Module constants

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Physical constants used throughout NEREIDS.

Values from CODATA 2018 recommended values. Reference: https://physics.nist.gov/cuu/Constants/

Constants§

AVOGADRO: Avogadro’s number in mol⁻¹.
BOLTZMANN_EV_PER_K: Boltzmann constant in eV/K.
DIVISION_FLOOR: Floor for denominators in physics evaluations (penetrability, shift, etc.) to avoid division by zero.
EV_TO_JOULES: 1 eV in joules.
HBAR_EV_S: Planck constant (reduced, ħ) in eV·s.
LM_DIAGONAL_FLOOR: Floor for Levenberg-Marquardt diagonal elements to ensure damping stability. Intentionally much larger than PIVOT_FLOOR — LM requires a meaningful minimum curvature for numerical stability of the trust-region step.
LOG_FLOOR: Floor for avoiding log(0) or division by zero in general computations.
NEAR_ZERO_FLOOR: Generic tiny positive floor used as a near-zero tolerance across physics calculations (e.g., cross-sections in barns, energies in eV, widths, dimensionless parameters). Values below this are treated as negligible.
NEUTRON_MASS_AMU: Neutron mass in atomic mass units (u).
NEUTRON_MASS_KG: Neutron mass in kg.
NEUTRON_MASS_MEV: Neutron mass in MeV/c².
PIVOT_FLOOR: Floor for pivot detection and division safety in numerical linear algebra (LM solver, Gaussian elimination). Values below this indicate a (near-)singular system.
POISSON_EPSILON: Floor for Poisson model values to avoid log(0) in NLL computation.
QUANTUM_NUMBER_EPS: Epsilon for floating-point comparison of quantum numbers (J, L, spin).
SPEED_OF_LIGHT: Speed of light in m/s.

energy_to_tof: Convert neutron energy (eV) to time-of-flight (μs) given flight path (m).
energy_to_wavelength_angstrom: Convert neutron energy (eV) to wavelength (Å).
tof_to_energy: Convert neutron time-of-flight (μs) and flight path (m) to energy (eV).