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Monday, July 18, 2022

Sortition

From Wikipedia, the free encyclopedia

In governance, sortition (also known as selection by lottery, selection by lot, allotment, demarchy, stochocracy, aleatoric democracy, and lottocracy) is the selection of political officials as a random sample from a larger pool of candidates. The system intends to ensure that all competent and interested parties have an equal chance of holding public office. It also minimizes factionalism, since there would be no point making promises to win over key constituencies if one was to be chosen by lot, while elections, by contrast, foster it. In ancient Athenian democracy, sortition was the traditional and primary method for appointing political officials, and its use was regarded as a principal characteristic of democracy.

Today, sortition is commonly used to select prospective jurors in common-law systems and is sometimes used in forming citizen groups with political advisory power.

History

Ancient Athens

Athenian democracy developed in the 6th century BC out of what was then called isonomia (equality of law and political rights). Sortition was then the principal way of achieving this fairness. It was utilized to pick most of the magistrates for their governing committees, and for their juries (typically of 501 men). Aristotle relates equality and democracy:

Democracy arose from the idea that those who are equal in any respect are equal absolutely. All are alike free, therefore they claim that all are free absolutely... The next is when the democrats, on the grounds that they are all equal, claim equal participation in everything.

It is accepted as democratic when public offices are allocated by lot; and as oligarchic when they are filled by election.

In Athens, "democracy" (literally meaning rule by the people) was in opposition to those supporting a system of oligarchy (rule by a few). Athenian democracy was characterised by being run by the "many" (the ordinary people) who were allotted to the committees which ran government. Thucydides has Pericles make this point in his Funeral Oration: "It is administered by the many instead of the few; that is why it is called a democracy."

A kleroterion in the Ancient Agora Museum (Athens)

The Athenians believed sortition, not elections, to be democratic and used complex procedures with purpose-built allotment machines (kleroteria) to avoid the corrupt practices used by oligarchs to buy their way into office. According to the author Mogens Herman Hansen, the citizen's court was superior to the assembly because the allotted members swore an oath which ordinary citizens in the assembly did not, therefore the court could annul the decisions of the assembly. Both Aristotle and Herodotus (one of the earliest writers on democracy) emphasize selection by lot as a test of democracy, writing, "The rule of the people has the fairest name of all, equality (isonomia), and does none of the things that a monarch does. The lot determines offices, power is held accountable, and deliberation is conducted in public."

Past scholarship maintained that sortition had roots in the use of chance to divine the will of the gods, but this view is no longer common among scholars. In Ancient Greek mythology, Zeus, Poseidon, and Hades used sortition to determine who ruled over which domain. Zeus got the sky, Poseidon the sea, and Hades the underworld.

In Athens, to be eligible to be chosen by lot, citizens self-selected themselves into the available pool, then lotteries in the kleroteria machines. The magistracies assigned by lot generally had terms of service of one year. A citizen could not hold any particular magistracy more than once in his lifetime, but could hold other magistracies. All male citizens over 30 years of age, who were not disenfranchised by atimia, were eligible. Those selected through lot underwent examination called dokimasia to avoid incompetent officials. Rarely were selected citizens discarded. Magistrates, once in place, were subjected to constant monitoring by the Assembly. Magistrates appointed by lot had to render account of their time in office upon their leave, called euthynai. However, any citizen could request the suspension of a magistrate with due reason.

Lombardy and Venice – 12th to 18th century

The brevia was used in the city states of Lombardy during the 12th and 13th centuries and in Venice until the late 18th century. Men, who were chosen randomly, swore an oath that they were not acting under bribes, and then they elected members of the council. Voter and candidate eligibility probably included property owners, councilors, guild members, and perhaps, at times, artisans. The Doge of Venice was determined through a complex process of nomination, voting and sortition.

Lot was used in the Venetian system only in order to select members of the committees that served to nominate candidates for the Great Council. A combination of election and lot was used in this multi-stage process. Lot was not used alone to select magistrates, unlike in Florence and Athens. The use of lot to select nominators made it more difficult for political sects to exert power, and discouraged campaigning. By reducing intrigue and power moves within the Great Council, lot maintained cohesiveness among the Venetian nobility, contributing to the stability of this republic. Top magistracies generally still remained in the control of elite families.

Florence – 14th and 15th century

Scrutiny was used in Florence for over a century starting in 1328. Nominations and voting together created a pool of candidates from different sectors of the city. The names of these men were deposited into a sack, and a lottery draw determined who would get to be a magistrate. The scrutiny was gradually opened up to minor guilds, reaching the greatest level of Renaissance citizen participation in 1378–1382.

In Florence, lot was used to select magistrates and members of the Signoria during republican periods. Florence utilized a combination of lot and scrutiny by the people, set forth by the ordinances of 1328. In 1494, Florence founded a Great Council in the model of Venice. The nominatori were thereafter chosen by lot from among the members of the Great Council, indicating a decline in aristocratic power.

Switzerland

Because financial gain could be achieved through the position of mayor, some parts of Switzerland used random selection during the years between 1640 and 1837 to prevent corruption.

India

Local government in parts of Tamil Nadu such as the village of Uttiramerur traditionally used a system known as kuda-olai where the names of candidates for the village committee were written on palm leaves and put into a pot and pulled out by a child.

Methods

USCAR Court select juries by sortition

Before the random selection can be done, the pool of candidates must be defined. Systems vary as to whether they allot from eligible volunteers, from those screened by education, experience, or a passing grade on a test, or screened by election by those selected by a previous round of random selection, or from the membership or population at large. A multi-stage process in which random selection is alternated with other screening methods can be used, as in the Venetian system.

One robust, general, public method of allotment in use since 1997 is documented in RFC 3797: Publicly Verifiable Nominations Committee Random Selection. Using it, multiple specific sources of random numbers (e.g., lotteries) are selected in advance, and an algorithm is defined for selecting the winners based on those random numbers. When the random numbers become available, anyone can calculate the winners.

David Chaum, a pioneer in computer science and cryptography, proposed Random-Sample Elections in 2012. Via recent advances in computer science, it is now possible to select a random sample of eligible voters in a verifiably valid manner and empower them to study and make a decision on a matter of public policy. This can be done in a highly transparent manner which allows anyone to verify the integrity of the election, while optionally preserving the anonymity of the voters. A related approach has been pioneered by James Fishkin, director of the Center for Deliberative Democracy at Stanford, to make legally binding decisions in Greece, China and other countries.

In Ancient Greece, a Kleroterion was used to select eligible and willing citizens to serve jury duty. This bolstered the initial Athenian system of democracy by getting new and different jury members from each tribe to avoid corruption.

Modern application

Sortition is most commonly used to form citizens' assemblies. As an example, Vancouver council initiated a citizens' assembly that met in 2014–15 in order to assist in city planning.

Sortition is commonly used in selecting juries in Anglo-Saxon legal systems and in small groups (e.g., picking a school class monitor by drawing straws). In public decision-making, individuals are often determined by allotment if other forms of selection such as election fail to achieve a result. Examples include certain hung elections and certain votes in the UK Parliament. Some contemporary thinkers have advocated a greater use of selection by lot in today's political systems, for example reform of the British House of Lords and proposals at the time of the adoption of the current Constitution of Iraq.

Sortition is also used in military conscription, as one method of awarding US green cards, and in placing students into some schools.

Democratic governance of non-governmental organizations

Sortition also has potential for helping large associations to govern themselves democratically without the use of elections. Co-ops, employee owned businesses, housing associations, Internet platforms, student governments, and countless other large membership organizations whose members generally do not know many other members yet seek to run their organization democratically often find that elections are problematic. The essential leadership decisions are made by the nomination process, often generating a self-perpetuating board whose nominating committee selects their own successors. Randomly selecting a representative sample of members to constitute a nominating panel is one procedure that has been proposed to keep fundamental control in the hands of ordinary members and avoid internal board corruption.

Examples

  • Law court juries are formed through sortition in some countries, such as the United States and United Kingdom.
  • Citizens' assemblies have been used to provide input to policy makers. In 2004, a randomly selected group of citizens in British Columbia convened to propose a new electoral system. This Citizens' Assembly on Electoral Reform was repeated three years later in Ontario's citizens' assembly. However, neither assembly's recommendations reached the required thresholds for implementation in subsequent referendums.
  • MASS LBP, a Canadian company inspired by the work of the Citizens' Assemblies on Electoral Reform, has pioneered the use of Citizens' Reference Panels for addressing a range of policy issues for public sector clients. The Reference Panels use civic lotteries, a modern form of sortition, to randomly select citizen-representatives from the general public.
  • Democracy In Practice, an international organization dedicated to democratic innovation, experimentation and capacity-building, has implemented sortition in schools in Bolivia, replacing student government elections with lotteries.
  • Danish Consensus conferences give ordinary citizens a chance to make their voices heard in debates on public policy. The selection of citizens is not perfectly random, but still aims to be representative.
  • The South Australian Constitutional Convention was a deliberative opinion poll created to consider changes to the state constitution.
  • Private organizations can also use sortition. For example, the Samaritan Ministries health plan sometimes uses a panel of 13 randomly selected members to resolve disputes, which sometimes leads to policy changes.
  • The Amish use sortition applied to a slate of nominees when they select their community leaders. In their process, formal members of the community each register a single private nomination, and candidates with a minimum threshold of nominations then stand for the random selection that follows.
  • Citizens' Initiative Review at Healthy Democracy uses a sortition based panel of citizen voters to review and comment on ballot initiative measures in the United States. The selection process utilizes random and stratified sampling techniques to create a representative 24-person panel which deliberates in order to evaluate the measure in question.
  • The environmental group Extinction Rebellion has as one of its goals the introduction of a Citizens' assembly that is given legislative power to make decisions about climate and ecological justice.
  • Following the 1978 Meghalaya Legislative Assembly election, due to disagreements amongst the parties of the governing coalition, the Chief Minister's position was chosen by drawing lots.
  • In 2015 the city of Utrecht randomly invited 10,000 residents, of whom 900 responded and 165 were eventually chosen, to participate in developing its 2016 energy and climate plan.
  • In 2019, the German speaking Ostbelgien region in Belgium, implemented the Ostbelgien Model, consisting of an 24-member Citizen's Council which convenes short term Citizen's Assemblies to provide non binding recommendations to its parliament. Later that same year both the main and French only Brussels Region parliaments voted to authorize setting up mixed parliamentary committees composed of parliamentarians and randomly selected citizens to draft recommendations on a given issue.
  • In 2013 the New Zealand Health Research council began awarding funding at random to applicants considered equally qualified.

Political proposals for sortition

As part of reworking the state

  • John Burnheim, in his book Is Democracy Possible?, describes a political system in which many small "citizen's juries" would deliberate and make decisions about public policies. His proposal includes the dissolution of the state and of bureaucracies. The term demarchy he uses was coined by Friedrich Hayek for a different proposal, unrelated to sortition, and is now sometimes used to refer to any political system in which sortition plays a central role.
  • Influenced by Burnheim, Marxist economists Allin Cottrell and Paul Cockshott propose that, to avoid formation of a new social elite in a post-capitalist society, "[t]he various organs of public authority would be controlled by citizens' committees chosen by lot" or partially chosen by lot.
  • L. León coined the word lottocracy for a sortition procedure that is somewhat different from Burnheim's demarchy. While "Burnheim ... insists that the random selection be made only from volunteers", León states "that first of all, the job must not be liked". Christopher Frey uses the German term Lottokratie and recommends testing lottocracy in town councils. Lottocracy, according to Frey, will improve the direct involvement of each citizen and minimize the systematical errors caused by political parties in Europe.
  • Anarcho-capitalist writer Terry Hulsey detailed a 28th Amendment to the U.S. Constitution to randomize the election of congressmen and senators, and indirectly, the President of the United States. The key to its success, in his opinion, is that the critical selection of the initial pool of candidates is left strictly to the states, to avoid litigation regarding "fairness" or perfect randomness.

To replace elected legislative bodies

Proposed changes to the legislature of the Parliament of Tasmania: A single legislative body of 50–100 people is selected randomly from the population and makes laws. One of their duties is the selection of seven members of an executive council
  • C. L. R. James's 1956 essay "Every Cook Can Govern" suggested to select, through sortition, a large legislative body (such as the U.S. Congress) from among the adult population at large.
  • Ernest Callenbach and Michael Phillips push for random selection of the U.S. House of Representatives in their book A Citizen Legislature (1985). They argue this scheme would ensure fair representation for the people and their interests, an elimination of many realpolitik behaviors, and a reduction in the influence of money and associated corruption, all leading to better legislation.
  • Étienne Chouard, a French political activist, proposes replacing elections with sortition.
  • Terry Bouricius, a former Vermont legislator and political scientist, proposes in a 2013 journal article how a democracy could function better without elections, through the use of many randomly selected bodies, each with a defined role.
  • In 2015, Graham Kirby proposed using sortition to reform the UK House of Lords in Disclaimer magazine.
  • In his 2017 presidential election platform, French politician Jean-Luc Mélenchon of La France Insoumise lays out a proposal for a sixth republic. The upper house of this republic would be formed through national sortition. Additionally, the constituent assembly to create this republic would have 50% of its members chosen in this way, with the remainder being elected.

To choose legislative juries

  • Simon Threlkeld, in the 1998 journal article "A Blueprint for Democratic Law-Making: Give Citizen Juries the Final Say" and later articles, proposes that laws be decided by legislative juries rather than by elected politicians or referenda. The existing legislatures would continue to exist and could propose laws to legislative juries, but would no longer be able to pass laws. Citizens, public interest groups and others would also be able to propose laws to legislative juries.

To decide the franchise

  • Simon Threlkeld, in the 1997 journal article "Democratizing Public Institutions: Juries for the selection of public officials" and later articles, proposes that a wide range of public officials be chosen by randomly sampled juries, rather than by politicians or popular election. As with "convened-sample suffrage", public officials are chosen by a random sample of the public from a relevant geographical area, such as a state governor being chosen by a random sample of citizens from that state.
  • "Convened-sample suffrage" uses sortition to choose an electoral college for each electoral district.

To supplement or replace some of the legislators

  • "Accidental Politicians: How Randomly Selected Legislators Can Improve Parliament Efficiency": shows how the introduction of a variable percentage of randomly selected independent legislators in a Parliament can increase the global efficiency of a Legislature, in terms of both number of laws passed and average social welfare obtained (this work is in line with the recent discovery that the adoption of random strategies can improve the efficiency of hierarchical organizations "Peter Principle Revisited: a Computational Study").
  • Political scientist Robert A. Dahl suggests in his book Democracy and its critics (p. 340) that an advanced democratic state could form groups which he calls minipopuli. Each group would consist "of perhaps a thousand citizens randomly selected out of the entire demos", and would either set an agenda of issues or deal with a particular major issue. It would "hold hearings, commission research, and engage in debate and discussion". Dahl suggests having the minipopuli as supplementing, rather than replacing, legislative bodies.
  • The House of Commons in both Canada and the United Kingdom could employ randomly selected legislators.
  • The ratio of legislators decided by election to those decided by the lottery is tied directly to the voter turnout percentage. Every absentee voter is choosing sortition, so, for example, with 60% voter turnout a number of legislators are randomly chosen to make up 40% of the overall parliament. Each election is simultaneously a referendum on electoral and lottery representation.
  • Political science scholars Christoph Houman Ellersgaard, Anton Grau Larsen and Andreas Møller Mulvad of the Copenhagen Business School suggest supplementing the Danish parliament, the Folketing, with another chamber consisting of 300 randomly selected Danish citizens to combat elitism and career politicians, in their book Tæm Eliten (Tame the Elite).

To replace an appointed upper house

  • The upper house of a parliament might be selected through sortition. Anthony Barnett, Peter Carty and Anthony Tuffin proposed this to the Royal Commission on the Reform of the House of Lords in the UK in 1999.

Advantages

Representation of the population

A modern advocate of sortition, political scientist John Burnheim, argues for systems of sortition as follows:

Let the convention for deciding what is our common will be that we will accept the decision of a group of people who are well informed about the question, well-motivated to find as good a solution as possible and representative of our range of interests simply because they are statistically representative of us as a group. If this group is then responsible for carrying out what it decides, the problem of control of the execution process largely vanishes.

This advantage does not equally apply to the use of juries.

Better efficiency

Magnus Vinding in his book Reasoned Politics argues that one of the main advantages of sortition is its comparative efficiency: first, according to the author, sortition “could allow political decision-makers to focus on studying and deciding on the relevant issues rather than worrying about sending the right signals to optimize their election prospects.” And second, “resources devoted to zero-sum pursuits, such as election campaigns and lobbies that fund opposing politicians, could instead be devoted to positive-sum endeavors.”

Cognitive diversity

Cognitive diversity is an amalgamation of different ways of seeing the world and interpreting events within it, where a diversity of perspectives and heuristics guide individuals to create different solutions to the same problems. Cognitive diversity is not the same as gender, ethnicity, value-set or age diversity, although they are often positively correlated. According to numerous scholars such as Page and Landemore, cognitive diversity is more important to creating successful ideas than the average ability level of a group. This "diversity trumps ability theorem" is essential to why sortition is a viable democratic option. Simply put, random selection of persons of average intelligence performs better than a collection of the best individual problem solvers.

Fairness

Sortition is inherently egalitarian in that it ensures all citizens have an equal chance of entering office irrespective of any bias in society:

Compared to a voting system – even one that is open to all citizens – a citizen-wide lottery scheme for public office lowers the threshold to office. This is because ordinary citizens do not have to compete against more powerful or influential adversaries in order to take office, and because the selection procedure does not favour those who have pre-existing advantages or connections – as invariably happens with election by preference.

Random selection has the ability to overcome the various demographic biases in race, religion, sex, etc. apparent in most legislative assemblies. Greater perceived fairness can be added by using stratified sampling. For example, the Citizens' Assembly on Electoral Reform in British Columbia sampled one woman and one man from each electoral district and also ensured representation for First Nations members. Bias may still exist if particular groups are purposefully excluded from the lottery such as happened in Ancient Athens where women, slaves, younger men and foreigners were not eligible.

Democratic

Greek writers who mention democracy (including Aristotle, Plato, and Herodotus) emphasise the role of selection by lot, or state outright that being allotted is more democratic than elections. For example, Plato says:

Democracy arises after the poor are victorious over their adversaries, some of whom they kill and others of whom they exile, then they share out equally with the rest of the population political offices and burdens; and in this regime public offices are usually allocated by lot.

The idea that democracy is associated with sortition remained common in the 18th century. Charles de Secondat, baron de Montesquieu writes in The Spirit of the Laws, "The suffrage by lot is natural to democracy, as that by choice is to aristocracy."

Anti-corruption

Sortition may be less corruptible than voting. Author James Wycliffe Headlam explains that the Athenian Council (500 administrators randomly selected), would commit occasional mistakes such as levying taxes that were too high. Additionally, from time to time, some in the council would improperly make small quantities of money from their civic positions. However, "systematic oppression and organized fraud were impossible." These Greeks recognized that sortition broke up factions, diluted power, and gave positions to such a large number of disparate people that they would all keep an eye on each other, making collusion fairly rare. Furthermore, power did not necessarily go to those who wanted it and had schemed for it. The Athenians used an intricate machine, a kleroterion, to allot officers. Headlam also explains that "the Athenians felt no distrust of the lot, but regarded it as the most natural and the simplest way of appointment."

Like Athenian democrats, critics of electoral politics in the 21st-century argue that the process of election by vote is subject to manipulation by money and other powerful forces, and because legislative elections give power to a few powerful groups, they are believed to be a less democratic system than selection by lot from among the population.

Empowering ordinary people

An inherent problem with electoral politics is the over-representation of politically active groups in society who tend to be those who join political parties. For example, in 2000 less than 2% of the UK population belonged to a political party, while in 2005 there were at best only 3 independent MPs (see List of UK minor party and independent MPs elected) so that 99.5% of all UK MPs belonged to a political party.

Additionally, participants grow in competence by contributing to deliberation. Citizens are more significantly empowered by being a part of decision-making that concerns them. Most societies have some type of citizenship education, but sortition-based committees allow ordinary people to develop their own democratic capacities through participation.

Less political polarization

Elected representatives typically rely on political parties in order to gain and retain office. This means they often feel a primary loyalty to the party and will vote contrary to conscience to support a party position. Representatives appointed by sortition do not owe anything to anyone for their position.

Sortition could also reduce political polarization by removing some of its sources like election campaigns and lobbies. In a broader cultural context, the media would potentially be less centered on presenting politics as a zero-sum game for votes between politicians or political parties, which could lead to less political polarization as well.

Statistical properties

The representativeness and statistical properties of institutions like councils (committees), magistrates (cabinets) and juries selected by lot were mathematically examined by Andranik Tangian, who confirmed the validity of this method of appointment.

Disadvantages

Incompetence

The most common argument against pure sortition (that is, with no prior selection of an eligible group) is that it takes no account of skills or experience that might be needed to effectively discharge the particular offices to be filled. Were such a position to require a specific skill set, sortition could not necessarily guarantee the selection of a person whose skills matched the requirements of being in office unless the group from which the allotment is drawn were itself composed entirely of sufficiently specialized persons. This is why sortition was not used to select military commanders (strategos) in ancient Athens.

By contrast, systems of election or appointment ideally limit this problem by encouraging the matching of skilled individuals to jobs for which they are suited.

According to Xenophon (Memorabilia Book I, 2.9), this classical argument was offered by Socrates:

[Socrates] taught his companions to despise the established laws by insisting on the folly of appointing public officials by lot, when none would choose a pilot or builder or flautist by lot, nor any other craftsman for work in which mistakes are far less disastrous than mistakes in statecraft.

The same argument is made by Edmund Burke in his essay Reflections on the Revolution in France (1790):

There is no qualification for government but virtue and wisdom, actual or presumptive. [...] Everything ought to be open, but not indifferently, to every man. No rotation; no appointment by lot; no mode of election operating in the spirit of sortition or rotation can be generally good in a government conversant in extensive objects. Because they have no tendency, direct or indirect, to select the man with a view to the duty or to accommodate the one to the other.

Misrepresentation

In case demographic stratification is not rigorously put in place, there is always the statistical possibility that sortition may put into power an individual or group that do not represent the views of the population from which they were drawn. This argument is mentioned by Isocrates in his essay Areopagiticus (section 23):

[It was] considered that this way of appointing magistrates [i.e., elections] was also more democratic than the casting of lots, since under the plan of election by lot chance would decide the issue and the partizans of oligarchy would often get the offices; whereas under the plan of selecting the worthiest men, the people would have in their hands the power to choose those who were most attached to the existing constitution.

This argument applies to juries, but less to larger groups where the probability of, for example, an oppressive majority, are statistically insignificant. The modern processes of jury selection and the rights to object to and exclude particular jurors by both the plaintiff and defence are used to potentially lessen the possibilities of a jury not being representative of the community or being prejudicial towards one side or the other. Today, therefore, even juries in most jurisdictions are not ultimately chosen through pure sortition.

Illegitimacy

Those who see voting as expressing the "consent of the governed" maintain that voting is able to confer legitimacy in the selection. According to this view, elected officials can act with greater authority than when randomly selected. With no popular mandate to draw on, randomly selected politicians lose a moral basis on which to base their authority and are open to charges of illegitimacy.

Since it is statistically unlikely that a given individual will participate in the deliberative body, sortition creates two groups of people, the few randomly chosen politicians and the masses. Identifying the source of sortition's legitimacy has proven difficult. As a result, advocates of sortition have suggested limiting the use cases of sortition to serving as consultative or political agenda-setting bodies.

Enthusiasm

In an elected system, the representatives are to a degree self-selecting for their enthusiasm for the job. Under a system of pure, universal sortition the individuals are not chosen for their enthusiasm. Many electoral systems assign to those chosen a role as representing their constituents; a complex job with a significant workload. Elected representatives choose to accept any additional workload; voters can also choose those representatives most willing to accept the burden involved in being a representative. Individuals chosen at random from a comprehensive pool of citizens have no particular enthusiasm for their role and therefore may not make good advocates for a constituency.

Unaccountability

Unlike elections, where members of the elected body may stand for re-election, sortition does not offer a mechanism by which the population expresses satisfaction or dissatisfaction with individual members of the allotted body. Thus, under sortition there is no formal feedback, or accountability, mechanism for the performance of officials, other than the law.

Radionuclide

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Radionuclide

A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferred to one of its electrons to release it as a conversion electron; or used to create and emit a new particle (alpha particle or beta particle) from the nucleus. During those processes, the radionuclide is said to undergo radioactive decay. These emissions are considered ionizing radiation because they are powerful enough to liberate an electron from another atom. The radioactive decay can produce a stable nuclide or will sometimes produce a new unstable radionuclide which may undergo further decay. Radioactive decay is a random process at the level of single atoms: it is impossible to predict when one particular atom will decay. However, for a collection of atoms of a single nuclide the decay rate, and thus the half-life (t1/2) for that collection, can be calculated from their measured decay constants. The range of the half-lives of radioactive atoms has no known limits and spans a time range of over 55 orders of magnitude.

Radionuclides occur naturally or are artificially produced in nuclear reactors, cyclotrons, particle accelerators or radionuclide generators. There are about 730 radionuclides with half-lives longer than 60 minutes (see list of nuclides). Thirty-two of those are primordial radionuclides that were created before the earth was formed. At least another 60 radionuclides are detectable in nature, either as daughters of primordial radionuclides or as radionuclides produced through natural production on Earth by cosmic radiation. More than 2400 radionuclides have half-lives less than 60 minutes. Most of those are only produced artificially, and have very short half-lives. For comparison, there are about 252 stable nuclides. (In theory, only 146 of them are stable, and the other 106 are believed to decay via alpha decay, beta decay, double beta decay, electron capture, or double electron capture.)

All chemical elements can exist as radionuclides. Even the lightest element, hydrogen, has a well-known radionuclide, tritium. Elements heavier than lead, and the elements technetium and promethium, exist only as radionuclides. (In theory, elements heavier than dysprosium exist only as radionuclides, but some such elements, like gold and platinum, are observationally stable and their half-lives have not been determined).

Unplanned exposure to radionuclides generally has a harmful effect on living organisms including humans, although low levels of exposure occur naturally without harm. The degree of harm will depend on the nature and extent of the radiation produced, the amount and nature of exposure (close contact, inhalation or ingestion), and the biochemical properties of the element; with increased risk of cancer the most usual consequence. However, radionuclides with suitable properties are used in nuclear medicine for both diagnosis and treatment. An imaging tracer made with radionuclides is called a radioactive tracer. A pharmaceutical drug made with radionuclides is called a radiopharmaceutical.

Origin

Natural

On Earth, naturally occurring radionuclides fall into three categories: primordial radionuclides, secondary radionuclides, and cosmogenic radionuclides.

  • Radionuclides are produced in stellar nucleosynthesis and supernova explosions along with stable nuclides. Most decay quickly but can still be observed astronomically and can play a part in understanding astronomic processes. Primordial radionuclides, such as uranium and thorium, exist in the present time because their half-lives are so long (>100 million years) that they have not yet completely decayed. Some radionuclides have half-lives so long (many times the age of the universe) that decay has only recently been detected, and for most practical purposes they can be considered stable, most notably bismuth-209: detection of this decay meant that bismuth was no longer considered stable. It is possible decay may be observed in other nuclides, adding to this list of primordial radionuclides.
  • Secondary radionuclides are radiogenic isotopes derived from the decay of primordial radionuclides. They have shorter half-lives than primordial radionuclides. They arise in the decay chain of the primordial isotopes thorium-232, uranium-238, and uranium-235. Examples include the natural isotopes of polonium and radium.
  • Cosmogenic isotopes, such as carbon-14, are present because they are continually being formed in the atmosphere due to cosmic rays.

Many of these radionuclides exist only in trace amounts in nature, including all cosmogenic nuclides. Secondary radionuclides will occur in proportion to their half-lives, so short-lived ones will be very rare. For example, polonium can be found in uranium ores at about 0.1 mg per metric ton (1 part in 1010). Further radionuclides may occur in nature in virtually undetectable amounts as a result of rare events such as spontaneous fission or uncommon cosmic ray interactions.

Nuclear fission

Radionuclides are produced as an unavoidable result of nuclear fission and thermonuclear explosions. The process of nuclear fission creates a wide range of fission products, most of which are radionuclides. Further radionuclides can be created from irradiation of the nuclear fuel (creating a range of actinides) and of the surrounding structures, yielding activation products. This complex mixture of radionuclides with different chemistries and radioactivity makes handling nuclear waste and dealing with nuclear fallout particularly problematic.

Synthetic

Artificial nuclide americium-241 emitting alpha particles inserted into a cloud chamber for visualisation

Synthetic radionuclides are deliberately synthesised using nuclear reactors, particle accelerators or radionuclide generators:

  • As well as being extracted from nuclear waste, radioisotopes can be produced deliberately with nuclear reactors, exploiting the high flux of neutrons present. These neutrons activate elements placed within the reactor. A typical product from a nuclear reactor is iridium-192. The elements that have a large propensity to take up the neutrons in the reactor are said to have a high neutron cross-section.
  • Particle accelerators such as cyclotrons accelerate particles to bombard a target to produce radionuclides. Cyclotrons accelerate protons at a target to produce positron-emitting radionuclides, e.g. fluorine-18.
  • Radionuclide generators contain a parent radionuclide that decays to produce a radioactive daughter. The parent is usually produced in a nuclear reactor. A typical example is the technetium-99m generator used in nuclear medicine. The parent produced in the reactor is molybdenum-99.

Uses

Radionuclides are used in two major ways: either for their radiation alone (irradiation, nuclear batteries) or for the combination of chemical properties and their radiation (tracers, biopharmaceuticals).

  • In biology, radionuclides of carbon can serve as radioactive tracers because they are chemically very similar to the nonradioactive nuclides, so most chemical, biological, and ecological processes treat them in a nearly identical way. One can then examine the result with a radiation detector, such as a Geiger counter, to determine where the provided atoms were incorporated. For example, one might culture plants in an environment in which the carbon dioxide contained radioactive carbon; then the parts of the plant that incorporate atmospheric carbon would be radioactive. Radionuclides can be used to monitor processes such as DNA replication or amino acid transport.
  • In nuclear medicine, radioisotopes are used for diagnosis, treatment, and research. Radioactive chemical tracers emitting gamma rays or positrons can provide diagnostic information about internal anatomy and the functioning of specific organs, including the human brain. This is used in some forms of tomography: single-photon emission computed tomography and positron emission tomography (PET) scanning and Cherenkov luminescence imaging. Radioisotopes are also a method of treatment in hemopoietic forms of tumors; the success for treatment of solid tumors has been limited. More powerful gamma sources sterilise syringes and other medical equipment.
  • In food preservation, radiation is used to stop the sprouting of root crops after harvesting, to kill parasites and pests, and to control the ripening of stored fruit and vegetables. Food irradiation usually uses beta-decaying nuclides with strong gamma emissions like Cobalt-60 or Caesium-137.
  • In industry, and in mining, radionuclides are used to examine welds, to detect leaks, to study the rate of wear, erosion and corrosion of metals, and for on-stream analysis of a wide range of minerals and fuels.
  • In spacecraft, radionuclides are used to provide power and heat, notably through radioisotope thermoelectric generators (RTGs) and radioisotope heater units (RHUs).
  • In astronomy and cosmology, radionuclides play a role in understanding stellar and planetary process.
  • In particle physics, radionuclides help discover new physics (physics beyond the Standard Model) by measuring the energy and momentum of their beta decay products (for example, neutrinoless double beta decay and the search for weakly interacting massive particles).[12]
  • In ecology, radionuclides are used to trace and analyze pollutants, to study the movement of surface water, and to measure water runoffs from rain and snow, as well as the flow rates of streams and rivers.
  • In geology, archaeology, and paleontology, natural radionuclides are used to measure ages of rocks, minerals, and fossil materials.

Examples

The following table lists properties of selected radionuclides illustrating the range of properties and uses.

Key:  = atomic number; N = neutron number; DM = decay mode; DE = decay energy; EC = electron capture

Household smoke detectors

Americium-241 container in a smoke detector.
 
Americium-241 capsule as found in smoke detector. The circle of darker metal in the center is americium-241; the surrounding casing is aluminium.

Radionuclides are present in many homes as they are used inside the most common household smoke detectors. The radionuclide used is americium-241, which is created by bombarding plutonium with neutrons in a nuclear reactor. It decays by emitting alpha particles and gamma radiation to become neptunium-237. Smoke detectors use a very small quantity of 241Am (about 0.29 micrograms per smoke detector) in the form of americium dioxide. 241Am is used as it emits alpha particles which ionize the air in the detector's ionization chamber. A small electric voltage is applied to the ionized air which gives rise to a small electric current. In the presence of smoke, some of the ions are neutralized, thereby decreasing the current, which activates the detector's alarm.

Impacts on organisms

Radionuclides that find their way into the environment may cause harmful effects as radioactive contamination. They can also cause damage if they are excessively used during treatment or in other ways exposed to living beings, by radiation poisoning. Potential health damage from exposure to radionuclides depends on a number of factors, and "can damage the functions of healthy tissue/organs. Radiation exposure can produce effects ranging from skin redness and hair loss, to radiation burns and acute radiation syndrome. Prolonged exposure can lead to cells being damaged and in turn lead to cancer. Signs of cancerous cells might not show up until years, or even decades, after exposure."

Summary table for classes of nuclides, stable and radioactive

Following is a summary table for the list of 989 nuclides with half-lives greater than one hour. A total of 252 nuclides have never been observed to decay, and are classically considered stable. Of these, 90 are believed to be absolutely stable except to proton decay (which has never been observed), while the rest are "observationally stable" and theoretically can undergo radioactive decay with extremely long half-lives.

The remaining tabulated radionuclides have half-lives longer than 1 hour, and are well-characterized (see list of nuclides for a complete tabulation). They include 30 nuclides with measured half-lives longer than the estimated age of the universe (13.8 billion years), and another four nuclides with half-lives long enough (> 100 million years) that they are radioactive primordial nuclides, and may be detected on Earth, having survived from their presence in interstellar dust since before the formation of the solar system, about 4.6 billion years ago. Another 60+ short-lived nuclides can be detected naturally as daughters of longer-lived nuclides or cosmic-ray products. The remaining known nuclides are known solely from artificial nuclear transmutation.

Numbers are not exact, and may change slightly in the future, as "stable nuclides" are observed to be radioactive with very long half-lives.

This is a summary table for the 989 nuclides with half-lives longer than one hour (including those that are stable), given in list of nuclides.

List of commercially available radionuclides

This list covers common isotopes, most of which are available in very small quantities to the general public in most countries. Others that are not publicly accessible are traded commercially in industrial, medical, and scientific fields and are subject to government regulation.

Gamma emission only

Beta emission only

Alpha emission only

Multiple radiation emitters

Isotope Z N half-life DM DE
keV
Mode of formation Comments
Tritium (3H) 1 2 12.3 y β 19 Cosmogenic lightest radionuclide, used in artificial nuclear fusion, also used for radioluminescence and as oceanic transient tracer. Synthesized from neutron bombardment of lithium-6 or deuterium
Beryllium-10 4 6 1,387,000 y β 556 Cosmogenic used to examine soil erosion, soil formation from regolith, and the age of ice cores
Carbon-14 6 8 5,700 y β 156 Cosmogenic used for radiocarbon dating
Fluorine-18 9 9 110 min β+, EC 633/1655 Cosmogenic positron source, synthesised for use as a medical radiotracer in PET scans.
Aluminium-26 13 13 717,000 y β+, EC 4004 Cosmogenic exposure dating of rocks, sediment
Chlorine-36 17 19 301,000 y β, EC 709 Cosmogenic exposure dating of rocks, groundwater tracer
Potassium-40 19 21 1.24×109 y β, EC 1330 /1505 Primordial used for potassium-argon dating, source of atmospheric argon, source of radiogenic heat, largest source of natural radioactivity
Calcium-41 20 21 99,400 y EC
Cosmogenic exposure dating of carbonate rocks
Cobalt-60 27 33 5.3 y β 2824 Synthetic produces high energy gamma rays, used for radiotherapy, equipment sterilisation, food irradiation
Krypton-81 36 45 229,000 y β+
Cosmogenic groundwater dating
Strontium-90 38 52 28.8 y β 546 Fission product medium-lived fission product; probably most dangerous component of nuclear fallout
Technetium-99 43 56 210,000 y β 294 Fission product most common isotope of the lightest unstable element, most significant of long-lived fission products
Technetium-99m 43 56 6 hr γ,IC 141 Synthetic most commonly used medical radioisotope, used as a radioactive tracer
Iodine-129 53 76 15,700,000 y β 194 Cosmogenic longest lived fission product; groundwater tracer
Iodine-131 53 78 8 d β 971 Fission product most significant short-term health hazard from nuclear fission, used in nuclear medicine, industrial tracer
Xenon-135 54 81 9.1 h β 1160 Fission product strongest known "nuclear poison" (neutron-absorber), with a major effect on nuclear reactor operation.
Caesium-137 55 82 30.2 y β 1176 Fission product other major medium-lived fission product of concern
Gadolinium-153 64 89 240 d EC
Synthetic Calibrating nuclear equipment, bone density screening
Bismuth-209 83 126 2.01×1019y α 3137 Primordial long considered stable, decay only detected in 2003
Polonium-210 84 126 138 d α 5307 Decay product Highly toxic, used in poisoning of Alexander Litvinenko
Radon-222 86 136 3.8 d α 5590 Decay product gas, responsible for the majority of public exposure to ionizing radiation, second most frequent cause of lung cancer
Thorium-232 90 142 1.4×1010 y α 4083 Primordial basis of thorium fuel cycle
Uranium-235 92 143 7×108y α 4679 Primordial fissile, main nuclear fuel
Uranium-238 92 146 4.5×109 y α 4267 Primordial Main Uranium isotope
Plutonium-238 94 144 87.7 y α 5593 Synthetic used in radioisotope thermoelectric generators (RTGs) and radioisotope heater units as an energy source for spacecraft
Plutonium-239 94 145 24,110 y α 5245 Synthetic used for most modern nuclear weapons
Americium-241 95 146 432 y α 5486 Synthetic used in household smoke detectors as an ionising agent
Californium-252 98 154 2.64 y α/SF 6217 Synthetic undergoes spontaneous fission (3% of decays), making it a powerful neutron source, used as a reactor initiator and for detection devices
Stability class Number of nuclides Running total Notes on running total
Theoretically stable to all but proton decay 90 90 Includes first 40 elements. Proton decay yet to be observed.
Theoretically stable to alpha decay, beta decay, isomeric transition, and double beta decay but not spontaneous fission, which is possible for "stable" nuclides ≥ niobium-93 56 146 All nuclides that are possibly completely stable (spontaneous fission has never been observed for nuclides with mass number < 232).
Energetically unstable to one or more known decay modes, but no decay yet seen. All considered "stable" until decay detected. 106 252 Total of classically stable nuclides.
Radioactive primordial nuclides. 34 286 Total primordial elements include uranium, thorium, bismuth, rubidium-87, potassium-40, tellurium-128 plus all stable nuclides.
Radioactive nonprimordial, but naturally occurring on Earth. 61 347 Carbon-14 (and other isotopes generated by cosmic rays) and daughters of radioactive primordial elements, such as radium, polonium, etc. 41 of these have a half life of greater than one hour.
Radioactive synthetic half-life ≥ 1.0 hour). Includes most useful radiotracers. 662 989 These 989 nuclides are listed in the article List of nuclides.
Radioactive synthetic (half-life < 1.0 hour). >2400 >3300 Includes all well-characterized synthetic nuclides.
Isotope Activity Half-life Energies (keV)
Barium-133 9694 TBq/kg (262 Ci/g) 10.7 years 81.0, 356.0
Cadmium-109 96200 TBq/kg (2600 Ci/g) 453 days 88.0
Cobalt-57 312280 TBq/kg (8440 Ci/g) 270 days 122.1
Cobalt-60 40700 TBq/kg (1100 Ci/g) 5.27 years 1173.2, 1332.5
Europium-152 6660 TBq/kg (180 Ci/g) 13.5 years 121.8, 344.3, 1408.0
Manganese-54 287120 TBq/kg (7760 Ci/g) 312 days 834.8
Sodium-22 237540 Tbq/kg (6240 Ci/g) 2.6 years 511.0, 1274.5
Zinc-65 304510 TBq/kg (8230 Ci/g) 244 days 511.0, 1115.5
Technetium-99m 1.95×107 TBq/kg (5.27 × 105 Ci/g) 6 hours 140
Isotope Activity Half-life Energies (keV)
Strontium-90 5180 TBq/kg (140 Ci/g) 28.5 years 546.0
Thallium-204 17057 TBq/kg (461 Ci/g) 3.78 years 763.4
Carbon-14 166.5 TBq/kg (4.5 Ci/g) 5730 years 49.5 (average)
Tritium (Hydrogen-3) 357050 TBq/kg (9650 Ci/g) 12.32 years 5.7 (average)
Isotope Activity Half-life Energies (keV)
Polonium-210 166500 TBq/kg (4500 Ci/g) 138.376 days 5304.5
Uranium-238 12580 kBq/kg (0.00000034 Ci/g) 4.468 billion years 4267
Isotope Activity Half-life Radiation types Energies (keV)
Caesium-137 3256 TBq/kg (88 Ci/g) 30.1 years Gamma & beta G: 32, 661.6 B: 511.6, 1173.2
Americium-241 129.5 TBq/kg (3.5 Ci/g) 432.2 years Gamma & alpha G: 59.5, 26.3, 13.9 A: 5485, 5443

Operator (computer programming)

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