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r capture and s capture
r capture and s capture
Published: 2016/02/18
Channel: Gideon Boulton
The s-Process - Sixty Symbols
The s-Process - Sixty Symbols
Published: 2016/10/25
Channel: Sixty Symbols
The r-process: Status & Challenges - Yong-Zhong Qian
The r-process: Status & Challenges - Yong-Zhong Qian
Published: 2014/07/24
Channel: UC-HiPACC
NUCLEAR MASSES AND THEIR IMPACT IN R-PROCESS NUCLEOSYNTHESIS
NUCLEAR MASSES AND THEIR IMPACT IN R-PROCESS NUCLEOSYNTHESIS
Published: 2015/01/19
Channel: Joel de Jesus Mendoza Temis
r-Process Nucleosynthesis Comparison
r-Process Nucleosynthesis Comparison
Published: 2014/12/09
Channel: A L
r-process
r-process
Published: 2016/01/22
Channel: WikiAudio
R-process Meaning
R-process Meaning
Published: 2015/04/25
Channel: ADictionary
Record to Report:  Getting to a Safer-Faster-Better Close
Record to Report: Getting to a Safer-Faster-Better Close
Published: 2014/12/15
Channel: Consider Solutions
Food Function Freddom 5-R Process
Food Function Freddom 5-R Process
Published: 2017/04/07
Channel: Dr. Arland Hill
R-PROCESS
R-PROCESS
Published: 2013/03/29
Channel: ywdskoreasign
How The 5 R Process Will Help You Achieve Your Goals
How The 5 R Process Will Help You Achieve Your Goals
Published: 2014/12/09
Channel: John Assaraf
The Four R Process In Action
The Four R Process In Action
Published: 2013/10/08
Channel: Tim Chittenden
S|R Process
S|R Process
Published: 2014/10/19
Channel: zac beard
5 R Process to Achieve your Goals - John Assaraf
5 R Process to Achieve your Goals - John Assaraf
Published: 2014/05/04
Channel: Adi Atar
Joseph R. Murray, Esq : Navigating the PDUFA Process for Rare Disease Patient Organizations
Joseph R. Murray, Esq : Navigating the PDUFA Process for Rare Disease Patient Organizations
Published: 2017/03/21
Channel: Rare Advocates
Sackler Conference 2016 -- Enrico Ramirez-Ruiz: r-Process Nucleosynthesis
Sackler Conference 2016 -- Enrico Ramirez-Ruiz: r-Process Nucleosynthesis
Published: 2016/07/22
Channel: ITC Video
Record to report
Record to report
Published: 2016/01/13
Channel: Audiopedia
SQ3R+R: A Recursive Reading Process
SQ3R+R: A Recursive Reading Process
Published: 2014/08/25
Channel: Aileen Farrar
rprocess
rprocess
Published: 2014/06/12
Channel: Nathan Parzuchowski
MIEX(R) Process Demo
MIEX(R) Process Demo
Published: 2009/05/15
Channel: mbourke01
S|R Process - SR-Tutorial N°31
S|R Process - SR-Tutorial N°31
Published: 2015/08/25
Channel: SR3780
Statistical Process Control |  R-Chart (Control Chart for Ranges)
Statistical Process Control | R-Chart (Control Chart for Ranges)
Published: 2015/07/19
Channel: Joshua Emmanuel
CD-R Production proceSS
CD-R Production proceSS
Published: 2009/12/01
Channel: Subhas4u
Senators Murkowski (R-AK) and Cassidy (R-LA) on Improving Process for Repealing-Replacing ACA
Senators Murkowski (R-AK) and Cassidy (R-LA) on Improving Process for Repealing-Replacing ACA
Published: 2017/01/10
Channel: senatormurkowski
Read and process files larger than RAM: Machine Learning with R
Read and process files larger than RAM: Machine Learning with R
Published: 2014/06/11
Channel: Manuel Amunategui
A Single Prolific r-process Event Preserved in an Ultra-faint Dwarf Galaxy - Anna Frebel
A Single Prolific r-process Event Preserved in an Ultra-faint Dwarf Galaxy - Anna Frebel
Published: 2016/09/21
Channel: Institute for Advanced Study
r:GEN - RPE Regeneration Process
r:GEN - RPE Regeneration Process
Published: 2017/05/03
Channel: Lutronic Vision
Thanka Painting Process HD-By R.Ghising
Thanka Painting Process HD-By R.Ghising
Published: 2016/08/21
Channel: R Ghising
Jonas Lippuner JINA-CEE online seminar "r-Process in neutron star mergers"
Jonas Lippuner JINA-CEE online seminar "r-Process in neutron star mergers"
Published: 2016/02/18
Channel: JINA-CEE
Waiver of service of process under Fed. R. Civ. P. 4(d)
Waiver of service of process under Fed. R. Civ. P. 4(d)
Published: 2016/10/07
Channel: PatriciaWickMoore
Supernova nucleosynthesis
Supernova nucleosynthesis
Published: 2015/12/06
Channel: Audiopedia
INT 14-2a: Yuichiro Sekiguchi, Binary neutron star merger and r-process (pt 2)
INT 14-2a: Yuichiro Sekiguchi, Binary neutron star merger and r-process (pt 2)
Published: 2014/11/06
Channel: INT UW Seattle
Supernova nucleosynthesis - Video Learning - WizScience.com
Supernova nucleosynthesis - Video Learning - WizScience.com
Published: 2015/09/29
Channel: Wiz Science™
Galactic chemical evolution of the r-process elements - Benjamin Wehmeyer
Galactic chemical evolution of the r-process elements - Benjamin Wehmeyer
Published: 2016/11/09
Channel: First Stars
R Programming: Simulating Random Walk Process
R Programming: Simulating Random Walk Process
Published: 2013/07/31
Channel: Mehul Khati
Run your A/R Process better using SAP Business One
Run your A/R Process better using SAP Business One
Published: 2016/09/17
Channel: deepak gridhar
Guage R and R, Process Capability studies
Guage R and R, Process Capability studies
Published: 2013/12/06
Channel: sushma v
JINA-CEE Online Seminar - Mathew Mumpower - Nuclear properties from r-process abundances
JINA-CEE Online Seminar - Mathew Mumpower - Nuclear properties from r-process abundances
Published: 2017/04/19
Channel: JINA-CEE
BB3024 tool assebmbly to frame R process
BB3024 tool assebmbly to frame R process
Published: 2010/05/07
Channel: jpeng99
(R)evolution: Innovation Process & Niobium. VIDEO: 13:01.
(R)evolution: Innovation Process & Niobium. VIDEO: 13:01.
Published: 2014/02/19
Channel: coinweek
NN 2015 - Where is the site of the r-process?
NN 2015 - Where is the site of the r-process?
Published: 2015/06/26
Channel: Eventi Laboratori Nazionali del Sud INFN
R. Koch / 2017 / mini prints N°13 ,14, 15 / in process.
R. Koch / 2017 / mini prints N°13 ,14, 15 / in process.
Published: 2017/05/09
Channel: Roberto Koch
MELSEC iQ-R  Process CPU/Redundant System
MELSEC iQ-R Process CPU/Redundant System
Published: 2016/07/05
Channel: MITSUBISHI ELECTRIC Factory Automation
TRU Pyrolysis process of waste to energy - R & R Technology
TRU Pyrolysis process of waste to energy - R & R Technology
Published: 2016/10/12
Channel: R & R Technology
Download [PDF] Managing Misbehavior in Kids: The Miskidding(r) Process
Download [PDF] Managing Misbehavior in Kids: The Miskidding(r) Process
Published: 2016/09/17
Channel: Ines Lamb
Banks to initiate SDR process for R-Com; Nifty closes beyond 9650
Banks to initiate SDR process for R-Com; Nifty closes beyond 9650
Published: 2017/06/02
Channel: ZeeBusiness
R. Koch / 2017 / mini print N°10 in process.
R. Koch / 2017 / mini print N°10 in process.
Published: 2017/05/03
Channel: Roberto Koch
(HW7,#4) The four-step process for r(x) = 8 + 2x^2
(HW7,#4) The four-step process for r(x) = 8 + 2x^2
Published: 2014/09/15
Channel: Michaela Stone
You R my Happiness Scrapbook layout process
You R my Happiness Scrapbook layout process
Published: 2017/06/19
Channel: tmeital
The culture of innovation -- process to results: Colonel (r) Al Faber at TEDxYoungstown
The culture of innovation -- process to results: Colonel (r) Al Faber at TEDxYoungstown
Published: 2014/01/31
Channel: TEDx Talks
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WIKIPEDIA ARTICLE

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The rapid neutron capture process or r-process is a set of reactions in nuclear astrophysics that are responsible for the creation (nucleosynthesis) of approximately half the atomic nuclei heavier than iron.

This process entails a succession of rapid neutron captures (hence the name) by heavy seed nuclei, typically beginning with 56Fe. The captures must be rapid in the sense that the nucleus does not have time to undergo radioactive decay before another neutron arrives to be captured. The r-process therefore occurs in locations where there is a high flux of free neutrons. These include the material ejected from a core-collapse supernovae (as part of supernova nucleosynthesis) and neutron-rich matter thrown off from a neutron star merger. The relative contributions of these, and other, sources to the astrophysical abundance of r-process elements is a matter of ongoing research.

The r-process also occurs to a minor extent in thermonuclear weapon explosions. This led to the historical discovery of the elements einsteinium (element 99) and fermium (element 100) in nuclear weapon fallout.

The r-process is distinguished from the s-process, the other predominant mechanism for the production of heavy elements, which is nucleosynthesis by means of slow captures of neutrons. The s-process primarily occurs within stars, particularly AGB stars, where the neutron flux is sufficient to cause reactions but too low for the r-process. The s-process is secondary, meaning that it requires pre-existing heavy isotopes as seed nuclei to be converted into other heavy nuclei. Taken together, the r- and s-processes account for the majority of abundance evolution of elements heavier than iron.

History[edit]

The need for some kind of rapid capture of neutrons was seen from the relative abundances of isotopes of heavy elements given in a newly published table of abundances by Hans Suess and Harold Urey in 1956. Radioactive isotopes must capture another neutron faster than they can undergo beta decay in order to create abundance peaks at germanium, xenon, and platinum. According to the nuclear shell model, radioactive nuclei that would decay into isotopes of these elements have closed neutron shells near the neutron drip line, where more neutrons cannot be added. Those abundance peaks created by rapid neutron capture implied that other nuclei could be accounted for by such a process. That process of rapid neutron capture in neutron-rich isotopes is called the r-process. A table apportioning the heavy isotopes phenomenologically between s-process and r-process was published in the famous B2FH review paper in 1957,[1] which named that process and outlined the physics that guide it. B2FH also elaborated the theory of stellar nucleosynthesis and set substantial frame-work for contemporary nuclear astrophysics.

The r-process described by the B2FH paper was first computed time-dependently at Caltech by Phillip Seeger, William A. Fowler and Donald D. Clayton,[2] who achieved the first successful characterization of the r-process abundances and showed its evolution in time. They were also able using theoretical production calculations to construct more quantitative apportionment between s-process and r-process of the abundance table of heavy isotopes, thereby establishing a more reliable abundance curve for the r-process isotopes than B2FH had been able to define. Today, the r-process abundances are determined using their technique of subtracting the more reliable s-process isotopic abundances from the total isotopic abundances and attributing the remainder to the r-process nucleosynthesis. That r-process abundance curve (vs. atomic weight) gratifyingly resembles computations of abundances synthesized by the physical process.

Most neutron-rich isotopes of elements heavier than nickel are produced, either exclusively or in part, by the beta decay of very radioactive matter synthesized during the r-process by rapid absorption, one after another, of free neutrons created during the explosions. The creation of free neutrons by electron capture during the rapid collapse to high density of the supernova core along with assembly of some neutron-rich seed nuclei makes the r-process a primary process; namely, one that can occur even in a star of pure H and He, in contrast to the B2FH designation as a secondary process building on preexisting iron.

Observational evidence of the r-process enrichment of stars, as applied to the abundance evolution of the galaxy of stars, was laid out by Truran in 1981.[3] He and many subsequent astronomers showed that the pattern of heavy-element abundances in the earliest metal-poor stars matched that of the shape of the solar r-process curve, as if the s-process component were missing. This was consistent with the hypothesis that the s-process had not yet begun in these young stars, for it requires about 100 million years of galactic history to get started. These stars were born earlier than that, showing that the r-process emerges immediately from quickly-evolving massive stars that become supernovae. The primary nature of the r-process from observed abundance spectra in old stars born when the galactic metallicity was still small but that nonetheless contain their complement of r-process nuclei.

Periodic table showing the cosmogenic origin of each element. The elements heavier than iron with origins in supernovae are typically those produced by the r-process, which is powered by supernovae neutron bursts

This scenario, though generally supported by supernova experts, has yet to achieve a totally satisfactory calculation of r-process abundances because the overall problem is numerically formidable; but existing results are very supportive.

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.

Nuclear physics[edit]

Immediately after the severe compression of electrons in a core-collapse supernova, beta-minus decay is blocked. This is because the high electron density fills all available free electron states up to a Fermi energy which is greater than the energy of nuclear beta decay. But nuclear capture of those free electrons still occurs, and causes increasing neutronization of matter. There results an extremely high density of free neutrons which cannot decay, and as a result a large neutron flux (on the order of 1022 neutrons per cm2 per second[citation needed]) and high temperatures. As this re-expands and cools, neutron capture by still-existing heavy nuclei occurs much faster than beta-minus decay. As a consequence, the r-process runs up along the neutron drip line and highly-unstable neutron-rich nuclei are created.

Three processes which affect the process of climbing the neutron drip line are; a notable decrease in the neutron-capture cross section at nuclei with closed neutron shells, the inhibiting process of photodisintegration, and the degree of nuclear stability in the heavy-isotope region. This last phenomenon terminates the r-process when its heaviest nuclei become unstable to spontaneous fission, which is currently believed to be in the neutron-rich region of the table of nuclides when the total number of nucleons approaches 270; even before this, the fission barrier may be low enough that neutron capture might induce fission instead of continuing up the neutron drip line.[4] After the neutron flux decreases, these highly unstable radioactive nuclei undergo a rapid succession of beta decays until they reach more stable, neutron-rich nuclei.[5] So, while the s-process creates an abundance of stable nuclei having closed neutron shells, the r-process creates an abundance of nuclei about 10 amu below the s-process peaks as a result of the decay back towards stability.[citation needed]

The r-process also occurs in thermonuclear weapons, and was responsible for the initial discovery of neutron-rich almost stable isotopes of actinides like plutonium-244 and the new elements einsteinium and fermium (atomic numbers 99 and 100) in the 1950s. It has been suggested that multiple nuclear explosions would make it possible to reach the island of stability, as the affected nuclides (starting with uranium-238 as seed nuclei) would not have time to beta decay all the way to the quickly spontaneously fissioning nuclides at the line of beta stability before the absorbed more neutrons in the next explosion, thus providing a chance to reach isotopes like copernicium-291 and -293 which should have half-lives of centuries or millennia.[6]

Astrophysical sites[edit]

The most probable candidate sites for the r-process has long been suggested to be core-collapse supernovae (spectral Type Ib, Ic and II), which may provide the necessary physical conditions for the r-process. However, the abundance of r-process nuclei requires that either only a small fraction of supernovae eject r-process nuclei to the interstellar medium, or that each supernova ejects only a very small amount of r-process material. In addition, the ejected material must be relatively neutron-rich, a condition which has been difficult to achieve in models.[7] An alternative site proposed in 1974[8] was decompressing neutron star matter. It was proposed such matter is ejected from neutron stars merging with black holes in compact binaries. In 1989[9] (see also [10]) this scenario was extended to binary neutron star mergers (a binary star system of two neutron stars that collide). These sites may now be starting to be observationally confirmed.[11]

References[edit]

  1. ^ E. M. Burbidge; G. R. Burbidge; W. A. Fowler & F. Hoyle (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. 
  2. ^ Seeger, Philip A.; Fowler, William A.; Clayton, Donald D. (1965). "Nucleosynthesis of heavy elements by neutron capture". Astrophysical Journal Supplement. 11: 121–66. Bibcode:1965ApJS...11..121S. doi:10.1086/190111. 
  3. ^ Truran, J. W. (1981). "A new interpretation of the heavy-element abundances in metal-deficient stars". Astronomy and Astrophysics. 97 (2): 391–93. Bibcode:1981A&A....97..391T. 
  4. ^ Boleu, R.; Nilsson, S. G.; Sheline, R. K. (7 August 1972). "On the termination of the r-process and the synthesis of superheavy elements". Physics Letters B. 40 (5): 517–521. doi:10.1016/0370-2693(72)90470-4. 
  5. ^ Clayton, Donald D. (1968). Principles of Stellar Evolution and Nucleosynthesis. New York: Mc-Graw-Hill. pp. 577–91. ISBN 978-0226109534. , provides a clear technical introduction to these features. More technical is the previously cited paper by Seeger et al.
  6. ^ Zagrebaev, Valeriy; Karpov, Alexander; Greiner, Walter (2013). "Future of superheavy element research: Which nuclei could be synthesized within the next few years?" (PDF). Journal of Physics. IOP Publishing Ltd. 420: 012001. doi:10.1088/1742-6596/420/1/012001. 
  7. ^ Thielemann, F. K.; et al. (April 2011). "What are the astrophysical sites for the r-process and the production of heavy elements?". Progress in Particle and Nuclear Astrophysics. 66: 346–353. Bibcode:2011PrPNP..66..346T. doi:10.1016/j.ppnp.2011.01.032. 
  8. ^ Lattimer, James M.; Schramm, David N. (1974). "Black Hole-Neutron Star Collisions". The Astrophysical Journal Letters. 192: L145–147. Bibcode:1974ApJ...192L.145L. doi:10.1086/181612. 
  9. ^ Eichler, David; Livio, Mario; Piran, Tsvi; Schramm, David N. (13 July 1989). "Nucleosynthesis, neutrino bursts and gamma-rays from coalescing neutron stars". Nature. 340: 126–128. Bibcode:1989Natur.340..126E. doi:10.1038/340126a0. 
  10. ^ Freiburghaus, C.; Rosswog, S.; Thielemann, F.-K (1999). "R-Process in Neutron Star Mergers". The Astrophysical Journal Letters. 525 (2): L121––L124. Bibcode:1999ApJ...525L.121F. doi:10.1086/312343. 
  11. ^ Tanvir, N.; et al. (2013). "A `kilonova' associated with the short-duration gamma-ray burst GRB 130603B". Nature. 500 (7464): 547–9. Bibcode:2013Natur.500..547T. PMID 23912055. arXiv:1306.4971Freely accessible. doi:10.1038/nature12505. 

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