2.25 MEASURED DIRECT RADIATION
When measurements are available to characterize radiation
fields where people are expected to reside, an estimate of the health impacts
from direct radiation exposure to the fields may be made.
- Transport Medium:
- direct radiation dose rate for radiation transport from source to the exposed individual, rem/yr, expressed as an instantaneous dose rate
- Special Process:
- reduction of dose rate with time according to a user-defined half-time
- Exposure Factors:
- exposure rate and exposure duration.
The total lifetime dose from external exposure to measured radiation
fields is evaluated as follows:
(111)
where
Ddr = total lifetime dose for exposure to the measured direct radiation field (rem)
DR = measured direct radiation dose rate at the exposure location (rem/h)
Udr = daily exposure time to the direct radiation field (h/d)
Fdr = fraction of days per year direct radiation occurs (dimensionless)
ldr = effective rate constant for reduction of the measured direct radiation rate (d-1)
EDdr = exposure duration for exposure to the direct radiation field (yr)
and 365.25 is as previously defined.
The user may supply a value for the dose reduction
half-time from which the effective rate constant, ldr,
is evaluated. If no value is given for the half-time, the dose rate is
assumed to be constant over time.