Depleted Hubium
Depleted Hubium (sometimes abbr. as dH) is the product of discharging a Super-charged Hubium (ScH) superparticle. It is smaller and lighter than regular Hubium, and charges much more efficiently than regular Hubium. (It can charge at 96% efficiency at 3 kW!) Rather than being able to be discharged, however, depleted Hubium will revert to its base state when its energy level reaches 75% of the HEST value, technically making Hubium a renewable resource given enough energy. However, because of the high energy levels involved, Hubium production is highly illegal and dangerous without proper certification.
An ScH superparticle will discharge into two Depleted Hubium particles, and each of the two Depleted Hubium particles (when charged to at least 75% of HEST) can produce a single Hubium superparticle. The produced superparticle carries a charge of 43% of HEST once the reaction is complete. This extra energy needs to be discharged immediately so that the Hubium can be made safe for regular use. Physicists believe the extra energy is spent re-establishing whatever internal mechanism allows Hubium to (dis)charge, but this internal mechanism isn't currently known.
Hubium Radiation: The name given to the dH particles generated by ScH explosions, especially in bulk.
Depleted Hubium Count (dHc)
The average measure of dH particles traveling through a unit of area, measured in particles per square meter. Requires specialized detection equipment. You can use a GHSS-22 compliant shielded Geiger Counter or dH Detector to measure the "density" (strength) of Hubium Radiation.
WARNING: Do NOT attempt to use any Geiger counters produced before 2053 or that are not certified as being GHSS-22 compliant, as they are not properly shielded against Hubium Radiation and will likely be destroyed by it.
Dangers
A large proportion of the ScH superparticle's stored energy is converted into kinetic energy in the two dH particles produced. They're estimated to travel at a minimum speed of 9.84 x 10^5 m/s (2.203 x 10^6 mph, or about 0.03% of the speed of light) away from each other when charged to the HEST value, but can easily reach up to 10x this speed or higher if charged enough. The true energy capacity of ScH hasn't been found, and likely won't be safe to discover.
Pollution and dH in the Atmosphere
Before the dangers of Hubium were well documented, mass production of the substance occurred globally without any of the safety and containment measures required today. As such, massive amounts of dH were released into the environment, and unknown amounts continue to "float" several miles above the Earth's surface.