Stable isotope

Gráfica de nucleidos (isótopos) by type of Decaimiento:
The nucleides in orange and blue are unstable, with the black squares between these regions representing stable isotopes. The continuous line that passes below many of the nucleides represents the theoretical position in the nucleides graph for which the number of protons is the same as the number of neutrons. The chart shows that the elements with more than 20 protons must have more neutrons than protons to be stable.

A stable isotope is a nuclide that is not radioactive (unlike radionuclides), so it does not spontaneously undergo radioactive decay.

A chemical element has one or several isotopes, all, some, or none of which may be stable isotopes. Isotopes that are not stable (radioisotopes), unlike stable ones, decay to give rise to other nuclides by emitting particles or electromagnetic radiation.

Stability conditions

About 2500 nuclides are known, of which less than 300 are stable. The representation of the number of neutrons (N) against the number of protons (atomic number, Z) indicating the stable isotopes is called the Segrè chart (designed by physicist Emilio Segrè).

For example, technetium has no stable isotopes, while tin has ten stable isotopes.

The stability region defined by this graph is narrow, fulfilling that for small mass numbers (A) the number of protons and neutrons is similar, while as A increases, the N/Z ratio also increases (up to a value of about 1.6).

Nuclides to the right of this stability band have too many protons for the neutrons they have, so the nuclei break apart due to repulsion.

The nuclides on the left have too many neutrons for the protons they have, thus producing a decay process that converts neutrons into protons.

It is verified that for Z=43, Z=61 or Z≥83 there is no stable nuclide.

The strong nuclear force is responsible for holding the atomic nucleus together, despite the fact that the electromagnetic force causes elements with the same sign of electrical charge (protons, which all have a positive charge) to repel each other. However, the strong nuclear force has a very small radius of action, which explains why stable nuclei are not found for Z≥83, since as the number of protons increases, the size of the nucleus increases, so the force strong nuclear force is overwhelmed by the electromagnetic force, which manages to expel some proton.

Employment

Stable isotopes are used in:

• Food quality control: To trace the origin and composition of food
• Ecology: To study the diet of wild species
• Paleoclimatology: To make measurements of gases trapped in ice

Definition of stability, and natural nuclides

Most of the nuclides present in nature are stable (currently 254; see the list at the end of this article). About 34 other nuclides are also known to be radioactive with a half-life (also known) long enough to also be present in nature (for a total of 288 "natural" nuclides). If the half-life of a nuclide is comparable to or greater than the age of the Earth (4.5 billion years), a significant amount will have survived since the formation of the Solar System, and is therefore called a primordial nuclide, thereby contributing to the natural isotopic composition of each chemical element. Primarily present radioisotopes are easily detected with half-lives on the order of 700 million years (such as 235U), although some primordial isotopes have been detected with half-lives as relatively short as 80 million years (for example, 244Pu).). However, this is the current limit of detection (the nuclide with the next shortest half-life (niobium-92 with a half-life of 34.7 million years, has not yet been detected in nature).

Many naturally occurring radioisotopes (about 51, for a total of about 339) have half-lives of less than 80 million years, but are currently generated as products of the decay processes of primordial nuclides (for example, radium from uranium) or from ongoing energetic reactions, such as cosmogenic nuclides produced by cosmic ray bombardment of elements present on Earth (for example, carbon-14 generated from nitrogen).

Some isotopes that are classified as stable (that is, in which no radioactivity has been observed) are predicted to have very long half-lives (sometimes as long as 10¹⁸ years or more). If the predicted half-life falls into an experimentally accessible range, such isotopes can be moved from the stable isotope list to the radioactive category, once their activity is observed. For example, bismuth-209 and tungsten-180 were previously considered stable, but were found to exhibit alpha particle activity in (2003). However, nuclides do not change their primordial status when they are eventually detected to be radioactive.

It is believed that the most stable isotopes present on Earth were formed in nucleosynthesis processes, either in the Big Bang, or in generations of stars that preceded the formation of the Solar System. However, some stable isotopes also show abundance variations on earth as a result of the decay of long-lived radioactive nuclides. These by-products of radioactive decay are called radiogenic isotopes, in order to distinguish them from the much larger group of 'non-radiogenic' isotopes.

The so-called island of stability reveals a good number of long-lived or even stable atoms that are heavier (and with more protons) than lead.

Isotopes by element

Of the known chemical elements, 80 have at least one stable nuclide. These comprise the first 82 elements from hydrogen to lead, with two exceptions, technetium (element 43) and promethium (element 61), which have no stable isotope. As of December 2011, there were a total of 254 "stable" acquaintances. In this definition, that a nuclide is "stable" means that its radioactive decay has never been observed in the natural context. Therefore, these elements have half-lives too long to be measured by any means, direct or indirect.

Stable isotopes are:

• 1 element (size) has 10 stable isotopes
• 1 element (xenon) has 8 stable isotopes
• 4 elements have 7 stable isotopes each
• 8 elements have 6 stable isotopes each
• 10 elements have 5 stable isotopes each
• 9 elements have 4 stable isotopes each
• 5 elements have 3 stable isotopes each
• 16 elements have 2 stable isotopes each
• 26 elements have only one stable isotope each

These last 26 are therefore called monoisotopic elements. The number of stable isotopes for elements that have at least one stable isotope represents an average of 254/80 = 3.2, that is that is, an average of approximately three stable isotopes for each stable element.

"Magic Numbers" and even and odd endowments of protons and neutrons

Isotopic stability is affected by the ratio of the number of protons to neutrons in each nucleus, and also by the presence of certain "magic numbers" of neutrons or protons that represent closed and complete contours from the quantum point of view. These quantum shells correspond to a set of energy levels within the model of complete shells of the nucleus; as the complete shell of 50 protons for tin, which confers an unusual stability to this nuclide. As in the case of tin, if the atomic number Z of an element matches a magic number, then its number of stable isotopes tends to increase.

As in the case of electrons, which have the lowest energy state when they occur in pairs in a given orbital, nucleons (both protons and neutrons) show a lowest energy state when their number is even instead of odd. This stability tends to prevent the beta decay (in two stages) of many even-even nuclides into another even-even nuclide of the same mass, but of lower energy (and of course with two more protons and two fewer neutrons), because a One-step decay procedure would have to pass through an odd nuclide, with a higher peak energy. This leads to a larger number of stable pair-pair nuclides, up to three for some mass numbers, and up to seven for some atomic (proton) numbers.

In contrast, of the 254 known stable isotopes, only five have an odd number of protons and an odd number of neutrons: hydrogen-2 (deuterium), lithium-6, boron-10, nitrogen-14, and tantalum-180m. Furthermore, only four naturally occurring odd-odd radioactive nuclides have a half-life of more than a billion years: potassium-40, vanadium-50, lanthanum-138, and lutetium-176. Odd-odd primordial nuclides are rare because odd-odd nuclei are very unstable with respect to beta decay, because the resulting decay byproducts are even-even, and thus more tightly bound due to pairing effects. nuclear.

Another effect of the instability of an odd number of either type of nucleon, however, is that odd elements tend to have fewer stable isotopes. Of the 26 elements that are monoisotopic (meaning they only have a single stable isotope), all but one have an odd atomic number (the only exception to both rules is beryllium). All of these elements also have an even number of neutrons, with the one exception being beryllium again.

Nuclear isomers, including one "metastable"

The count of the 254 known stable nuclides includes tantalum-180m, since despite the decay process and instability automatically implied by its "metastable" condition, these phenomena have not yet been they have been able to observe. All "stable" (stable by observation, not theory) are the ground states of nuclei, with the exception of tantalum-180m, which is a nuclear isomer or excited state. The ground state of this particular nucleus (Ta-180) is radioactive, with a relatively short half-life of 8 hours. In contrast, the decay of the excited nuclear isomer is extremely unlikely due to spin-parity selection rules. It has been reported by direct experimental observation that the half-life of ^180mTa by gamma radiation should be greater than 10¹⁵ years. Other possible decay modes of ^180mTa (beta decay, electron capture and alpha decay) have never been observed either.

Disintegration not yet observed

Energy of binding by nucleon of the common isotopes.

It is expected that some continuous improvement in the sensitivity of the experiments will allow the detection of the presence of very slight signs of radioactivity (instability) of some isotopes that are currently considered stable. An example of a recent discovery: it was not until 2003 that bismuth-209 (the only naturally occurring isotope of bismuth) was shown to be very slightly radioactive. Prior to this discovery, there were theoretical predictions from nuclear physics based on the that bismuth-209 should decay very slowly by alpha particle emission. These calculations were confirmed by experimental observations made in 2003.

Summary table of the numbers of each class of nuclides

This is a summary table of the list of nuclides. Please note that the numbers are not exact and may change slightly in the future, as new detections of radioactivity are made in more nuclides, or as certain half-lives are determined with greater precision.

Stable isotopes in the Periodic Table

The following is a Periodic Table with the number of stable isotopes of each element:

List of stable isotopes

A for alpha decay, B for beta decay, 2B for double beta decay, E for electron capture, 2E for double electron capture, IT for isomeric transition, SF for spontaneous fission.

* Tantalum-180m is a "metastable isotope" which means that it is an excited nuclear isomer of tantalum-180 (see: Isotopes of tantalum). However, the half-life of this nuclear isomer is so long that its decay has never been observed, and therefore it behaves as an "observationally non-radioactive" primordial nuclide, like a minor isotope of tantalum. This is the only case of a nuclear isomer having such a long half-life that its decay has never been observed, so it is included in this list.

** Bismuth-209 had long been considered stable, due to its unusually long half-life of more than 1.9 10¹⁹ years, which is more than a billion times the age of the universe.

Related reading

• Various (2002). Lide, David R., ed. Handbook of Chemistry " Physics (88th edition). CRC. ISBN 0-8493-0486-5. OCLC 179976746. Archived from the original on July 24, 2017. Consultation on 23 May 2008.