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You are watching: Element with the shortest half life

If you ask somebody that remembers a little of their high college chemistry, “What"s the heaviest stable (non-radioactive) element?” they"ll typically answer “Lead.”If friend pose the same concern to a chemist, they"llprobably glance in ~ the periodic table top top the wall surface and respond“Bismuth.”Reality is somewhat much more complicated, and interesting in that details.

The chemist is correct in noting that all elements heavier 보다 bismuth (element 83) have no steady isotopes, and only a couple of which have isotopes with very longhalf-livessuch as thorium anduraniumoccur in comprehensive quantities in nature. (Others, such aspolonium andradon, are uncovered in nature asdaughter commodities from the degeneration of thorium and uranium but are not primordial .)

But is bismuth actually stable? Naturally arising bismuth is composed specifically of the isotopebismuth-209 (209Bi), who atoms save on computer 83 protons and also 126 neutrons. Now, nuclear framework is fairly well understood, and it is possible to calculate from concept that the bismuth-209 nucleus is in a greater energy state 보다 the sum of the energies that a nucleus ofthallium-205 and also analpha particle (nucleus ofhelium-4).In quantum mechanics, whatever is not forbidden by a conservation law must happen eventually, and also since alpha decay of bismuth-209 to thallium-205 does no violate conservation of power or any type of other law, it has long been meant to occur, however had no been it was observed to happen.

This all adjusted in 2003, when a group of researchers at theInstitut d"Astrophysique Spatiale in Orsay, France report in apaper in Nature the straight detection of alpha particles resulting from the decay of bismuth-209 using a detector cooled to simply two hundredths of a degree above absolute zero (20 mK). They to be able to calculate the half-life of bismuth-209 as 1.9×1019 years.

This is a long time. Just how long? Well, the world is about1.38×1010 years old (time from thebig bang come the present), therefore the half-life of bismuth-209 (henceforth I"ll write simply “bismuth”as this is the just naturally-occurring isotope) is about a billion (109) time the age of the universe. Based top top our understanding of astrophysics and the procedure of star formation in galaxies, all of the stars in the world will have melted out in around 1014 years, for this reason you"ll have to wait a time a hundreds thousand times much longer than the era in i beg your pardon stars shone in the cosmos for half of the bismuth atom in your party ofPepto-Bismol to degeneration away, which more than likely substantially postdates the “use before” date on the label.

What will the universe be choose 1019 year in the future? Well before the last stars burn out at 1014 years, every one of the galaxies in theLocal group will have merged into one enormous galaxy. The inexorable acceleration the the expansion of the world due todark energy willred-shift even the many energetic radiation indigenous othersuperclusters that galaxies come wavelengths longer than the dimension of the observable universe by about 2×1012 years: astronomers in that distant epoch will certainly observe only asingle galaxy in an otherwise entirely empty universe. If reports of observations of the universe from our era remain, one marvels whether anybody would think them.

By roughly 1015 years, planets i beg your pardon orbit the burned-out continues to be of stars (this gift a time ten times longer that that in which stars shone) will certainly be ejected from their orbits by to meet with other stellar remnants or crash into and also merge through their own main body as result of orbital decay bygravitational radiation. And after an interval ten thousands times longer than this, fifty percent the bismuth will still be around.

Let"s look v the other end of the telescope and also see just how radioactive bismuth yes, really is. Radioactive degeneration is administer by the equations:


where t½ is the-half life, λ the decay constant, τ the typical lifetime, N the number of particles in the sample, and also A the number of decays every unit time (using the same time unit as half-life). Let"s assume we have actually a one gram sample of bismuth: a cube about fifty percent a centimetre ~ above a side. The atomic weight of bismuth is approximately 209, for this reason our one gram sample is 1/209mole. A mole of any kind of substance is written of Avogadro"s number,6.022×1023 the constituents. Splitting this by 209, we uncover our sample contains 2.9×1021 atoms of bismuth. Utilizing the formulæ above, we discover that 105 atoms of bismuth in our sample will certainly decay, top top average, every year, or about one every three and a half days. However these are alpha decays. Alpha particles have very tiny penetrating power—a paper of file or person skin fully stops them, and bismuth is a heavy aspect with far greater absorption than those light substances. So, in terms of alpha corpuscle emitted from these rarely decays, just those which occur an extremely near the surface ar will ever be emitted external the sample: all the remainder will it is in trapped inside. Together the overwhelming bulk of a macroscopic sample is in the volume, no on the surface, emitted alpha particles will certainly be correspondingly rare. The French team who measured the degeneration rate work the clever strategy of using a detector which to be a link includingbismuth and also germanium, therefore that nearly every degeneration would an outcome in a signal native the detector.

Getting ago to the original question, was the non-professional"s guess that lead is the most difficult stable aspect correct? Well, not so fast…. Naturally emerging lead is composed of 4 isotopes: lead-204, lead-205, lead-207, and lead-208, with the latter making up an ext than half. Indigenous the exact same energetic calculate which led to nuclear chemists to doubt that bismuth was slightly radioactive, each of thesenuclides need to be exothermic to alpha decay with really long half-lives. No such decays have ever before been it was observed experimentally, so only a reduced bound on their half-lives, top top the stimulate of the of bismuth, have the right to be given. From a theoretical and also experimental standpointthallium (element 81) is thought to be absolutely stable.

Still, when it pertains to barely radiation elements, bismuth doesn"t take the prize.Barium-130 decays intoxenon-130 v the procedure ofdouble electron capture with a half-life that 0.5–2.7×1021 years, around a hundreds times the of bismuth, andtellurium-128 is the every time champion, disc intoxenon-128 bydouble beta decay with a half-life of 2.2×1024 years. This, the longest experimentally-measured half-life in ~ this writing, is a hundred thousand times much longer than that of bismuth, and also 160 sunshine times the current age of the universe.If you had a one gram sample that pure tellurium-128 (which would beexpensive come prepare, because you"d have to perform isotope separationto isolation the 128Te, which renders up around a third ofnaturally-occurring tellurium), you"d just observe a degeneration event onaverage when every 674 years.

In wilder worlds of speculation, somegrand merged theories of particle physics predict that the proton, and by implication, all aspects should ultimately decay. Experiments have displayed that proton decay, if that occurs, must have a half-life in overfill of 1033 years, more than 50 sunshine times longer than the of bismuth and also 72 billiontrillion time the current age the the universe.

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You might wonder i m sorry naturally-occurring facet has theshortest half-life. That would certainly befrancium, element 87, whose longest-lived isotope, francium-223, has actually a half-life of 22 minutes, decaying either right into radium through beta decay or astatine by alpha emission. It was discovered in nature in 1939 (the critical radioactive facet to be discovered in nature fairly than by synthesis) and also is present in trace quantities in uranium and also thorium ores. At any given time, that is estimated that only 20–30 grams that francium are existing in the Earth"s crust.All facets from hydrogen to californium (element 98) have been discovered in nature, but most of the radioactive facets were very first discovered by synthesis and also then later detected in trace amounts in natural uranium ore.There is a difference between “found in nature” andprimordial.While the an initial 98 elements are found in nature, only 84 have actually atoms current in nature which day from the development of the solar system. The these, 80 space stable and four (bismuth, thorium, uranium, and plutonium) space radioactive.