In a Certain Particle Accelerator, a Current of 300 μA

In a certain particle accelerator, a current of 300 μA is carried by a 4.00-MeV proton beam that has a radius of 1.30 mm. The mass of a proton is 1.67 × 10^-27 kg. What is the number of protons per unit volume in this beam?

A) 3.64 × 10¹³ protons/m³
B) 2.76 × 10¹³ protons/m³
C) 1.28 × 10¹³ protons/m³
D) 5.98 × 10¹³ protons/m³
E) 4.17 × 10¹³ protons/m³