Radiation

jaff.physics.RadiationProps, jaff.physics.Radiation, jaff.physics.RadiationGroup

The radiation field is split into contiguous photon-energy bands. RadiationProps holds the configuration and checks it, Network builds a Radiation from it (net.radiation), and Radiation creates one RadiationGroup per band. Each group stores its band-averaged quantities and the rate data for every photo-reaction in that band.

See Photochemistry for the physics, and [network.radiation] for the jaffgen.toml equivalent.

Photon spectrum

Within band \(i\) the photon-number spectrum is a power law with that band's own spectral index \(\alpha_i\):

\[ n(E) \propto E^{\alpha_i - 2}, \qquad u(E) = E\,n(E) \propto E^{\alpha_i - 1} \]

A scalar profile_index gives every band the same \(\alpha\). A list gives one \(\alpha_i\) per band. Each band is normalised on its own, so the spectrum is a histogram and is discontinuous at band edges by design. Common values are \(\alpha = 1\) (flat energy spectrum) and \(\alpha = 2\) (flat photon spectrum).

RadiationProps

RadiationProps(
    bands=[],
    profile_index=0.0,
    mode="nph",
    c=constants.c.cgs.value,
    background_field="draine",
    pi_database="norad",
)

Argument	Type	Default	Description
`bands`	`list[float]` (+ `"inf"`)	`[]`	Band edges in eV, ascending, at least two. `"inf"` in the last slot means an open upper band (`sympy.oo`)
`profile_index`	`float` or `list[float]`	`0.0`	Spectral index \(\alpha\). A list must have `len(bands) - 1` entries, one per band
`mode`	`str`	`"nph"`	`"nph"` tracks photon number density (`photden`, cm⁻³); `"u"` tracks energy density (`radeden`, erg cm⁻³)
`c`	`float` or `str`	`constants.c.cgs.value`	Speed of light in cm/s. A string (e.g. `"c_hat"`) becomes a symbol, for a reduced speed of light
`background_field`	`str`	`"draine"`	Reference field used to scale `chi_pe`: `bb_4000`, `bb_10000`, `bb_20000`, `draine`, `habing`, `mathis`, `solar`, `tw_hydra`
`pi_database`	`str`	`"norad"`	Photoionization cross-section database: `norad`, `verner` or `leiden` (case-insensitive). Falls back `norad` → `verner` → `leiden` with one summary warning after loading; photodissociation always uses Leiden

The arguments are validated at construction; the table of ParserError / RuntimeError conditions is in Valid band / index combinations. The validated values are stored as attributes of the same names, with "inf" replaced by sympy.oo and mode / background_field / pi_database lower-cased.

Radiation

Built by Network from radiation_props; available as net.radiation (None when radiation is off).

Attributes

Attribute	Type	Description
`bands`	`list`	Band edges in eV (from `RadiationProps.bands`)
`nbands`	`int`	Number of bands, `len(bands) - 1`
`mode`	`str`	`"nph"` or `"u"`
`c`	`float` or `sympy.Symbol`	Speed of light used in `k = c · den · <σ>`
`den`	`sympy.IndexedBase`	Band density variable, shape `(nbands,)`, named `photden` (`"nph"`) or `radeden` (`"u"`)
`groups`	`list[RadiationGroup]`	One group per band, in ascending energy order
`background_field`	`BackgroundField`	Reference field built from `RadiationProps.background_field`
`E_sym`	`sympy.Symbol`	Photon-energy symbol `E` (eV) used in the profiles
`nph_profile`	`sympy.Piecewise`	Photon-number profile over all bands, `E**(α_i - 2)` in band i
`energy_profile`	`sympy.Piecewise`	Energy-density profile over all bands, `E**(α_i - 1)` in band i
`photden_tot`	`float`	\(\int n(E)\,dE\) over the full range, i.e. the sum of the groups' `photden`

In the piecewise profiles a point on an interior edge belongs to the band above it. Energies below bands[0] use the first band's profile and energies above bands[-1] use the last band's.

Methods

Method	Returns	Description
`get_photden_profile(ph_energy)`	`numpy.ndarray`	Evaluates `E**(α_i - 2)` on an energy grid (eV), each point using the index of its band (same edge rules as above)
`get_eden_profile(ph_energy)`	`numpy.ndarray`	`ph_energy * get_photden_profile(ph_energy)`, i.e. `E**(α_i - 1)`
`ordered_index(idx, order)`	`tuple[int, int]`	Positions `(density, flux)` of band `idx` in the flat radiation ODE array for layout `order` (0–3)
`set_reaction_rate_coefficient(reaction)`	`None`	Band-averages the reaction's tabulated cross section, fills `grp.props[reaction]` and sets `reaction.rate`
`set_custom_rate(reaction)`	`None`	Splits a user-supplied `reaction.rate` across bands in proportion to the band integral of `dRad`

Network calls the last two methods while building the network; you normally only read their results. The order layouts are:

`order`	Layout
`0`	`[den_0, flux_0, den_1, flux_1, ...]`
`1`	`[flux_0, den_0, flux_1, den_1, ...]`
`2`	`[den_0, den_1, ..., flux_0, flux_1, ...]`
`3`	`[flux_0, flux_1, ..., den_0, den_1, ...]`

RadiationGroup

One band, [lower, upper] in eV.

Attribute	Type	Description
`index`	`int`	Band index in `Radiation.groups`
`sym`	`sympy.Indexed`	This band's density variable, `den[index]`
`lower`, `upper`	`float` / `sympy.oo`	Band edges in eV
`band`	`tuple`	`(lower, upper)`
`dE`	`float` or `None`	`upper - lower`; `None` for an open band
`profile_idx`	`float`	This band's spectral index \(\alpha_i\)
`nph_profile`	`sympy.Expr`	`E**(profile_idx - 2)`
`energy_profile`	`sympy.Expr`	`E**(profile_idx - 1)`
`photden`	`float`	\(\int_\text{lower}^\text{upper} n(E)\,dE\), the normalisation for band averages
`eavg`	`float`	Band-average photon energy \(\langle E\rangle_i = \int E\,n\,dE / \int n\,dE\), in erg
`props`	`dict[Reaction, dict]`	Per-reaction band data, keys below

props[reaction] keys:

Key	Description
`k`	Symbolic rate coefficient for this band
`xsec`	Photon-number-weighted band-average cross section \(\langle\sigma\rangle_i\) (cm²); `None` for custom-rate reactions
`xsec_frac`	Tabulated reactions: \(\langle\sigma\rangle_i\) divided by the full-spectrum average (`reaction.rad_xsecs`), so values need not sum to 1. Custom-rate reactions: this band's share of the total `dRad` integral
`delta_rad`	Band integral of `dRad`, the radiation energy added per reaction event (erg)

The same values per reaction are available as a table through Reaction.band_xsecs (there eavg is in eV).

Example

import numpy as np
from jaff import Network
from jaff.physics import RadiationProps

net = Network(
    "networks/h_photoionization/h_photo.jet",
    radiation_props=RadiationProps(bands=[13.6, 20.0, 100.0], profile_index=[0, 1]),
)
rad = net.radiation

[grp.profile_idx for grp in rad.groups]   # [0, 1]
[grp.nph_profile for grp in rad.groups]   # [E**(-2), 1/E]
rad.nph_profile                           # Piecewise((E**(-2), E < 20.0), (1/E, True))
float(rad.photden_tot)                    # 1.6329...  (= 0.02353 + ln 5)
rad.get_photden_profile(np.array([15.0, 50.0]))   # [0.00444, 0.02]
rad.ordered_index(1, order=2)             # (1, 3)