[Paper Review] Re-publication of the data from the BILL magnetic spectrometer: The cumulative $β$ spectra of the fission products of $^{235}$U, $^{239}$Pu, and $^{241}$Pu

N. Haag, W. Gelletly+5 more|arXiv (Cornell University)|May 14, 2014

Nuclear Physics and Applications3 citations

TL;DR

This paper re-publishes high-resolution cumulative β spectra of fission products from ²³⁵U, ²³⁹Pu, and ²⁴¹Pu, originally measured at the BILL magnetic spectrometer at ILL in the 1980s, with improved energy binning (50 keV for ²³⁵U, 100 keV for ²³⁹Pu and ²⁴¹Pu). The data are provided with detailed statistical and systematic uncertainties to support precise reactor antineutrino spectrum calculations and to address the reactor antineutrino anomaly.

ABSTRACT

In the 1980s, measurements of the cumulative $β$ spectra of the fission products following the thermal neutron induced fission of $^{235}$U, $^{239}$Pu, and $^{241}$Pu were performed at the magnetic spectrometer BILL at the ILL in Grenoble. This data was published in bins of 250 keV. In this paper, we re-publish the original data in a binning of 50 keV for $^{235}$U and 100 keV for $^{239}$Pu and $^{241}$Pu.

Motivation & Objective

• To make high-resolution cumulative β spectra of fission products from ²³⁵U, ²³⁹Pu, and ²⁴¹Pu available to the scientific community with finer energy binning than previously published.
• To support precise calculations of reactor antineutrino spectra, which are critical for neutrino oscillation experiments and non-proliferation monitoring.
• To address the reactor antineutrino anomaly by providing accurate input data for modeling the total antineutrino spectrum from nuclear reactors.
• To preserve and re-publish original, high-precision data from the BILL experiment with updated binning and error estimates, without re-evaluation of the underlying measurements.

Proposed method

• Re-analysis of original raw data from the BILL magnetic spectrometer experiment at the ILL, which measured β spectra from fission products of ²³⁵U, ²³⁹Pu, and ²⁴¹Pu after thermal neutron irradiation.
• Re-binning of the original 250 keV data into 50 keV bins for ²³⁵U and 100 keV bins for ²³⁹Pu and ²⁴¹Pu to improve energy resolution.
• Application of statistical error propagation using the factor √2.5 to scale uncertainties from 250 keV to 100 keV bins, accounting for bin size differences.
• Incorporation of energy-dependent bin-to-bin correlated errors and absolute normalization uncertainties (1.7–1.9% for ²³⁵U, 2.0–2.6% for ²³⁹Pu, 1.8–1.9% for ²⁴¹Pu) at 68% confidence level.
• Exclusion of data taken too early after irradiation to minimize off-equilibrium effects: >12 h for ²³⁵U, >1.5 d for ²³⁹Pu, and >1.8 d for ²⁴¹Pu.

Experimental results

Research questions

• RQ1 What is the high-resolution cumulative β spectrum of fission products from ²³⁵U following thermal neutron-induced fission, with improved energy binning?
• RQ2 How do the re-binned β spectra of ²³⁹Pu and ²⁴¹Pu compare to the original 250 keV-binned data in terms of resolution and uncertainty?
• RQ3 To what extent can the re-published data improve the precision of reactor antineutrino spectrum predictions?
• RQ4 What is the impact of reduced statistical and systematic uncertainties on the modeling of the reactor antineutrino anomaly?

Key findings

• The cumulative β spectrum of ²³⁵U fission products is published in 50 keV-wide energy bins, with statistical uncertainties at the 68% confidence level and a 1.7% to 1.9% bin-to-bin correlated normalization error.
• For ²³⁹Pu, the β spectrum is re-binned into 100 keV-wide bins using a √2.5 scaling factor for uncertainties derived from the original 250 keV data, with a 2.0% to 2.6% normalization uncertainty.
• The ²⁴¹Pu β spectrum is re-published with refined errors, smaller than those obtained by the same scaling method as for ²³⁹Pu, and a 1.8% to 1.9% normalization uncertainty.
• Data for all three isotopes are restricted to times after 12 h (²³⁵U), 1.5 d (²³⁹Pu), and 1.8 d (²⁴¹Pu) post-irradiation to minimize off-equilibrium effects.
• The re-published data provide a critical input for precise reactor antineutrino spectrum calculations, supporting experiments like Daya Bay, RENO, and Double Chooz.
• The availability of high-resolution β spectra with detailed error budgets enables improved modeling of the reactor antineutrino anomaly and non-proliferation monitoring.