Asymmetric Positron Interactions with Chiral Quartz Crystals?

Abstract

We have studied the interaction of the positron with chiral left-or right-handed quartz crystals. In Doppler-broadening experiments, using a mono-energetic positron beam there is a differential depth profile for positrons implanted in LH or RH z-cut quartz as identified by a shape parameter (S). Further, in bulk positron annihilation lifetime spectroscopy (PALS) experiments, the lifetime (τ 2) attributed to free annihilation of the positron interacting with the chiral lattice exhibits a larger value for the LH quartz, and the associated intensity (I2) is also significantly different—RH quartz is consistently 10% greater than the LH crystal. The τ3 lifetime and its intensity, I3, attributed to positronium interacting with defects in the quartz, also appears to exhibit differences between the enantiomeric sets of crystals. These observations may demonstrate chiral recognition using a positron annihilation technique, pave the way for a broad range of positron experiments, and may help inform hypotheses of chirality recognition, selection, or induction by beta radiation.

Positron annihilation lifetime spectroscopy using fast scintillators and digital electronics

“…The intensities and lifetimes are shown in Table 3. The lifetimes τ 1 and τ 2 are 159 ps and 366 ps, respectively, and are in good agreement with the reported values of 156 ps [3] and 358 ps [6]. τ 2…”

“…The PALS spectra are usually resolved into three components. The first component results from the decay of p-Ps, the second one from the mixture of decays of o-Ps and free positron, and the third one is due to the delayed decay of o-Ps trapped in defects [6]. The PALS spectrum can therefore be modeled as the convolution of exponential decay function and detector time resolution function, as shown in Eq.…”

Positron Annihilation Lifetime Analysis of Left- and Right-Handed Alanine Single Crystals

“…The small and similar values for I 3 suggest that the crystals are of good quality and have a low defect concentration. Comparable values for quartz crystals are τ 3 = 1.3−1.6 ns and I 3 = 3.5−7.7% [26].…”

“…For an initial test of these hypotheses, we selected leftand right-handed forms of quartz single crystals and observed free positron lifetime (τ 2 ) and intensity (I 2 ) differences in PALS experiments with the asymmetric forms of these crystals [26]. We consider this result to be an example of "particle stereorecognition", as described above.…”

“…The D-alanine I 3 results are very comparable between the sample crystals grown from water and polished (3.8-4.1%, compare Tables I and II), but is significantly lower (2.1%) for crystals grown from acetone/water. While these results show some variability and we expect some amount of defect in the crystals as grown, we do not think that this is an indicator of poor crystal quality, given the results here taken together, and in comparison to I 3 values observed in synthetic single crystal quartz [26]. Finally, PALS data were evaluated with the statistical maximum entropy lifetime (MELT) method [22].…”