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Type B uncertainty … cross sections
Probability distributions are in the form of a
cross section data base
.
Total partial and differential photon cross sections are required including atomic form
factors F(x, Z) and incoherent scatter factors S(x, Z)
These cross sections must be: complete (in terms of E, Z) self-consistent and up to
date/accurate.
Self-consistency is also required with mass energy absorption data used for kerma
calculation from energy fluence
Up to date cross sections are used in all current versions of benchmarked MC codes:
EPDL97 (LLNL) in the ENDL or ENDF/B-VI formats or the DLC-146 format (ORNL) or
XCOM (NIST) database. Mass energy-absorption coefficients for water by Seltzer and
Hubbell (available on line at NIST).
Data readily available online through NIST
( http://www.nist.gov/pml/data/xraycoef/ )
TG-138 (AAPM/ESTRO) cites ~1% cross section type B that contributes to dosimetric
uncertainty at r=5 cm about 0 76 % (low E) and 0 12% (high E)
.
.