What traditional unit is valid up to 3 MeV?

• A. Rad
• B. Roentgen
• C. Gray
• D. rem

Answer: (B)

The roentgen is a traditional unit of measurement that is specifically utilized to quantify exposure to ionizing radiation. It is defined in terms of the amount of ionization produced in air by X-rays or gamma rays and is valid for photon energies typically up to 3 MeV. Above this energy threshold, the relationship between exposure and ionization becomes less straightforward, and other metrics may provide better assessment for radiation doses.

In contrast, the other units listed serve different purposes and are applicable in broader contexts. The rad and gray are primarily used to measure absorbed dose, which pertains to the amount of energy absorbed by any material from ionizing radiation. The rem, along with its SI equivalent, the sievert, caters to the biological effect of radiation by factoring in the type of radiation and the susceptibility of different tissues.

The validity of the roentgen up to 3 MeV underscores its relevance in scenarios involving lower-energy X-rays and gamma rays, thus making it suitable for radiation measurement in medical and diagnostic contexts where exposure rates are typically measured.