Experimental conditions generated from the Design-Expert 13 software based on the central composite (CCD).

Run	Factor 1 A: distance (cm)	Factor 2 B: high voltage (kV)
1	12.5	15
2	12.5	15
3	10	20
4	12.5	15
5	16.04	15
6	12.5	15
7	8.96	15
8	10	10
9	12.5	15
10	12.5	22.07
11	15	20
12	12.5	7.93
13	15	10