Difficulties replicating a spectra using /gps/hist

Particles, Track, Event, Run and Biasing
1

I have been trying to replicate some neutron spectra using /gps/hist
I have the data as a flux with an associated maximum energy, logarithmically binned into 640 groups between 1E-10 and 20MeV:

Neutron_Spectra
Neutron_Spectra.png1152×864 49.6 KB

I calculated a integral spectrum from these and put these values into a file EnergySpectrum.mac in the format:
/gps/hist/point
and use:
/gps/ene/type Arb
/gps/ene/diffspec 0
/gps/hist/type arb
/control/execute share/EnergySpectrum.mac
/gps/hist/point 20.1 0
/gps/hist/inter Lin

as demonstrated in test24.mac of examples/extended/eventgenerator/exgps/macros

The resulting energy distribution has both the fast and thermal peaks that were there originally. However, the ratio between the two peaks is off. Instead of a 5:1 Thermal:Fast, I have something closer to a 7:1 ratio. The jump in flux just above 1MeV seems to have been cut off. In fact, it looks pretty similar to what happens if I make a lethargy spectrum of the original data.

Any help or insight into how the /gps/hist functions or how to get the correct peak ratio out would be greatly appreciated.

2

So, I continued working on this, and tried a differential spectrum instead. This time I had much better luck, and got a result where the relative peak ratio was correct and the shape matched nicely.

Histogram_Output_Neutron

If anyone could explain to me why this didn’t work as an integral spectrum but did as a point wise distribution I would be grateful.

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