At body temperature

PHYSICS · Multi-part · Fermi University Physics · Quantum Mechanics · Biophysics & Medical Physics · Origins of quantum theory

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

Problem

At body temperature

k_BT = 26.7\,\mathrm{meV}

. A red laser pointer emits photons of

1.9\,\mathrm{eV}

, and a mammography tube emits X-ray photons of about

20\,\mathrm{keV}

. Ionising a water molecule takes about

12.6\,\mathrm{eV}

. ((a)) Express each photon's energy in units of

k_BT

. ((b)) How many red photons carry the same total energy as one

20\,\mathrm{keV}

photon? ((c)) Explain why a red beam delivering that many photons still ionises no water, while a single X-ray photon can.