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Inverse relationship - neutron flux density with sunspot cycle

  1. Nov 8, 2009 #1
    Just over half-way down this page:-
    http://www.embedded.com/columns/technicalinsights/220301380?cid=RSSfeed_embedded_news

    it says:-
    "These sunspot counts show variation on a cycle of roughly 11 years. By overlaying Oulu neutron measurements with sunspot count data since 1964, we see that the neutron count measured at Oulu varies inversely with the sunspot count (Figure 3 below)."

    Can someone explain this? I can't get a satisfactory clear explanation from Googling - AFAIK the solar magnetic (which affects the earth's magnetic field) changes over the 11 year cycle. There are 2 main sources of "cosmic rays" several specific galactic sources (GCR's) and the sun (SCR's) itself.

    http://wattsupwiththat.com/2009/03/...uggest-we-may-not-have-hit-solar-minimum-yet/
    is also helpful but I'm not clear about the mechanisms underlying this inverse relationship.

    I don't know if I understand exactly what is happening during the the sunspot maxima. Does the solar magnetic field during the maxima offer more protection from the GCR's? What happens to the SCR's during the maxima? (I thought they increased - originating from the solar flares). This article does say:-

    "Most solar cosmic ray events correlate relatively well with solar flares. However, they tend to be at much lower energies than their galactic cousins."

    I assume the correlation is positive (not negative) but it seems to say that SCR's also increase but because they are less energetic does this mean that overall, taking into account the more important factor(?) that because there is an increase in protection from the GCR's(due to influence of solar magnetic fiel), there is a minima in the neutron flux at sea level? Shouldn't this correlate with a decrease in the number of failures in electronic equipment using FPGA's during periods of high sunspot activity? I thought the relationship was the other way around, i.e. more failures during high sunspot activity. As you can tell - I'm slightly confused.

    cheers
    Neil
     
  2. jcsd
  3. Nov 8, 2009 #2
  4. Nov 8, 2009 #3

    D H

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    The magnetic bubble (the heliosphere) cannot keep galactic neutrons from getting to the Earth. Neutrons are neutral and don't interact with the heliosphere. Fortunately, there aren't very many galactic neutrons. The vast majority of cosmic particles are protons, and almost all the rest are alpha particles (helium nuclei). A zoo of particles, including neutrons, is generated when these charged particles hit the Earth's upper atmosphere. The vast majority of the neutrons observed by the detectors mentioned in the original post are secondary radiation products resulting from charged cosmic particles hitting the atmosphere. What the heliosphere does do is to keep those charged cosmic particles from getting into the solar system.
     
  5. Nov 8, 2009 #4
    I read this:-
    www.actel.com/documents/FPGA_Reliability_WP.pdf
    It looks like increased sunspot activity is a "good thing" for electronic equipment reliability because of the shielding effect that the increased solar magnetic field has - I had originally thought that the mass ejections from the sunspots was linked to an increase in electronic failures but it doesn't seem that that is the case. Can someone confirm that? Apart from the link above has anyone seen a document anywhere linking the cause and effect i.e. sunspot activity to equipment failure?
     
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