A problem occurs when one uses copper that contains a lot of disolved diatomic hydrogen (H ). Diatomic hydrogen has two states, ortho and para, corresponding to the spin-1 and spin-0 states. At room temperature the ratio is 3-1 corresponding to the state degeneracy. At zero temperature, the hydrogen will fall into the parahydrogen state, however, the conversion process is slow.
This poses a problem at base because the heat capacity of orthohydrogen is considerably higher than parahydrogen, and the latent heat release in the conversion can cause heating.
To solve this issue, warm the cold mass up to about 15K, where the conversion from ortho to parahydrogen is faster. Hold here for several hours (depending on the mass and the concentration of diatomic hydrogen). Then cool back to base.