Linear Energy Transfer

Linear energy transfer (LET) is the linear density of energy lost by a charged ionizing particle travelling through matter. Since the energy loss is part of the definition, LET is a positive quantity. LET depends on the nature of the radiation as well as on the material traversed. A high LET will attenuate the beam more quickly, generally making shielding more effective and preventing deep penetration. On the other hand, the higher concentration of deposited energy can cause more severe damage to any microscopic structures near the particle track. If a microscopic defect can cause larger-scale failure, as is the case in biological cells and microelectronics, the LET helps explain why radiation damage is sometimes disproportionate to the absorbed dose. Dosimetry attempts to factor in this effect with radiation weighting factors.

Linear energy transfer is closely related to stopping power, since both equal the energy loss per unit distance, dE/dx. Whereas stopping power is usually discussed as a property of the material, especially in shielding, linear energy transfer is usually discussed as a property of the radiation, especially in radiobiology. In fact, they both describe interactions that depend on both the beam and the absorber. Values are typically given in units of keV/μm or MeV/cm. While medical physicists and radiobiologists usually speak of linear energy transfer, most non-medical physicists talk about stopping power.

The stopping power and LET concepts are different at least in the respect that total stopping power also has the nuclear stopping power component, and this component does not cause electronic excitations. Hence nuclear stopping power is not LET (but is very similar to the concept of Non-ionizing energy loss, NIEL.

Read more about Linear Energy Transfer:  Restricted and Non-restricted LET, Application To Radiation Types, Biological Effects, Application Fields

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