RSDetection
User’s Manual
Copyright
©
2016 General Electric Company. All Rights Reserved
S131-200-UM Rev A
Page 55
g
Source calibration
Indicates the exposure rate at one meter on a specific
date. This exposure rate must be corrected for the decay of
the source from date of certification to the date of the
calibration run as follows:
K
d
= e-0.693(t/T)
where K
d
= the coefficient of decay
e = natural logarithm base
t = time between the date of source certification and
calibration
T = the half-life of the source (5.26 years for Co
60
)
The values of t and T must both be expressed in the same
unit of time, such as days or years.
Kd
e
D
D
E
E
*
)
100
(
*
2
)
100
(
*
1 0 0
E
100
= exposure rate produced by gamma source at a
distance of one meter as indicated on the source certificate
µ = the linear attenuation factor for air (6.8 x 10
-5
cm
-1
)
D = distance in cm between the center of the source and
center of the ion chamber
K
d
= the decay coefficient calculated for the source
calibration
k(Co
60
or Cs137)
The value of amps (P) divided by the Exposure Rate for the
source-to-ion-chamber distance being used. Units will be
amps/R/hr.
k
The average value of k.
σ
The standard deviation
1)
-
n(n
)
k
(
-
k
n
OR
1
-
n
k
n
-
k
2
i
2
i
2
2
i
where n = number of measurements of k, typically 4.
V = σ/k
Should be less than 1%. If it is not, the readings show too
much variation, and they may not be valid. Repeat the
readings carefully.
k
(Ra
226
)
The average value of k corrected for the radiation energy
spectrum of Ra
226
by the relation:
k
( Ra226) = (0.91) x
k
(Cs
137
) or (1.022) x
k
(Co
60
)
HPIC Sensitivity
k
(amps/R/hr)
