Guidance on Selection of Radiation Type

External Exposure

Photons

1. E > 250 keV - Applies to photons from fission reactions, including nuclear detonations, decay of mixed fission or activation products, and unknown sources. This energy range applies to many common photon-emitting radionuclides including, for example, ⁵⁸Co, ⁶⁰Co, ⁶⁵Zn, ¹⁰⁶Ru+¹⁰⁶Rh, ¹³⁴Cs, and ¹³⁷Cs+^137mBa.
2. E = 30-250 keV - Applies to diagnostic x rays generated at peak tube potential greater than 45 kVp, or diagnostic x rays of unknown energy. Radionuclides that emit photons in this energy range include, for example, ⁵⁷Co, ¹⁴⁴Ce+¹⁴⁴Pr decay products, ¹⁵⁵Eu, ²³⁵U, and ²⁴¹Am.
3. E < 30 keV - Applies to diagnostic x rays generated at peak tube potential less than 45 kVp. Radionuclides that emit photons in this energy range normally should not be important contributors to external dose.

If a dose is identified with external exposure to specific radionuclides, select the energy range for each radionuclide on the basis of the average energy of emitted photons.

Electrons

Select E > 15 keV in all cases of external electron exposure of skin and lens of the eye.

Neutrons

1. E = 0.1-2 MeV - Applies to fission neutrons, other neutrons with average energies known to be in this range, and neutrons of unknown energies.
2. Select other range of neutron energies only if average energies are known to be in that range [for example, E < 10 keV applies to thermal neutrons, E = 2-20 MeV applies to neutrons from ³H(d,n)⁴Hereaction at low projectile energies].