Probes visiting Jupiter and its moons protect their equipment from X-rays with titanium shielding. Juno had 180 kg of the stuff. Europa Clipper is expected to have about that much too.
Terrestrial shielding such as the apron you wear at the dentist uses denser materials such as lead. (Almost anything is denser than titanium!)
Compared to titanium, lead has 4x the atomic weight and 2.5x the density, so per kg you'd expect lead to shield better, because 4 / 2.5 > 1.
This is confirmed by the Health Physics Society:
A titanium [dentist's patient] apron would weigh about 6.6 times a lead apron.
Their calculations use a NIST table of mass attenuation coefficients and mass energy-absorption coefficients as a function of photon energy, 0.001 to 100 MeV. That range covers (I think) most of what Jupiter spews at its moons.
If low mass is so important on a space probe, why is titanium preferred to lead, which would be lighter, cheaper, easier to machine, etc?