diff --git a/README.md b/README.md
index 1c24f4b091a4312bf6eabbdd9cc4a3c5d3ca9046..aadd3d5e6f4c6dbd8d90fa6dc1605e5521260759 100644
--- a/README.md
+++ b/README.md
@@ -20,6 +20,7 @@
 ## Table of Contents
 
 * [About the Project](#about-the-project)
+  * [Built With](#built-with)
 * [Usage](#usage)
 * [License](#license)
 * [Contact](#contact)
@@ -37,15 +38,26 @@ WP 9.3.c "Understanding the interaction between soft protons and X-ray mirrors"
 (1)INAF OAS Bologna, (2)INAF IASF Palermo, (3)INAF IAPS Roma, (4)INAF IASF Milano 
 
 * Description: The proton response matrix for the XMM-Newton telescope is composed by a Redistribution Matrix File (RMF)
-mapping the proton energy space (from tens to hundreds of keV) into detector pulse height and an Auxiliary Response File (ARF) 
+mapping the proton energy space (from 2 to 300 keV) into detector pulse height and an Auxiliary Response File (ARF) 
 collecting the grasp of the optics, the filter transmission efficiency and the detector quantum efficiency.
 
 The files are formatted according to the NASA OGIP (Office of Guest Investigators Program) calibration database (caldb) format, and they are tested with the NASA HEASARC XSPEC analysis software tool.
 
+### Built With
+The current release of the proton response files is based on:
+* Geant4 v10.4
+* BoGEMMS v2.1 [Fioretti et al., Proc. SPIE, 118221F, 2021]
+* Ray-tracing Monte Carlo code [Mineo et al., Exp. Astr., 44, 287, 2017] 
+
+
 <!-- USAGE -->
 ## Usage
 
-The RMF and ARF files can be loaded with any X-ray analysis software compliant with the NASA caldb format.
+* The RMF and ARF files can be loaded with any X-ray analysis software compliant with the NASA caldb format.
+* Since the accuracy of the Geant4 modeling of the proton stopping power degrades below 1 keV (20% at 1 keV reported in the Geant4 Physics Reference Manual), the energy redistribution is modelled from 1 keV to the upper threshold of the instrument X-ray RMF.
+* Validity energy range: due to biases at the boundary of the RMF modeling, induced by features in the interpolation because of limited statistics in the simulation, the spectral analysis must be performed within the following intervals:
+* * MOS: 1.5 - 11.5 keV
+* * PN: 1.5 - 20 keV
 
 <!-- LICENSE -->
 ## License