Dear Lujain Khalayleh

F4 tally is average flux in a cell. You can obtain the average flux in output data. Maybe i can help you if you extend your question a bit more. 

mode p

sdef pos=0 0 100 axs=0 0 -1 erg=0.120 par=2

f4:p 4

m1 1000 .040402 6000 .123247 7000 .011862 &

8000 .357394 74000 .467094

ctme 1

Here you see the F4 tally appropriate syntax. There i giving command the input that "Consider the Photon and Give me the average flux in cell 4" and also when you look the output file, you will see and average value in the down of cell part. This is your average flux.

Tally F4 is the averaged tracklength in a predefined volume divided by volume for one primary particle BUT you can use it freely as volume flux. They have equivalent meanings and applications.

Mohamed S. Ali