The proton–proton chain reaction is one of two known sets of nuclear fusion reactions by which stars convert hydrogen to helium. It dominates in stars with masses less than or equal to that of the Sun, whereas the CNO cycle, the other known reaction, is suggested by theoretical models to dominate in stars with masses greater than about 1.3 times that of the Sun. In general, proton–proton fusion can occur only if the kinetic energy of the protons is high enough to overcome their mutual electrostatic or Coulomb repulsion. In the Sun, deuterium-producing events are rare. Diprotons are the much more common result of proton–proton reactions within the star, diprotons immediately decay back into two protons. Since the conversion of hydrogen to helium is slow, the complete conversion of the hydrogen in the core of the Sun is calculated to take more than ten billion years. Although called the "proton–proton chain reaction", it is not a chain reaction in the normal sense of the word, it does not produce particles.
In fact, the rate is self-limiting. It is however a chain and a reaction, or more a branched chain of reactions starting with two protons coming together and yielding deuterium; the theory that proton–proton reactions are the basic principle by which the Sun and other stars burn was advocated by Arthur Eddington in the 1920s. At the time, the temperature of the Sun was considered to be too low to overcome the Coulomb barrier. After the development of quantum mechanics, it was discovered that tunneling of the wavefunctions of the protons through the repulsive barrier allows for fusion at a lower temperature than the classical prediction. So, it was unclear how proton–proton fusion might proceed, because the most obvious product, helium-2, is unstable and instantly dissociates back into two protons. In 1939, Hans Bethe proposed that one of the protons could decay by beta emission into a neutron via the weak interaction during the brief moment of fusion, making deuterium a vital product in the chain.
This idea was part of the body of work in stellar nucleosynthesis for which Bethe won the Nobel Prize in Physics in 1967. The first step in all the branches is the fusion of two protons into deuterium; as the protons fuse, one of them undergoes beta plus decay, converting into a neutron by emitting a positron and an electron neutrino. The positron will annihilate with an electron from the environment into two gamma rays. Including this annihilation the whole reaction has a Q value of 1.442 MeV. This reaction is slow due to it being initiated by the weak nuclear force; the average proton in the core of the Sun waits 9 billion years before it fuses with another proton. It has not been possible to measure the cross-section of this reaction experimentally because of these long time scales. After it is formed, the deuterium produced in the first stage can fuse with another proton to produce the light isotope of helium, 3He: This process, mediated by the strong nuclear force rather than the weak force, is fast by comparison to the first step.
It is estimated that, under the conditions in the Sun's core, each newly created deuterium nucleus exists for only about four seconds before it is converted to helium-3. In the Sun, each helium-3 nucleus produced in these reactions exists for only about 400 years before it is converted into helium-4. Once the helium-3 has been produced, there are four possible paths. In p–p I, helium-4 is produced by fusing two helium-3 nuclei. In the Sun, 4He synthesis via branch p–p I occurs with a frequency of 83.30 percent, p–p II with 16.68 percent, p–p III with 0.02 percent. There is the rare p–p IV branch. Other rarer reactions may occur; the rate of these reactions is low due to small cross-sections, or because the number of reacting particles is so low that any reactions that might happen are statistically insignificant. This is why no mass-5 or mass-8 elements are seen. While the reactions that would produce them, such as a proton + helium-4 producing lithium-5, or two helium-4 nuclei coming together to form beryllium-8, may happen, these elements are not detected because there are no stable isotopes of atomic masses 5 or 8.
The overall reaction is: 4 ¹H⁺ → ⁴He²⁺ + 2e⁺ + 2νₑ The complete p–p I chain reaction releases a net energy of 26.732 MeV. Two percent of this energy is lost to the neutrinos; the p–p I branch is dominant at temperatures of 10 to 14 MK. Below 10 MK, the p–p chain does not produce much 4He; the p–p II branch is dominant at temperatures of 14 to 23 MK. Note that the energies in the equation above are not the energy released by the reaction. Rather, they are the energies of the neutrinos. 90 percent of the neutrinos produced in the reaction of 7Be to 7Li carry an energy of 0.861 MeV, while the remaining 10 percent carry 0.383 MeV. The difference is whether the lithium-7 produced is in the ground state or an excited state, respectively; the p–p III chain is dominant if the temperature exceeds 23 MK. The p–p III chain is not a major source of energy in the Sun, but it was important in the solar neutrino problem because it generates high energy neutrinos (up to
Maximianopolis was an ancient city in Palaestina Secunda, within the Byzantine Empire. The name Maximianopolis was given to it in honour of his co-emperor Maximian, it was located 17 M. P. from Caesarea and 10 M. P. from Jezreel. The town earlier bore the names Caporcotani, its site is near Israel. Jerome identified Maximianopolis with the Hadad-rimmon of Zechariah 12:11 – On that day the mourning in Jerusalem will be as great as the mourning for Hadad-rimmon in the plain of MegiddoThe mention of the Hadad-rimmon mourning may be a reference to pagan worship ceremonies or to an event such as the death of Josiah, mortally wounded in the Battle of Megiddo. Maximianopolis in Palaestina was a seat of a Bishop in the province of Palestina II. In the time of the so-called Pilgrim of Bordeaux and of Jerome, the town bore the name of Maximianopolis; the camp of the Legio VI Ferrata was within the same Catholic see, at a place, known as Legio. In the Latin version of an episcopal Notitia Episcopatuum of the 11th century, the name "Legionum" is given to what in the original Greek text is Maximianopolis.
Legio became Lajjun the site of Kibbutz Meggido, closer than Maximianopolis to Megiddo. Only three of its residential bishops are known: Paul, in 325 Megas, in 518 Domnus, in 536 The ancient episcopal see is now included, under the name Maximianopolis in Palaestina, in the list of titular sees of the Roman Catholic Church given in the Annuario Pontificio. Gaetano Mantegazza, B. † Alexander Cameron † Kajetan von Kowalski † William Walsh † Aleksander Kazimierz Beresniewicz † Ferdinand Maria Ossi, O. C. D. † John Hutchinson, O. S. A. † Auguste François Louis Grimault, C. S. Sp. † Megiddo church, located in the area of ancient Legio Maximianopolis This article incorporates text from a publication now in the public domain: Smith, William, ed.. "Maximianopolis". Dictionary of Greek and Roman Geography. London: John Murray
Out to an Other Side is the third solo album by master uilleann piper and prominent Irish traditional musician Liam O'Flynn. Produced by Shaun Davey and recorded at Windmill Lane Studios in Dublin, the album was released on the Tara Music label in 1993; as with a number of Liam's other album titles, Out to an Other Side comes from the writing of Nobel Laureate Seamus Heaney with whom Liam has performed live on numerous occasions. The Allmusic web site gave the album four and a half out of five stars, calling it O'Flynn's "most eclectic album" featuring "solo tracks as well as folk revival and orchestral arrangements". All songs are Traditional, except. "The Foxchase" – 9:5 "The Wild Geese" – 5:51 "The Dean's Pamphlet" – 3:55 "Gynt at the Gate" – 4:33 "The Winter's End" – 3:22 "After Aughrim's Great Disaster" – 3:21 "Blackwells" – 4:08 "Ar Bhruach na Laoi" – 6:11 "Lady Dillon" – 4:13 "Dollards and the Harlequin Hornpipes" – 3:10 "Sean O Duibhir a Ghleanna – 3:59 Liam O'Flynn – uilleann piper, whistle Bill Dowdall – flute, piccolo Matthew Manning – oboe, Cor anglais Carl Geraghty – saxophone Fergus O'Carroll – French horn Graham Hastings – trumpet, flugelhorn Noel Eccles – percussion Arty McGlynn – guitar Des Moore – guitar Helen Davies – Irish harp Sean Keane – violin Nollaig Casey – violin, viola Adele O'Dwyer – cello Joe Czibi jnr. – double bass Rod McVey – synthesizer Peter Connolly – electric bass Steve Cooney – electric bass Paul McAteer – drums The Voice Squad – vocals Rita Connolly – vocals Liam Ó Maonlaí – vocals Record Label Catalogue 2009 Album Sleevenotes