Figure 2-5. 238U Decay Product Ingrowth

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiation Protection in Uranium Facilities

beta levels from decay products may be many orders of magnitude greater than the exposure rates from

the uranium.

Figure 2-5. 238U Decay Product Ingrowth

2.3.1 Alpha-Neutron External Hazard

The interaction of alpha particles from uranium with the nuclei of fluorine and other low-Z atoms

generates neutrons of approximately 2-MeV energy. The magnitude of the neutron flux varies, based on

the total activity of uranium (which is a function of enrichment) and the chemical compound in question

(mixing of U and F). In the case of UF6, the typically measured neutron dose rates for cooled storage

cylinders are as follows:

Natural-5% enrichment:

0.01-0.2 mrem/h

Very high enrichment (97+%) : 2-4 mrem/h (contact)

1-2 mrem/h (3 ft)

The preceding values were measured with a 9-in. spherical BF3 rem meter. In general, the exposure

potential of personnel to neutrons generated by the (alpha, n) reaction is not high. However, if personnel

are required to spend more than a few hours per week in close proximity to containers of uranium fluoride

compounds or if their assignments require them to spend time near storage or processing areas for large

quantitie s of uranium fluoride compounds, the exposure to neutrons should be evaluated. This is

particularly necessary since the personnel monitoring badges may not be neutron-sensitive or may need to

be calibrated to the specific spectra. Penetrating radiation exposures from

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