Editing Input syntax manual (section)

=== set ngamma ===

 '''set ngamma''' ''MODE'' [ ''WMIN'' ''NMAX'' ]
Sets the coupled neutron-photon transport simulation on. Input values:

{|
| <tt>''MODE''</tt>
| : simulation mode (0 = off, 1 = analog, 2 = implicit). The default option is "<tt>off</tt>"
|-
| <tt>''WMIN''</tt>
| : weight limit for implicit mode (default value: 0.1)
|-
| <tt>''NMAX''</tt>
| : maximum number of emitted photons in implicit mode (default value: 10)
|}

<u>Notes:</u>
*This input card invokes the production of prompt gammas in neutron reactions. 
**The coupled simulation mode requires that both neutron and photon data libraries are defined.
*Simulation mode:
**Analog mode: the average number of secondary photons produced per collision is defined by the ratio of photon production cross section to material total. 
***Each emitted photon assumes the weight of the incident neutron.
**Implicit mode: can be used to produce more photons by allowing variation in their statistical weight. 
***The weight limit defines the minimum allowed weight of emitted photons. 
***This method is close to what is used in MCNP.
**Both calculation modes produce photons in all collisions without any correlation to the sampled reaction mode.
**The <tt>''MODE''</tt> option was incorrectly described until Dec. 12, 2017.
*The methodology behind the coupled neutron/gamma transport mode is described in a related paper<ref name="ngamma">Leppänen, J., Kaltiaisenaho, T., Valtavirta, V. and Metsälä, M. ''"Development of a Coupled Neutron / Photon Transport Mode in the Serpent 2 Monte Carlo Code"''. In proc. M&C 2017, Jeju, Korea, Apr. 16-20, 2017</ref>