Nuclear cross-sections are more in my line.

The qualification of "rms" (for "root mean square") arises because it is the nuclear cross-section, proportional to the square of the radius, which is determining for electron scattering.

A physics laboratory run by Henry Barschall was destroyed by the bombing; the records of 25 years of his research, measuring nuclear cross-sections under neutron bombardment, were destroyed, there having been no off-site data storage.