Per 
(I don't quite understand how writing actual SCPs work, this is just my ideas)
Idea 1: A multiplying radioactive rubbery ball.
Object class: Safe
Appearance: SCP-? is a sphere 5 inches in diameter which glows purple if the air pressure SCP-? is exposed to is under 25 kilo pascals, likely due to less energetic light particles being emitted in low pressure. SCP-? is the texture of soft rubber similar to a rubber bouncy ball toy.
Origin: SCP-?s were accidentally discovered by Enrico Fermi during the Manhattan project. He discovered them while experimenting if strong magnetic fields could be used to cause fast enough fission for a nuclear detonation. The magnetic field caused SCP-? to appear inside the magnetic field.
Effects: SCP-? multiplies when exposed to magnetic fields at a rate which changes depending on the relative strength of the field. When put under pressure it emits radiation which increases exponentially in emission rate as pressure increases. If the pressure exerted on it exceeds 1 tera pascal, SCP-?'s radiation emission will spike and a large detonation nuclear detonation will occur (the pressure required for detonation will be referred to as its overpressure). If SCP-? is in contact with radioactive isotopes such as uranium 235, SCP-?'s overpressure will reduce. If SCP-? is near to a magnetic field strong enough, it will slowly travel to the source of the magnetic field which causes there to be a massive quantity of SCP-? in the core of the earth. Estimates for the quantity of SCP-? in the core of the earth exceeds 135.9 million.
Containment procedures: SCP-? is to be contained in a 1 ft X 1 ft X 1 ft vacuum chamber and surrounded by neutron absorbing foam. SCP-? will multiply once every 2 months,
Extra: SCP-?'s explosive ability directly caused the destruction of the Japanese cities Hiroshima and Nagasaki.
