The Light Elements Be and B as Stellar Chronometers in the Early Galaxy
  Recent detailed simulations of Galactic Chemical Evolution have shown that the heavy elements, in particular [Fe/H], are expected to exhibit a weak, or absent, correlation with stellar ages in the early Galaxy due to the lack of efficient mixing of interstellar material enriched by individual Type II supernovae. A promising alternative "chronometer" of stellar ages is suggested, based on the expectation that the light elements Be and B are formed primarily as spallation products of Galactic Cosmic Rays. 
Timothy C. Beers, Takeru K. Suzuki, Yuzuru Yoshii