The Weak Interaction is 100% left-handed. Energetic beta-decay (~50keV and larger energies) gives chiral relativistic electrons. The higher the energy the greater the chiral excess. As they collide with and decompose the neighborhood their energy drops. Non-relativistic beta-rays have helicity not chirality. Early interactions give chiral excess in the products.
Willam Bonner, among others, in the 1970s demonstrated that chiral beta-rays preferentally decomposed one optical isomer of a given racemic amino acid mixture. Review article:
Chirality 12(3) 114-26 (2000)
Cosmic sources of deep UV and relativistic electrons tend to give chiral excesses in their emissions. One then has a consistent pervasive natural mechanism for a pan-cosmic excess of one optical isomer in alpha-amino acids when life starts poking around.
