Question 655
{"accessible":false,"alternatives":[{"id":3278,"text":"1/Z"},{"id":3279,"text":"Z"},{"id":3280,"text":"Z³"},{"id":3281,"text":"Z for kV \u003c50 and Z^2 for kV \u003e50"}],"archived":false,"correctAlternativeId":3280,"explanation":"\u003cp\u003eThe photoelectric effect is related to the atomic number of the attenuating medium (Z), the energy of the incident photon (E) and the physical density of the attenuating medium (p) by:\u0026nbsp;Z\u003csup\u003e3\u003c/sup\u003e p / E\u003csup\u003e3\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eTherefore, if Z doubles, PEA will increase by a factor of 8 (because 2\u003csup\u003e3\u003c/sup\u003e is 8) and if E doubles, PEA will reduce by 8. As small changes in Z can have quite profound changes in PEA this has practical implications in the field of radiation protection and is why materials with a high Z such as lead (Z = 82) are useful shielding materials.\u003c/p\u003e\u003cp\u003eAdapted from\u0026nbsp;\u003ca href=\"https://en.wikibooks.org/wiki/Basic_Physics_of_Digital_Radiography\"\u003eBasic Physics of Digital Radiography\u003c/a\u003e\u0026nbsp;by\u0026nbsp;Kieran Maher,\u0026nbsp;with author's permission (License:\u0026nbsp;\u003ca href=\"https://creativecommons.org/licenses/by-sa/3.0/\"\u003eCreative Commons\u0026nbsp;BY-SA 3.0\u003c/a\u003e).\u003c/p\u003e","id":655,"imageUrl":null,"imageAttribution":null,"imageAttributionCaseInfo":null,"firstQuestionPath":"/questions/2748","nextQuestionPath":"/articles/photoelectric-effect/questions/640","relatedArticles":[],"alsoUsedIn":[],"stem":"\u003cp\u003eFor the photoelectric effect, the absorption per unit mass of the absorber depends approximately on the atomic number (Z) of the absorber according to...\u003c/p\u003e","menuLinks":[{"text":"Report problem with question","url":"https://docs.google.com/forms/d/e/1FAIpQLSfO3soWYhOjJ7yErSysyCe5V4A1CqW7WK3rDA7MtAkecMGqNw/viewform?entry.1624461248\u0026entry.553583435=https://radiopaedia.org/questions/655"}],"attemptsPercentages":[{"alternativeId":"3280","percentage":73},{"alternativeId":"3281","percentage":9},{"alternativeId":"3278","percentage":10},{"alternativeId":"3279","percentage":9}],"promptToLogin":false,"questionManager":false,"articleId":"photoelectric-effect"}