Gray (unit)

From Freepedia

The gray (symbol: Gy) is the SI unit of absorbed dose.

Contents 1 Definition 2 SI multiples 3 Origin 4 Explanation 5 Conversions

Definition

One gray is the absorption of one joule of radiation energy by one kilogram of matter.

1 Gy = 1 J/kg = 1 m²·s^–2

Note that these are the same units as the sievert. To avoid any risk of confusion between the absorbed dose and the equivalent dose, one must use the corresponding special units, namely the gray instead of the joule per kilogram for absorbed dose and the sievert instead of the joule per kilogram for the dose equivalent.

SI multiples

Multiple	Name	Symbol		Multiple	Name	Symbol
100	gray	Gy
101	decagray	daGy		10–1	decigray	dGy
102	hectogray	hGy		10–2	centigray	cGy
103	kilogray	kGy		10–3	milligray	mGy
106	megagray	MGy		10–6	microgray	µGy
109	gigagray	GGy		10–9	nanogray	nGy
1012	teragray	TGy		10–12	picogray	pGy
1015	petagray	PGy		10–15	femtogray	fGy
1018	exagray	EGy		10–18	attogray	aGy
1021	zettagray	ZGy		10–21	zeptogray	zGy
1024	yottagray	YGy		10–24	yoctogray	yGy

Origin

The Gray was defined in 1975 in honor of Louis Harold Gray (1905-1965), who used a similar concept, “that amount of neutron radiation which produces an increment of energy in unit volume of tissue equal to the increment of energy produced in unit volume of water by one röntgen of radiation,” in 1940.

Explanation

The gray measures the physical effects of radiation. The biological effects can vary by the type and energy of the radiation and the organism and tissues involved. The separate unit sievert attempts to account for these variations.

Conversions

1 gray is equivalent to 100 rad