Total Absorption Spectroscopy Measurement of the β-Decay of ¹⁰⁴Nb

Nuclear reactors are an intense source of anti-ν_e which are commonly used for high energy particle physics experiments (e.g. RENO, Chooz, Daya Bay). These experiments have revealed a discrepancy in the measured anti-ν_e flux from a reactor and the expected anti-ν_e flux based on the present nuclear data. In order to compute an accurate reference anti-ν_e flux, the β-feeding intensities of fission products must be known. Additionally, β-feeding intensities of fission products are of interest for the safe and optimized operation of nuclear reactors since they are essential to modeling the decay heat. Current nuclear data is often incomplete or incorrect because of an unforeseen weakness of high precision measurements: the Pandemonium Effect. The Modular Total Absorption Spectrometer (MTAS) was designed to overcome this weakness with nearly 99% γ ray detection efficiency. The first measurement of the β-feeding intensities of ¹⁰⁴Nb was made at Argonne National Laboratory using MTAS. We find that a lower proportion of the total Q_β energy is distributed to γ radiation than previous theoretical calculations indicated.