Imagine one day the moon suddenly transformed into a colossal elephant's foot and we need to get to the moon to obtain sample... Could it be done using modern day technology to mine the uranium for science? I don't need man on the moon just a good sizable sample in the most economic reusable rocket will do. The moon now is consist of 50% U235, 49% radium and 1% other.
The soviets successfully performed three automated lunar sample return missions in the early 70's. https://en.m.wikipedia.org/wiki/Luna_16 A sample return mission is not too difficult, just very expensive. This is assuming the moon becomes natural uranium.
The Chernobyl elephants foot is radioactive and dangerous because of fission byproducts, not because of the uranium content. Uranium, especially naturally occurring uranium, is relatively harmless. It needs to be pureified and then run in a nuclear fission reactor to break parts of it down into very dangerous, radioactive, fission byproducts.
Radium decays quickly, and is produced as a trace element in the decay chain of uranium, so there is no real explanation for half of the moon to become radium, whether natural or as a result of critical nuclear reactor operation. I am unsure of the bahavior of vast amounts of radium, since it does not occur. The principle danger wïh radium is the gas released, which would probably form ao extremely toxic atmosphere given the quantities you mention. Even if it all outgassed into space, the rate of production would likely leave a faint radon atmosphere. If you insist on having half the moon be made of radium, you probably want to check this with a physicist to see if an atmosphere would exist.
If the moon suddenly transformed into a giant elephants foot (a mix of uranium and concrete, only trace amounds of radium) there would be some difficulty in retrieving samples, but not impossible. Modern electronics can be hardened against those levels of radiation (see the fukushima robotic exploration of the reactor vessels), but a successful sample return mission under these circumstances would be extremely challenging with todays technology.
(note this answer was written before the question was edited to say the moon is 50% u-235. In that case, it just simply and immediately explodes)
If the Moon were to be instantly transformed as you describe there would be a huge nuclear explosion. A Moon sized chunk of U235 even diluted as described would be fissile and the detonation of the outer layers in a damp squib explosion would compress the inner layers. The shockwave would propagate down into the Moon creating enough explosive force to destroy the Moon in it’s entirely and probably the Earth as well. The Radium would also serve to heat the explosion by virtue of its intense radioactivity.
The solar system will be vaporized, and the entire galaxy likely sterilized.
U-235 is fissile, meaning that it will emit a heck of a lot of energy if 50kg or so is put in one place. If half the mass of the moon is suddenly transformed into U-235, this is around 3.6x10^22 kg, and able to start a supercritical nuclear reaction (explosion). The fissile energy of uranium is approximately 82 TJ per kilo, times the moons mass is 2.4x10^36 J. To put that into perspective, this is an energy output on the order of a billion billion suns, briefly dwarfing the entire galactic energy output.
There will be nothing left of the Earth. There might not even be anything left of the rest of the solar system. This event will probably sterilize the rest of the galaxy.