Co-60

Some facts about Co-60

It doesn't use a flattening filter to produce a uniform flat beam because the emission is not forward peaked and is more isotropic compared to a linac beam.

There is some radiation from a Co-60 machine when the machine is switched off due to leakage (unlike a linac)

A Co-60 source is produced by activating small pellets or thin discs and they are tightly packed into the source capsule to produce a Co-60 source. This avoids problems of self shielding which would result in nonuniform activity in the source.

One reason output has to be measured periodically is due to the source movement. If the source does not come to the same position every time the output can vary due to partical shielding.