Rad Data Handbook 20.. - Voss Associates

Combining Radiation Types to Determine Total Dose
An individual radionuclide may have several different types of
emissions. Those different types of emissions and the shortlived
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 shortlived
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 shortlived
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 shortlived
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