Tissue–air ratios for narrow gamma‐ray beams

Abstract
This study introduces a table of tissue–air ratios (TAR) for narrowgamma‐ray beams. The table is consistent with recently published TAR data for broadgamma‐ray beams [Table 4.1, Br. J. Radiol. Suppl.25(1996)]. Narrow‐beam TARs are derived analytically from broad‐beam data of Table 4.1 and are tabulated for circular fields ranging from 0.2 to 2.2 cm in radius— an approximate equivalent of atosquare‐field range. The extent of depths is from 0.5 to 30 cm in water.