The fission products 81Se and 83Se

Croall, I.F.; Willis, H.H.

doi:10.1016/0022-1902(62)80174-2

Cited by 4 publications

(2 citation statements)

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“…But changes of the order of 20% are not ruled out. There have been some experiments to examine [40][41][42] changes in the fission yields of isotopes that sit at the peaks of the mass distribution, but the results are discrepant: some experiments observe changes [40,41] and others do not [42]. One issue in considering the hardness of the spectrum is that since epithermal fission-yield effects are observed [38] to be larger in 239 Pu than in 235 U, the larger shoulder but smaller 239 Pu contribution at RENO would seem at odds with the shoulder being solely induced by a harder neutron flux.…”

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confidence: 99%

Possible origins and implications of the shoulder in reactor neutrino spectra

et al. 2015

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We analyze within a nuclear database framework the shoulder observed in the antineutrino spectra in current reactor experiments. We find that the ENDF/B-VII.1 database predicts that the antineutrino shoulder arises from an analogous shoulder in the aggregate fission beta spectra. In contrast, the JEFF-3.1.1 database does not predict a shoulder for two out of three of the modern reactor neutrino experiments, and the shoulder that is predicted by JEFF-3.1.1 arises from 238 U. We consider several possible origins of the shoulder, and find possible explanations. For example, there could be a problem with the measured aggregate beta spectra, or the harder neutron spectrum at a light-water power reactor could affect the distribution of beta-decaying isotopes. In addition to the fissile actinides, we find that 238 U could also play a significant role in distorting the total antineutrino spectrum. Distinguishing these and quantifying whether there is an anomaly associated with measured reactor neutrino signals will require new short-baseline experiments, both at thermal reactors and at reactors with a sizable epithermal neutron component.Modern reactor neutrino experiments measuring θ 13 , such as Daya Bay [1], RENO [2], and Double Chooz [3], involve detectors both near and far from the reactors. The shape and magnitude of the antineutrino spectra emitted from the reactors have been measured to high accuracy in the near detectors of both Daya Bay and RENO. The Daya Bay near-detector has also provided an absolute determination of the reactor antineutrino flux, and this is consistent in magnitude with the previous world average short-baseline reactor neutrino experiments. As such, the measured magnitude is consistent with a deficit with respect to the most recent estimates [4,5] of the expected reactor antineutrino flux. The absolute magnitude of the RENO flux has yet to be published. However, in the near detector of both RENO and Daya Bay the shapes of the measured spectra are not consistent with the antineutrino spectrum predictions [4,5] that we refer to as the Huber-Mueller model. Most notably, the measured antineutrino spectra exhibit a significant shoulder relative to the model predictions at antineutrino energies ∼ 5 − 7 MeV. The spectra measured at Daya Bay, RENO, and Double Chooz all exhibit this shoulder. Thus, there are two puzzles associated with measured reactor antineutrino spectra: (1) the yield in all short-baseline experiments is lower than current models, and (2) the shape of the measured spectra deviate from these model predictions. However, these two issues are not necessarily related.In the Daya Bay, RENO and Double Chooz experiments the antineutrinos are measured by detecting the positrons produced in inverse beta decay on the protons (ν e + p → n + e + ) in the detector, and the positron energy is reconstructed from the scintillation light created by the kinetic energy of the positron and its annihilation. The antineutrino spectrum S(E ν ) emitted from a reactor is determined by [6] the reactor ther...

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