Gd-157 has the highest thermal neutron capture cross section (σ) of 254,000 barns (e.g. the probability of neutron capture with the following nuclear reaction is very high).

Gadolinium neutron capture is associated with production of gammas (energy range from 0,15 to 7 MeV). As well as short range Auger and IC electrons. The last two induce high levels of DNA damage (mainly double-strand DNA brakes).

Gd-157(n,g)Gd-158 reaction (physics)

Gd-157(n,g)Gd0158 reaction (biology)