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m1omg
2008-Oct-21, 01:32 PM
Could neutrinos go unharmed even through a neutron/quark star?

antoniseb
2008-Oct-21, 01:58 PM
Unharmed? If you mean without interacting, the answer is no. Statistically it is unlikely for a neutrino to pass the radius of a neutron star without interacting.

m1omg
2008-Oct-21, 02:21 PM
Unharmed? If you mean without interacting, the answer is no. Statistically it is unlikely for a neutrino to pass the radius of a neutron star without interacting.

Well, so how much (percentually) of the neutrinos would pass through without interacting?And how it can be calculated?

SagoSans
2008-Oct-21, 03:00 PM
Well, so how much (percentually) of the neutrinos would pass through without interacting?And how it can be calculated?

There are still a lot of things missing in neutrino physics. It's even unclear, how many "flavors" there are (e. g. Sterile Neutrinos (http://www.nu.to.infn.it/Sterile_Neutrinos/), without weak interaction). It may be difficult to give a meaningful answer to your question (at least for me :cry: ).

trinitree88
2008-Oct-21, 03:28 PM
m10mg. Radiation lengths and mean free paths apply. Try:http://en.wikipedia.org/wiki/Mean_free_path
A lecture by David W. Arnett gave the mean free path of a neutrino in degenerate matter as ~3 cm. White dwarfs are not quite that dense, but neutron stars approach it. The Earth intercepts ~ 14 % of the solar neutrino flux with about a million times less mass...see the Sudbury Neutrino Observatory. Typically, a forward scattering neutrino delivers ~ 10% of it's momentum and energy to the interaction. For neutrino-opaque substances, this constitutes heating, similar conceptually to microwaves heating your blueberry muffin for breakfast. pete

grant hutchison
2008-Oct-21, 03:34 PM
The Earth intercepts ~ 14 % of the solar neutrino flux with about a million times less mass...This seems remarkable to me, given the usual "light-year of lead" given as a dramatic approximation for the mean free path of a neutrino.
Why the spectacularly huge difference?

Grant Hutchison

Ken G
2008-Oct-21, 04:21 PM
A lecture by David W. Arnett gave the mean free path of a neutrino in degenerate matter as ~3 cm. Taking the density of a neutron star to be something like a few times 1014 g/cm3, over 3 cm, that's a "column depth" of about 1015 g/cm2 as the stopping column depth, assuming Arnett is quoted correctly. The column depth of the Earth is about 1010 g/cm2, so the Earth should stop about 1 neutrino in 100,000, if we are talking about the same neutrinos as Arnett, and if the stopping mechanism doesn't care if the neutrons are in nuclei or in a degenerate star (I don't know if that is an issue or not).

Taking lead, the thickness that would correspond to the stopping power of Arnett's 3 cm in a neutron star would be about 1014 cm, which is about a light hour. So I'm not sure where the "light year of lead" comes from, but these numbers are also not consistent with the Earth stopping 14%. It may be that degenerate neutrons have a much different interaction with these neutrinos than do neutrons in silicon or lead, or it may be that the neutrinos Arnett is talking about have very different energies than solar neutrinos. Whatever is going on is more complicated than all these simple numbers seem to suggest, because they don't seem consistent.

mugaliens
2008-Oct-21, 04:26 PM
Typically, a forward scattering neutrino delivers ~ 10% of it's momentum and energy to the interaction. For neutrino-opaque substances, this constitutes heating, similar conceptually to microwaves heating your blueberry muffin for breakfast. pete

That's good news! I've often wondered what those few of the trillion-trillion neutrinos that pass through me every day were doing when the rarity actually hit something.

Ilya
2008-Oct-21, 04:39 PM
This seems remarkable to me, given the usual "light-year of lead" given as a dramatic approximation for the mean free path of a neutrino.
Why the spectacularly huge difference?

Grant Hutchison

Because that "light-year or lead" is a perfect example of what I call Bad Truisms -- what "everybody knows", and is wrong (http://www.bautforum.com/small-media-large/14194-bad-truisms-what-everybody-knows-wrong.html).

grant hutchison
2008-Oct-21, 04:52 PM
Because that "light-year or lead" is a perfect example of what I call Bad Truisms -- what "everybody knows", and is wrong (http://www.bautforum.com/small-media-large/14194-bad-truisms-what-everybody-knows-wrong.html).I doubt if it meets your criteria, since it is quite properly founded on sensible calculations applied to real-world data. See, for instance, the lower panel here (http://hyperphysics.phy-astr.gsu.edu/hbase/particles/neutrino3.html), on the (generally reliable) HyperPhysics site.

Grant Hutchison

trinitree88
2008-Oct-21, 05:49 PM
The Sudbury Neutrino Observatory results are here:http://www.sno.phy.queensu.ca/sno/results_04_02/NC/page00.html

I just read them. I suppose it's possible that oscillations drop the interaction rate without dropping a lot of energy during the oscillation, but I don't think that's particularly clear from the initial results.What would be clearer is a corresponding drop in the the interaction rate of the other families diurnally. pete

grant hutchison
2008-Oct-21, 06:11 PM
The Sudbury Neutrino Observatory results are here:http://www.sno.phy.queensu.ca/sno/results_04_02/NC/page00.htmlHmmm. I can't figure out where your 14% figure comes from. :(

Grant Hutchison

trinitree88
2008-Oct-21, 06:15 PM
I doubt if it meets your criteria, since it is quite properly founded on sensible calculations applied to real-world data. See, for instance, the lower panel here (http://hyperphysics.phy-astr.gsu.edu/hbase/particles/neutrino3.html), on the (generally reliable) HyperPhysics site.

Grant Hutchison


grant. I use the Hyperphysics site,too, and yes it is generally good. The issue arises because core collapse supernovae models routinely use the words...neutrino opaque...meaning the neutrinos are bound until the core rebounds, loses density, and neutrino opacity is lost...hence a prompt neutrino burst. This cools the expansion considerably.
A couple of factors come into play. Neutrino/nucleon cross-sections vary as the square of the energy. See the Ultimate Neutrino Page: http://cupp.oulu.fi/neutrino/nd-cross.html ....and there's a big difference between inverse beta decays, and the other cross-sections.
"Normal" beta decay involves a neutron making a proton, electron, and electron -type antineutrino. The inverse process can occur in two ways. The proton can combine with an electron and an electron-type anti-neutrino...a triple conjunction far unlikely....or kinetic energy of collision of some nucleons can kick a proton up to a neutron by flipping an up quark to a down with emission of a neutrino and a positron...more likely. Both require energy being added, so they're endothermic.
The cross-sections will vary with the average temperature of the nucleons, so it isn't too surprising to see these effects in core collapse, briefly at ~200,000,000 Kelvins.
I think a lot of people have a conceptual impasse with the SNO result being so high, we are talking about some ~ 5 light-milliseconds of material having an effect on 14% of the transiting solar neutrinos. Surprising? Yes, but it's not inverse beta decay. pete

grant hutchison
2008-Oct-21, 06:35 PM
The Sudbury Neutrino Observatory results are here:http://www.sno.phy.queensu.ca/sno/re...NC/page00.htmlHmmm. I can't figure out where your 14% figure comes from. :(Ah. I think you linked to the wrong paper.
This (http://eta.physics.uoguelph.ca/sno/ian/0204009.pdf) looks like the origin of the figure you quoted.

I still have the conceptual impasse. :) I find myself wondering how solar neutrinos get out of the sun, if the Earth can stop 14% of them.

Grant Hutchison

peteshimmon
2008-Oct-21, 06:35 PM
And I bet there is a big high energy BANG
when supernovae neutrinos fall onto a
neutron star:)

Ken G
2008-Oct-22, 05:31 AM
See, for instance, the lower panel here (http://hyperphysics.phy-astr.gsu.edu/hbase/particles/neutrino3.html), on the (generally reliable) HyperPhysics site.
That site seems to indicate that the MeV-type neutrino cross section for a nucleon is about 10-44 cm2. That would correspond to a distance of 10-6 cm deep in a neutron star. So maybe Arnett was talking about the low density surface of a neutron star as having a mean free path of 3 cm. In any event, for MeV-type neutrinos, the light year of lead does seem to be how it works out.

trinitree88
2008-Oct-22, 10:02 AM
Ah. I think you linked to the wrong paper.
This (http://eta.physics.uoguelph.ca/sno/ian/0204009.pdf) looks like the origin of the figure you quoted.

I still have the conceptual impasse. :) I find myself wondering how solar neutrinos get out of the sun, if the Earth can stop 14% of them.

Grant Hutchison

Grant. Yup, I did, I quoted the wrong paper. :shifty::doh:Pardonez - moi, thanks...pete.

trinitree88
2008-Oct-22, 10:13 AM
Ah. I think you linked to the wrong paper.
This (http://eta.physics.uoguelph.ca/sno/ian/0204009.pdf) looks like the origin of the figure you quoted.

I still have the conceptual impasse. :) I find myself wondering how solar neutrinos get out of the sun, if the Earth can stop 14% of them.

Grant Hutchison

The ones that interact can still forward-scatter their way out, or sail along after flavor switching. If they forward scatter, they transfer about 10% of their energy to the scatterer ...nucleons, or electrons...(James Losecco, Univ. Notre Dame, Ap.J.)....and as the cross-section varies as ~ the square of the energy...a neutrino of 0.9 times the original energy, ought to interact ~(0.9) times (0.9) = ~ 81% as effectively, which would just about do it for the data. Since SNO is working with very low stats, that might turn out to be the case, and as more years of data accumulate, the interactions should clarify.
pete

Eroica
2008-Oct-22, 11:15 AM
and if the stopping mechanism doesn't care if the neutrons are in nuclei or in a degenerate star (I don't know if that is an issue or not).I would have thought that that was a crucial issue. Aren't degenerate neutrons much more energetic than non-degenerate neutrons? Therefore they have a much greater probability of reacting weakly with the neutrinos. I don't know either - I'm just thinking out loud. But when I read the OP I thought degeneracy was more relevant than density. :think:

trinitree88
2008-Oct-24, 06:03 PM
I would have thought that that was a crucial issue. Aren't degenerate neutrons much more energetic than non-degenerate neutrons? Therefore they have a much greater probability of reacting weakly with the neutrinos. I don't know either - I'm just thinking out loud. But when I read the OP I thought degeneracy was more relevant than density. :think:

Eroica. I don't have a subscription to Phys. Rev. D. but this might help.http://prola.aps.org/abstract/PRD/v58/i1/e013009

blueshift
2008-Oct-25, 02:19 AM
Grant,

AFAIK, 14% is way off. The reason a supernova occurs has to do with it being a neutrino event with all of the nuclei going through fusion, producing such an enormous number of neutrinos that 100% of the surrounding gases experience collisions from them. In fact, a physicist at Argonne Labs told me that the light year of lead is an underestimate. He claims that neutrinos can go through several light years of lead. Sudbury would be realizing far more events daily if 14% was a reliable figure. Billions of those things are going through every cubic centimeter of my body each second.

mugaliens
2008-Oct-25, 04:44 PM
And I bet there is a big high energy BANG
when supernovae neutrinos fall onto a
neutron star:)

If so, I wonder if we might one day witness a the dim reflection of a supernova off a neaby neutron star. Probably not neutrinos, but energy resulting from neutrino-matter interactions.

rodin
2008-Oct-26, 11:49 AM
Could the extreme high temps of Solar corona be due to neutrino capture by flares inducing fission? The flux close to the surface must be Biblical in intensity. A recent study showed that fission occurs more quickly the closer we are to the sun and speculation is that this is due to neutrino flux.

http://arxiv.org/PS_cache/arxiv/pdf/0808/0808.3283v1.pdf

trinitree88
2008-Oct-26, 09:55 PM
Grant,

AFAIK, 14% is way off. The reason a supernova occurs has to do with it being a neutrino event with all of the nuclei going through fusion, producing such an enormous number of neutrinos that 100% of the surrounding gases experience collisions from them. In fact, a physicist at Argonne Labs told me that the light year of lead is an underestimate. He claims that neutrinos can go through several light years of lead. Sudbury would be realizing far more events daily if 14% was a reliable figure. Billions of those things are going through every cubic centimeter of my body each second.

blushift. 14 % is the best fit to the data. ~180 authors on the paper say so in the SNO collaboration, just about every one a PhD in Physics with theoretical or experimental neutrino backgrounds.
All of the nuclei in a supernova do not go through fusion. In the core collapse models, several solar masses of hydrogen are cast off in the ejecta, and are available for forming water with the substantial quantities of oxygen also cast off...see Woosley's Isotope table for a 25 Solar Mass Supernova.
The regime in which 100% of the surrounding material experiences collisions with the neutrinos is the neutrinosphere which is transiently opaque to their passage, as it's density peaks...(and it's not spherical, it goes oblate then prolate as it bounces, giving the explosion it's inherent asymmetry, evidenced in the barrel shapes of the remnants of all types of supernovae). There are scant "gas" molecules, or atoms there at a temperature of 200,000,000 Kelvins...it's plasma.
Grant's reference to the Hyperphysics text and Ken G's verification of their numbers is correct for beta decays...similar to the Homestake mine converting chlorine in perchlorethylene to argon by swapping a neutron for a proton. That'a a charged current CC interaction. The total cross-section for MSW flavor oscillation, and elastic scattering and neutral currents is higher as is shown by the data. 188 authors.
pete

I am reminded of the day I spent at the San Diego Zoo, with my daughter....site of the famous visitor from Arkansas (don't send me letters)...who stood by the giraffe's cage with his son for five minutes, and then said..."Son, they ain,t no sech animule...tipped his hat and walked off in a huff"... I didn't expect he'd find his way into non-Abelian quantum field theory, cosmology, quantum chromodynamics, general relativistics, and weak currents.

grant hutchison
2008-Oct-26, 10:12 PM
I had no idea that scientific papers got righter in proportion to the number of authors involved. Those error bars are pretty wide, so I dread to think what they'd have looked like with just fifty authors. :)

Grant Hutchison

trinitree88
2008-Oct-27, 10:59 AM
I had no idea that scientific papers got righter in proportion to the number of authors involved. Those error bars are pretty wide, so I dread to think what they'd have looked like with just fifty authors. :)

Grant Hutchison

Grant. Actually, the idea that more people believing in something (mainstream)...makes it correct ...is a proponent of some physics forums, not my personal philosophy. ;) pete

grant hutchison
2008-Oct-27, 01:21 PM
Grant. Actually, the idea that more people believing in something (mainstream)...makes it correct ...is a proponent of some physics forums, not my personal philosophy. ;) peteWhat a curious cartoon of the concept "mainstream"!
We can usually assume that the authors of the paper believe the results they present are an undistorted summary of the data recorded, and that they are sufficiently interesting to merit publication, and that being involved in that publication will bring them kudos rather than damage.
The "mainstream" has a quite different organization: it's a huge network of interlocking models, data and assumptions, which can ingest certain additional data without disturbance, but which will view other data as "anomalous" because they do not fit readily into the existing explanatory network.

I'm asking how 14% neutrino interception by the Earth fits into our current understanding. "180 authors" is not an answer to that question.

Grant Hutchison

Ken G
2008-Oct-27, 01:48 PM
I can't say I know much about this, but I think the idea is that 14% of the neutrinos undergo flavor oscillations, not absorption or scattering, as they pass through the Earth. The presence of Earth matter mediates that oscillation, but the trajectory of the neutrinos is hardly affected (if at all). So the problem here is that just what is meant by an interaction of the neutrinos is not uniform-- trinitree just means some sort of interaction has occured, grant hutchison means that the neutrino has been scattered or absorbed (especially the latter if we are talking about an actual detection, as in the homestake mine that trinitree mentioned). I think we would need at this point to retrace the steps of the actual argument being presented, in a way that accounts for all the different possible meanings of a neutrino interaction, at what energy, and in what kind of substrate. I cannot recreate those various factors, my information is too incomplete.

grant hutchison
2008-Oct-27, 03:22 PM
So the problem here is that just what is meant by an interaction of the neutrinos is not uniform-- trinitree just means some sort of interaction has occured, grant hutchison means that the neutrino has been scattered or absorbed ...Well, I confess I'm having trouble understanding exactly what trinitree88 is saying, and I've now been distracted by the whole "180 authors" thing. :)
But it seems pretty clear to me that the 14% asymmetry for electron neutrinos in the relevant SNO paper (http://eta.physics.uoguelph.ca/sno/ian/0204009.pdf) is an unadjusted raw figure, with 7% (and broad error bars) quoted when the total neutrino flux asymmetry is locked to zero. Indeed, from Table I, it seems we'd need to accept that the total (electron+mu+tau) neutrino flux is greater at night if we want to run with the 14% figure.

So while I understand that trinitree88 is invoking neutrino flavour oscillation, I think I don't understand much else at present. Which I'm quite prepared to believe is a defect in my understanding. :)

Grant Hutchison

blueshift
2008-Oct-28, 12:31 AM
blushift. 14 % is the best fit to the data. ~180 authors on the paper say so in the SNO collaboration, just about every one a PhD in Physics with theoretical or experimental neutrino backgrounds.You misread the paper.
"The Sudbury Neutrino Observatory (SNO) has measured day and night solar neutrino energy spectra and rates. For charged current events, assuming an undistorted B spectum, the night minus day rate is 14% plus and minus 6.3% (plus 1.5% minus 1.4%) of the average rate."

That does not say that 14% of the neutrinos plunging through earth have collisions. It is just a difference between the day and night rates. BTW, thanks for the input on SN and neutrino activity.

Ken G
2008-Oct-28, 12:38 AM
I'm not sure what distinctions are being drawn here. I haven't seen the paper, but it seems to me that day/night variations are all about neutrino oscillations mediated by nuclei in the Earth (the neutrinos come through Earth at night). So although the error bars are large, it seems plausible that a significant number of neutrinos are having their flavor changed by the Earth. I think this is what trinitree is saying, though I've rather lost what point is being made by it. What is clear is that this is not the same kind of interaction as the "light year of lead" kinds of absorptions.

grant hutchison
2008-Oct-28, 01:05 AM
I'm not sure what distinctions are being drawn here. I haven't seen the paper, but it seems to me that day/night variations are all about neutrino oscillations mediated by nuclei in the Earth (the neutrinos come through Earth at night). So although the error bars are large, it seems plausible that a significant number of neutrinos are having their flavor changed by the Earth.I think that's correct, although the error bars are in fact large enough (95% level) to be compatible with no diurnal variation in flux, either in total count or in electron neutrino count. I guess that might be the default assumption if we didn't already have theory and evidence to support flavour change as the neutrinos pass through the sun.


I think this is what trinitree is saying, though I've rather lost what point is being made by it. What is clear is that this is not the same kind of interaction as the "light year of lead" kinds of absorptions.I think that's clear. The solar neutrino spectrum seems to be pretty close to the MeV range for which the "light year of lead" is calculated: tailing off towards 20MeV. So a reasonable expectation would seem to be very little actual attentuation of the total flux on passage through the Earth, but with perhaps some sort of shift in the flavour populations.

But blueshift and I both seem to have gained the impression that trinitree88 is making rather more of this than I've outlined above. Perhaps we're mistaken.

Grant Hutchison

Ken G
2008-Oct-28, 06:54 AM
I suspect the issue is in what is meant by "unharmed" from the OP. Although trinitree has alluded to heating effects in a few places, it is nevertheless a possible interpretation of "harm" to undergo flavor oscillations, and that's where the 14% comes from. Most of us interpret the OP as asking about the absorption (i.e., destruction) of neutrinos, so that's where the light year of lead comes from. The OPer will have to say if he/she counts a flavor oscillation as a form of harm! Until then, I think we've resolved the discrepancies, notwithstanding the now typical stance by trinitree that neutrinos might engender some significance elevated above what is generally accepted.

blueshift
2008-Oct-28, 11:17 PM
Good points Ken. If 14% of my body mass experienced collisions with neutrinos moving at relativistic speeds, I wouldn't be here along with everybody else. A bullet moves more slowly and can collide with my body to bring death and it takes up way less than 14% of my body mass. In fact, the earth would be in pretty bad shape with that kind of impact. It would make Comet Shoemaker-Levy look like a pebble. Nonetheless, it was a nice exchange.