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@ARTICLE{Ioffe:1034920,
      author       = {Ioffe, Alexander and Konik, Peter and Batkov, Konstantin},
      title        = {{A} concept of a para-hydrogen-based cold neutron source
                      for simultaneous high flux and high brightness},
      journal      = {Journal of nuclear engineering},
      volume       = {6},
      number       = {1},
      issn         = {2673-4362},
      address      = {Basel},
      publisher    = {MDPI},
      reportid     = {FZJ-2025-00035},
      pages        = {3 -},
      year         = {2025},
      abstract     = {A novel concept of cold neutron source employing chessboard
                      or staircase assemblies of high-aspect-ratio rectangular
                      para-hydrogen moderators with well-developed and practically
                      fully illuminated surfaces of the individual moderators is
                      proposed. An analytic approach for calculating the
                      brightness of para-hydrogen moderators is introduced.
                      Because the brightness gain originates from a near-surface
                      effect resulting from the prevailing single-collision
                      process during thermal-to-cold neutron conversion,
                      high-aspect-ratio rectangular cold moderators offer a
                      significant increase, up to a factor of 10, in cold neutron
                      brightness compared to a voluminous moderator. The obtained
                      results are in excellent agreement with MCNP calculations.
                      The chessboard or staircase assemblies of such moderators
                      facilitate the generation of wide neutron beams with
                      simultaneously higher brightness and intensity compared to a
                      para-hydrogen-based cold neutron source made of a single
                      moderator (either flat or voluminous) of the same
                      cross-section. Analytic model calculations indicate that
                      gains of up to approximately 2.5 in both brightness and
                      intensity can be achieved compared to a source made of a
                      single moderator of the same width. However, these gains are
                      affected by details of the moderator–reflector assembly
                      and should be estimated through dedicated Monte Carlo
                      simulations, which can only be conducted for a particular
                      neutron source and are beyond the scope of this general
                      study. The gain reduction in our study, from a higher value
                      to 2.5, is mostly caused by these two factors: the limited
                      volume of the high-density thermal neutron region
                      surrounding the reactor core or spallation target, which
                      restricts the total length of the moderator assembly, and
                      the finite width of moderator walls. The relatively large
                      length of moderator assemblies results in a significant
                      increase in pulse duration at short pulse neutron sources,
                      making their straightforward use very problematic, though
                      some applications are not excluded. The concept of
                      “low-dimensionality” in moderators is explored,
                      demonstrating that achieving a substantial increase in
                      brightness necessitates moderators to be low-dimensional
                      both geometrically, implying a high aspect ratio, and
                      physically, requiring the moderator’s smallest dimension
                      to be smaller than the characteristic scale of moderator
                      medium (about the mean free path for thermal neutrons). This
                      explains why additional compression of the moderator along
                      the longest direction, effectively giving it a tube-like
                      shape, does not result in a significant brightness increase
                      comparable to the flattening of the moderator.},
      cin          = {JCNS-FRM-II / MLZ},
      ddc          = {620},
      cid          = {I:(DE-Juel1)JCNS-FRM-II-20110218 / I:(DE-588b)4597118-3},
      pnm          = {6G4 - Jülich Centre for Neutron Research (JCNS) (FZJ)
                      (POF4-6G4) / 632 - Materials – Quantum, Complex and
                      Functional Materials (POF4-632)},
      pid          = {G:(DE-HGF)POF4-6G4 / G:(DE-HGF)POF4-632},
      experiment   = {EXP:(DE-MLZ)NOSPEC-20140101},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:001482835400001},
      doi          = {10.3390/jne6010003},
      url          = {https://juser.fz-juelich.de/record/1034920},
}