Impact of the I-value of diamond on the energy deposition in different beam qualities

Abstract

Diamond detectors are increasingly employed in dosimetry. Their response has been investigated by means of Monte Carlo (MC) methods, but there is no consensus on what mass density ρ, mean excitation energy I and number of conduction electrons per atom n ce to use in the simulations. The ambiguity occurs due to its seeming similarity with graphite (both are carbon allotropes). Except for the difference in ρ between crystalline graphite (2.265 g cm −3 ) and diamond (3.515 g cm −3 ), their dielectric properties are assumed to be identical. This is incorrect, and the two materials should be distinguished: (ρ = 2.265 g cm −3 , I = 81.0 eV, n ce = 1) for graphite and (ρ = 3.515 g cm −3 , I = 88.5 eV, n ce = 0) for diamond. Simulations done with the MC code penelope show that the energy imparted in diamond decreases by up to 1% with respect to 'pseudo-diamond' (ρ = 3.515 g cm −3 , I = 81.0 eV, n ce = 0) depending on the beam quality and cavity thickness. The energy imparted changed the most in cavities that are small compared with the range of electrons. The difference in the density-effect term relative to graphite was the smallest for diamond owing to an interplay effect that ρ, I and n ce have on this term, in contrast to pseudo-diamond media when either ρ or I alone were adjusted. The study also presents a parameterized density-effect correction function for diamond that may be used by MC codes like EGSnrc. The estar program assumes that n ce = 2 for all carbon-based materials, hence it delivers an erroneous density-effect correction term for graphite and diamond. Despite the small changes of the energy imparted in diamond simulated with two different I values and expected close-to-negligible deviation from the published smallfield output correction data, it is important to pay attention to material properties and model the medium faithfully.

Energy loss of MeV protons in diamond: Stopping power and mean ionization energy

“…Transport codes are commonly used to quantify radiation-related effects in these applications, such as energy deposition per penetration length, total absorbed dose, or range of ionizing particles. The reliability of the ion transport simulations is limited for diamond due to the aforementioned problem of scarce experimental stopping cross-section data, that are used to fit the parameters of the underlying physics [24,25]. One of the key parameters is the mean excitation potential I, a material-specific constant used in Bethe formula.…”