单项选择题若距离x射线源的距离R1的射线剂量率P1,在同一径向R2处的射线剂量率为P2;则有()

A.P1/P2=R1/R2
B.P2/P1=R1/R2
C.P1/P2=(R1/R22
D.P2/P1=(R1/R22


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