A device capable of collimating radiation,as a long narrow tube in which strongly absorbing or reflecting walls permit only radiation traveling parallel to the tube axis to traverse the entire length.

• 准直仪，平行光管一种能使射线成平行状的仪器，如一个狭长试管的强烈吸收或反射的内壁，使得射线只有在和试管轴线相平行时才能穿过整个试管