The very long-lived isotopes produced by fission would overtake the Co again after about 75 years.

In such a system it may be preferable to have an inert matrix that doesn't produce additional long-lived isotopes.

It undergoes alpha decay to the extremely long-lived isotope (in practice, a stable one) bismuth-209.

After sitting for several years, the radioactivity falls to a point where extraction of the long-lived isotopes, including technetium-99, becomes feasible.

Long-lived isotopes in reactors may not have decayed to background level in only sixty years.

Since the relatively long-lived isotope plutonium-240 occurs in the decay chain of plutonium-244 it should also be present, albeit 10,000 times rarer still.

Bismuth (Bi) has no stable isotopes, but does have one very long-lived isotope; thus, the standard atomic mass can be given.

In other words, the radiation from a long-lived isotope like iodine-129 will be much less intense than that of short-lived isotope like iodine-131.

They make and study atomic nuclei that cannot be found on earth-where they have long decayed into the known, stable or long-lived isotopes.

That means that the original injections, before radioactive decay over the years and decades, had a strength of up to three billion curies of long-lived isotopes.

Thus, the element's natural isotopic abundance is dominated either by one stable isotope or by one very long-lived isotope.

More long-lived isotopes of curium (Cm, all α-emitters) are formed as a mixture during neutron irradiation of plutonium or americium.

Astatine was first produced by bombarding bismuth-209 with energetic alpha particles, and this is still the major route used to create the relatively long-lived isotopes astatine-209 through astatine-211.

This result throws considerable doubt on the results of the Marinov collaboration with regards to their claims of long-lived isotopes of thorium, roentgenium and unbibium.

Long-lived isotopes of nobelium and isotopes of lawrencium (and of heavier elements) have relatively small half-lives.

When an isotope decays into a very short-lived isotope and then decays again to a relatively long-lived isotope, the products of the second decay are delayed.

Other long-lived isotopes were unsuccessfully targeted by a team at Lawrence Livermore National Laboratory (LLNL) in 1988 by bombarding einsteinium-254 with neon-22.

Put another way, human history is so short in comparison to a half-life of a billion years, that the activity of these long-lived isotopes has been effectively constant throughout our time on this planet.

In 1917, she and Hahn discovered the first long-lived isotope of the element protactinium, for which she was awarded the Leibniz Medal by the Berlin Academy of Sciences.

But I'd guess at its being a stellar simulacrum, variations determined by a solid-state minicomputer, energized by sunlight or a long-lived isotope, for space navigation or teaching or-" He sighed.

Only chemists working with physicists to make short-lived isotopes (and long-lived isotopes) of atoms in giant collision experiments and in nuclear reactors can really be said to be synthesizing "elements."

Scientists have been hoping for a way to use Kr-81 for dating since the 1960s; it's a remarkably long-lived isotope that can be used to date back much further than carbon-perhaps as far back as a million years.

If it were possible to produce sufficient quantities of sufficiently long-lived isotopes of these elements that would allow the study of their chemistry, these elements may well behave very differently from those of previous periods.

Dr. Livingston added that the Russian oceanic wastes appear to have a level of radioactivity roughly akin to the long-lived isotopes thrown into the atmosphere by the Chernobyl explosion in 1986, the world's worst nuclear accident.

Men thought its plan of battle was chosen by the random disintegrations of atoms in a block of some long-lived isotope buried deep inside it, and was not even in theory predictable by opposing brains, human or electronic.