Skip to main content


Log in

Geant4 simulations of soft proton scattering in X-ray optics

A tentative validation using laboratory measurements

  • Original Article
  • Published:
Experimental Astronomy Aims and scope Submit manuscript


Low energy protons (< 300 keV) can enter the field of view of X-ray telescopes, scatter on their mirror surfaces at small incident angles, and deposit energy on the detector. This phenomenon can cause intense background flares at the focal plane decreasing the mission observing time (e.g. the XMM-Newton mission) or in the most extreme cases, damaging the X-ray detector. A correct modelization of the physics process responsible for the grazing angle scattering processes is mandatory to evaluate the impact of such events on the performance (e.g. observation time, sensitivity) of future X-ray telescopes as the ESA ATHENA mission. The Remizovich model describes particles reflected by solids at glancing angles in terms of the Boltzmann transport equation using the diffuse approximation and the model of continuous slowing down in energy. For the first time this solution, in the approximation of no energy losses, is implemented, verified, and qualitatively validated on top of the Geant4 release 10.2, with the possibility to add a constant energy loss to each interaction. This implementation is verified by comparing the simulated proton distribution to both the theoretical probability distribution and with independent ray-tracing simulations. Both the new scattering physics and the Coulomb scattering already built in the official Geant4 distribution are used to reproduce the latest experimental results on grazing angle proton scattering. At 250 keV multiple scattering delivers large proton angles and it is not consistent with the observation. Among the tested models, the single scattering seems to better reproduce the scattering efficiency at the three energies but energy loss obtained at small scattering angles is significantly lower than the experimental values. In general, the energy losses obtained in the experiment are higher than what obtained by the simulation. The experimental data are not completely representative of the soft proton scattering experienced by current X-ray telescopes because of the lack of measurements at low energies (< 200 keV) and small reflection angles, so we are not able to address any of the tested models as the one that can certainly reproduce the scattering behavior of low energy protons expected for the ATHENA mission. We can, however, discard multiple scattering as the model able to reproduce soft proton funnelling, and affirm that Coulomb single scattering can represent, until further measurements at lower energies are available, the best approximation of the proton scattered angular distribution at the exit of X-ray optics.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9
Fig. 10
Fig. 11

Similar content being viewed by others


  1. Flexible Image Transport System (






  1. Agostinelli, S., et al.: Geant4–a simulation toolkit. NIM A 506, 250–303 (2003)

    Article  ADS  Google Scholar 

  2. Allison, J., et al.: Geant4 developments and applications. IEEE Trans. Nucl. Sci. 53(1), 270–278 (2006)

    Article  ADS  Google Scholar 

  3. Allison, J., et al.: Recent developments in GEANT4. NIM A 835, 186–225 (2016).

    Article  ADS  Google Scholar 

  4. Briel, U.G., et al.: In-orbit performance of the EPIC-PN CCD camera on board XMM-Newton. Proc. SPIE 4012, 154–164 (2000)

    Article  ADS  Google Scholar 

  5. Bulgarelli, A., et al.: BoGEMMS: the Bologna Geant4 multi-mission simulator. Proc. SPIE, 845335 (2012).

  6. Burrows, D.N., et al.: The swift X-ray telescope. Space Sci. Rev. 120, 165–195 (2005).

    Article  ADS  Google Scholar 

  7. Carter, J.A., Read, A.M.: The XMM-Newton EPIC background and the production of background blank sky event files. A&A 464, 1155–1166 (2007).

    Article  ADS  Google Scholar 

  8. Conti, G., et al.: X-ray characteristics of the Italian X-Ray Astronomy Satellite (SAX) flight mirror units. Proc. SPIE 2279, 101–109 (1994)

    Article  ADS  Google Scholar 

  9. Cusumano, G., et al.: In-flight calibration of the Swift XRT effective area. AIPC 836, 664–667 (2006).

    ADS  Google Scholar 

  10. De Luca, A., Molendi, S.: The 2-8 keV cosmic X-ray background spectrum as observed with XMM-Newton. A&A 419, 837–848 (2004).

    Article  ADS  Google Scholar 

  11. Diebold, S., et al.: Soft proton scattering efficiency measurements on X-ray mirror shells. Exp. Astron. 39, 343–365 (2015).

    Article  ADS  Google Scholar 

  12. Fioretti, V., et al.: Monte Carlo simulations of gamma-ray space telescopes: a BoGEMMS multi-purpose application. Proc. SPIE 9144, 91443N (2014).

    Article  Google Scholar 

  13. Garmire, G.P., et al.: Advanced CCD imaging spectrometer (ACIS) instrument on the Chandra X-ray observatory. Proc. SPIE 4851, 28–44 (2003).

    Article  ADS  Google Scholar 

  14. Ivanchenko, V., et al.: Validation of Geant4 10.3 simulation of proton interaction for space radiation effects. Exp. Astron. 835, 186–225 (2017).

    Article  Google Scholar 

  15. Ivanchenko, V.N., et al.: Geant4 models for simulation of multiple scattering. J. Phys. Conf. Ser. 219, 032045 (2010).

    Article  Google Scholar 

  16. Jansen, F., et al.: XMM-Newton observatory. I. The spacecraft and operations. A&A 365, L1–L6 (2001).

    Article  ADS  Google Scholar 

  17. Kimura, K., Hasegawa, M., Mannami, M.H.: Energy loss of MeV light ions specularly reflected from a SnTe(001) surface. Phys. Rev. B 36, 7–12 (1987).

    Article  ADS  Google Scholar 

  18. Lei, F., et al.: Update on the use of Geant4 for the simulation of low-energy protons scattering off X-ray mirrors at grazing incidence angles. IEEE Trans. Nucl. Sci. 51, 3408–3412 (2004).

    Article  ADS  Google Scholar 

  19. Lumb, D.H., et al.: X-ray background measurements with XMM-Newton EPIC. A&A 389, 93–105 (2002).

    Article  ADS  Google Scholar 

  20. Mashkova, E.S., et al.: Small-angle particle reflection from random solids: theory and experiments. Rad. Effects p. 85 (1983)

  21. Mineo, T., et al.: Validation of the ray-tracing code: A first evaluation of the proton transmission of XMM-Newton optics. INAF Tech. Report INAF-XIFU-TM-2015-1 (2015)

  22. Mitsuda, K., et al.: The X-ray observatory Suzaku. PASJ 59, 1–7 (2007).

    Article  Google Scholar 

  23. Nandra, K., et al.: The hot and energetic universe: a white paper presenting the science theme motivating the Athena+ mission. ArXiv e-prints (2013)

  24. Nartallo, R., et al.: Low-angle scattering of protons on the XMM-Newton optics and effects on the on-board CCD detectors. IEEE Trans. Nucl. Sci. 48(6), 1815–1821 (2001)

    Article  ADS  Google Scholar 

  25. Predehl, P., et al.: eROSITA on SRG. Proc. SPIE 9144, 91441T (2014).

    Article  Google Scholar 

  26. Remizovich, V.S., Ryazanov, M.I., Tilinin, I.S.: Energy and angular distributions of particles reflected in glancing incidence of a beam of ions on the surface of a material. Sov. J. Exp. Th. Phys. 52, 225 (1980)

    ADS  Google Scholar 

  27. Spiga, D., et al.: A magnetic diverter for charged particle background rejection in the SIMBOL-X telescope. Proc. SPIE 7011, 70112Y (2008).

    Article  ADS  Google Scholar 

  28. Villa, G.E., et al.: Epic system onboard the ESA XMM. Proc. SPIE 2808, 402–413 (1996)

    Article  ADS  Google Scholar 

  29. Weisskopf, M.C., et al.: Chandra X-ray observatory (cxo): overview. Proc. SPIE 4012, 2–16 (2000)

    Article  ADS  Google Scholar 

  30. Wentzel, G.: Zwei Bemerkungen uber die Zerstreuung korpuskularer Strahlen als Beugungserscheinung. Z. Phys. 40, 590 (1927)

    Article  ADS  MATH  Google Scholar 

  31. Willingale, R.: An electron diverter for the Swift telescope. XRT-LUX-RE-011/1Technical Report (2000)

Download references


This work is supported by the ESA Contract No 4000116655/16/NL/BW. The AHEAD project (grant agreement n. 654215) which is part of the EU-H2020 programm is acknowledged for partial support.

Author information

Authors and Affiliations



Corresponding author

Correspondence to Valentina Fioretti.


Appendix A: Scattering efficiency

Fig. 12
figure 12

Scattering efficiency at E0 = 250 keV for an incident angle ranging from 0.36 to 1.23

Fig. 13
figure 13

Scattering efficiency at E0 = 500 keV for an incident angle ranging from 0.33 to 1.19

Fig. 14
figure 14

Scattering efficiency at E0 = 1000 keV for an incident angle ranging from 0.3 to 1.17

Appendix B: Energy losses

Fig. 15
figure 15

The proton energy loss as a function of the scattering angle at E0 = 250 keV in the 0.36− 1.23 incident angle range

Fig. 16
figure 16

The proton energy loss as a function of the scattering angle at E0 = 500 keV in the 0.33− 1.19 incident angle range

Fig. 17
figure 17

The proton energy loss as a function of the scattering angle at E0 = 1000 keV in the 0.3− 1.17 incident angle range

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Fioretti, V., Mineo, T., Bulgarelli, A. et al. Geant4 simulations of soft proton scattering in X-ray optics. Exp Astron 44, 413–435 (2017).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: