What is deep-dose equivalent, H_d?

• A. The external dose to the deep portion of the body; used for regulatory compliance.
• B. The deep in-tissue dose due to neutron exposure.
• C. The collective dose across a population.
• D. The dose rate at the body's surface.

Answer: (A)

The concept tested is the external dose that reaches deep tissues of the body, expressed as the deep-dose equivalent, H_d. This quantity represents the average dose in tissues about 1 centimeter beneath the skin from external radiation, with the dose converted to a dose equivalent using the radiation’s quality factor. It is used for regulatory compliance to set limits on occupational exposure for deep organs.

This is different from a surface or shallow tissue dose (which relates to H_p at the skin surface) and from internal or populationwide metrics like collective dose. It’s also not specific to neutrons; it’s a general external-exposure measure focused on deep tissues, at a depth of 1 cm, for regulatory purposes.