Know your dose: RADDOSE.

Area of Science:

• Crystallography
• Structural Biology
• Computational Science

Background:

• Macromolecular crystallography (MX) experiments are sensitive to radiation damage, with a known dose limit of 30 MGy at 100 K.
• Accurate estimation of absorbed dose is crucial for planning MX experiments and preserving structural information.
• The RADDOSE program is a key tool for calculating radiation dose in MX.

Purpose of the Study:

• To report the inclusion of incoherent (Compton) scattering in RADDOSE (version 3) for improved dose calculations.
• To evaluate the impact of Compton scattering on dose calculations, especially at higher X-ray energies (>20 keV).
• To re-examine the 'diffraction-dose efficiency' parameter for optimizing data collection strategies.

Main Methods:

• Modification of the RADDOSE code to incorporate Compton scattering.
• Comparison of dose calculations between RADDOSE versions 2 and 3.
• Analysis of absorbed dose and diffraction intensity at different X-ray energies.

Main Results:

• RADDOSE version 3 accounts for fluorescent X-ray escape and Compton scattering.
• Compton scattering becomes significant for dose calculations at incident energies above 20 keV.
• Higher X-ray energies lead to reduced absorbed dose but also lower diffraction intensities.

Conclusions:

• RADDOSE v3 provides more accurate dose estimations, particularly at higher X-ray energies.
• Collecting data at higher energies can extend sample lifetime but reduces diffraction signal.
• Optimizing MX experiments requires balancing dose reduction with diffraction intensity using the 'diffraction-dose efficiency' parameter.