Table 1.

Composition of GAFCHROMIC EBT (Ref. ¹⁸) and EBT2 films (Ref. ²⁰). Effective atomic number calculated using Eq. A4 from McCullough and Holmes (Ref. ¹⁹). Water included for comparison purposes. The composition of lot 020609, in mass percent, is the same as that currently provided by ISP for the EBT2 active layer, in atomic percent (http://www.gafchromic.com, accessed 4 November 2009).

Layer	Composition (Mass %)								Zeff	Density (g∕cm3)
	C	H	O	N	Li	Cl	K	Br
EBT
Active	57.4	9.4	16.4	13.2	0.8	2.9	⋯	⋯	7.05	1.1
Surface	32.3	6.5	20.5	21.6	2.3	16.8	⋯	⋯	9.90	1.2
Clear Polyester	62.5	4.2	33.3	⋯	⋯	⋯	⋯	⋯	6.64	1.35
EBT2
Active (lot 020609)	57.8	9.6	27.8	0.2	0.9	1.7	0.6	1.3	9.18	1.2
Active (lot 031109)	59.7	9.5	26.1	0.2	0.9	2.3	1.3	⋯	7.44	1.2
Adhesive	65.6	9.4	24.9	⋯	⋯	⋯	⋯	⋯	6.26	1.2
Surface	47.2	8.8	38.2	⋯	1.0	4.9	⋯	⋯	7.82	1.2
Polyester	62.5	4.2	33.3	⋯	⋯	⋯	⋯	⋯	6.64	1.35
Water
Water	⋯	11.2	88.8	⋯	⋯	⋯	⋯	⋯	7.42	0.998