Towards 14C-free liquid scintillator

A series of measurements has been started where the 14C concentration is determined from several liquid scintillator samples. A dedicated setup has been designed and constructed with the aim of measuring concentrations smaller than 10−18. Measurements take place in two underground laboratories: in the Baksan Neutrino Observatory, Russia, and in the new Callio Lab in the Pyhäsalmi mine, Finland. Low-energy neutrino detection with a liquid scintillator requires that the intrinsic 14C concentration in the liquid is extremely low. In the Borexino CTF detector the concentration of 2 × 10−18 has been achieved being the lowest value ever measured. In principle, the older the oil or gas source that the liquid scintillator is derived from and the deeper it situates, the smaller the 14C concentration is supposed to be. This, however, is not generally the case and the concentration is probably due to the U and Th content of the local environment.peerReviewe

Measuring the 14C content in liquid scintillators

We are going to perform a series of measurements where the 14C/12C ratio will be measured from several liquid scintillator samples with a dedicated setup. The setup is designed with the aim of measuring ratios smaller than 10−18. Measurements take place in two underground laboratories: in the Baksan Neutrino Observatory, Russia and in the Pyh¨asalmi mine, Finland. In Baksan the measurements started in 2015 and in Pyh¨asalmi they start in the beginning of 2015. In order to fully understand the operation of the setup and its background contributions a development of simulation packages has also been started. Low-energy neutrino detection with a liquid scintillator requires that the intrinsic 14C content in the liquid is extremely low. In the Borexino CTF detector at Gran Sasso, Italy the 14C/12C ratio of 2 × 10−18 has been achieved being the lowest 14C concentration ever measured. In principle, the older the oil or gas source that the liquid scintillator is derived of and the deeper it situates, the smaller the 14C/12C ratio is supposed to be. This, however, is not generally the case, and the ratio is probably determined by the U and Th content of the local environment.peerReviewe

Concentration of ¹⁴C in liquid scintillator

Abstract The main background hindering low-energy (≲ 200 keV) neutrino measurements with liquid scintillators comes from the minute remanence of the cosmogenic ¹⁴C (T₁/₂ ≃ 5700 a) present in the organic oil constituting the bulk of the scintillator. The β-decay endpoint energy of ¹⁴C is quite low, Q = 156 keV, and the counting rate from ¹⁴C is often reduced by threshold settings. However, too high concentration of ¹⁴C may results in pile-up pulses. For example, in the Borexino detector at Gran Sasso, Italy, being the most sensitive neutrino detector, the trigger rate is largely dominated by the ¹⁴C isotope [1] with the concentration of 2 × 10⁻¹⁸ [2] It is the lowest ¹⁴C concentration value ever measured. There are only a few results available on the ¹⁴C concentration. In addition to the one in Ref. [2] there are three other measurements reported in Refs. [3, 4, 5]. Obviously ¹⁴C cannot be removed from liquid scintillators by chemical methods, or by other methods in large quantities (liters). In principle, the older is the oil or gas source that the liquid scintillator is made of and the deeper it situates, the smaller the ¹⁴C concentration should be. This, however, is not generally the case and it is believed that the ratio depends on the activity (U and Th content) in the environment of the source. We are performing a series of measurements where the ¹⁴C concentration will be measured from several liquid scintillator samples. They need low-background environment and are taking place in two deep underground laboratories: in the new CallioLab laboratory in the Pyhäsalmi mine, Finland, and at the Baksan Neutrino Observatory, Russia, in order to reduce and better understand the systematical uncertainties. Preliminary results will be presented

Towards ¹⁴C-free liquid scintillator

Abstract A series of measurements has been started where the ¹⁴C concentration is determined from several liquid scintillator samples. A dedicated setup has been designed and constructed with the aim of measuring concentrations smaller than 10−18. Measurements take place in two underground laboratories: in the Baksan Neutrino Observatory, Russia, and in the new Callio Lab in the Pyhäsalmi mine, Finland. Low-energy neutrino detection with a liquid scintillator requires that the intrinsic ¹⁴C concentration in the liquid is extremely low. In the Borexino CTF detector the concentration of 2 × 10−18 has been achieved being the lowest value ever measured. In principle, the older the oil or gas source that the liquid scintillator is derived from and the deeper it situates, the smaller the ¹⁴C concentration is supposed to be. This, however, is not generally the case and the concentration is probably due to the U and Th content of the local environment