The Nu-SNS proposal - ORNL Physics Division - Oak Ridge ...

supernovae. Measurements on Ba and Ta are possible and would provide meaningful constraints
on the theoretical rates used in models thus far.
Observations of the abundance of boron in stars as a function of metallicity do not show the
strictly quadratic dependence that is expected from secondary production mechanisms, like
cosmic-ray spallation, that operate after the galaxy has been enriched with metals. This implies
[58] that primary mechanisms that operate early in the history of our galaxy, such as neutrino
nucleosynthesis, also contribute significantly. According to current supernova nucleosynthesis
models, neutrino nucleosynthesis in supernovae favors the production of 11 B over 10 B. These two
isotopes are produced through the following spallation channels:
12
12
' 11
C( ν
x
, ν
x
p)
B
' 11 +
C( ν
x
, ν
xn)
C(
e ν
e
)
12
'
C d 10
( ν
x
, ν
x
) B
12
' 10
C( ν , ν pn)
B ,
x
which need laboratory calibration. Neutrino spallation measurements, used in conjunction with
future Hubble Space Telescope observations discriminating between 10 B and 11 B, would be
invaluable in resolving this controversy and supporting (or refuting) the suggestion that neutrino
nucleosynthesis in supernovae is an important source of 11 B in the galaxy [59].
It has been suggested [60] that the final abundance of 19 F produced in a supernova can serve as a
“supernova thermometer” because the ratio of [ 19 F/ 20 Ne]/[ 19 F/ 20 Ne]
(the denominator is the
measured ratio in our sun) is a measure of the µ and τ neutrinosphere temperatures (provided the
abundance of 19 F produced in the supernova is due to neutrino nucleosynthesis). 19 F is produced
through the following spallation channels:
20
x
11
' 19 +
Ne( ν
x
, ν
xn)
Ne(
e , ν
e
)
20
' 19
Ne(
ν , p)
F.
x
ν
x
Recent models [57], using improved neutrino nucleus reaction rates, show marked decreases in
the production of 19 F, casting some doubt on the possibility that 19 F is made in supernovae.
Laboratory measurements of the relevant rates are clearly necessary to resolve this.
Experiments to directly measure the cross sections for these reactions are extremely
challenging and are not the goal of the initial suite of experiments at the ν-SNS facility.
However, they are worthy of future consideration, since they provide direct insight into the
productions sites of these rare isotopes and shed light on the conditions within these sites.
3.3.3 Nucleosynthesis in the Neutrino-Driven Wind
Neutrino interactions may aid or prevent the r-process in a neutrino driven wind.
The astrophysical r-process is responsible for roughly half of the Solar System’s supply of
elements heavier than iron, with the remainder originating from the s-process occurring in
Asymptotic Giant Branch stars. While the nuclear conditions necessary to produce the r-process
are well established (see, e.g., [61]), the astrophysical site remains uncertain. The leading
candidate is the neutrino-driven wind emanating from the proto-neutron star after a core collapse
B
19
F
ν-SNS Proposal 28 8/4/2005