In what situation is one gray different from one sievert?

1. In what situation is one gray different from one sievert? • High energy highly charged particles, z>2, (HZE particles), such as the carbon, nitrogen, oxygen and iron ions in the GCR, are more effective in causing biological effects per unit of absorbed dose than are high energy protons. A quality factor (Q) has been defined as the ratio of a dose of sparsely ionizing radiation (e.g., high energy electrons from gamma rays) to the dose of a radiation in question to produce the same low level biological effect. When Q>1, one sievert differs from one gray. Q is the ratio of sieverts to grays.

2. Radiation Exposure Quantities & Units • Absorbed dose: Energy absorbed per unit mass Units: 1 gray (Gy) = 1 joule/kg [old unit: 1 rad = 0.01 Gy] Dose Equivalent: The absorbed dose of sparsely ionizing radiation (gamma rays) to produce the stochastic effect in question. Units: 1 sievert (Sv) = 1 Gy of gamma rays (sparsely ionizing reference radiation) [old unit: 1 rem = 0.01 Sv]

3. Biological effects are known to depend on the dE/dx of the particles. In radiation protection, this quantity is called the LET (linear energy transfer).

4. In general:For low LET (sparsely ionizing particles), effects are proportional to LET (dE/dx).For high LET (HZE particles, Z>2), effects are supralinear with LET

5. New Strategy Present Strategy Surrogate system(s) of human carcinogenesis Human consensus carcinogenesis model input Surrogate systems of carcinogenic processes LET, dose, and protraction dependence of the carcinogenic processes LET, dose, and protraction dependence of the system(s) Quality factor and DDREF variation Human Risk Human Risk