Nucleosynthesis

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Diagram illustration the creation of new elements by the alpha process Kernfusionen1 en.png
Diagram illustration the creation of new elements by the alpha process

Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in a process called Big Bang nucleosynthesis. [1] After about 20 minutes, the universe had expanded and cooled to a point at which these high-energy collisions among nucleons ended, so only the fastest and simplest reactions occurred, leaving our universe containing hydrogen and helium. The rest is traces of other elements such as lithium and the hydrogen isotope deuterium. Nucleosynthesis in stars and their explosions later produced the variety of elements and isotopes that we have today, in a process called cosmic chemical evolution. The amounts of total mass in elements heavier than hydrogen and helium (called 'metals' by astrophysicists) remains small (few percent), so that the universe still has approximately the same composition.

Contents

Stars fuse light elements to heavier ones in their cores, giving off energy in the process known as stellar nucleosynthesis. Nuclear fusion reactions create many of the lighter elements, up to and including iron and nickel in the most massive stars. Products of stellar nucleosynthesis remain trapped in stellar cores and remnants except if ejected through stellar winds and explosions. The neutron capture reactions of the r-process and s-process create heavier elements, from iron upwards.

Supernova nucleosynthesis within exploding stars is largely responsible for the elements between oxygen and rubidium: from the ejection of elements produced during stellar nucleosynthesis; through explosive nucleosynthesis during the supernova explosion; and from the r-process (absorption of multiple neutrons) during the explosion.

Neutron star mergers are a recently discovered major source of elements produced in the r-process. When two neutron stars collide, a significant amount of neutron-rich matter may be ejected which then quickly forms heavy elements.

Cosmic ray spallation is a process wherein cosmic rays impact nuclei and fragment them. It is a significant source of the lighter nuclei, particularly 3He, 9Be and 10,11B, that are not created by stellar nucleosynthesis. Cosmic ray spallation can occur in the interstellar medium, on asteroids and meteoroids, or on Earth in the atmosphere or in the ground. This contributes to the presence on Earth of cosmogenic nuclides.

On Earth new nuclei are also produced by radiogenesis, the decay of long-lived, primordial radionuclides such as uranium, thorium, and potassium-40.

History

Periodic table showing the currently believed origins of each element. Elements from carbon up to sulfur may be made in stars of all masses by charged-particle fusion reactions. Iron group elements originate mostly from the nuclear-statistical equilibrium process in thermonuclear supernova explosions. Elements beyond iron are made in high-mass stars with slow neutron capture (s-process), and by rapid neutron capture in the r-process, with origins being debated among rare supernova variants and compact-star collisions. Note that this graphic is a first-order simplification of an active research field with many open questions. Nucleosynthesis periodic table.svg
Periodic table showing the currently believed origins of each element. Elements from carbon up to sulfur may be made in stars of all masses by charged-particle fusion reactions. Iron group elements originate mostly from the nuclear-statistical equilibrium process in thermonuclear supernova explosions. Elements beyond iron are made in high-mass stars with slow neutron capture (s-process), and by rapid neutron capture in the r-process, with origins being debated among rare supernova variants and compact-star collisions. Note that this graphic is a first-order simplification of an active research field with many open questions.

Timeline

It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma around 13.8 billion years ago during the Big Bang as it cooled below two trillion degrees. A few minutes afterwards, starting with only protons and neutrons, nuclei up to lithium and beryllium (both with mass number 7) were formed, but hardly any other elements. Some boron may have been formed at this time, but the process stopped before significant carbon could be formed, as this element requires a far higher product of helium density and time than were present in the short nucleosynthesis period of the Big Bang. That fusion process essentially shut down at about 20 minutes, due to drops in temperature and density as the universe continued to expand. This first process, Big Bang nucleosynthesis, was the first type of nucleogenesis to occur in the universe, creating the so-called primordial elements.

A star formed in the early universe produces heavier elements by combining its lighter nuclei – hydrogen, helium, lithium, beryllium, and boron –which were found in the initial composition of the interstellar medium and hence the star. Interstellar gas therefore contains declining abundances of these light elements, which are present only by virtue of their nucleosynthesis during the Big Bang, and also cosmic ray spallation. These lighter elements in the present universe are therefore thought to have been produced through thousands of millions of years of cosmic ray (mostly high-energy proton) mediated breakup of heavier elements in interstellar gas and dust. The fragments of these cosmic-ray collisions include helium-3 and the stable isotopes of the light elements lithium, beryllium, and boron. Carbon was not made in the Big Bang, but was produced later in larger stars via the triple-alpha process.

The subsequent nucleosynthesis of heavier elements (Z ≥ 6, carbon and heavier elements) requires the extreme temperatures and pressures found within stars and supernovae. These processes began as hydrogen and helium from the Big Bang collapsed into the first stars after about 500 million years. Star formation has been occurring continuously in galaxies since that time. The primordial nuclides were created by Big Bang nucleosynthesis, stellar nucleosynthesis, supernova nucleosynthesis, and by nucleosynthesis in exotic events such as neutron star collisions. Other nuclides, such as 40Ar, formed later through radioactive decay. On Earth, mixing and evaporation has altered the primordial composition to what is called the natural terrestrial composition. The heavier elements produced after the Big Bang range in atomic numbers from Z = 6 (carbon) to Z = 94 (plutonium). Synthesis of these elements occurred through nuclear reactions involving the strong and weak interactions among nuclei, and called nuclear fusion (including both rapid and slow multiple neutron capture), and include also nuclear fission and radioactive decays such as beta decay. The stability of atomic nuclei of different sizes and composition (i.e. numbers of neutrons and protons) plays an important role in the possible reactions among nuclei. Cosmic nucleosynthesis, therefore, is studied among researchers of astrophysics and nuclear physics ("nuclear astrophysics").

History of nucleosynthesis theory

The first ideas on nucleosynthesis were simply that the chemical elements were created at the beginning of the universe, but no rational physical scenario for this could be identified. Gradually it became clear that hydrogen and helium are much more abundant than any of the other elements. All the rest constitute less than 2% of the mass of the Solar System, and of other star systems as well. At the same time it was clear that oxygen and carbon were the next two most common elements, and also that there was a general trend toward high abundance of the light elements, especially those with isotopes composed of whole numbers of helium-4 nuclei (alpha nuclides).

Arthur Stanley Eddington first suggested in 1920 that stars obtain their energy by fusing hydrogen into helium and raised the possibility that the heavier elements may also form in stars. [2] [3] This idea was not generally accepted, as the nuclear mechanism was not understood. In the years immediately before World War II, Hans Bethe first elucidated those nuclear mechanisms by which hydrogen is fused into helium.

Fred Hoyle's original work on nucleosynthesis of heavier elements in stars, occurred just after World War II. [4] His work explained the production of all heavier elements, starting from hydrogen. Hoyle proposed that hydrogen is continuously created in the universe from vacuum and energy, without need for universal beginning.

Hoyle's work explained how the abundances of the elements increased with time as the galaxy aged. Subsequently, Hoyle's picture was expanded during the 1960s by contributions from William A. Fowler, Alastair G. W. Cameron, and Donald D. Clayton, followed by many others. The seminal 1957 review paper by E. M. Burbidge, G. R. Burbidge, Fowler and Hoyle [5] is a well-known summary of the state of the field in 1957. That paper defined new processes for the transformation of one heavy nucleus into others within stars, processes that could be documented by astronomers.

The Big Bang itself had been proposed in 1931, long before this period, by Georges Lemaître, a Belgian physicist, who suggested that the evident expansion of the Universe in time required that the Universe, if contracted backwards in time, would continue to do so until it could contract no further. This would bring all the mass of the Universe to a single point, a "primeval atom", to a state before which time and space did not exist. Hoyle is credited with coining the term "Big Bang" during a 1949 BBC radio broadcast, saying that Lemaître's theory was "based on the hypothesis that all the matter in the universe was created in one big bang at a particular time in the remote past." It is popularly reported that Hoyle intended this to be pejorative, but Hoyle explicitly denied this and said it was just a striking image meant to highlight the difference between the two models. Lemaître's model was needed to explain the existence of deuterium and nuclides between helium and carbon, as well as the fundamentally high amount of helium present, not only in stars but also in interstellar space. As it happened, both Lemaître and Hoyle's models of nucleosynthesis would be needed to explain the elemental abundances in the universe.

The goal of the theory of nucleosynthesis is to explain the vastly differing abundances of the chemical elements and their several isotopes from the perspective of natural processes. The primary stimulus to the development of this theory was the shape of a plot of the abundances versus the atomic number of the elements. Those abundances, when plotted on a graph as a function of atomic number, have a jagged sawtooth structure that varies by factors up to ten million. A very influential stimulus to nucleosynthesis research was an abundance table created by Hans Suess and Harold Urey that was based on the unfractionated abundances of the non-volatile elements found within unevolved meteorites. [6] Such a graph of the abundances is displayed on a logarithmic scale below, where the dramatically jagged structure is visually suppressed by the many powers of ten spanned in the vertical scale of this graph.

Abundances of the chemical elements in the Solar System. Hydrogen and helium are most common, residuals within the paradigm of the Big Bang. The next three elements (Li, Be, B) are rare because they are poorly synthesized in the Big Bang and also in stars. The two general trends in the remaining stellar-produced elements are: (1) an alternation of abundance of elements according to whether they have even or odd atomic numbers, and (2) a general decrease in abundance, as elements become heavier. Within this trend is a peak at abundances of iron and nickel, which is especially visible on a logarithmic graph spanning fewer powers of ten, say between logA=2 (A=100) and logA=6 (A=1,000,000). SolarSystemAbundances.svg
Abundances of the chemical elements in the Solar System. Hydrogen and helium are most common, residuals within the paradigm of the Big Bang. The next three elements (Li, Be, B) are rare because they are poorly synthesized in the Big Bang and also in stars. The two general trends in the remaining stellar-produced elements are: (1) an alternation of abundance of elements according to whether they have even or odd atomic numbers, and (2) a general decrease in abundance, as elements become heavier. Within this trend is a peak at abundances of iron and nickel, which is especially visible on a logarithmic graph spanning fewer powers of ten, say between logA=2 (A=100) and logA=6 (A=1,000,000).

Processes

There are a number of astrophysical processes which are believed to be responsible for nucleosynthesis. The majority of these occur within stars, and the chain of those nuclear fusion processes are known as hydrogen burning (via the proton–proton chain or the CNO cycle), helium burning, carbon burning, neon burning, oxygen burning and silicon burning. These processes are able to create elements up to and including iron and nickel. This is the region of nucleosynthesis within which the isotopes with the highest binding energy per nucleon are created. Heavier elements can be assembled within stars by a neutron capture process known as the s-process or in explosive environments, such as supernovae and neutron star mergers, by a number of other processes. Some of those others include the r-process, which involves rapid neutron captures, the rp-process, and the p-process (sometimes known as the gamma process), which results in the photodisintegration of existing nuclei.

Major types

Big Bang nucleosynthesis

Big Bang nucleosynthesis [8] occurred within the first three minutes of the beginning of the universe and is responsible for much of the abundance of 1
H (protium), 2
H (D, deuterium), 3
He (helium-3), and 4
He (helium-4). Although 4
He continues to be produced by stellar fusion and alpha decays and trace amounts of 1
H continue to be produced by spallation and certain types of radioactive decay, most of the mass of the isotopes in the universe are thought to have been produced in the Big Bang. The nuclei of these elements, along with some 7
Li and 7
Be are considered to have been formed between 100 and 300 seconds after the Big Bang when the primordial quark–gluon plasma froze out to form protons and neutrons. Because of the very short period in which nucleosynthesis occurred before it was stopped by expansion and cooling (about 20 minutes), no elements heavier than beryllium (or possibly boron) could be formed. Elements formed during this time were in the plasma state, and did not cool to the state of neutral atoms until much later.[ citation needed ]

Chief nuclear reactions responsible for the relative abundances of light atomic nuclei observed throughout the universe.

Stellar nucleosynthesis

Stellar nucleosynthesis is the nuclear process by which new nuclei are produced. It occurs in stars during stellar evolution. It is responsible for the galactic abundances of elements from carbon to iron. Stars are thermonuclear furnaces in which H and He are fused into heavier nuclei by increasingly high temperatures as the composition of the core evolves. [9] Of particular importance is carbon because its formation from He is a bottleneck in the entire process. Carbon is produced by the triple-alpha process in all stars. Carbon is also the main element that causes the release of free neutrons within stars, giving rise to the s-process, in which the slow absorption of neutrons converts iron into elements heavier than iron and nickel. [10] [11]

The products of stellar nucleosynthesis are generally dispersed into the interstellar gas through mass loss episodes and the stellar winds of low mass stars. The mass loss events can be witnessed today in the planetary nebulae phase of low-mass star evolution, and the explosive ending of stars, called supernovae, of those with more than eight times the mass of the Sun.

The first direct proof that nucleosynthesis occurs in stars was the astronomical observation that interstellar gas has become enriched with heavy elements as time passed. As a result, stars that were born from it late in the galaxy, formed with much higher initial heavy element abundances than those that had formed earlier. The detection of technetium in the atmosphere of a red giant star in 1952, [12] by spectroscopy, provided the first evidence of nuclear activity within stars. Because technetium is radioactive, with a half-life much less than the age of the star, its abundance must reflect its recent creation within that star. Equally convincing evidence of the stellar origin of heavy elements is the large overabundances of specific stable elements found in stellar atmospheres of asymptotic giant branch stars. Observation of barium abundances some 20–50 times greater than found in unevolved stars is evidence of the operation of the s-process within such stars. Many modern proofs of stellar nucleosynthesis are provided by the isotopic compositions of stardust, solid grains that have condensed from the gases of individual stars and which have been extracted from meteorites. Stardust is one component of cosmic dust and is frequently called presolar grains. The measured isotopic compositions in stardust grains demonstrate many aspects of nucleosynthesis within the stars from which the grains condensed during the star's late-life mass-loss episodes. [13]

Explosive nucleosynthesis

Supernova nucleosynthesis occurs in the energetic environment in supernovae, in which the elements between silicon and nickel are synthesized in quasiequilibrium [14] established during fast fusion that attaches by reciprocating balanced nuclear reactions to 28Si. Quasiequilibrium can be thought of as almost equilibrium except for a high abundance of the 28Si nuclei in the feverishly burning mix. This concept [11] was the most important discovery in nucleosynthesis theory of the intermediate-mass elements since Hoyle's 1954 paper because it provided an overarching understanding of the abundant and chemically important elements between silicon (A = 28) and nickel (A = 60). It replaced the incorrect although much cited alpha process of the B2FH paper, which inadvertently obscured Hoyle's 1954 theory. [15] Further nucleosynthesis processes can occur, in particular the r-process (rapid process) described by the B2FH paper and first calculated by Seeger, Fowler and Clayton, [16] in which the most neutron-rich isotopes of elements heavier than nickel are produced by rapid absorption of free neutrons. The creation of free neutrons by electron capture during the rapid compression of the supernova core along with the assembly of some neutron-rich seed nuclei makes the r-process a primary process, and one that can occur even in a star of pure H and He. This is in contrast to the B2FH designation of the process as a secondary process. This promising scenario, though generally supported by supernova experts, has yet to achieve a satisfactory calculation of r-process abundances. The primary r-process has been confirmed by astronomers who had observed old stars born when galactic metallicity was still small, that nonetheless contain their complement of r-process nuclei; thereby demonstrating that the metallicity is a product of an internal process. The r-process is responsible for our natural cohort of radioactive elements, such as uranium and thorium, as well as the most neutron-rich isotopes of each heavy element.

The rp-process (rapid proton) involves the rapid absorption of free protons as well as neutrons, but its role and its existence are less certain.

Explosive nucleosynthesis occurs too rapidly for radioactive decay to decrease the number of neutrons, so that many abundant isotopes with equal and even numbers of protons and neutrons are synthesized by the silicon quasi-equilibrium process. [14] During this process, the burning of oxygen and silicon fuses nuclei that themselves have equal numbers of protons and neutrons to produce nuclides which consist of whole numbers of helium nuclei, up to 15 (representing 60Ni). Such multiple-alpha-particle nuclides are totally stable up to 40Ca (made of 10 helium nuclei), but heavier nuclei with equal and even numbers of protons and neutrons are tightly bound but unstable. The quasi-equilibrium produces radioactive isobars 44Ti, 48Cr, 52Fe, and 56Ni, which (except 44Ti) are created in abundance but decay after the explosion and leave the most stable isotope of the corresponding element at the same atomic weight. The most abundant and extant isotopes of elements produced in this way are 48Ti, 52Cr, and 56Fe. These decays are accompanied by the emission of gamma-rays (radiation from the nucleus), whose spectroscopic lines can be used to identify the isotope created by the decay. The detection of these emission lines were an important early product of gamma-ray astronomy. [17]

The most convincing proof of explosive nucleosynthesis in supernovae occurred in 1987 when those gamma-ray lines were detected emerging from supernova 1987A. Gamma-ray lines identifying 56Co and 57Co nuclei, whose half-lives limit their age to about a year, proved that their radioactive cobalt parents created them. This nuclear astronomy observation was predicted in 1969 [17] as a way to confirm explosive nucleosynthesis of the elements, and that prediction played an important role in the planning for NASA's Compton Gamma-Ray Observatory.

Other proofs of explosive nucleosynthesis are found within the stardust grains that condensed within the interiors of supernovae as they expanded and cooled. Stardust grains are one component of cosmic dust. In particular, radioactive 44Ti was measured to be very abundant within supernova stardust grains at the time they condensed during the supernova expansion. [13] This confirmed a 1975 prediction of the identification of supernova stardust (SUNOCONs), which became part of the pantheon of presolar grains. Other unusual isotopic ratios within these grains reveal many specific aspects of explosive nucleosynthesis.

Neutron star mergers

The merger of binary neutron stars (BNSs) is now believed to be the main source of r-process elements. [18] Being neutron-rich by definition, mergers of this type had been suspected of being a source of such elements, but definitive evidence was difficult to obtain. In 2017 strong evidence emerged, when LIGO, VIRGO, the Fermi Gamma-ray Space Telescope and INTEGRAL, along with a collaboration of many observatories around the world, detected both gravitational wave and electromagnetic signatures of a likely neutron star merger, GW170817, and subsequently detected signals of numerous heavy elements such as gold as the ejected degenerate matter decays and cools. [19] The first detection of the merger of a neutron star and black hole (NSBHs) came in July 2021 and more after but analysis seem to favor BNSs over NSBHs as the main contributors to heavy metal production. [20] [21]

Black hole accretion disk nucleosynthesis

Nucleosynthesis may happen in accretion disks of black holes. [22] [23] [24] [25] [26] [27] [28]

Cosmic ray spallation

Cosmic ray spallation process reduces the atomic weight of interstellar matter by the impact with cosmic rays, to produce some of the lightest elements present in the universe (though not a significant amount of deuterium). Most notably spallation is believed to be responsible for the generation of almost all of 3He and the elements lithium, beryllium, and boron, although some 7
Li
 and 7
Be
 are thought to have been produced in the Big Bang. The spallation process results from the impact of cosmic rays (mostly fast protons) against the interstellar medium. These impacts fragment carbon, nitrogen, and oxygen nuclei present. The process results in the light elements beryllium, boron, and lithium in the cosmos at much greater abundances than they are found within solar atmospheres. The quantities of the light elements 1H and 4He produced by spallation are negligible relative to their primordial abundance.

Beryllium and boron are not significantly produced by stellar fusion processes, since 8Be has an extremely short half-life of 8.2×10−17 seconds. [29]

Empirical evidence

Theories of nucleosynthesis are tested by calculating isotope abundances and comparing those results with observed abundances. Isotope abundances are typically calculated from the transition rates between isotopes in a network. Often these calculations can be simplified as a few key reactions control the rate of other reactions.[ citation needed ]

Minor mechanisms and processes

Tiny amounts of certain nuclides are produced on Earth by artificial means. Those are our primary source, for example, of technetium. However, some nuclides are also produced by a number of natural means that have continued after primordial elements were in place. These often act to create new elements in ways that can be used to date rocks or to trace the source of geological processes. Although these processes do not produce the nuclides in abundance, they are assumed to be the entire source of the existing natural supply of those nuclides.

These mechanisms include:

See also

Related Research Articles

A chemical element is a chemical substance that cannot be broken down into other substances by chemical reactions. The basic particle that constitutes a chemical element is the atom. Elements are identified by the number of protons in their nucleus, known as the element's atomic number. For example, oxygen has an atomic number of 8, meaning each oxygen atom has 8 protons in its nucleus. Atoms of the same element can have different numbers of neutrons in their nuclei, known as isotopes of the element. Two or more atoms can combine to form molecules. Chemical compounds are molecules made of atoms of different elements, while mixtures contain atoms of different elements not necessarily combined as molecules. Atoms can be transformed into different elements in nuclear reactions, which change an atom's atomic number.

<span class="mw-page-title-main">Big Bang nucleosynthesis</span> Process during the early universe

In physical cosmology, Big Bang nucleosynthesis is the production of nuclei other than those of the lightest isotope of hydrogen during the early phases of the universe. This type of nucleosynthesis is thought by most cosmologists to have occurred from 10 seconds to 20 minutes after the Big Bang. It is thought to be responsible for the formation of most of the universe's helium, along with small fractions of the hydrogen isotope deuterium, the helium isotope helium-3 (3He), and a very small fraction of the lithium isotope lithium-7 (7Li). In addition to these stable nuclei, two unstable or radioactive isotopes were produced: the heavy hydrogen isotope tritium and the beryllium isotope beryllium-7 (7Be). These unstable isotopes later decayed into 3He and 7Li, respectively, as above.

<span class="mw-page-title-main">Triple-alpha process</span> Nuclear fusion reaction chain converting helium to carbon

The triple-alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei are transformed into carbon.

<span class="mw-page-title-main">Stellar nucleosynthesis</span> Creation of chemical elements within stars

In astrophysics, stellar nucleosynthesis is the creation of chemical elements by nuclear fusion reactions within stars. Stellar nucleosynthesis has occurred since the original creation of hydrogen, helium and lithium during the Big Bang. As a predictive theory, it yields accurate estimates of the observed abundances of the elements. It explains why the observed abundances of elements change over time and why some elements and their isotopes are much more abundant than others. The theory was initially proposed by Fred Hoyle in 1946, who later refined it in 1954. Further advances were made, especially to nucleosynthesis by neutron capture of the elements heavier than iron, by Margaret and Geoffrey Burbidge, William Alfred Fowler and Fred Hoyle in their famous 1957 B2FH paper, which became one of the most heavily cited papers in astrophysics history.

<span class="mw-page-title-main">Nuclide</span> Atomic species

A nuclide is a class of atoms characterized by their number of protons, Z, their number of neutrons, N, and their nuclear energy state.

<i>r</i>-process Nucleosynthesis pathway

In nuclear astrophysics, the rapid neutron-capture process, also known as the r-process, is a set of nuclear reactions that is responsible for the creation of approximately half of the atomic nuclei heavier than iron, the "heavy elements", with the other half produced by the p-process and s-process. The r-process usually synthesizes the most neutron-rich stable isotopes of each heavy element. The r-process can typically synthesize the heaviest four isotopes of every heavy element; of these, the heavier two are called r-only nuclei because they are created exclusively via the r-process. Abundance peaks for the r-process occur near mass numbers A = 82, A = 130 and A = 196.

The slow neutron-capture process, or s-process, is a series of reactions in nuclear astrophysics that occur in stars, particularly asymptotic giant branch stars. The s-process is responsible for the creation (nucleosynthesis) of approximately half the atomic nuclei heavier than iron.

The abundance of the chemical elements is a measure of the occurrence of the chemical elements relative to all other elements in a given environment. Abundance is measured in one of three ways: by mass fraction, by mole fraction, or by volume fraction. Volume fraction is a common abundance measure in mixed gases such as planetary atmospheres, and is similar in value to molecular mole fraction for gas mixtures at relatively low densities and pressures, and ideal gas mixtures. Most abundance values in this article are given as mass fractions.

<span class="mw-page-title-main">Oddo–Harkins rule</span> Relative abundance of chemical elements

The Oddo–Harkins rule holds that an element with an even atomic number is more abundant than the elements with immediately adjacent atomic numbers. For example, carbon, with atomic number 6, is more abundant than boron (5) and nitrogen (7). Generally, the relative abundance of an even atomic numbered element is roughly two orders of magnitude greater than the relative abundances of the immediately adjacent odd atomic numbered elements to either side. This pattern was first reported by Giuseppe Oddo in 1914 and William Draper Harkins in 1917. The Oddo–Harkins rule is true for all elements beginning with carbon produced by stellar nucleosynthesis but not true for the lightest elements below carbon produced by big bang nucleosynthesis and cosmic ray spallation.

Supernova nucleosynthesis is the nucleosynthesis of chemical elements in supernova explosions.

Cosmic ray spallation, also known as the x-process, is a set of naturally occurring nuclear reactions causing nucleosynthesis; it refers to the formation of chemical elements from the impact of cosmic rays on an object. Cosmic rays are highly energetic charged particles from beyond Earth, ranging from protons, alpha particles, and nuclei of many heavier elements. About 1% of cosmic rays also consist of free electrons.

Helium (2He) has nine known isotopes, but only helium-3 (3He) and helium-4 (4He) are stable. All radioisotopes are short-lived; the longest-lived is 6He with half-life 806.92(24) milliseconds. The least stable is 10He, with half-life 260(40) yoctoseconds, though 2He may have an even shorter half-life.

<span class="mw-page-title-main">Nuclear astrophysics</span> Field of nuclear physics and astrophysics

Nuclear astrophysics is an interdisciplinary part of both nuclear physics and astrophysics, involving close collaboration among researchers in various subfields of each of these fields. This includes, notably, nuclear reactions and their rates as they occur in cosmic environments, and modeling of astrophysical objects where these nuclear reactions may occur, but also considerations of cosmic evolution of isotopic and elemental composition (often called chemical evolution). Constraints from observations involve multiple messengers, all across the electromagnetic spectrum (nuclear gamma-rays, X-rays, optical, and radio/sub-mm astronomy), as well as isotopic measurements of solar-system materials such as meteorites and their stardust inclusions, cosmic rays, material deposits on Earth and Moon). Nuclear physics experiments address stability (i.e., lifetimes and masses) for atomic nuclei well beyond the regime of stable nuclides into the realm of radioactive/unstable nuclei, almost to the limits of bound nuclei (the drip lines), and under high density (up to neutron star matter) and high temperature (plasma temperatures up to 109 K). Theories and simulations are essential parts herein, as cosmic nuclear reaction environments cannot be realized, but at best partially approximated by experiments. In general terms, nuclear astrophysics aims to understand the origin of the chemical elements and isotopes, and the role of nuclear energy generation, in cosmic sources such as stars, supernovae, novae, and violent binary-star interactions.

A nucleogenic isotope, or nuclide, is one that is produced by a natural terrestrial nuclear reaction, other than a reaction beginning with cosmic rays. The nuclear reaction that produces nucleogenic nuclides is usually interaction with an alpha particle or the capture of fission or thermal neutrons. Some nucleogenic isotopes are stable and others are radioactive.

The B2FH paper was a landmark scientific paper on the origin of the chemical elements. The paper's title is Synthesis of the Elements in Stars, but it became known as B2FH from the initials of its authors: Margaret Burbidge, Geoffrey Burbidge, William A. Fowler, and Fred Hoyle. It was written from 1955 to 1956 at the University of Cambridge and Caltech, then published in Reviews of Modern Physics in 1957.

Beryllium-8 is a radionuclide with 4 neutrons and 4 protons. It is an unbound resonance and nominally an isotope of beryllium. It decays into two alpha particles with a half-life on the order of 8.19×10−17 seconds. This has important ramifications in stellar nucleosynthesis as it creates a bottleneck in the creation of heavier chemical elements. The properties of 8Be have also led to speculation on the fine tuning of the Universe, and theoretical investigations on cosmological evolution had 8Be been stable.

<span class="mw-page-title-main">Isotope</span> Different atoms of the same element

Isotopes are distinct nuclear species of the same chemical element. They have the same atomic number and position in the periodic table, but different nucleon numbers due to different numbers of neutrons in their nuclei. While all isotopes of a given element have similar chemical properties, they have different atomic masses and physical properties.

<span class="mw-page-title-main">Nuclear transmutation</span> Conversion of an atom from one element to another

Nuclear transmutation is the conversion of one chemical element or an isotope into another chemical element. Nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus of an atom is changed.

p-nuclei (p stands for proton-rich) are certain proton-rich, naturally occurring isotopes of some elements between selenium and mercury inclusive which cannot be produced in either the s- or the r-process.

<span class="mw-page-title-main">Even and odd atomic nuclei</span> Nuclear physics classification method

In nuclear physics, properties of a nucleus depend on evenness or oddness of its atomic number Z, neutron number N and, consequently, of their sum, the mass number A. Most importantly, oddness of both Z and N tends to lower the nuclear binding energy, making odd nuclei generally less stable. This effect is not only experimentally observed, but is included in the semi-empirical mass formula and explained by some other nuclear models, such as the nuclear shell model. This difference of nuclear binding energy between neighbouring nuclei, especially of odd-A isobars, has important consequences for beta decay.

References

  1. ↑ "DOE Explains...Nucleosynthesis". Energy.gov. Retrieved 2022-03-22.
  2. ↑ Eddington, A. S. (1920). "The Internal Constitution of the Stars". The Observatory . 43 (1341): 233–40. Bibcode:1920Obs....43..341E. doi:10.1126/science.52.1341.233. PMID   17747682.
  3. ↑ Eddington, A. S. (1920). "The Internal Constitution of the Stars". Nature . 106 (2653): 14–20. Bibcode:1920Natur.106...14E. doi: 10.1038/106014a0 . PMID   17747682.
  4. ↑ Actually, before the war ended, he learned about the problem of spherical implosion of plutonium in the Manhattan project. He saw an analogy between the plutonium fission reaction and the newly discovered supernovae, and he was able to show that exploding super novae produced all of the elements in the same proportion as existed on Earth. He felt that he had accidentally fallen into a subject that would make his career. Autobiography William A. Fowler
  5. ↑ Burbidge, E. M.; Burbidge, G. R.; Fowler, W. A.; Hoyle, F. (1957). "Synthesis of the Elements in Stars". Reviews of Modern Physics . 29 (4): 547–650. Bibcode:1957RvMP...29..547B. doi: 10.1103/RevModPhys.29.547 .
  6. ↑ Suess, Hans E.; Urey, Harold C. (1956). "Abundances of the Elements". Reviews of Modern Physics . 28 (1): 53–74. Bibcode:1956RvMP...28...53S. doi:10.1103/RevModPhys.28.53.
  7. ↑ Stiavelli, Massimo (2009). From First Light to Reionization the End of the Dark Ages. Weinheim, Germany: Wiley-VCH. p. 8. ISBN   9783527627370.
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  9. ↑ Clayton, D. D. (1983). Principles of Stellar Evolution and Nucleosynthesis (Reprint ed.). Chicago, IL: University of Chicago Press. Chapter 5. ISBN   978-0-226-10952-7.
  10. ↑ Clayton, D. D.; Fowler, W. A.; Hull, T. E.; Zimmerman, B. A. (1961). "Neutron Capture Chains in Heavy Element Synthesis". Annals of Physics . 12 (3): 331–408. Bibcode:1961AnPhy..12..331C. doi:10.1016/0003-4916(61)90067-7.
  11. 1 2 Clayton, D. D. (1983). Principles of Stellar Evolution and Nucleosynthesis (Reprint ed.). Chicago, IL: University of Chicago Press. Chapter 7. ISBN   978-0-226-10952-7.
  12. ↑ Merrill, S. P. W. (1952). "Spectroscopic Observations of Stars of Class". The Astrophysical Journal . 116: 21. Bibcode:1952ApJ...116...21M. doi:10.1086/145589.
  13. 1 2 Clayton, D. D.; Nittler, L. R. (2004). "Astrophysics with Presolar Stardust". Annual Review of Astronomy and Astrophysics . 42 (1): 39–78. Bibcode:2004ARA&A..42...39C. doi:10.1146/annurev.astro.42.053102.134022.
  14. 1 2 Bodansky, D.; Clayton, D. D.; Fowler, W. A. (1968). "Nuclear Quasi-Equilibrium during Silicon Burning". The Astrophysical Journal Supplement Series . 16: 299. Bibcode:1968ApJS...16..299B. doi:10.1086/190176.
  15. ↑ Clayton, D. D. (2007). "Hoyle's Equation". Science . 318 (5858): 1876–1877. doi:10.1126/science.1151167. PMID   18096793. S2CID   118423007.
  16. ↑ Seeger, P. A.; Fowler, W. A.; Clayton, D. D. (1965). "Nucleosynthesis of Heavy Elements by Neutron Capture". The Astrophysical Journal Supplement Series . 11: 121. Bibcode:1965ApJS...11..121S. doi:10.1086/190111.
  17. 1 2 Clayton, D. D.; Colgate, S. A.; Fishman, G. J. (1969). "Gamma-Ray Lines from Young Supernova Remnants". The Astrophysical Journal . 155: 75. Bibcode:1969ApJ...155...75C. doi:10.1086/149849.
  18. ↑ Stromberg, Joseph (16 July 2013). "All the Gold in the Universe Could Come from the Collisions of Neutron Stars". Smithsonian . Retrieved 27 April 2014.
  19. ↑ Chu, J. (n.d.). "GW170817 Press Release". LIGO/Caltech . Retrieved 2018-07-04.
  20. ↑ Chen, Hsin-Yu; Vitale, Salvatore; Foucart, Francois (2021-10-01). "The Relative Contribution to Heavy Metals Production from Binary Neutron Star Mergers and Neutron Star–Black Hole Mergers". The Astrophysical Journal Letters. 920 (1): L3. arXiv: 2107.02714 . Bibcode:2021ApJ...920L...3C. doi: 10.3847/2041-8213/ac26c6 . ISSN   2041-8205. S2CID   238198587.
  21. ↑ "Neutron star collisions are a "goldmine" of heavy elements, study finds". MIT News | Massachusetts Institute of Technology. 25 October 2021. Retrieved 2021-12-23.
  22. ↑ Chakrabarti, S. K.; Jin, L.; Arnett, W. D. (1987). "Nucleosynthesis Inside Thick Accretion Disks Around Black Holes. I – Thermodynamic Conditions and Preliminary Analysis". The Astrophysical Journal . 313: 674. Bibcode:1987ApJ...313..674C. doi:10.1086/165006. OSTI   6468841.
  23. ↑ McLaughlin, G.; Surman, R. (2 April 2007). "Nucleosynthesis from Black Hole Accretion Disks" (PDF). Archived (PDF) from the original on 2016-09-10.
  24. ↑ Frankel, N. (2017). Nucleosynthesis in Accretion Disks Around Black Holes (PDF) (MSc). Lund Observatory/Lund University. Archived (PDF) from the original on 2020-03-24.
  25. ↑ Surman, R.; McLaughlin, G. C.; Ruffert, M.; Janka, H.-Th.; Hix, W. R. (2008). "Process Nucleosynthesis in Hot Accretion Disk Flows from Black Hole-Neutron Star Mergers". The Astrophysical Journal . 679 (2): L117–L120. arXiv: 0803.1785 . Bibcode:2008ApJ...679L.117S. doi:10.1086/589507. S2CID   17114805.
  26. ↑ Arai, K.; Matsuba, R.; Fujimoto, S.; Koike, O.; Hashimoto, M. (2003). "Nucleosynthesis Inside Accretion Disks Around Intermediate-mass Black Holes". Nuclear Physics A . 718: 572–574. Bibcode:2003NuPhA.718..572A. doi:10.1016/S0375-9474(03)00856-X.
  27. ↑ Mukhopadhyay, B. (2018). "Nucleonsynthesis in Advective Accretion Disk Around Compact Object". In Jantzen, R. T.; Ruffini, R.; Gurzadyan, V. G. (eds.). Proceedings of the Ninth Marcel Grossmann Meeting on General Relavitity. World Scientific. pp. 2261–2262. arXiv: astro-ph/0103162 . Bibcode:2002nmgm.meet.2261M. CiteSeerX   10.1.1.254.7490 . doi:10.1142/9789812777386_0544. ISBN   9789812389930. S2CID   118008078.
  28. ↑ Breen, P. G. (2018). "Light element variations in globular clusters via nucleosynthesis in black hole accretion discs". Monthly Notices of the Royal Astronomical Society: Letters . 481 (1): L110–114. arXiv: 1804.08877 . Bibcode:2018MNRAS.481L.110B. doi: 10.1093/mnrasl/sly169 . S2CID   54001706.
  29. ↑ Surdoval, Wayne; Berry, David (2021). "A New Approach for Calculating the Alpha-Decay Half-Life for the Heavy and Super-heavy Elements and an Exact A Priori Result for Beyllium-8". osti.gov. U.S. Department of Energy Office of Scientific and Technical Information. doi:10.2172/1773479. OSTI   1773479 . Retrieved 17 April 2024.

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