The fission cross section of uranium-238 by g-quanta with an energy of 3 MeV is 0.1 nb (10-34 cm2). What should be the total flux of quanta incident on the target so that forced fission of 1 mg of 235U can be noticed against the background of spontaneous fission (T1/2 = 1015 years) with an experiment duration of t = 100 hours?

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