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tu144
2011-Jun-06, 10:27 PM
These are the energies for solar neutrions:
pp < 0.420 MeV
pep = 1.442 MeV
7Be = 0.862 MeV, 0.384 MeV
8Be < 14.02 MeV
hep < 18.773 MeV

I've encountered a sentence "The energy is important, because it is easier to detect higher-energy neutrinos than the main part of the spectrum"
HOW it is easier? if the thresholds for neutrino detectors are:
71Ga 0.233 MeV
37Cl 0.814 Mev

71Ga should be able to detect them all, no matter what energy they carry, right?

Second question.
Diagram below shows suns luminosity, radious and neutrino readings of past sun:
http://img848.imageshack.us/img848/4599/slide8.jpg
Now, luminosity increases, means number of reactions increases, thus number of neutrinos increases.
The quesitons is: why readings of 71Ga and 37Cl have different curves? And why don't they increase lineary, like luminosity?

ngc3314
2011-Jun-07, 03:10 AM
Hint: the rates of many nuclear reactions scale as a very high power of the temperature. As core hydrogen s exhausted, the temperature in the core to maintain hydrostatic equilibrium rises.

chornedsnorkack
2011-Jun-07, 06:39 AM
These are the energies for solar neutrions:
pp < 0.420 MeV
pep = 1.442 MeV
7Be = 0.862 MeV, 0.384 MeV
8Be < 14.02 MeV
hep < 18.773 MeV

and, presumably, heep=19,795 MeV

I've encountered a sentence "The energy is important, because it is easier to detect higher-energy neutrinos than the main part of the spectrum"
HOW it is easier? if the thresholds for neutrino detectors are:
71Ga 0.233 MeV
37Cl 0.814 Mev

71Ga should be able to detect them all, no matter what energy they carry, right?

71Ga detects only a fraction of pp neutrinos (those between 0,233 MeV and 0,420 MeV).

How does the probability of neutrino detection deend on energy above the threshold?

Second question.
Diagram below shows suns luminosity, radious and neutrino readings of past sun:
http://img848.imageshack.us/img848/4599/slide8.jpg
Now, luminosity increases, means number of reactions increases, thus number of neutrinos increases.
The quesitons is: why readings of 71Ga and 37Cl have different curves? And why don't they increase lineary, like luminosity?

The ratio of low-energy branches (pp) to high energy branches (7Be, 8Be) depends on temperature.

tu144
2011-Jun-07, 11:48 AM
71Ga detects only a fraction of pp neutrinos (those between 0,233 MeV and 0,420 MeV).

Hmm, that's odd. There is an upper limit?!
From where that upper limit comes from?

chornedsnorkack
2011-Jun-07, 12:24 PM
Hmm, that's odd. There is an upper limit?!
From where that upper limit comes from?

From the energy of the reaction.

Two protons give a deuteron, a positron and an electron neutrino. The upper limit of neutrino energy comes when neutrino gets most energy and positron has little energy; but the division of energy between positron and neutrino is widely distributed so neutrino may get little energy if most ends up with positron.

Technically the uppwer limit might be exceeded by the kinetic energy of protons, but in Sun that is small compared to reaction energy.

tu144
2011-Jun-07, 01:43 PM
From the energy of the reaction.

Two protons give a deuteron, a positron and an electron neutrino. The upper limit of neutrino energy comes when neutrino gets most energy and positron has little energy; but the division of energy between positron and neutrino is widely distributed so neutrino may get little energy if most ends up with positron.

Technically the uppwer limit might be exceeded by the kinetic energy of protons, but in Sun that is small compared to reaction energy.
Didn't know that, so it's useful, but here you talk about the neutrino production.
I understand from your previous post that there is an upper energy limit in detection by 71Ga.

71Ga detects only a fraction of pp neutrinos (those between 0,233 MeV and 0,420 MeV).

So the question is why 71Ga, can't detect higher energy neutrinos from one of these:
pep = 1.442 MeV
7Be = 0.862 MeV, 0.384 MeV
8Be < 14.02 MeV
hep < 18.773 MeV
?

chornedsnorkack
2011-Jun-07, 03:28 PM
Didn't know that, so it's useful, but here you talk about the neutrino production.
I understand from your previous post that there is an upper energy limit in detection by 71Ga.

There isn´t, but there is an upper energy limit for neutrino production.
71Ga detector cannot detect pp neutrinos with energies below 0,233 MeV (lots of them are produced, but 71Ga cannot detect them), nor above 0,420 MeV (71Ga could detect them, but pp process does not produce any.

So the question is why 71Ga, can't detect higher energy neutrinos from one of these:
pep = 1.442 MeV
7Be = 0.862 MeV, 0.384 MeV
8Be < 14.02 MeV
hep < 18.773 MeV
?

It can and does.

71Ga can detect all neutrinos from pep and 7Be. As well as almost all neutrinos from 8Be and hep (these are continuous distribution where a tiny fraction of total is below threshold).

However, a significant proportion of pep neutrinos cannot be detected because of low energy.

tu144
2011-Jun-07, 04:16 PM
Ok, got it! Thank you!

trinitree88
2011-Jun-08, 03:11 PM
For energies < 1 Gev, most of the interactions scale as the square of the energy, so the energy is important beyond the threshold value, unlike the photoelectric effect which is linear to energy....SEE:http://cupp.oulu.fi/neutrino/nd-cross.html

pete