Radiohalos in a Radiochronological
Figure 1. The scale for all photomicrographs is 1 cm = 25.0 μm, except for (h') and (r'), which are enlargements of (h) and (r).
(a) Schematic drawing of 238U halo with radii proportional to ranges of alpha particles in air.
(b) Schematic of 210Po halo.
[(c) Schematic of 214Po halo.
(d) Schematic of 218Po halo.]
(e) Coloration band formed in mica by 7.7-Mev 4He ions. Arrow shows direction of beam penetration.
(f) A 238U halo in biotite formed by sequential α-decay of the 238U decay series.
(g) Embryonic 238U halo in fluorite with only two rings developed.
(h) Normally developed 238U halo in fluorite with nearly all rings visible.
(h') Same halo as in (h) but at higher magnification.
(i) Well-developed 238U halo in fluorite with slightly blurred rings.
(j) Overexposed 238U halo in fluorite, showing inner ring obliteration.
(k) Two overexposed 238U halos in fluorite, showing outer ring reversal effects.
[(l) More overexposed 238U halo in fluorite, showing outer ring reversal effects.]
(m) Second-stage reversal in a 238U halo in fluorite. The ring sizes are unrelated to 238U alpha particle ranges.
(n) Three 210Po halos of light, medium, and very dark coloration in biotite. Note the difference in radius.
(o) Three 210Po halos of varying degrees of coloration in fluorite.
(p) A 214Po halo in biotite.
(q) Two 218Po halos in biotite.
(r) Two 218Po halos in fluorite.
(r') Same halos as in (r) but at higher magnification.
(Reprinted from ref. (2) by permission of the AAAS.)