Linear energy transfer

The linear energy transfer (LET, English linear energy transfer ) is a term from dosimetry and is a measure of the effect of radiation . It describes how much energy an ionizing particle gives per unit length to the penetrated material and is usually given in kiloelectron volts per micrometer . The linear energy transfer is an indirect measure of the number of ionizations per distance and describes in particular the effect of radiation on biological material .

description

The linear energy transfer is closely related to the braking capacity of a material. While the braking capacity describes the total energy loss of the particle per distance , the linear energy transfer is the energy that is given off to the material by secondary electrons . In contrast to the braking capacity , the energy output taken into account is limited to the immediate vicinity of the particle track. Therefore one excludes secondary electrons whose energy is greater than a certain value Δ, since a greater energy also means a greater range , and thus an energy release further away from the original particle track. ${\displaystyle {\text{d}}E/{\text{d}}x}$

The linear energy transfer (or the limited linear electronic braking capacity) is therefore defined by

${\displaystyle L_{\Delta }={\frac {{\text{d}}E_{\Delta }}{{\text{d}}x}}}$,

where means the energy loss through collisions with electrons, reduced by the kinetic energies of all secondary electrons with energy greater than Δ. If Δ approaches infinity, then there are no electrons with even greater energy, and the linear energy transfer becomes identical to the linear electronic braking capacity. ${\displaystyle {\text{d}}E_{\Delta }}$

In relation to the density of silicon , an LET of approx. 100 MeV · cm ² / mg corresponds to a charge of approx. 1 pC / µm.

Mixed fields

In mixed radiation fields with particles of different kinetic energy and / or mass is considered depending on the problem to dose-weighted mean LET (engl. Dose-averaged LET ) or fluenzgewichteten average LET (engl. Fluence-averaged LET ).

${\displaystyle {\text{LET}}_{\mathrm {dosisgewichtet} }={\dfrac {\sum _{{\text{Teilchenart}}=i}\int LET(i,E)D_{\text{i}}(E)\mathrm {\text{d}} E}{\sum _{{\text{Teilchenart}}=i}\int D_{\text{i}}(E)\mathrm {\text{d}} E}}}$

${\displaystyle {\text{LET}}_{\mathrm {fluenzgewichtet} }={\frac {\sum _{{\text{Teilchenart}}=i}\int LET(i,E)\Phi _{\text{i}}(E)\mathrm {\text{d}} E}{\sum _{{\text{Teilchenart}}=i}\int \Phi _{\text{i}}(E)\mathrm {\text{d}} E}}}$

Here, and the absorbed dose - or Fluenzbeitrag all particles of the variety with the kinetic energy . ${\displaystyle D_{\text{i}}(E)}$ ${\displaystyle \Phi _{\text{i}}(E)}$ ${\displaystyle i}$ ${\displaystyle E}$

Individual evidence

1. ↑ ^{a b} ICRU Report 60. International Commission on Radiation Units and Measurements. Bethesda, MD 1998.