The primary effect of all kinds of radiation is to heat the material it hits. This statement includes electromagnetic radiation (visible, ultraviolet, and infrared radiation); ionizing particles such as protons, electrons, and alpha particles; and non-ionizing particles such as neutrons. You can feel the heat when you hold a lump of plutonium, a flask of tritium, or a recently irradiated accelerator target. Intense irradiation can cause enough heat to explode explosives and burn metals (think of laser effects).
Cellulose molecules are folded back and forth in a fairly regular arrangement, and they show the properties of crystallinity. This is called a "fibrillar structure." When you rotate the stage of a petrographic microscope with crossed polarizers while looking at a linen fiber, straight lengths change from black through colored to black again every 90?. The fiber is birefringent and has an ordered structure.
When cellulose fibers are heated enough to color them, whether by conduction, convection, or radiation of any kind, water is eliminated from the structure (the cellulose is "dehydrated"). When water is eliminated, C-OH chemical bonds are broken. The C? free radicals formed are extremely reactive, and they will combine with any material in their vicinity. In cellulose, other parts of the cellulose chains may be the closest reactants. The chains crosslink. Crosslinking changes the crystal structure of the cellulose, and you can see the effect with a polarizing microscope.
When cellulose starts to scorch (dehydrate and crosslink), its characteristic crystal structure becomes progressively more chaotic. Its birefringence changes, and not all parts of a straight fiber go through clear transitions from dark to light at the same angle. Zones of order get smaller and smaller. It finally takes on the appearance of a pseudomorph and just scatters light. A significantly scorched fiber does not change color as the stage is rotated between crossed polarizers.
Proton-irradiated fibers by Rinaudo. Little, white, straight lines
cutting across the fiber are the paths of the protons.
Specific types of radiation cause specific types of defects in the crystals of flax fibers. For example, protons ionize the cellulose as they pass through the fiber. This warps the crystals, making the protons’ paths birefringent. You can see where they went in the fiber by the straight lines of their paths (see the "Proton-irradiated" figure).
Neutron-irradiated fibers from the Lyma mummy wrapping by Moroni.
Observe the small, white, vertical streaks made by recoil protons
between the bright growth nodes. There is also a faint haze in the
background that was made by an associated gamma flux from the re actor.
Not all kinds of radiation ionize the material they penetrate. Neutrons and neutrinos donot have any electrical charge. Neutrinos hardly interact with matter at all, the fact that made them so difficult to detect. They have practically no chance of being stopped as they shoot through the entire diameter of the earth. The effects of neutrons depend on their energy, but they normally interact with hydrogen-containing materials to produce "recoil protons." They knock a hydrogen nucleus out of the material, producing an ionizing proton. You can see the ionization streaks of these (usually lower energy) protons (see the "Neutron-irradiation" figure).
The crystal structure of the flax fibers of the Shroud shows the effects of aging, but it has never been heated enough to change the structure. It has never suffered chemically significant irradiation with either protons or neutrons. No type of radiation that could produce either color in the linen fibers or change the 14C content (radiocarbon age) could go unnoticed. All radiation has some kind of an effect on organic materials.
This proves that the image color could not have been produced by thermal or radiation induced dehydration of the cellulose. Image formation proceeded at normal temperatures in the absence of energetic radiation of any kind.