1.

We have seen that a gamma-ray does of 3 Gy is lethal to half the people exposed to it. If the equivalnet energy were absorbed as heat, what rise in body temperature would result ?

Answer»

`300 muK`
`700 muK`
`455 muK`
`390 muK`

Solution :We can relate an absorbed ENERGY `Q` and the resulting temperature increase `DeltaT` with RELATION `Q = cmDeltaT`. In that equation, `m` is the mass of the materical obsorbing the energy and `c` is the specific heat of that material. An absorbed dose of `3Gy` correconds to an absorbed energy per unit mass of `3J//kg`. Let us assume that `c` the specific heat of human body, is the same as that of water, `4180 J//kg K`. then we find that
`DeltaT = (Q//m)/(c) = (3)/(4180) = 7.2 xx 10^(-4) K~~ 700 muK`
Obviously the damage done by ionizing radiation has nothing to do with thermal HEATING. The harmful effects arise because the radiation damages `DNA` and thus interferes with the normal functioning of tissues in which it is obsorbed.


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