The blood count is depressed after a whole-body dose equivalent of at least how many mSv?

The blood count is depressed after a whole-body dose equivalent of at least how many mSv?

• A. 10 mSv
• B. 0.25 mSv
• C. 5 mSv
• D. 0.01 mSv

Answer: (B)

Hematopoietic depression from whole-body radiation appears because the bone marrow is extremely radiosensitive, and circulating blood cells—especially lymphocytes—show declines early after exposure. The dose at which you start to see measurable changes in blood counts is around a quarter of a sievert (about 0.25 Gy for gamma radiation), which translates to roughly 250 mSv. Among the options, the value in the ballpark of a few hundred millisieverts corresponds to this threshold for hematologic effects. Note that the unit in that option is often misprinted as 0.25 mSv, but the biologically meaningful threshold is about 0.25 Sv (250 mSv). Small exposures like 10 mSv, 5 mSv, or 0.01 mSv would not produce noticeable blood-count depression.

Hematopoietic depression from whole-body radiation appears because the bone marrow is extremely radiosensitive, and circulating blood cells—especially lymphocytes—show declines early after exposure. The dose at which you start to see measurable changes in blood counts is around a quarter of a sievert (about 0.25 Gy for gamma radiation), which translates to roughly 250 mSv. Among the options, the value in the ballpark of a few hundred millisieverts corresponds to this threshold for hematologic effects. Note that the unit in that option is often misprinted as 0.25 mSv, but the biologically meaningful threshold is about 0.25 Sv (250 mSv). Small exposures like 10 mSv, 5 mSv, or 0.01 mSv would not produce noticeable blood-count depression.