# 2. Source File Format¶

Normally, source data is stored in a state point file. However, it is possible to request that the source be written separately, in which case the format used is that documented here.

When surface source writing is triggered, a source file named surface_source.h5 is written with only the sources on specified surfaces, following the same format.

/

Attributes
• filetype (char[]) – String indicating the type of file.

Datasets
• source_bank (Compound type) – Source bank information for each particle. The compound type has fields r, u, E, wgt, delayed_group, surf_id and particle, which represent the position, direction, energy, weight, delayed group, surface ID, and particle type (0=neutron, 1=photon, 2=electron, 3=positron), respectively.