What do these characteristic peaks stand for?

[phantasuson]

I built a typical accelerator using BEAMnrc and generated a phase space file. These characteristic peaks are shown when I drive the electrons spectrum from the phase space file. Where these electrons came from?

The red line is some of the electrons inherent in the beam, and the gray one is the electrons generated on the surface of a water phantom.

[rtownson]

Hard to guess without more information. Did you use DBS in BEAMnrc? These might just be high weight ("fat") particles...

[phantasuson]

Yes I did，but I didn't split the charged particles

[rtownson]

The high-weight split photons can create secondary electrons who carry the same weight and those are what you're seeing.

[phantasuson]

emmm，the photon spectrum looks normal. Would that have the same effect?

[rtownson]

I suggest double checking that your rejection plane is above your scoring plane, and also turning on e- splitting with DBS splitting closer to 1000. This is suggested in the documentation, section 6.3 of the BEAMnrc manual.