Photon Fluence Rate
ö
from a Point Source
ö
=
AY / 4
ð
r = photon fluence rate (
ã
/ cm -hr)
2
2
A
=
source activity (decay per hr)
Y
=
photon yield (
ã
/ decay)
r
=
distance from point source (cm)
Exposure Rate (X) from a Point Source
X (R/hr) =
Ã
A / r
2
Ã
=
specific gamma ray constant (R/hr @ 1 meter per Ci)
A
=
activity of source in curies
r
=
distance from source in meters
Exposure Rate (X) from a Line Source
1
1
2
2
Inside L / 2:
X (d )
=
X (d )
1
1
2
2
Outside L / 2:
X (d ) =
X (d )
2
2
1
d = distance from source at location 1
2
d = distance from source at location 2
L = length of line
Note that outside of L / 2 the equation is the same as the
inverse square law.
Exposure Rate (X) from a Disk Source
a
X (R/hr) =
ð
R A
Ã
x ln[(R + D ) / D ]/R
2
2
2
2
2
Ã
= R/hr @ 1 meter per Ci
a
A = activity per unit area (curies per sq. meter)
R = radius of source surface in meters
D = distance from source surface in meters
Simplify the formula by canceling the R s
2
a
X (R/hr) =
ð
A
Ã
x ln[(R + D ) / D ]
2
2
2
62
Photon Fluence Rate
ö
from a Point Source
ö
=
AY / 4
ð
r = photon fluence rate (
ã
/ cm -hr)
2
2
A
=
source activity (decay per hr)
Y
=
photon yield (
ã
/ decay)
r
=
distance from point source (cm)
Exposure Rate (X) from a Point Source
X (R/hr) =
Ã
A / r
2
Ã
=
specific gamma ray constant (R/hr @ 1 meter per Ci)
A
=
activity of source in curies
r
=
distance from source in meters
Exposure Rate (X) from a Line Source
1
1
2
2
Inside L / 2:
X (d )
=
X (d )
1
1
2
2
Outside L / 2:
X (d ) =
X (d )
2
2
1
d = distance from source at location 1
2
d = distance from source at location 2
L = length of line
Note that outside of L / 2 the equation is the same as the
inverse square law.
Exposure Rate (X) from a Disk Source
a
X (R/hr) =
ð
R A
Ã
x ln[(R + D ) / D ]/R
2
2
2
2
2
Ã
= R/hr @ 1 meter per Ci
a
A = activity per unit area (curies per sq. meter)
R = radius of source surface in meters
D = distance from source surface in meters
Simplify the formula by canceling the R s
2
a
X (R/hr) =
ð
A
Ã
x ln[(R + D ) / D ]
2
2
2
62
Photon Fluence Rate
ö
from a Point Source
ö
=
AY / 4
ð
r = photon fluence rate (
ã
/ cm -hr)
2
2
A
=
source activity (decay per hr)
Y
=
photon yield (
ã
/ decay)
r
=
distance from point source (cm)
Exposure Rate (X) from a Point Source
X (R/hr) =
Ã
A / r
2
Ã
=
specific gamma ray constant (R/hr @ 1 meter per Ci)
A
=
activity of source in curies
r
=
distance from source in meters
Exposure Rate (X) from a Line Source
1
1
2
2
Inside L / 2:
X (d )
=
X (d )
1
1
2
2
Outside L / 2:
X (d ) =
X (d )
2
2
1
d = distance from source at location 1
2
d = distance from source at location 2
L = length of line
Note that outside of L / 2 the equation is the same as the
inverse square law.
Exposure Rate (X) from a Disk Source
a
X (R/hr) =
ð
R A
Ã
x ln[(R + D ) / D ]/R
2
2
2
2
2
Ã
= R/hr @ 1 meter per Ci
a
A = activity per unit area (curies per sq. meter)
R = radius of source surface in meters
D = distance from source surface in meters
Simplify the formula by canceling the R s
2
a
X (R/hr) =
ð
A
Ã
x ln[(R + D ) / D ]
2
2
2
62
Photon Fluence Rate
ö
from a Point Source
ö
=
AY / 4
ð
r = photon fluence rate (
ã
/ cm -hr)
2
2
A
=
source activity (decay per hr)
Y
=
photon yield (
ã
/ decay)
r
=
distance from point source (cm)
Exposure Rate (X) from a Point Source
X (R/hr) =
Ã
A / r
2
Ã
=
specific gamma ray constant (R/hr @ 1 meter per Ci)
A
=
activity of source in curies
r
=
distance from source in meters
Exposure Rate (X) from a Line Source
1
1
2
2
Inside L / 2:
X (d )
=
X (d )
1
1
2
2
Outside L / 2:
X (d ) =
X (d )
2
2
1
d = distance from source at location 1
2
d = distance from source at location 2
L = length of line
Note that outside of L / 2 the equation is the same as the
inverse square law.
Exposure Rate (X) from a Disk Source
a
X (R/hr) =
ð
R A
Ã
x ln[(R + D ) / D ]/R
2
2
2
2
2
Ã
= R/hr @ 1 meter per Ci
a
A = activity per unit area (curies per sq. meter)
R = radius of source surface in meters
D = distance from source surface in meters
Simplify the formula by canceling the R s
2
a
X (R/hr) =
ð
A
Ã
x ln[(R + D ) / D ]
2
2
2
62