Delayed emission of cold positronium from mesoporous materials

Journal Article · Mon Nov 15 00:00:00 EST 2010 · Physical Review. A

DOI:https://doi.org/10.1103/PHYSREVA.82.052511· OSTI ID:21528632

Cassidy, D B; Hisakado, T H; Meligne, V E; Tom, H W. K.; Mills, Jr, A P ^[1]

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1. Department of Physics and Astronomy, University of California, Riverside, California 92521-0413 (United States)

It is well known that ortho-positronium (ortho-Ps) atoms are emitted with high efficiency from various porous materials following the implantation of positrons. Since the ortho-Ps lifetime in a mesoporous material may be a substantial fraction of the ortho-Ps vacuum lifetime (142 ns), the time dependence of Ps emission may have to be considered when conducting certain types of experiments, such as time of flight measurements or pulsed ortho-Ps-laser interactions, when using this kind of target as a positronium source. By taking into account the positron implantation profile and subsequent Ps diffusion and decay in a mesoporous film we calculate the time dependent ortho-Ps emission rate {Gamma}(t), which in turn allows us to establish the total annihilation rate, arising from the decay of ortho-Ps both inside and outside the sample. Using time-delayed laser spectroscopy and single-shot lifetime measurements we have directly probed the rate at which Ps is emitted into vacuum from a target with {approx}3-nm diameter pores and have observed delayed ortho-Ps emission that is consistent with our model. From the ortho-Ps decay spectrum we find that, whereas a simple two-component lifetime fit gives a short lifetime of 25.3{+-}0.3 ns, an analysis that properly takes into account the emission rate yields an ortho-Ps lifetime inside the porous material of 32.3{+-}1.2 ns, demonstrating that the ortho-Ps escape rate into vacuum can significantly modify the apparent lifetime of ortho-Ps inside a mesoporous material. Our measurements yield a Ps diffusion coefficient D = 0.07 {+-} 0.01 cm{sup 2} s{sup -1}, which is consistent with a tunneling limited diffusion process.

• OSTI ID: 21528632
• Journal Information: Physical Review. A, Vol. 82, Issue 5; Other Information: DOI: 10.1103/PhysRevA.82.052511; (c) 2010 The American Physical Society; ISSN 1050-2947
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ANNIHILATION
ATOMS
DIFFUSION
EFFICIENCY
LASER SPECTROSCOPY
LIFETIME
NANOSTRUCTURES
POROUS MATERIALS
POSITRONIUM
POSITRONS
SPECTRA
THIN FILMS
TIME DEPENDENCE
TIME-OF-FLIGHT METHOD
TUNNEL EFFECT
ANTILEPTONS
ANTIMATTER
ANTIPARTICLES
ELEMENTARY PARTICLES
FERMIONS
FILMS
INTERACTIONS
LEPTONS
MATERIALS
MATTER
PARTICLE INTERACTIONS
SPECTROSCOPY