Production of collimated positronium by positron scattering from CO2, N2 and Xe

Collimated positronium production from gases

“…where N Ps corresponds to the Ps counts, N + to that for positrons entering the production cell, S = exp(−t/τ Ps ) is the Ps fraction that reaches the detector in time t, and η Ps and η + are the detection efficiencies for Ps atoms and positrons, respectively, the ratio η + /η Ps having been found to be approximately constant across different detectors and over long periods of time [17]. In terms of the total cross sections for positrons and Ps (Q + T and Q Ps T , respectively), the production efficiency may be expressed as:…”

“…The production efficiency from O 2 was investigated at twelve Ps energies between 10.5 and 399 eV. Figure 1 shows the present results for O 2 as a function of pressure in comparison to those for H 2 [13,17,21], N 2 [13,17,21], Ar [13] and CO 2 [17] ( Ps for each data set has been corrected for the detector solid angle and in-flight annihilation as in Eq. (1), but uncorrected for the final term, η+ ηPs ).…”

“…Circles: O2; squares: H2; up triangles: N2; diamonds: CO2; down triangles: Xe. Black points: this study; white points: Shipman et al [17]; grey points: Leslie [21]. Lines are the measurements of Garner et al [13]: ---: H2; ---: He; · · · · · · · · · : Ar.…”

“…Below ∼100 eV, H 2 has been found to be the most efficient production target. More recently, motivated by the results of Cooke et al [18] who found that the integrated Ps formation cross section, Q Ps , for both CO 2 and N 2 remained significant up to about 800 eV, Shipman et al [17] investigated N 2 and CO 2 as a production gas up to E Ps ∼ 400 eV. CO 2 was found to be the best converter above 250 eV and twice as efficient as the next best, N 2 , at these energies.…”

“…Over the years, the efficiency of this conversion has been investigated for various targets as a function of energy and target pressure, e.g. [16,17]. Below ∼100 eV, H 2 has been found to be the most efficient production target.…”