The bomb pulse is the sudden increase of carbon-14 (14C) in the Earth's atmosphere due to the hundreds of aboveground nuclear bombs tests that started in 1945 and intensified between 1950 until 1963, when the Limited Test Ban Treaty was signed by the United States, the Soviet Union and the United Kingdom.[1] These hundreds of blasts were followed by a doubling of the concentration of 14C in the atmosphere.[2] Since then, the concentration of 14C has decreased towards the previous level. Carbon-14, the radioisotope of carbon-12, is naturally developed in trace amounts in the atmosphere and it can be detected in all living organisms. Carbon of all types is continually used to form the molecules of the cells of organisms. Doubling of the concentration of 14C in the atmosphere is reflected in the tissues and cells of all organisms that lived around the period of nuclear testing. This property has many applications in the fields of biology and forensics.
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Atmospheric 14C, New Zealand and Austria. The New Zealand curve is representative for the Southern Hemisphere, the Austrian curve is representative for the Northern Hemisphere. Atmospheric nuclear weapon tests almost doubled the concentration of 14C in the Northern Hemisphere.[3]
Background[edit]
The radioisotope carbon-14 is constantly formed from nitrogen-14 (14N) in the higher atmosphere by incoming cosmic rays which generate neutrons. These neutrons collide with 14N to produce 14C which then combines with oxygen to form 14CO2. This radioactive CO2 spreads through the lower atmosphere and the oceans where it is absorbed by the plants and the animals that eat the plants. The radioisotope 14C thus becomes part of the biosphere so that all living organisms contain a certain amount of 14C. Nuclear testing caused a rapid increase in atmospheric 14C (see figure), since the explosion of an atomic bomb also creates neutrons which collide again with 14N and produce 14C. Since the ban on nuclear testing in 1963, atmospheric 14C is slowly decreasing at a pace of 4% annually. This continuous decrease permits scientists to determine among others the age of deceased people and allows them to study cell activity in tissues. By measuring the amount of 14C in a population of cells and comparing that to the amount of 14C 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.[2]
Difference with classical radiocarbon dating[edit]
Radiocarbon dating has been used since 1946 to determine the age of organic material as old as 50,000 years. As the organism dies, the exchange of 14C with the environment ceases and the incorporated 14C decays. Given the steady decay of radioisotopes (the half-life of 14C is about 5,730 years), the amount of 14C 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. As discussed above and in the Radiolab episode, Elements (section 'Carbon'),[4] in bomb pulse dating the slow absorption of atmospheric 14C by the biosphere, can be considered as a chronometer. Starting from the pulse around the years 1963 (see figure), atmospheric radiocarbon decreased with 4% a year. So in bomb pulse dating it is the amount of 14C in the atmosphere that is decreasing and not the amount of 14C in a dead organisms, as is the case in classical radiocarbon dating. This decrease in atmospheric 14C can be measured in cells and tissues and has permitted scientists to determine the age of individual cells and of deceased people.[5][6][7] 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 ethically be administered to people just to study the turnover of their cells so the bomb pulse results may be considered as a useful side effect of nuclear testing.[4]
Applications[edit]
The fact that cells and tissues reflect the doubling of 14C 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.[8]
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Biology[edit]
Biological studies carried out by Kirsty Spalding demonstrated that neuronal cells are essentially static and do not regenerate during life.[9] She also showed that the number of fat cells is set during childhood and adolescence. Considering the amount of 14C present in DNA she could establish that 10% of fat cells are renewed annually.[10] The radiocarbon bomb pulse has been used to validate otolith annuli (ages scored from otolith sections) across several fish species including the freshwater drum[11], lake sturgeon[12], pallid sturgeon[13], bigmouth buffalo[14], arctic salmonids[15], Pristipomoides filamentosus[16], several reef fishes[17], 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[11][14][15]. The bomb pulse has also been used to estimate (not validate) the age of Greenland sharks by measuring the incorporation of 14C 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.[18]
Forensics[edit]
At the moment of death, carbon uptake is ended. Considering that after the bomb pulse 14C 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.[5] Another important application has been the identification of victims of the Southeast Asian tsunami 2004 by examining their teeth.[6]
Other[edit]
Atmospheric bomb 14C has been used to validate tree ring ages and to date recent trees that have no annual growth rings.[19]
See also[edit]
References[edit]
- ^'Radioactive Fallout From Nuclear Weapons Testing'. USEPA. Retrieved 2016-08-16.
- ^ abGrimm, David (2008-09-12). 'The Mushroom Cloud's Silver Lining'. Science. 321 (5895): 1434–1437. doi:10.1126/science.321.5895.1434. ISSN0036-8075. PMID18787143.
- ^'Radiocarbon'. web.science.uu.nl. Retrieved 2016-08-15.
- ^ ab'Elements – Radiolab'. Retrieved 2015-10-24.
- ^ ab'First 14C results from archaeological and forensic studies at the Vienna environmental research accelerator'. Radiocarbon. 40 (1). ISSN0033-8222.
- ^ abSpalding, Kirsty L.; Buchholz, Bruce A.; Bergman, Lars-Eric; Druid, Henrik; Frisén, Jonas (2005-09-15). 'Forensics: Age written in teeth by nuclear tests'. Nature. 437 (7057): 333–334. doi:10.1038/437333a. ISSN0028-0836. PMID16163340.
- ^'14C 'Bomb Pulse' Pulse Forensics'. Lawrence Livermore National Laboratory. Retrieved 2015-10-24.
- ^Zoppi, U; Skopec, Z; Skopec, J; Jones, G; Fink, D; Hua, Q; Jacobsen, G; Tuniz, C; Williams, A (2004-08-01). 'Forensic applications of 14C bomb-pulse dating'. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. Proceedings of the Ninth International Conference on Accelerator Mass Spectrometry. 223–224: 770–775. doi:10.1016/j.nimb.2004.04.143.
- ^Spalding, Kirsty L.; Bhardwaj, Ratan D.; Buchholz, Bruce A.; Druid, Henrik; Frisén, Jonas (2005-07-15). 'Retrospective birth dating of cells in humans'. Cell. 122 (1): 133–143. doi:10.1016/j.cell.2005.04.028. ISSN0092-8674. PMID16009139.
- ^Spalding, Kirsty L.; Arner, Erik; Westermark, Pål O.; Bernard, Samuel; Buchholz, Bruce A.; Bergmann, Olaf; Blomqvist, Lennart; Hoffstedt, Johan; Näslund, Erik (2008-06-05). 'Dynamics of fat cell turnover in humans'. Nature. 453 (7196): 783–787. doi:10.1038/nature06902. ISSN0028-0836. PMID18454136.
- ^ abDavis-Foust, Shannon L.; Bruch, Ronald M.; Campana, Steven E.; Olynyk, Robert P.; Janssen, John (2009-03-01). 'Age Validation of Freshwater Drum using Bomb Radiocarbon'. Transactions of the American Fisheries Society. 138 (2): 385–396. doi:10.1577/T08-097.1. ISSN0002-8487.
- ^Janssen, John; Hansen, Michael J.; Davis‐Foust, Shannon L.; Campana, Steven E.; Bruch, Ronald M. (2009-03-01). 'Lake Sturgeon Age Validation using Bomb Radiocarbon and Known‐Age Fish'. Transactions of the American Fisheries Society. 138 (2): 361–372. doi:10.1577/t08-098.1.
- ^Braaten, P. J.; Campana, S. E.; Fuller, D. B.; Lott, R. D.; Bruch, R. M.; Jordan, G. R. (2015). '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 of Applied Ichthyology. 31 (5): 821–829. doi:10.1111/jai.12873. ISSN1439-0426.
- ^ abLackmann, Alec R.; Andrews, Allen H.; Butler, Malcolm G.; Bielak-Lackmann, Ewelina S.; Clark, Mark E. (2019-05-23). 'Bigmouth Buffalo Ictiobus cyprinellus sets freshwater teleost record as improved age analysis reveals centenarian longevity'. Communications Biology. 2 (1). doi:10.1038/s42003-019-0452-0. ISSN2399-3642.
- ^ abCampana, Steven E; Casselman, John M; Jones, Cynthia M (2008-04-01). 'Bomb radiocarbon chronologies in the Arctic, with implications for the age validation of lake trout (Salvelinus namaycush) and other Arctic species'. Canadian Journal of Fisheries and Aquatic Sciences. 65 (4): 733–743. doi:10.1139/f08-012. ISSN0706-652X.
- ^Andrews, Allen H.; DeMartini, Edward E.; Brodziak, Jon; Nichols, Ryan S.; Humphreys, Robert L. (2012-11-01). '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'. Canadian Journal of Fisheries and Aquatic Sciences. 69 (11): 1850–1869. doi:10.1139/f2012-109. ISSN0706-652X.
- ^Johnston, Justine M.; Newman, Stephen J.; Kalish, John M.; Andrews, Allen H. (2011-11-23). 'Bomb radiocarbon dating of three important reef-fish species using Indo-Pacific Δ14C chronologies'. Marine and Freshwater Research. 62 (11): 1259–1269. doi:10.1071/MF11080. ISSN1448-6059.
- ^Nielsen, Julius; Hedeholm, Rasmus B.; Heinemeier, Jan; Bushnell, Peter G.; Christiansen, Jørgen S.; Olsen, Jesper; Ramsey, Christopher Bronk; Brill, Richard W.; Simon, Malene (2016-08-12). 'Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus)'. Science. 353 (6300): 702–704. doi:10.1126/science.aaf1703. ISSN0036-8075. PMID27516602.
- ^Atmospheric Radiocarbon for the Period 1950–2010. 55. 2013-03-25. doi:10.2458/azu_js_rc.55.16177.
Retrieved from 'https://en.wikipedia.org/w/index.php?title=Bomb_pulse&oldid=931858640'
There’s a whole list of abilities that Mercy can increase the damage of in Overwatch. Some of them are less useful than others. Here are the abilities that you might not have known you can damage boost and ones which will do a lot for your team.
1. Reinhardt’s Fire Strike
One of the most important abilities to add that 30 percent damage increase to is Reinhardt’s Fire Strike. Why? Because it travels through barriers and deals considerable damage. Not only can you potentially eliminate some low-health targets or force them to back off and heal, you can greatly increase the amount of Ultimate charge your Reinhardt receives — which only gets him his incredible Earthshatter faster.
2. Ashe’s Dynamite
Ashe’s Dynamite is another fantastic abilities to damage boost. It’s a damage-over-time ability that puts a ton of pressure on the enemy team, and it will get your Ashe a ton of Ultimate charge. I’ve been on the receiving end of the damage-boosted Dynamite, and it’s rough. With so many people suddenly on fire, it makes it almost impossible for healers to keep everyone alive.
3. Genji’s Dragonblade
Genji’s Dragonblade has him using a sword and not his normal shuriken. It’s probably not too hard to understand that you can damage boost it, especially considering Ana’s Nano Boost Genjis — but it’s also a smart move if you’re Mercy. Download os x dmg. Basically, if you damage boost your Genji during his Ultimate, his sword attacks can kill most enemy heroes in one swipe plus a Swift Strike — and that means he can efficiently kill more targets. Better Genji players will know how to react to killing enemies faster and will likely do a lot more work with their Ultimate than they would have by themselves.
4. McCree’s Deadeye
McCree’s Ultimate Deadeye can be damage boosted too. Usually it locks onto enemies and closes a circle onto them as the potential damage increases. With a damage boost, the circles will close faster, making it less likely that your McCree will get killed while he’s standing there.
5. Tracer’s Pulse Bomb
Tracer’s Pulse Bomb is actually susceptible to damage boost, even though it might not seem like it. It’s not a very useful thing to damage boost unless your Tracer is tossing it into a Graviton Surge, but it doesn’t hurt if you have nothing else to do. It’s one of those leftover projectile-based Ultimates that can still be modified.
While we’re here, it’s worth mentioning that turrets, like Torbjorn’s turret and Symmetra’s Sentry Turrets, can’t be damage boosted. Nor can stuff like Wrecking Ball’s Minefield. So, don’t let your teammate Torbjorn get mad at you for not linking your damage beam to him.
How Much Damage Does Pulse Bomb Do
As with any damage boosts in Overwatch, all of these work the same way with Ana’s Nano Boost and Orisa’s Supercharger Ultimates. They’re not as useful as a free, damage-boosting beam from Mercy, but they’re still applicable. It might sound like a small thing to try and damage boost certain things in a game, but even the tiniest advantages can determine the victor of a fight — or even the entire match.
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