Combining Radiation Types to Determine Total Dose
An individual radionuclide may have several different types of
emissions. Those different types of emissions and the short-
lived progeny of
the individual radionuclide must be
considered when determining a total dose.
Particulate radiation should be treated as a “shallow” dose
while photons and neutrons should be treated as a “deep”
dose and these two types of doses should not be summed.
This example with sodium-22 will clarify this concept.
Na-22 2.605 y Beta+ 0.546 MeV (89.8% Abundance)
1 mCi Gamma 1.275 MeV (99.9% Abundance)
From the table of Beta Dose Rates we find 320 rad/hr at 1 cm
and 0.4 rad/hr at 30 cm. The near contact dose rate is much
higher than the dose rate at 30 cm.
Using 6CEN for the gamma dose rate we find;
6CEN = 6 x 1 mCi x 1.275 MeV x 0.999 = 7.64 mRem/hr at
30 cm.
We can also use 6CEN for the annihilation photons from the
positron.
6CEN = 6 x 1 mCi x 0.511 MeV x 2 x 0.898 = 5.51 mRem/hr
at 30 cm.
The “shallow” dose from the positron at 30 cm is 400 mrad/hr
and the “deep” dose from the gamma and photon radiation is
7.64 mRem/hr + 5.51 mRem/hr = 13.15 mRem/hr.
57
Combining Radiation Types to Determine Total Dose
An individual radionuclide may have several different types of
emissions. Those different types of emissions and the short-
lived progeny of the individual radionuclide must be
considered when determining a total dose.
Particulate radiation should be treated as a “shallow” dose
while photons and neutrons should be treated as a “deep”
dose and these two types of doses should not be summed.
This example with sodium-22 will clarify this concept.
Na-22 2.605 y Beta+ 0.546 MeV (89.8% Abundance)
1 mCi Gamma 1.275 MeV (99.9% Abundance)
From the table of Beta Dose Rates we find 320 rad/hr at 1 cm
and 0.4 rad/hr at 30 cm. The near contact dose rate is much
higher than the dose rate at 30 cm.
Using 6CEN for the gamma dose rate we find;
6CEN = 6 x 1 mCi x 1.275 MeV x 0.999 = 7.64 mRem/hr at
30 cm.
We can also use 6CEN for the annihilation photons from the
positron.
6CEN = 6 x 1 mCi x 0.511 MeV x 2 x 0.898 = 5.51 mRem/hr
at 30 cm.
The “shallow” dose from the positron at 30 cm is 400 mrad/hr
and the “deep” dose from the gamma and photon radiation is
7.64 mRem/hr + 5.51 mRem/hr = 13.15 mRem/hr.
57
Combining Radiation Types to Determine Total Dose
An individual radionuclide may have several different types of
emissions. Those different types of emissions and the short-
lived progeny of
the individual radionuclide must be
considered when determining a total dose.
Particulate radiation should be treated as a “shallow” dose
while photons and neutrons should be treated as a “deep”
dose and these two types of doses should not be summed.
This example with sodium-22 will clarify this concept.
Na-22 2.605 y Beta+ 0.546 MeV (89.8% Abundance)
1 mCi Gamma 1.275 MeV (99.9% Abundance)
From the table of Beta Dose Rates we find 320 rad/hr at 1 cm
and 0.4 rad/hr at 30 cm. The near contact dose rate is much
higher than the dose rate at 30 cm.
Using 6CEN for the gamma dose rate we find;
6CEN = 6 x 1 mCi x 1.275 MeV x 0.999 = 7.64 mRem/hr at
30 cm.
We can also use 6CEN for the annihilation photons from the
positron.
6CEN = 6 x 1 mCi x 0.511 MeV x 2 x 0.898 = 5.51 mRem/hr
at 30 cm.
The “shallow” dose from the positron at 30 cm is 400 mrad/hr
and the “deep” dose from the gamma and photon radiation is
7.64 mRem/hr + 5.51 mRem/hr = 13.15 mRem/hr.
57
Combining Radiation Types to Determine Total Dose
An individual radionuclide may have several different types of
emissions. Those different types of emissions and the short-
lived progeny of the individual radionuclide must be
considered when determining a total dose.
Particulate radiation should be treated as a “shallow” dose
while photons and neutrons should be treated as a “deep”
dose and these two types of doses should not be summed.
This example with sodium-22 will clarify this concept.
Na-22 2.605 y Beta+ 0.546 MeV (89.8% Abundance)
1 mCi Gamma 1.275 MeV (99.9% Abundance)
From the table of Beta Dose Rates we find 320 rad/hr at 1 cm
and 0.4 rad/hr at 30 cm. The near contact dose rate is much
higher than the dose rate at 30 cm.
Using 6CEN for the gamma dose rate we find;
6CEN = 6 x 1 mCi x 1.275 MeV x 0.999 = 7.64 mRem/hr at
30 cm.
We can also use 6CEN for the annihilation photons from the
positron.
6CEN = 6 x 1 mCi x 0.511 MeV x 2 x 0.898 = 5.51 mRem/hr
at 30 cm.
The “shallow” dose from the positron at 30 cm is 400 mrad/hr
and the “deep” dose from the gamma and photon radiation is
7.64 mRem/hr + 5.51 mRem/hr = 13.15 mRem/hr.
57
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