THE EGS5 CODE SYSTEM

Ī adj = average adjusted mean ionization energy, (2.266)δ = density effect correction, (2.267)F − (τ, ∆) = −1 − β 2 + ln[(τ − ∆)∆] + τ/(τ − ∆)[∆2+(12 + (2τ + 1)ln − ∆ ) ] /γ 2 (2.268)τF + (τ, ∆) = ln(τ∆) − β2τ{τ + 2∆ − 3∆2 y2− (∆ − ∆ 3 /3)y 2 − (∆ 2 /2 − τ∆ 3 /3 + ∆ 4 /4)y 3} . (2.269)Since EGS3 was released there has been considerable effort devoted to establishing accuratevalues for the parameters in the above equations and considerable changes have occurred, especiallyin the recommended I values. The values recommended in 1983 by Berger and Seltzer[20] havealso been recommend by the International Commission on Radiation Units and Measurements[79].PEGS contains a table of I values for all elements and these are presented in Table 2.2 along withthe default atomic weights and elemental densities used in PEGS (any of which can be overriddenby the user).The values of Īadj for mixtures and compounds are derived fromln Īadj =( Ne∑i=1)/ ( Ne)∑p i Z i (ln I adj (Z i )) p i Z ii=1(2.270)or taken from Table 2.3 for a select group of materials as discussed below.75