1. Feasibility of geochemical galactic neutrino flux measurement
C. Lunardini (Arizona University), C. Volpe (IPN Orsay), R.L.

2. Introduction Massive stars (M>8Msun) explode
(nuclear fusion ends with Fe, gravity driven core collapse, neutrino cooling, bounce back, shock, explosion..)
Neutrino burst time: ~L2/d~10s
99% of the energy in neutrinos: 1053 ergs/s=3*1019 Lsun
53I

3. Introduction
Massive stars (M>8Msun) explode
(nuclear fusion ends with Fe, gravity driven core collapse, neutrino cooling, bounce back, shock, explosion..)
Neutrino burst time: ~L2/d~10s
99% of the energy in neutrinos: 1053 ergs/s=3*1019 Lsun
SN1054 « On a Ji-Chou day in the 5-th month of the 1st year of the Zhi-He reign-period (1054 July 4), a guest star appear near Tian Guan; after more than one year it faded away»
How to detect? Astronomic observations, historic records..
Neutrino telescopes (water, liquid scintilator, liquid argon, … detectors)
Individual burst: events (galactic)
Wait for nearby SN:~30-50 years. The only detection: SN1987 (Magellanic Cloud, D=50 kpc)

4. Geochemical observation
Time-averaged flux of SN neutrinos is weak only of solar neutrinos, however their detection might be possible for the reactions with the high threshold (W.C. Haxton, C. W. Johnson, Nature 333 (1988) 325).
ne,ne
Conditions
e+,e-
ne,ne
Y should be radioactive and with t1/2<<108 y (earth geological age) in order to get rid of primordial deposits.
Y is not produced by other reactions (need to separate cosmic background, deep-rock excavation), large threshold (to eliminate natural & solar neutrino backgrounds)
Y is easily detectable, commercial explotation of X
Quantity of Y will be ~ t1/2rx (Y – longlived t1/2~ 106 y, X– geologically abundant)
Quantity of Y will be ~s(X’Y), large neutrino cross sections

5. Possible reactions Reactions
Cross section requirement: single nucleon emission
Reactions
ne,ne
Thermal n! N
Z X !N¡1
Z¡1 Y + N
e+,e-
ne,ne
Long-lived isotopes are many, but..
Detection!
Neutrinos always participate! Cosmic rays for neutral channel!
Thermal n capture reactions! (9Be+ng10Be)

6. Probably the best case: 98Mo
Solar neutrino flux:
J=0+,T=14 n
E=8.96 MeV
(n,e)
t1/2=2.6*106y
J=0+,T=14
Direct production threshold at only ~0.4 MeV

7. Possible reactions SN neutrino flux is mostly due to galactic events
SN density in our galaxy

8. SN neutrino flux Thermal n distribution at the source:
(M. T. Keil, G. G. Raffelt and H.-T. Janka, Astrophys. J. 590 (2003) 971)
(Ee;Ex) (MeV)
(13; 22)
(12; 18)
(10; 16)
(Le;Lx)/L0
(1; 2)
(1; 1)
(1; 0.5)
(ae;ax)
(3,5; 2,5)
With L0=5*1052 erg
+/- survival probability (n n & ne scattering, oscillations inside the Earth)
Final flux:

9. Neutrino cross sections
1) Fermi Transitions using sum rule:
J=0+,T=14 n
(n,e)
J=0+,T=14
2) GT strengths from 98Mo(p,n)98Tc
Measurement (PRL 54 (1985) 2325):
3) Other multipoles: QRPA

10. Drawback…
Direct production involves low energy solar n

11. 97Tc production rates HJ* Our Solar 4.17 5.21 31 37.6 SN best 5.4
1.7
SN(natural)
SN(worst)
~ 0.5
~0.2
Failed SN
<0.6
<0.1
Numbers given in units of 10-37s-1, SN rate is 0.03 y-1
HJ* is from W.C. Haxton, C. W. Johnson, Nature 333 (1988) 325

12. How much 97Tc in the rock? Total HJ* total Solar 2.7 7.8 10.6 8.0
Solar+SN
3.5
7.9
11.4
11.2
Solar+SN+failed SN
3.7
11.6
Numbers given in 106 atoms for 10 kton of the rock sample
HJ* is from W.C. Haxton, C. W. Johnson, Nature 333 (1988) 325

13. Conclusion
SN neutrino signal is close to current detection limits for large scale geochemical experiment.
However 97Tc production is strongly dominated by the solar background
A better knowledge of the solar neutrino spectrum and of the 97Mo(n,e)97Tc and 98Mo(n,en)97Tc cross sections are necessary. New experiments of (p,n) reactions in these nuclei would be very appreciated.