There's also the isotope Helium-3, which is far more scarce than Helium-4 and is rapidly running out. It's used to detect radiation and to reach ultralow temper

There's also the isotope Helium-3, which is far more scarce than Helium-4 and is rapidly running out. It's used to detect radiation and to reach ultralow temperatures in low-temperature physics research and medical cryogenics. It's scarcity has been a national security concern.