[Paper Review] Intensive neutrino source on the base of lithium converter

Vladimir Lyashuk, Yu. S. Lutostansky|arXiv (Cornell University)|Mar 4, 2015

Particle accelerators and beam dynamics9 references3 citations

TL;DR

This paper proposes a novel, intense antineutrino source based on the beta decay of ⁸Li, produced via neutron activation of ⁷Li in a lithium converter. By using high-purity ⁷Li or LiOD in heavy water, and coupling it with a powerful neutron source (e.g., from accelerators or reactors), the method enables a hard antineutrino spectrum (up to 13 MeV, average 6.5 MeV) with significantly reduced spectral uncertainties compared to reactor-based sources, offering a new pathway for precision neutrino experiments.

ABSTRACT

An intensive antineutrino source with a hard spectrum (with energy up to 13 MeV, average energy 6.5 MeV) can be realized on the base of beta-decay of short living isotope 8Li (0.84 s). The 8Li isotope (generated in activation of 7Li isotope) is a prime perspective antineutrino source owing to the hard antineutrino spectrum and square dependence of cross section on the energy. Up today nuclear reactors are the most intensive neutrino sources. Antineutrino reactor spectra have large uncertainties in the summary antineutrino spectrum at energy E>6 MeV. Use of 8Li isotope allows to decrease sharply the uncertainties or to exclude it completely. An intensive neutron fluxes are requested for rapid generation of 8Li isotope. The installations on the base of nuclear reactors can be an alternative for nuclear reactors as traditional neutron sources. It is possible creation of neutrino sources another in principle: on the base of tandem of accelerators, neutron generating targets and lithium converter. An intensive neutron flux (i.e., powerful neutron source) is requested for realization of considered neutrino sources (neutrino factories). Different realizations of lithium antineutrino sources (lithium converter on the base of high purified 7Li isotope) are discussed: static regime (i.e., without transport of 8Li isotope to the neutrino detector); dynamic regime (transport of 8Li isotope to the remote detector in a closed cycle); an operation of lithium converter in tandem of accelerator with a neutron-producing target on the base of tungsten, lead or bismuth. Different chemical compounds of lithium (as the substance of the converter) are considered. Heavy water solution of LiOD is proposed as a serious alternative to high-pure 7Li in a metallic state.

Motivation & Objective

• To develop a new, intense antineutrino source with a hard energy spectrum (up to 13 MeV) to improve precision in neutrino oscillation and cross-section measurements.
• To reduce the large uncertainties in reactor antineutrino spectra at energies above 6 MeV, which currently limit experimental accuracy.
• To explore alternative neutrino source designs based on accelerator-driven neutron production and lithium-based ⁸Li generation, independent of nuclear reactors.
• To evaluate different lithium compounds (e.g., metallic ⁷Li, LiOD in heavy water) as viable converter materials for efficient ⁸Li production and antineutrino emission.

Proposed method

• Utilize neutron irradiation of ⁷Li to produce short-lived ⁸Li (half-life 0.84 s), which decays via β⁻ decay to emit high-energy antineutrinos.
• Employ a tandem accelerator system with a neutron-generating target (e.g., tungsten, lead, or bismuth) to produce intense neutron fluxes for efficient ⁷Li activation.
• Implement two operational regimes: static (fixed converter near detector) and dynamic (transport of ⁸Li in a closed cycle to remote detectors) for flexibility in experimental design.
• Use high-purity ⁷Li in metallic form or LiOD dissolved in heavy water as the lithium converter medium, with heavy water offering advantages in neutron moderation and chemical stability.
• Leverage the square-law energy dependence of the cross-section for ⁸Li decay to maximize antineutrino yield at higher energies.
• Design the system to minimize background and maximize antineutrino flux by optimizing neutron flux density and ⁸Li production efficiency.

Experimental results

Research questions

• RQ1 Can a lithium-based converter system produce a sufficiently intense antineutrino flux with a hard spectrum (up to 13 MeV) for precision neutrino experiments?
• RQ2 How do different lithium compounds (e.g., metallic ⁷Li vs. LiOD in heavy water) compare in terms of ⁸Li production efficiency and practicality?
• RQ3 To what extent can such a source reduce spectral uncertainties in the E > 6 MeV range compared to reactor-based antineutrino sources?
• RQ4 What are the technical and operational challenges in transporting ⁸Li in a dynamic regime to remote detectors while maintaining high yield?
• RQ5 Can accelerator-driven neutron sources replace nuclear reactors as the primary neutron source for ⁸Li production in such a system?

Key findings

• The ⁸Li decay produces a hard antineutrino spectrum with a maximum energy of 13 MeV and an average energy of 6.5 MeV, significantly harder than typical reactor spectra.
• The antineutrino spectrum from ⁸Li has a square-law energy dependence of the cross-section, which enhances yield at higher energies, improving signal-to-background ratios.
• Using high-purity ⁷Li or LiOD in heavy water as the converter medium enables efficient ⁸Li production with reduced chemical and thermal challenges.
• The dynamic transport regime allows for remote deployment of the antineutrino source, enabling new experimental geometries and reduced background in detectors.
• The proposed system can drastically reduce or eliminate spectral uncertainties in the E > 6 MeV region, a major limitation in current reactor-based neutrino sources.
• The use of accelerator-driven neutron sources (e.g., tandem accelerators with W/Pb/Bi targets) provides a viable, scalable alternative to nuclear reactors for neutron production.