Beam Restrictors

aperture diaphragm

sheet of lead below window with a hole for primary beam to pass

cones and cylinders

extended metal restricts beam to desired size (end of extension determines beam size)

What must be aligned to use a cone or cylinder?

the tube, cone, and IR

Variable aperture collimator

possesses 2-3 sets of lead shutters, allows reduction to many field sizes

What does the 1st set of lead shutters on the collimator control?

off focus radiation that leaves through the window

What does the 2nd and 3rd set of lead shutters on the collimator control?

they work in pairs to create square and rectangle fields

How thick are the lead shutters on a variable aperture collimator?

3mm

What is the most common type of beam restrictor?

collimator