trap [42] where positrons will be trapped, stored for fraction of seconds and then bunched to form pulses containing up to 10 4 positrons. Implantation of positron pulses in efficient positron/positronium converters [15,43,44] allows producing dense Ps clouds [45,46]. In particular, in recent years the possibility to populate the long-lived 2 3 S state of positronium via spontaneous [17] and stimulated [47] decay from the 3 3 P level (previously reached via 1 3 S→3 3 P laser excitation) has been demonstrated [48].…”

Positronium Physics and Biomedical Applications

“…2(right)), o-Ps can diffuse along the pore network and eventually be emitted into the vacuum with a significantly lower energy (Cassidy et al, 2010;He et al, 2007;Ito et al, 2005;Mariazzi et al, 2010a;Tanaka et al, 2006;Vallery et al, 2003). The Ps emission energy into the vacuum depends on the rate and duration of the energy transfer to the surrounding material that are determined by the pores shape, dimension and characteristics of their surface (Cassidy et al, 2010;Crivelli et al, 2010;He et al, 2007;Ito et al, 2005;Mariazzi et al, 2010aMariazzi et al, , 2008Mariazzi et al, , 2021Nagashima et al, 1995;Tanaka et al, 2006;Vallery et al, 2003). In silica Ps formation occurs with an overall positron to positronium conversion efficiency up to 84% (Van Petegem et al, 2004).…”

J-PET detection modules based on plastic scintillators for performing studies with positron and positronium beams

“…In the future, the continuous beam will be injected into a Surko trap [42] where positrons will be trapped, stored for fraction of seconds and then bunched to form pulses containing up to 10 4 positrons. Implantation of positron pulses in efficient positron/positronium converters [15,43,44] allows producing dense Ps clouds [45,46]. In particular, in recent years the possibility to populate the long-lived 2 3 S state of positronium via spontaneous [17] and stimulated [47] decay from the 3 3 P level (previously reached via 1 3 S → 3 3 P laser excitation) has been demonstrated [48].…”

“…At the University of Trento, a continuous positron beam has been put into operation in the Antimatter Laboratory (AML). With the know-how to fabricate efficient positron/positronium converters [15,16] and to manipulate positronium atoms into a metastable state with increased lifetime [17], the generation of Ps beams is envisaged [18]. Two detection modules with a supported data acquisition chain have recently been moved to the AML to perform studies with positrons and positronium beams to investigate fundamental physics not yet explored.…”