WIPP: Waste Isolation Pilot Plant

WIPP finally ready for radioactive waste

Are long half-life materials bad?

The shorter the half-life, 
the more radioactive the substance

The longer the half-life, the less radioactive the substance.

At long last, the nation's first repository for long-term disposal radioactive waste from the weapons program --- the Waste Isolation Pilot Plant, WIPP, in New Mexico --- is accepting its first shipments of radioactive waste.  These radioactive materials are long-lived transuranics (elements beyong uranium in the periodic table).

The half-life is the time required for the number of atoms in a sample to be cut in half, or actually, transmuted to other atoms.  Since the transmutation is the process that gives off radiation, the radioactivity is cut in half by the time one half-life has transpired.

Compare two radioactive elements, one with a short half-life and one with a long one.  Most people would imagine that the element with the long half-life would be the more dangerous.  Indeed, they sometimes become very emotional about the issue, asking how we can keep that stuff isolated for 2,784,221 years (or some other time, chosen almost at random).

Imagine that we have an equal number of atoms in our two samples, and imagine that the half-lives are 1 year and 1 million years.  For the one-year sample, half of the atoms have been transmuted in one year.  For every one of those atoms, radiation has been emitted.  For the one-million-year sample, the same number of events will be spread out over a million years.

That much said, which one would you rather carry around in your pocket?

Rule: the longer the half-life, the less radioactive the substance.

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