The Naked Scientists

The Naked Scientists Forum

Author Topic: Life Span & Travels of Neutrons  (Read 1444 times)

Offline ralphbk

  • First timers
  • *
  • Posts: 2
    • View Profile
Life Span & Travels of Neutrons
« on: 30/11/2012 07:21:33 »
I think it was Martin Dove in the latest podcast who told us that neutrons outside of the nucleus have a life span of about 15 minutes. And yet earlier in the podcast we heard about cosmic radiation - consisting of high energy free neutrons - that originate from outside the Solar system. So, does the cosmic radiation take less than 15 minutes to get to us? Or is it some sort of relativity effects of near light speed travel that allows the cosmic neutrons to outlive their earth-bound brothers?


 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4130
  • Thanked: 249 times
    • View Profile
Re: Life Span & Travels of Neutrons
« Reply #1 on: 30/11/2012 09:25:54 »
It is true that cosmic rays travel at close to the speed of light, and so they would experience relativistic effects - but time dilation would have to be rather extreme to survive the interstellar journey from their somewhat mysterious origin around supernovae, black holes and galactic particle accelerators in less than a few hours of experienced time. (50% decay in about 15 minutes; 75% in 30 minutes, 88% in 45 minutes, etc)

Cosmic rays mostly consist of protons, and atomic nuclei. These are stable over interstellar distances. A neutron would decay into a proton, electron and neutrino during the journey; the neutrino is almost undetectable, and the proton has far more mass and energy than the electron, so it is mostly the impact of protons and nuclei we detect at the bottom of the atmosphere.

The neutrons they described are knocked loose when the cosmic rays collide with gas molecules in the atmosphere, along with a shower of other particles heading in the same general direction as the original cosmic ray. It would take less than a second for these neutrons to reach the surface of the earth, so there is not much time for them to decay within the atmosphere.

The impact on electronics comes from a neutron striking and fusing with a silicon nucleus, which then decays over the next few days into a Phosphorus atom. Phosphorus is used as a "dopant" in semiconductors, and increasing concentrations of Phosphorus over time changes the electrical properties of the semiconductor, eventually causing it to fail.

This same transmutation technique using neutron bombardment is used commercially in research nuclear reactors to produce Phosphorus-doped silicon, as input to the semiconductor manufacturing process.
« Last Edit: 30/11/2012 09:32:49 by evan_au »
 

Offline yor_on

  • Naked Science Forum GOD!
  • *******
  • Posts: 12001
  • Thanked: 4 times
  • (Ah, yes:) *a table is always good to hide under*
    • View Profile
Re: Life Span & Travels of Neutrons
« Reply #2 on: 30/11/2012 09:29:51 »
You know, reading it I got a momentary headache :) putting those two together made for a really hard nut..

But maybe this can explain it?
http://en.wikipedia.org/wiki/Cosmic_ray

"Cosmic rays are high speed, i. e. high energy particles, mainly originating in outer space, outside the Solar system. They may produce showers of secondary particles that penetrate the Earth's atmosphere and sometimes even Earth's surface." and "When cosmic rays enter the Earth's atmosphere they collide with molecules, mainly oxygen and nitrogen. The interaction produce a cascade of lighter particles, a so-called air shower. All of the produced particles stay within about one degree of the primary particle's path. Typical particles produced in such collisions are neutrons, charged mesons e.g. positive and negative pions and kaons. Some of these subsequently decay into muons, which are able to reach the surface of the Earth, and even penetrate for some distance into shallow mines."
=

(As for if a particle can be seen as 'time dilated'? It's observer dependent naturally but if you observe a neutron to have a life span of fifteen minutes as defined from you locality, then it shouldn't matter from where they originate as long as they are in free space. Gravitation and 'Gravitational wells' as a neutron star will increase that life span as observed by you, but approximately, fifteen minutes should be fifteen minutes (locally measured) at all times :)
« Last Edit: 30/11/2012 09:40:04 by yor_on »
 

Offline ralphbk

  • First timers
  • *
  • Posts: 2
    • View Profile
Re: Life Span & Travels of Neutrons
« Reply #3 on: 30/11/2012 09:45:25 »
Thanks both for your answers. Great explanations. (I'd better try and listen more carefully to the podcast in future. :-))
 

The Naked Scientists Forum

Re: Life Span & Travels of Neutrons
« Reply #3 on: 30/11/2012 09:45:25 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums