Solubility, light output and energy resolution studies of molybdenum-loaded liquid scintillators

Abstract

The search for neutrinoless double-beta decay is an important part of the global neutrino physics program. One double-beta decay isotope currently under investigation is 100 Mo. In this article, we discuss the results of a feasibility study investigating the use of molybdenum-loaded liquid scintillator. A large, molybdenum-loaded liquid scintillator detector is one potential design for a low-background, internal-source 0νββ search with 100 Mo. The program outlined in this article included the selection of a solute containing molybdenum, a scintillating solvent and the evaluation of the mixture's performance as a radiation detector. Double Beta Decay of 100 MoThe study of neutrino physics, particularly of neutrinoless double-beta decay (0νββ) presents an exciting opportunity in the search for physics beyond the standard model and is well-motivated in the literature [1,2,3]. One isotope of experimental interest in the search for 0νββ is 100 Mo. 100 Mo is currently under investigation by the MOON (Molybdenum Observatory Of Neutrinos) [4,5,6,7] and NEMO (Neutrino Ettore Majorana Observatory) [8,9,10,11] projects. All 0νββ searches examine the Majorana nature of the neutrino (that is, whether the neutrino is its own anti-particle) as well as the absolute neutrino mass scale and spectrum. The experimental signature of most 0νββ searches is a pair of electrons in the final state of the decay whose total kinetic energy equals the endpoint of the two-neutrino double-beta decay (2νββ) spectrum, Q ββ (3034.4 keV for 100 Mo[12]). 100 Mo is a particularly attractive 0νββ candidate for several reasons. First, its Q ββ is both above most γ ray related backgrounds and below most α decay energies. Second, 100 Mo has a rather large natural abundance at 9.6%. Both MOON and NEMO look for this signature by interleaving source foils/films of ββ isotope between radiation detectors. MOON is focused on 100 Mo (with a secondary effort on 82 Se), and NEMO looks at several isotopes in addition to 100 Mo. This article will focus on attempts to load molybdenum into organic liquid scintillator as an alternative to the foil/tracking detector design.We begin by discussing the motivation for the interest in liquid scintillators for ββ search experiments in section 2. We then move on to molybdenum solubility and stability studies for different organometallic solutes in different scintillating solvents in Section 3. We next discuss the evaluation of the scintillation performance (light output and energy resolution) of a subset of the best performing solute/solvent combinations in Section 4. Last, we draw some conclusions and outline potential extensions to this program in Section 5. Molybdenum Loaded Liquid ScintillatorsAs discussed in Section 1, most of the current experimental interest in ββ of 100 Mo involves sandwiching thin layers of Molybdenum foil/film between radiation detectors, such as large scintillator plates or some kind of tracking Email address: vmg@lanl.gov (V.M. Gehman)

Theory of neutrinoless double-beta decay

“…MOON (Molybdenum Observatory Of Neutrinos): This is an extension of ELEGANT V [233]. It is a hybrid ββ and solar ν experiment with 100 Mo to study the Majorana ν masses with the QD -IH mass sensitivities of 100 -20 meV and the low energy solar νs [244,245,246,247,248]. Double beta decays to both the ground and the 1.132 MeV excited 0 + states are studied to confirm the 0νββ events and to study the 0νββ-decay mechanism.…”

Recent progress of organic scintillators

“…Various compounds of Mo, such as Mo(CO) 6 , [CH 3 COCH=C(O−)CH 3 ]2MoO 2 , or ammonium molybdate were attempted to be loaded in liquid scintillators. 80) In addition, In acetylacetonate 81) or In tris(2,4-pentanedionate), 82) Te complex with 1,2-butandiol, 83) or Nd complex with methylvaleric acid 84) have been loaded in liquid scintillators.…”

Neutrinoless double beta decay and neutrino mass

“…The 8 B solar-ν CC and NC interactions with atomic electrons in DBD isotopes and those in liquid scintillators used for DBD experiments [160][161][162][163] are also BG sources for medium energy-resolution experiments 164,165 The BG contribution for the liquid scintillator loaded with DBD isotopes of interest is expressed as…”