Stopping Power V Linear Energy Transfer Let

STOPPING POWER refers to the inelastic energy losses by an electron moving through a medium with density r are described by the total mass–energy stopping power $\left ( \frac{S}{\rho} \right )_{tot}$, which represents the kinetic energy $E_K$ loss by the electron per unit path length x, or:

(1)

\begin{align} \left ( \frac{S}{\rho} \right )_{tot}= \frac{1}{\rho}.\frac{dE_K}{dx} (MeV.cm^2/g) \end{align}

$\left ( \frac{S}{\rho} \right )_{tot}$ consists of two components: the mass collision stopping power ($\left ( \frac{S}{\rho} \right )_{col}$), resulting from electron–orbital electron interactions (atomic excitations and ionizations), and the mass radiative stopping power ($\left ( \frac{S}{\rho} \right )_{rad}$), resulting from electron–nucleus interactions (bremsstrahlung production):

(S/ρ)tot = (S/ρ)col + (S/ρ)rad

(2)

\begin{align} \frac{S}{\rho} = \left ( \frac{S}{\rho} \right )_{col} + \left ( \frac{S}{\rho} \right )_{rad} \end{align}

LINEAR ENERGY TRANSFER of charged particles in a medium is the quotient dE/dl, where dE is the average energy locally imparted to the medium by a charged particle of specified energy in traversing a distance of dl.

(3)

\begin{align} L.E.T = \left ( \frac{dE}{dl} \right ) \end{align}

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Stopping Power is closely related to LET except that LET does not include radiative losses of energy (which is lost to the medium and so not absorbed!)