Just for fun I’ll see your 600 mile slug of Neutronium and raise you my 4,000 mile wad of molten iron the Earth’s core is supposed to be made of. That hit is going to cause a lot of jiggling. You’re thinking the next time I drill a deep well I’d have to strain the Netronies out of the water? If the Neutronium lands on somebody else’s house?
Ceres is 600 miles, and just rock/metal. Neutronium, or neutron star material (neutrons) would have much less volume, but I was figuring you’d need Ceres level mass condensed to that.
Apparently though, neutrons in the state that exists in a neutron star but in a volume outside of that which would keep it gravitationally cohesive is extremely unstable and poses its own management problem :-)