When the time of exposure is doubled:
EXPOSURE TIME (s):
Changing the exposure time—typically measured in fractions of a second (s)—modifies the duration of the exposure and thus the number of photons generated. When the exposure time is doubled, the number of photons generated at all energies in the X-ray emission spectrum is doubled. The range of photon energies is unchanged.
The number of photons generated is doubled
The energy of photons generated is doubled
The velocity of photons is doubled
The mass of photons is doubled