GRB Hypothesis for Terrestrial C14 and Be10 Spike

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Discussion Overview

The discussion revolves around the hypothesis that a spike in C14 and Be10 isotopes found in tree rings from 775 AD may be linked to a short gamma-ray burst (GRB) occurring between 3,000 to 12,000 light-years away. Participants explore the mechanisms by which gamma rays could contribute to the production of these isotopes, particularly focusing on nuclear reactions and photodisintegration processes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how gamma rays could induce C14 production, noting that C14 is typically produced through neutron interactions with N14 in the atmosphere.
  • Another participant suggests that the gamma-ray burst might increase the number of available neutrons for the C14 production reaction.
  • A participant expresses uncertainty about whether gamma rays can induce nuclear reactions, prompting further exploration of the topic.
  • It is mentioned that photons can interact with nuclei to emit neutrons, which could relate to the production of C14 and Be10.
  • Participants seek examples or discussions related to the process of gamma rays inducing nuclear reactions.
  • A reference to photodisintegration is provided, explaining how high-energy photons can lead to neutron production through interactions with nuclei.
  • Discussion includes details about the energy levels required for photoneutron production and its potential relevance to N14 and C14 production.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and uncertainty regarding the mechanisms by which gamma rays could contribute to isotope production. There is no consensus on the specifics of how this process occurs, and multiple viewpoints are presented.

Contextual Notes

Participants acknowledge limitations in their understanding of nuclear physics and the specific conditions under which gamma rays might induce reactions. The discussion reflects a range of assumptions and interpretations regarding the interaction of gamma rays with matter.

GerdankenDonuts
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This may be (probably is) a stupid question but in a popular current story in astronomical news, scientists have put forth the idea that a spike in C14 and Be10 isotopes found in tree rings in Japan and a few other locations in 775 AD could have been due to a short GRB 3kly to 12kly away.

http://phys.org/news/2013-01-8th-century-gamma-ray-irradiated.html

What is puzzling me is that short GRB's have most of their flux in gamma rays in my understanding and I thought that C14 could only be produced by n + N14 -> p + C14 where the neutron comes from cosmic ray collisions with nucleii in the upper atmosphere. How could gamma rays induce C14 production? Similarly for Be10?
 
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I don't have a definite answer, but I would guess the gamma ray burst led to a sharp increase in the number of neutrons available for the reaction you described.
 
I suppose that is possible, not being a nuclear physicist I don't know but can gamma rays even induce nuclear reactions?
 
That is possible - a photon can hit a nucleus, and a neutron (or something else) can be emitted.
 
Interesting, is there some example or discussion of such a process that can be linked to?
 
Found this on Wikipedia: interesting

High energy photoneutron
Neutrons (photoneutrons) are produced when photons above the nuclear binding energy of a substance are incident on that substance, causing it to undergo giant dipole resonance after which it either emits a neutron (photodisintegration) or undergoes fission (photofission). The number of neutrons released by each fission event is dependent on the substance. Typically photons begin to produce neutrons on interaction with normal matter at energies of about 7 to 40 MeV,

Good info on photoneutron cross section here: http://prola.aps.org/abstract/PR/v91/i3/p659_1 Interesting if the most common species for phototransmutation is the N14 that also produces the C14.
 

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