Alpha ionization damage as a cause of low helium ratios

The possibility has been investigated that helium atoms escape from the crystal structures of minerals only as these structures become damaged by intense alpha‐particle ionization. The escape of helium from zircon and sphene has been found to be almost zero for cases of low alpha bombardment, and increases progressively until almost all of the helium is lost in cases where the samples have suffered a bombardment of 1016 α/mg. The zircons in granites are well up in the range of activity where this damage will be important so that it is concluded that one of the principal causes of the high loss of helium from granitic rocks is the concentration of the radioactive elements and consequently helium into centers in which the damage will be great enough for the helium to escape.