Theory

Material properties from elemental composition

The following quantities are calculated:  relative electron density (RED), Effective atomic number (Zeff), Mean excitation 

energy (I) and Stopping power ratio (SPR).

The value of m (Zeff equation) depends on the spectra and X-ryas interactions varying depending on the reference and considerations. Common values are 3.1 or 3.3.

Note that m value can be specified by the user.

SPR (ratio - not the actual Stopping power) is "almost" independent of the energy which is accounted for by Beta (β). β is a parameter representing the velocity of a charged particle relative to the speed of light.  Typically 100 MeV can be used.

Z/A and I-Value per element from NIST are used as reference

https://physics.nist.gov/PhysRefData/XrayMassCoef/tab1.html 

While many values are sourced from [NIST](https://physics.nist.gov/PhysRefData/XrayMassCoef/tab1.html), the values for H, O, C, N, Cl, Ca, P, Na, Mg, S, Si, B, Al, and I have been adjusted based on ICRU37. It's crucial to acknowledge that the I-values vary for gases and liquids! Some different I-values have been discussed and proposed in the resources below, but those are not implemented in this context.

DOI: 10.1088/1361-6560/aad312