Contact density and hyperfine splitting of positronium in naphthalene

Positron bound systems in benzene and in naphthalene

“…The experimental technique and measuring method were much the same as in previous works [8]. We think it is useful to mention only a few essential points.…”

“…Its attribution to the decay of an ortho-Ps atom seems to us to face serious difficulties. In fact recent measurements made in our laboratory [8] have shown that this component certainly arises from the decay of a magnetically quenchable system; however, the properties of this system are markedly different (*) This work was supported by CISM (Centro Interuniversitario di Struttura della Materia) del Ministero della Pubblica Istruzione, and by GNSM (Gruppo Nazionale di Struttura della Materia) del CNR. from those which characterize Ps in other molecular media [9].…”

“…1 as a function of the field. The analysis of these data performed with the criteria already adopted by us [8,9] shows that the observed where a is a phenomenological parameter which describes the perturbing effect of the medium. From eq.…”

Anisotropic Magnetic Quenching of Positronium Formed by Polarized Positrons in Oriented Crystals

“…The electron-positron anisotropic hyperfine constants should, therefore, be similar to the electron-electron ones in triplet molecules of comparable size [2].) The parameters α =λ s / γ t t , α ' = ω / ω o , a n d λ p a c c o u n t i n g f o r a n i n f l u e n c e o f medium on "anomalous" Ps in naphthalene, were taken to be 0.25, 0.13, and (1.03 x 10 -9 s) -1 , respectively [5] (see, however, [18]). These parameters were used for the calculation of the anisotropic enhancement of the ACAR narrow component in naphthalene as a function of an external magnetic field and positron polarization.…”

“…[1][2][3]. It was shown in [3] that anisotropic hyperfine coupling of an electron and a positron in a Ps atom is appropriate not only to the Ps complexes ("anomalous" Ps) in crystalline polymers [2,4,5] but also to quasi-Ps (qPs, "normal' Ps) in noncubic inorganic crystals [6]. An anisotropy in the latter can be caused by an effective quadrupole interaction of qPs.…”