• An ENDF "tape" is a file that contains one or more ENDF materials. We are fond of the word "tape" out of respect for the history of computing. As an example, Tape 511 was the ENDF/B-V Standards Tape.

• MAT labels an ENDF material. In older versions of ENDF/B, these numbers were assigned as the evaluations were completed, e.g., MAT1301 is H-1 and MAT1395 is U-235 for ENDF/B-V. For ENDF/B-VI, CSEWG moved to MAT numbers computed from the target Z and A. The numbers step by threes to allow for isomers, and a last two digits of 25 point to the lightest of the common isotopes. Thus, 125 is H-1, 128 is H-2, 2625 is Fe-54, 6153 is Pm-148m, and 9228 is U-235. For ENDF/B-VI Tape and MAT numbers, see the Index to ENDF/B-VI Neutron Data.

• MF labels an ENDF file. "Files" are usually used to store different types of data, thus:
  • MF=1 contains descriptive and miscellaneous data,
  • MF=2 contains resonance parameter data,
  • MF=3 contains reaction cross sections vs energy,
  • MF=4 contains angular distributions,
  • MF=5 contains energy distributions,
  • MF=6 contains energy-angle distributions,
  • MF=7 contains thermal scattering data,
  • MF=8 contains radioactivity data
  • MF=9-10 contain nuclide production data,
  • MF=12-15 contain photon production data, and
  • MF=30-36 contain covariance data.

• MT labels an ENDF section. Sections are usually used to hold different reactions. For example, MT=1 is the total cross section, MT=2 is elastic scattering, MT=16 is the (n,2n) reaction., MT=18 is fission, and MT=102 is radiative capture. The ever increasing scope of use for the ENDF-format data has led to a continual increase in the number and types of reactions that can be represented: ENDF MT list. More discussion of the labeling of reactions will be found later in this presentation.

An ENDF tape contains one or more materials in increasing order by MAT. Each material contains several files in increasing order by MF. Each file contains several sections in increasing order by MT.