Spoilers are precisely defined here. Rules vary by the story's medium. Info from television stories can't be added here until after the top or bottom of the hour, British time, closest to the end credits roll on BBC One. Therefore, fans in the Americas who are sensitive to spoilers should avoid Tardis on Sundays until they've seen the episode.
X-rays (or Röntgen radiation) (TV: Smith and Jones) were a type of electromagneticradiation. They were used in medical examinations because they penetrated soft tissue, allowing a non-invasive exam of the internal anatomy; they could also be used to examine the interiors of sealed objects using the same method. High levels of X-ray radiation could be harmful to many forms of life. When focused into a coherent beam or laser, X-rays could be used as an offensive weapon.