Fig. 7: Schematic representation of radiation damage expansion in bone.

a Macroscopically, exposure to an incident X-ray beam (magenta) during typical XRD experiments will result in increased damage as a function of exposure time: (1) 80 s, (2) 160 s, and (3) 320 s. Following irradiation of the bone (beige), collagen becomes increasingly damaged (dark gray) and the damage is most intense in the center of the entry site of impingement on the bone sample. Damage expands laterally with increasing exposure time. At lower irradiation time (80 s), damage is smaller, but with increasing exposure the size grows (160 s), to significantly exceed (320 s) the lateral beam diameters. Though collagen absorbs only a small portion of the incident intensity, calcium (Ca) and phosphorous (P) in the bone absorb and emit significant photoelectrons and fluorescence as the beam propagates through the specimen. Due to absorption, the beam intensity decays towards the ‘Back’ of the sample. b At the ultra-structural level, a cascade of electron scattering (black circles with minus symbol) and fluorescence is created, dominated by Ca (rings) delivering energy that is highly absorbed by both P and the organic components of the bone (cyan). Secondary emission by P and other sources of ionization will lead to accumulation of broken backbone C–C and C–N bonds. The Ca photoelectrons scatter many micrometers beyond the rims of the incident beam. c At the level of crystals and collagen fibers, the incoming radiation excites Ca and creates secondary radiation sources in the bone with an attenuation length of several μm. Excitation of the elements comprising the mineral nanoparticles (brown/yellow), results in ejection of electrons (black circles) that scatter in the matrix (attenuation length ~1.5 μm). The combined effects of lower energy fluorescence and secondary electron scattering are main contributors to damage of collagen in the matrix (illustrated as cyan wavy pillars).