The sample "lived" three times longer in the X-ray beam with smallest compared to largest beam size studied.

How can eurosceptics and the like complain about the EU when they have beam the size of a house in their own eye.

Therefore, there is no hard and fast rule to select the optimal beam size.

It is related to the transverse beam size as follows:

The beta function is typically adjusted to have a local minimum at such points (in order to minimize the beam size and thus the interaction rate).

Commonly the smallest beam size for imaging is 2.5-6 nm.

For example, the object to be imaged can be initially assumed to reside in a region no larger than roughly the beam size.

If the cavity is unstable, the beam size will grow without limit, eventually growing larger than the size of the cavity mirrors and being lost.

This generally causes the beam size to grow.

The maximum impact parameter should be taken to be the minimum beam size.