Bomb pulse

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The bomb pulse is the sudden increase of

radioisotope of carbon, 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.

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

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 relative concentration 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

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

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]

Biology

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

At the moment of death, carbon uptake is ended. Considering that tissue that contained 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]

Carbon Transport Modeling

The perturbation in atmospheric 14C 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.[19]

Other

Atmospheric bomb 14C has been used to validate tree ring ages and to date recent trees that have no annual growth rings.[20] It can also be used to obtain the growth rate of tropical trees and palms that have no visible annual rings.[21]

See also

References

  1. ^ "Radioactive Fallout From Nuclear Weapons Testing". USEPA. Retrieved 2016-08-16.
  2. ^
    S2CID 35790984
    .
  3. ^ "Radiocarbon". web.science.uu.nl. Retrieved 2016-08-15.
  4. ^ a b "Elements – Radiolab". Retrieved 2015-10-24.
  5. ^
    ISSN 0033-8222
    .
  6. ^
    S2CID 4407447
    .
  7. ^ "14C "Bomb Pulse" Pulse Forensics". Lawrence Livermore National Laboratory. Retrieved 2015-10-24.
  8. S2CID 95325450
    .
  9. S2CID 16604223
    .
  10. S2CID 4431237
    .
  11. ^
    ISSN 0002-8487
    .
  12. doi:10.1577/t08-098.1
    .
  13. ISSN 1439-0426
    .
  14. ^
    PMID 31149641
    .
  15. ^
    ISSN 0706-652X
    .
  16. ISSN 0706-652X
    .
  17. S2CID 84397450
    .
  18. S2CID 206647043
    .
  19. S2CID 129623525
    .
  20. doi:10.2458/azu_js_rc.v55i2.16177
    .
  21. doi:10.2458/56.16486
    .
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