A trainee makes two claims about an accident in which a worker is exposed

PHYSICS · Multi-part · Fermi University Physics · Biophysics & Medical Physics · Radiation physics and diagnostic imaging · Nuclear medicine, dosimetry and radiotherapy

Life at Thermal Energy, Ch Radiation in tissue: interaction, dose and risk

Problem

A trainee makes two claims about an accident in which a worker is exposed, whole-body, to a

100\,\mathrm{keV}

photon beam that delivers an absorbed dose of

3\,\mathrm{Gy}

. Claim 1: "

100\,\mathrm{keV}

photons in soft tissue (

\mu/\rho = 0.1707\,\mathrm{cm^2\,g^{-1}}

, taking water's value, and density

1.06\,\mathrm{g\,cm^{-3}}

) have used up all their energy by a depth of

10\,\mathrm{cm}

, the same way a charged particle has a range, so tissue beyond

10\,\mathrm{cm}

receives no dose at all. "Claim 2: "Since

3\,\mathrm{Gy}

can make people seriously ill, the worker's tissue must have been heated by several kelvin, like a fever gone wrong, and it is this heat that does the damage." ((a)) Compute the actual fraction of the beam transmitted through

10\,\mathrm{cm}

of this tissue, and explain why a photon beam does not have a range in the sense that a charged particle does. ((b)) Using

c_p = 3600\,\mathrm{J\,kg^{-1}\,K^{-1}}

for tissue, compute the actual temperature rise from

3\,\mathrm{Gy}

, say whether this exposure lies in the range of deterministic effects and whether it also carries a stochastic risk, and explain why the damage mechanism is not heating.

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