Linear energy transfer
The linear energy transfer (LET, sometimes simply L) is the average amount of energy that radiation imparts to the medium per unit length. Since TLE is the energy donated by incident radiation to the medium, it is usually measured in units of energy per unit length. Generally in J/m, although it is usual to be expressed in experimental values in keV/µm. By definition, TLE is a positive quantity. The concept was first coined in 1952, on some occasions TLE refers to the quality of radiation. It is identical to the retarding force acting on an ionized charged particle traveling through matter. TLE depends exclusively on the nature of the radiation as well as the material passing through it.
Radiation (X-rays, alpha rays, beta rays, neutrons, gamma rays, etc.) have different TLE values. Radiation with low TLE ((L < 10 keV/µm) cause slight ionization along its path, like X-rays, while radiation with high TLE value (L > 10 keV/µm) cause intense ionizations in the medium, discharging higher linear energy densities. Electromagnetic radiation has a low TLE and particle radiation has a high TLE. High TLE radiation produces an ionization density (ionizations per distance unit traveled) about a thousand times greater than those with low LET.
A high value of TLE attenuates the intensity of the incident radiation more quickly as it penetrates through matter, generally making the protective shield with which it is made more effective, and preventing the deep penetration of said radiation. Radiation with high TLE causes dense ionization of the medium during its path, which implies a higher concentration of energy deposited and can cause more severe damage to the microscopic structures of the matter close to the trajectory of the particle than radiation with lower TLE. If a microscopic defect can cause large-scale failure, as is the case with biological cells and microelectronics, and in these cases TLE helps explain why the damage from certain radiations is sometimes disproportionate to the value of the absorbed dose of radiation. Dosimetry resolves this mismatch by using specific radiation factors.
The linear transfer of energy is related to the braking power, because both suppose a penetration value in the environment. Certainly linear unrestrained energy transfer is identical to linear stopping power.
Restricted/Unrestricted Transfer
The linear loss of energy from incident radiation on a material can generate ionization, with the consequent release of secondary electrons (known as delta rays). It is possible that these electrons have kinetic energies capable of continuing to ionize the material, also depositing energy in the medium. Many studies determine their test focus on the effects produced by the primary particles, excluding the possible interactions of the secondary electrons above a certain value Δ. This energy limit comes to exclude secondary electrons that carry kinetic energies far removed from the primary incident radiation. Because more energy means more range. This approximation neglects the directional distribution of the secondary radiation and the non-linear paths of delta rays, but simplifies the analytical evaluation. Using the mathematical formula, we have that the restricted linear energy transfer is you can define as:
- LΔ Δ =dEΔ Δ dx{displaystyle L_{Delta }={frac {{text{d}}E_{Delta }{{{text{d}}x}}}}}},
Where dEΔ Δ {displaystyle {text{d}E_{Delta}}} is the value of the average loss of energy from the particle due to collisions with the medium during its trajectory differential: dx{displaystyle {{text{d}x}}. In the energy computation is exclude all secondary electrons with kinetic energies greater than Δ. If Δ tends to very large (infinite) values, in this case there will be no electrons with large energies, and the transfer of energy will be equal to the Linear transfer of restricted energy which is similar to the braking power.
