Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gamma-ray emission from novae related to positron annihilation:
  constraints on its observability posed by new experimental nuclear data   Classical novae emit gamma-ray radiation at 511 keV and below, with a cut-off
at around (20-30) keV, related to positron annihilation and its Comptonization
in the expanding envelope. This emission has been elusive up to now, because it
occurs at epochs well before the maximum in optical luminosity, but it could be
detected by some sensitive intrument on board a satellite, provided that the
nova is close enough and that it is observed at the right moment. The detection
of this emission, which is a challenge for the now available and for the future
gamma-ray instruments, would shed light into the physical processes occurring
in the early phases of the explosion, which are invisible in other lower energy
ranges. A good prediction of the emitted fluxes and of the corresponding
detectability distances with different instruments relies critically on a good
knowledge of reaction rates relevant to f18 destruction, which have been
subject to a strong revision after recent nuclear spectroscopy measurements.
With respect to previous results, smaller ejected masses of f18 are predicted,
leading to smaller emitted fluxes in the (20-511) keV range and shorter
detectability distances.

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The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
26
The categories of this paper are: bayes-an
17
The categories of this paper are: q-fin
37
The categories of this paper are: supr-con
1
The categories of this paper are: cs
11
The categories of this paper are: hep-lat
15
The categories of this paper are: nucl-ex
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
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The categories of this paper are: solv-int
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The categories of this paper are: patt-sol
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The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat