What helium is available is depleted in helium-3 relative to what we see in the sun, because most of Earth's helium-4 is freshly made via naturalradioactive decay of the elements uranium and thorium.
Our modern supply of helium has gradually built up over billions of years in subterranean pockets of natural gas as a byproduct of decaying radioactiveelements.
我们现在的氦源，是地下天然气田中放射元素衰变的副产品，经过数十亿年的累积，逐渐形成的。
3
During the production of uranium mining and metallurgy, some waste ores and mill tailings with radioactiveelements are produced, which may do harm to natural environment and people.