Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Dynamic nuclear polarization and relaxation of H and D atoms in solid
  mixtures of hydrogen isotopes   We report on a study of Dynamic Nuclear Polarization and electron and nuclear
spin relaxation of atomic hydrogen and deuterium in solid molecular matrices of
H$_{2}$, D$_{2}$, and HD mixtures. The electron and nuclear spin relaxation
times ($T_{1e}$ and $T_{1N}$) were measured within the temperature range
0.15-2.5$\,$K in a magnetic field of 4.6 T, conditions which ensure a high
polarization of electron spins. We found that $T_{1e}$ is nearly temperature
independent in this temperature range, while $T_{1N}$ decreased by 2 orders of
magnitude. Such strong temperature dependence is typical for the nuclear Orbach
mechanism of relaxation via the electron spins. We found that the nuclear spins
of H atoms in solid D$_{2}$ and D$_{2}:$HD can be efficiently polarized by the
Overhauser effect. Pumping the forbidden transitions of H atoms also leads to
DNP, with the efficiency strongly dependent on the concentration of D atoms.
This behaviour indicates the Cross effect mechanism of the DNP and nuclear
relaxation, which turns out to be well resolved in the conditions of our
experiments. Efficient DNP of H atoms was also observed when pumping the middle
D line located in center of the ESR spectrum. This phenomenon can be explained
in terms of clusters or pairs of H atoms with strong exchange interaction.
These clusters have partially allowed transitions in the center of the ESR
spectrum and DNP may be created via the resolved Cross effect.

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The categories of this paper are: bayes-an
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The categories of this paper are: acc-phys
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The categories of this paper are: eess
1
The categories of this paper are: cs
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The categories of this paper are: hep-th
5
The categories of this paper are: gr-qc
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The categories of this paper are: q-bio
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The categories of this paper are: plasm-ph
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The categories of this paper are: econ
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The categories of this paper are: q-alg
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: nlin
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The categories of this paper are: funct-an
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The categories of this paper are: dg-ga