Purpose

Point source calculation, Page 1 of 1Point sourceProcedure E1, Pg. 5 of 8

Calculation of effective dose due to exposure to a point source

1) Discussion and equations

Effective doses calculated at 1 m from the point source are used to calculate the dose at other distances XE "radiation source: point source" , assuming no shielding XE "radiation source: lost" . For distances shorter than 0.5 m, the calculation is will significantly overestimate the real dose rate. For distances less than 0.2 m, the equation should not be used. The equation is:

Where

Epoint=Effective dose from point source XE "radiation source: point source" [mSv]

A =Source activity [kBq]. 1 Ci = 3.7 x 107 kBq.

CFpoint= Conversion factor for a point source, see section 2 [(mS XE "conversion factor: CF6" v . m2)/(kBq . h)]

distance =Distance in meters from the point source XE "radiation source: point source" [m]

t =Exposure duration [h]

When information on the source shielding (material and thickness) is available, the calculated effective dose from the point source may be reduced by using the half value layer (HVL) for the material in question. The half value layer is the thickness required to reduce the dose by a half. The following equation should be used:

Where

Epoint shielded=Effective dose from shielded point source XE "radiation source: point source" [mSv]

thickness = material thickness [cm]

HVL = half value layer for the material [cm], see the HVL table in section 3.

2) Conversion factors

RadionuclideCFpoint(mSv . m2)/(kBq . h)

Na22

Na242.2E-07

3.8E-07

K40

K421.6E-08

2.8E-08

Sc462.1E-07

Ti441.1E-08

V482.9E-07

Cr513.4E-09

Mn54

Mn568.6E-08

1.7E-07

Fe55

Fe593.2E-10

1.2E-07

Co58

Co601.0E-07

2.5E-07

Cu642.0E-08

Zn656.0E-08

Ga689.8E-08

Ge68+Ga689.8E-08

Se753.9E-08

Kr85

Kr85m

Kr87

Kr88+Rb882.3E-10

1.5E-08

7.8E-08

2.5E-07

Rb86

Rb889.6E-09

5.7E-08

Sr89

Sr911.4E-11

7.1E-08

Y91

Y91m3.7E-10

5.5E-08

Zr957.6E-08

Nb94

Nb951.6E-07

7.9E-08

Mo991.6E-08

Tc99m1.2E-08

Rh1032.1E-08

Ru103

Ru105

Ru1065.0E-08

8.1E-08

1.4E-09

Ru106+Rh1061.4E-09

Ag110m2.8E-07

Cd109+Ag109m1.6E-07

In114m1.0E-08

Sn113

Sn1233.4E-09

7.0E-10

Sn126+Sb126m5.7E-09

Sb124

Sb126

Sb126m

Sb127

Sb1291.9E-07

2.8E-07

4.9E-10

6.8E-08

1.5E-07

Te127

Te127m

Te129

Te129m+Te129

Te131

Te131m

Te1326.0E-09

1.6E-09

4.2E-08

4.6E-08

4.5E-08

1.5E-07

2.3E-08

I125

I129

I131

I132

I133

I1345.9E-09

3.4E-09

3.9E-08

2.4E-07

6.2E-08

2.7E-07

I135+Xe1353.8E07

Xe131m

Xe133

Xe133m

Xe135

Xe1382.7E-09

4.6E-09

4.8E-09

2.4E-08

1.1E-07

Cs134

Cs136

Ba137m

Cs137+Ba137m

Ba133

Cs138

Ba1401.6E-07

2.2E-07

6.2E-08

6.2E-08

4.1E-08

3.0E-09

2.0E-08

La1402.3E-07

Ce141

Ce144+ Pr1447.2E-09

3.1E09

Pr144m

Pr1442.9E-09

1.2E-09

Pm1453.6E-09

Eu152

Eu154

Eu1551.2E-07

1.3E-07

5.3E-09

Gd1531.1E-08

Tb1601.1E-07

Ho166m1.6E-07

Tm1705.0E-10

Yb1692.9E-08

Hf172

Hf1812.2E-08

5.5E-08

Ta1821.3E-07

W1874.9E-08

Ir1928.3E-08

Au1984.1E-08

Hg2032.3E-08

Ti2041.0E-10

Pb2106.9E-10

Bi2071.6E-07

Ra2266.2E-10

Ac2289.5E-08

Th227

Th228

Th230

Th231

Th2321.1E-08

3.9E-10

2.3E-10

2.5E-10

2.1E-10

Pa2314.3E-09

U-Dep & Nat

U-Enriched

U232

Pa233

U233

U234

U235

U2382.3E-10

2.8E-10

3.2E-10

1.7E-08

1.2E-10

2.8E-10

1.4E-08

2.3E-10

Np237

Pu236

Pu238

Pu239

Pu240

Pu2423.8E-09

3.4E-10

3.0E-10

1.2E-10

2.8E-10

2.3E-10

Am241

Am242

Am2433.1E-09

8.5E-10

5.4E-09

Cm242

Cm243

Cm244

Cm2453.1E-10

1.3E-08

2.8E-10

7.5E-09

Cf2522.1E-10

Calculations made by Oak Ridge National Laboratory (ORNL) using the CONDOS programme. All other radionuclides have a CFpoint < 10 -10 XE "conversion factor: CF6" (mS XE "conversion factor: CF6" v . m2)/(kBq . h) and need not be considered. Information based on IAEA TECDOC 1162: Generic procedures for assessment and response during a radiological emergency. IAEA, August 2000.

3) Half Value Layers

The half value layer (HLV) is the thickness of a substance that, when introduced in the path of a beam of radiation, reduces the exposure rate by one-half. Values are given for "good geometry" for which build-up of secondary radiation is not important.

RadionuclideHalf Value Layer (cm)

LeadIronAlWaterConcrete

Na220.671.383.859.44.35

Na241.322.146.2214.756.88

K401.151.84.9911.975.63

K421.181.845.112.215.75

Sc460.821.484.29.844.66

Ti440.040.210.61.410.67

V480.81.484.189.954.67

Cr510.170.822.385.692.68

Mn540.681.333.89.04.22

Mn560.941.654.7811.135.27

Fe590.941.594.5110.585.02

Co6011.664.6510.995.2

Cu640.411.083.017.613.43

Zn650.871.534.3410.154.81

Ga680.421.093.047.673.47

Ge68+Ga680.421.093.047.673.47

Se750.120.621.794.262.01

Kr850.411.0737.593.43

Kr85m0.10.51.463.461.64

Kr870.831.674.8411.465.36

Kr88+Rb881.171.895.5112.746.05

Rb860.871.534.3510.134.81

Rb881.171.895.5112.746.05

Sr890.741.449.354.42

Sr910.711.383.949.314.38

Y910.961.624.5710.745.09

Zr950.61.263.588.614.0

Nb940.641.303.708.844.13

Nb950.621.283.638.724.06

Mo99+Tc99m0.491.113.167.63.54

Mo990.491.113.167.63.54

Tc990.050.250.731.730.82

Tc99m0.070.391.132.681.27

Ru1030.41.062.977.533.4

Ru1050.481.163.287.983.69

Rh1060.491.173.298.163.73

Ag110m0.711.383.919.364.38

Cd1090.010.060.180.430.2

In114m0.230.752.145.182.41

Sn1130.020.090.270.650.31

Sn1230.881.534.3610.164.83

Sn126+Sb126m0.481.153.277.993.68

Sn1260.040.190.551.30.62

Sb1240.831.554.3910.494.9

Sb1260.521.193.378.213.79

Sb126m0.481.153.277.993.68

Sb1270.471.143.247.923.65

Sb1290.721.43.989.454.43

Te127m0.010.080.230.540.26

Te1290.330.932.636.532.99

Te129m0.380.822.335.652.61

Te131m0.651.313.748.884.17

Te1320.10.531.543.661.73

I1250.010.080.230.540.26

I1290.020.090.250.60.28

I1310.250.932.676.53.02

I1320.631.313.78.914.14

I1330.471.153.238.053.67

I1340.721.43.989.434.43

I135+Xe135m0.981.664.711.065.23

I1350.981.664.711.065.23

Xe131m0.020.10.290.70.33

Xe1330.030.160.471.110.53

Xe133m0.050.250.731.720.82

Xe1350.140.722.14.992.36

Xe135m0.411.072.997.543.41

Xe1380.91.644.7911.095.26

Cs1340.571.243.58.53.93

Cs1360.651.323.768.864.18

Cs137+Ba137m0.531.193.358.23.77

Ba1330.160.671.924.632.17

Ba137m0.531.193.358.23.77

Ba1400.330.962.696.723.06

La1400.931.644.6311.045.19

Ce1410.070.371.072.521.2

Ce144+Pr144m0.050.280.821.950.93

Pr144m0.020.10.280.670.32

Pm1450.020.110.310.740.35

Pm1470.060.340.992.351.12

Sm1510.010.030.090.210.1

Eu1520.661.323.738.844.17

Eu1540.741.383.919.244.35

Eu1550.040.230.661.560.74

Gd1530.030.180.511.210.57

Tb1600.681.353.849.014.26

Ho166m0.451.093.17.463.48

Tm1700.030.180.511.210.57

Yb1690.060.30.872.050.97

Hf1810.270.862.416.022.75

Ta1820.81.393.949.264.39

W1870.431.032.917.173.29

Ir1920.240.922.646.422.98

Au1980.290.972.746.773.11

Hg2030.140.732.135.042.39

Tl2040.030.180.531.270.6

Pb2100.010.050.150.350.17

Bi2070.651.33.688.794.11

Po2100.651.313.738.884.15

Ra2260.090.481.43.321.58

Ac2270.010.080.220.520.25

Ac2280.671.353.849.054.27

Th2270.110.581.694.011.9

Th2280.020.130.370.880.42

Th2300.010.050.140.340.16

Th2320.010.040.120.280.13

Pa2310.090.461.353.21.51

U2320.010.040.120.290.14

U2330.010.060.160.390.18

U2340.010.040.120.280.13

U2350.090.461.353.191.51

U2380.010.040.110.270.13

Np2370.030.120.410.980.46

Pu2360.010.040.110.270.13

Pu2380.010.040.110.270.13

Pu2390.010.040.120.290.14

Pu2400.010.040.110.270.13

Pu2420.010.040.110.270.13

Am2410.020.120.350.820.39

Am242m0.010.040.130.30.14

Am2430.030.180.521.240.59

Cm2420.010.040.120.280.13

Cm2430.080.431.262.981.41

Cm2440.010.040.120.280.13

Cm2450.050.270.791.860.88

Cf2520.010.040.120.30.14

4) Example A worker remained one hour at a distance of 5 meters from a 27 Ci 192Ir source. What was his effective dose?

Ir192 : CFpoint = 8.3E-08 (mS XE "conversion factor: CF6" v . m2)/(kBq . h)

Epoint= 3.3 mSv.

XE "radiation source: point source" Total effective dose from this source at 5 meters in 1 hour = 3.3 mSv.

If the Ir-192 source was shielded with 5 mm of lead what is the dose calculated with the shielding taken into account?

Ir192: HVL for lead = 0.24 cm.

XE "conversion factor: CF6"

5) References

INTERNATIONAL ATOMIC ENERGY AGENCY, Generic Procedures for Assessment and Response during an Radiological Emergency, IAEA TECDOC- 1162, IAEA, Vienna (2000).

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