Bomb pulse

{{sup|14}}C is constantly formed from nitrogen-14 ({{sup|14}}N) in the upper atmosphere by cosmic rays which generate neutrons. These neutrons hit {{sup|14}}N to produce {{sup|14}}C which then combines with oxygen to form {{sup|14}}CO{{sub|2}}. This radioactive Carbon dioxide spreads through the lower atmosphere and the oceans where it is absorbed by plants, and animals that eat the plants. {{sup|14}}C thus becomes part of the biosphere, so all living things contain some {{sup|14}}C. Nuclear tests caused a rapid increase in atmospheric {{sup|14}}C (see figure), since a nuclear explosion also creates neutrons which collide with {{sup|14}}N and produce {{sup|14}}C. Since the nuclear test ban in 1963, atmospheric {{sup|14}}C relative concentration is decreasing at 4% per year. This continuous decrease permits scientists to determine among other things the age of deceased people and allows them to study cell activity in tissues. By measuring the amount of {{sup|14}}C in a population of cells and comparing that to the amount of {{sup|14}}C in the atmosphere during or after the bomb pulse, scientists can estimate when the cells were created and how often they've turned over since then.

Carbon dating has been used since 1946 to determine the age of organic material as old as 50,000 years. When an organism dies, the exchange of {{sup|14}}C with the environment ends and the incorporated {{sup|14}}C decays. Given radioactive decay ({{sup|14}}C's half-life is about 5,730 years), the relative amount of {{sup|14}}C left in the dead organism can be used to calculate how long ago it died. Bomb pulse dating should be considered a special form of carbon dating. In bomb pulse dating the slow absorption of atmospheric {{sup|14}}C by the biosphere can be considered a chronometer.{{cite web|url=http://www.radiolab.org/story/elements|title=Elements – Radiolab|access-date=2015-10-24}} Starting from the pulse around the year 1963 (see figure), atmospheric radiocarbon relative abundance decreased by about 4% a year. So in bomb pulse dating it is the relative amount of {{sup|14}}C in the atmosphere that is decreasing and not the amount of {{sup|14}}C in dead organisms, as is the case in classical carbon dating. This decrease in atmospheric {{sup|14}}C can be measured in cells and tissues and has permitted scientists to determine the age of individual cells and of deceased people.{{cite web|url=https://cams.llnl.gov/cams-competencies/forensics/14c-bomb-pulse-forensics|title=14C "Bomb Pulse" Pulse Forensics|work=Lawrence Livermore National Laboratory|access-date=2015-10-24}} These applications are very similar to the experiments conducted with pulse-chase analysis in which cellular processes are examined over time by exposing the cells to a labeled compound (pulse) and then to the same compound in an unlabeled form (chase). Radioactivity is a commonly used label in these experiments. An important difference between pulse-chase analysis and bomb-pulse dating is the absence of the chase in the latter.

Around the year 2030 the bomb pulse will die out. Every organism born after this will not bear detectable bomb pulse traces and their cells cannot be dated in this way. Radioactive pulses cannot be ethically administered to people just to study the turnover of their cells, so the bomb pulse results are a useful side effect of nuclear testing.

The fact that cells and tissues reflect the doubling of {{sup|14}}C in the atmosphere during and after nuclear testing, has been of great use for several biological studies, for forensics and even for the determination of the year in which certain wine was produced.{{Cite journal|last1=Zoppi|first1=U|last2=Skopec|first2=Z|last3=Skopec|first3=J|last4=Jones|first4=G|last5=Fink|first5=D|last6=Hua|first6=Q|last7=Jacobsen|first7=G|last8=Tuniz|first8=C|last9=Williams|first9=A|date=2004-08-01|title=Forensic applications of 14C bomb-pulse dating|journal=Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms|series=Proceedings of the Ninth International Conference on Accelerator Mass Spectrometry|volume=223–224|pages=770–775|doi=10.1016/j.nimb.2004.04.143|bibcode=2004NIMPB.223..770Z|s2cid=95325450}}

Biological studies carried out by Kirsty Spalding demonstrated that neuronal cells are essentially static and do not regenerate during life.{{Cite journal|last1=Spalding|first1=Kirsty L.|last2=Bhardwaj|first2=Ratan D.|last3=Buchholz|first3=Bruce A.|last4=Druid|first4=Henrik|last5=Frisén|first5=Jonas|date=2005-07-15|title=Retrospective birth dating of cells in humans|journal=Cell|volume=122|issue=1|pages=133–143|doi=10.1016/j.cell.2005.04.028|issn=0092-8674|pmid=16009139|s2cid=16604223|doi-access=free}} She also showed that the number of fat cells is set during childhood and adolescence. Considering the amount of {{sup|14}}C present in DNA she could establish that 10% of fat cells are renewed annually.{{Cite journal|last1=Spalding|first1=Kirsty L.|last2=Arner|first2=Erik|last3=Westermark|first3=Pål O.|last4=Bernard|first4=Samuel|last5=Buchholz|first5=Bruce A.|last6=Bergmann|first6=Olaf|last7=Blomqvist|first7=Lennart|last8=Hoffstedt|first8=Johan|last9=Näslund|first9=Erik|date=2008-06-05|title=Dynamics of fat cell turnover in humans|journal=Nature|language=en|volume=453|issue=7196|pages=783–787|doi=10.1038/nature06902|issn=0028-0836|pmid=18454136|bibcode=2008Natur.453..783S|s2cid=4431237}} The radiocarbon bomb pulse has been used to validate otolith annuli (ages scored from otolith sections) across several fish species including the freshwater drum,{{Cite journal|last1=Davis-Foust|first1=Shannon L.|last2=Bruch|first2=Ronald M.|last3=Campana|first3=Steven E.|last4=Olynyk|first4=Robert P.|last5=Janssen|first5=John|date=2009-03-01|title=Age Validation of Freshwater Drum using Bomb Radiocarbon|journal=Transactions of the American Fisheries Society|volume=138|issue=2|pages=385–396|doi=10.1577/T08-097.1|bibcode=2009TrAFS.138..385D |issn=0002-8487}} lake sturgeon,{{Cite journal|title=Lake Sturgeon Age Validation using Bomb Radiocarbon and Known-Age Fish|journal = Transactions of the American Fisheries Society|volume = 138|issue = 2|pages = 361–372|last1=Janssen|first1=John|last2=Hansen|first2=Michael J.|date=2009-03-01|language=en|doi=10.1577/t08-098.1|last3=Davis-Foust|first3=Shannon L.|last4=Campana|first4=Steven E.|last5=Bruch|first5=Ronald M.| bibcode=2009TrAFS.138..361B }} pallid sturgeon,{{Cite journal|last1=Braaten|first1=P. J.|last2=Campana|first2=S. E.|last3=Fuller|first3=D. B.|last4=Lott|first4=R. D.|last5=Bruch|first5=R. M.|last6=Jordan|first6=G. R.|date=2015|title=Age estimations of wild pallid sturgeon (Scaphirhynchus albus, Forbes & Richardson 1905) based on pectoral fin spines, otoliths and bomb radiocarbon: inferences on recruitment in the dam-fragmented Missouri River|journal=Journal of Applied Ichthyology|language=en|volume=31|issue=5|pages=821–829|doi=10.1111/jai.12873|issn=1439-0426|doi-access=free|bibcode=2015JApIc..31..821B }} bigmouth buffalo,{{Cite journal|last1=Lackmann|first1=Alec R.|last2=Andrews|first2=Allen H.|last3=Butler|first3=Malcolm G.|last4=Bielak-Lackmann|first4=Ewelina S.|last5=Clark|first5=Mark E.|date=2019-05-23|title=Bigmouth Buffalo Ictiobus cyprinellus sets freshwater teleost record as improved age analysis reveals centenarian longevity|journal=Communications Biology|language=En|volume=2|issue=1|pages=197|doi=10.1038/s42003-019-0452-0|pmid=31149641|pmc=6533251|issn=2399-3642}} arctic salmonids,{{Cite journal|last1=Campana|first1=Steven E|last2=Casselman|first2=John M|last3=Jones|first3=Cynthia M|date=2008-04-01|title=Bomb radiocarbon chronologies in the Arctic, with implications for the age validation of lake trout (Salvelinus namaycush) and other Arctic species|journal=Canadian Journal of Fisheries and Aquatic Sciences|volume=65|issue=4|pages=733–743|doi=10.1139/f08-012|bibcode=2008CJFAS..65..733C |issn=0706-652X}} Pristipomoides filamentosus{{Cite journal|last1=Andrews|first1=Allen H.|last2=DeMartini|first2=Edward E.|last3=Brodziak|first3=Jon|last4=Nichols|first4=Ryan S.|last5=Humphreys|first5=Robert L.|date=2012-11-01|title=A long-lived life history for a tropical, deepwater snapper (Pristipomoides filamentosus): bomb radiocarbon and lead–radium dating as extensions of daily increment analyses in otoliths|journal=Canadian Journal of Fisheries and Aquatic Sciences|volume=69|issue=11|pages=1850–1869|doi=10.1139/f2012-109|bibcode=2012CJFAS..69.1850A |issn=0706-652X}}, several reef fishes,{{Cite journal|last1=Johnston|first1=Justine M.|last2=Newman|first2=Stephen J.|last3=Kalish|first3=John M.|last4=Andrews|first4=Allen H.|date=2011-11-23|title=Bomb radiocarbon dating of three important reef-fish species using Indo-Pacific Δ14C chronologies|journal=Marine and Freshwater Research|language=en|volume=62|issue=11|pages=1259–1269|doi=10.1071/MF11080|issn=1448-6059|hdl=1885/64620|s2cid=84397450 |hdl-access=free}} among numerous other validated freshwater and marine species. The precision for bomb radiocarbon age validation is typically within ±2 years because the rise period (1956-1960) is so steep. The bomb pulse has also been used to estimate (not validate) the age of Greenland sharks by measuring the incorporation of {{sup|14}}C in the eye lens during development. After having determined the age and measured the length of sharks born around the bomb pulse, it was possible to create a mathematical model in which length and age of the sharks were correlated in order to deduce the age of the larger sharks. The study showed that the Greenland shark, with an age of 392 ± 120 years, is the oldest known vertebrate.{{Cite journal|last1=Nielsen|first1=Julius|last2=Hedeholm|first2=Rasmus B.|last3=Heinemeier|first3=Jan|last4=Bushnell|first4=Peter G.|last5=Christiansen|first5=Jørgen S.|last6=Olsen|first6=Jesper|last7=Ramsey|first7=Christopher Bronk|last8=Brill|first8=Richard W.|last9=Simon|first9=Malene|date=2016-08-12|title=Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus)|journal=Science|language=en|volume=353|issue=6300|pages=702–704|doi=10.1126/science.aaf1703|issn=0036-8075|pmid=27516602|bibcode=2016Sci...353..702N|s2cid=206647043|url=https://ora.ox.ac.uk/objects/uuid:6c040460-9519-4720-9669-9911bdd03b09|hdl=2022/26597|hdl-access=free}}

At the moment of death, carbon uptake ends. Considering that tissue that contained the bomb pulse {{sup|14}}C was rapidly diminishing with a rate of 4% per year, it has been possible to establish the time of death of two women in a court case by examining tissues with a rapid turnover.{{Cite journal|title=First 14C results from archaeological and forensic studies at the Vienna environmental research accelerator|url=http://cat.inist.fr/?aModele=afficheN&cpsidt=2461733|journal=Radiocarbon|volume=40|issue=1| bibcode=1997Radcb..40..273W |issn=0033-8222 | last1=Wild | first1=Eva | last2=Golser | first2=Robin | last3=Hille | first3=Peter | last4=Kutschera | first4=Walter | last5=Priller | first5=Alfred | last6=Puchegger | first6=Stephan | last7=Rom | first7=Werner | last8=Steier | first8=Peter | last9=Vycudilik | first9=Walter | date=1997 | page=273 | doi=10.1017/S0033822200018142 }} Another important application has been the identification of victims of the Southeast Asian tsunami 2004 by examining their teeth.{{Cite journal|last1=Spalding|first1=Kirsty L.|last2=Buchholz|first2=Bruce A.|last3=Bergman|first3=Lars-Eric|last4=Druid|first4=Henrik|last5=Frisén|first5=Jonas|date=2005-09-15|title=Forensics: Age written in teeth by nuclear tests|journal=Nature|language=en|volume=437|issue=7057|pages=333–334|doi=10.1038/437333a|issn=0028-0836|pmid=16163340|bibcode=2005Natur.437..333S|s2cid=4407447}}

The perturbation in atmospheric {{sup|14}}C from the bomb testing was an opportunity to validate atmospheric transport models, and to study the movement of carbon between the atmosphere and oceanic or terrestrial sinks.{{cite journal |last1=Caldeira |first1=Ken |title=Predicted net efflux of radiocarbon from the ocean and increase in atmospheric radiocarbon content |journal=Geophysical Research Letters |date=1998 |volume=25 |issue=20 |page=3811-3814|doi=10.1029/1998GL900010 |bibcode=1998GeoRL..25.3811C |s2cid=129623525 |doi-access=free }}

Atmospheric bomb {{sup|14}}C has been used to validate tree ring ages and to date recent trees that have no annual growth rings.{{Cite journal|url=https://journals.uair.arizona.edu/index.php/radiocarbon/article/view/16177|title=Atmospheric Radiocarbon for the Period 1950–2010|journal=Radiocarbon|date=2013-03-25|volume=55|issue=4|pages=2059–2072|language=en|doi=10.2458/azu_js_rc.v55i2.16177|last1=Rakowski|first1=Andrzej Z.|last2=Barbetti|first2=Mike|last3=Hua|first3=Quan|doi-access=free|bibcode=2013Radcb..55.2059H }} It can also be used to obtain the growth rate of tropical trees and palms that have no visible annual rings.{{cite journal |last1=del Valle |first1=J.I. |last2=Guarin |first2=J.R. |last3=Sierra |first3=C.A. |title=Unambiguous and Low-Cost Determination of Growth Rates and Ages of Tropical Trees and Palms |journal=Radiocarbon |date=2014 |volume=56 |issue=1 |pages=39–52 |doi=10.2458/56.16486 |bibcode=2014Radcb..56...39D |url=https://doi.org/10.2458/56.16486}}

• Effects of nuclear explosions
• Pulse-chase analysis
• Suess effect
• Miyake event

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Category:Nuclear weapons

Category:Nuclear weapons testing

Category:Radioactivity

Category:Carbon-14

Category:Molecular biology