In proton beam therapy, a beam of high-energy protons is used to kill cancerous cells in a tumor. In one system, the beam, which consists of protons with an energy of 2.8×10−11J, has a current of 80 nA. The protons in the beam mostly come to rest within the tumor. The radiologist has ordered a total dose corresponding to 3.6×10−3J of energy to be deposited in the tumor. How long should the beam be in order to deliver the required dose?