Bismuth 209 — Wikipedia

The bismuth 209 , note ²⁰⁹ With a , is the isotope of the bismuth whose mass number is equal to 209: its atomic nucleus has 83 protons and 126 neutrons with a spin 9/2 ^– For an atomic mass of 208.980 40 G/Mol . It is characterized by an excess mass of −18 258.6 ± 1.4 convey and nuclear liaison energy by nucleon 7 847,987 ± 0.007 convey ^{[ first ]} . It is the only natural isotope of bismuth, as well as the product of β disintegration of Lead 209 :

209
82 Pb ⟶ 209
83 With a + and ^– + n _{It is} .

The Bismuth 209 was still considered stable in 2003, until the highlighting of its radioactivity by a team from the Orsay Spatial Astrophysics Institute (IAS-CNRS, Paris 11) ^{[ 2 ] , [ 3 ]} : he gives thallium 205 out of disintegration α with a radioactive period of the order of 2 × 10 ¹⁹ years (close to two billion times the age of the universe) and an energy of disintegration of 3,137 MeV :

209
83 With a ⟶ 205
81 Tl + 4
2 He .

It has long been considered the final product of the disintegration chain of Neptune 237 (4N+1 Series):

Neptunium disintegration channel.

But in all rigor, it is the thallium 205 which is the final product of the 4N+1 series. However, its very long radioactive period made bismuth an element on tiny radioactivity, which remained unnoticed until the beginning of XXI ^{It is} century ; It can therefore be considered stable and be handled and stored without any particular precaution related to its radioactivity.

The Bismuth 209 is the radioactive isotope having the longest half-life by radioactivity α, but it does not have the longest radioactive period (measured): the record belongs to the planet 128 , with a period of double beta disintegration estimated at 7.7 × 10 ²⁴ years ^{[ 4 ]} .

The Bismuth 209 radioactive period was confirmed in 2012 by an Italian team from Gran Sasso which postponed a value of (2.01 ± 0.08) × 10 ¹⁹ years ^{[ 5 ]} . The same team also postponed the first observation of the disintegration of bismuth 209 By alpha radioactivity to the first ^is excited state of Thallium 205, located in 204 convey of the fundamental state, with an even longer lifespan estimated at 1.66 × 10 ²¹ years. Even if this value does not outdo the record of lifespan measured by planet 128 , these two alpha disintegrations of bismuth 209 hold the record for the greatest virtual finesse of measurable physical excitement, with natural line widths estimated respectively at Δε ~ 5.5 × 10 ⁻⁴³ this et ~ 1.26 × 10 ⁻⁴⁴ this under the principle of uncertainty of Heisenberg ^{[ 6 ]} (double beta disintegration only gives a line to the extent that no neutrino is issued during disintegration, which has not been observed so far).