While medical physicists and radiobiologists usually speak of linear energy transfer, most non-medical physicists talk about stopping power. Values are typically given in units of keV/μm or MeV/cm. In fact, they both describe interactions that depend on both the beam and the absorber. 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. Linear energy transfer is closely related to stopping power, since both equal the energy loss per unit distance, dE/dx. Dosimetry attempts to factor in this effect with radiation weighting factors. 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. On the other hand, the higher concentration of deposited energy can cause more severe damage to any microscopic structures near the particle track. A high LET will attenuate the beam more quickly, generally making shielding more effective and preventing deep penetration. LET depends on the nature of the radiation as well as on the material traversed. Since the energy loss is part of the definition, LET is a positive quantity. Linear energy transfer (LET) is the linear density of energy lost by a charged ionizing particle travelling through matter.
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