Radon Mitigation Applications at the Laboratorio Subterráneo de Canfranc (LSC)

Abstract

The Laboratorio Subterráneo de Canfranc (LSC) is the Spanish national hub for low radioactivity techniques and the associated scientific and technological applications. The concentration of the airborne radon is a major component of the radioactive budget in the neighborhood of the detectors. The LSC hosts a Radon Abatement System, which delivers a radon suppressed air with 1.1±0.2 mBq/m3 of 222Rn. The radon content in the air is continuously monitored with an Electrostatic Radon Monitor. Measurements with the double beta decay demonstrators NEXT-NEW and CROSS and the gamma HPGe detectors show the important reduction of the radioactive background due to the purified air in the vicinity of the detectors. We also discuss the use of this facility in the LSC current program which includes NEXT-100, low background biology experiments and radiopure copper electroformation equipment placed in the radon-free clean room.

Long term measurement of the $^{222}$Rn concentration in the Canfranc Underground Laboratory

“…The possible contribution of some modulation of some tiny 222 Rn activity to the expected signal in ANAIS-112 is negligible because if we would take the above upper limit of 0.06 Bq m −3 as a true 222 Rn concentration with a modulation amplitude ∼ 10%, similar to the one observed in the Hall B (Table 4), its contribution to the ANAIS-112 modulation signal would be 4 × 10 −5 counts keV −1 kg −1 d −1 in the region [1][2][3][4][5][6] keV, much below the modulation observed by the DAMA/LIBRA collaboration [47] and the sensitivity of ANAIS-112 experiment [53].…”

“…This value is one order of magnitude better than our previous estimate based on the NaI(Tl) spectrometry data and it is not affected by the systematic uncertainty of f m because the dominant one is statistical. According to the ANAIS-112 background model [48], this upper limit means that the contribution of the 222 Rn to the total rate is < 4 × 10 −4 counts keV −1 kg −1 d −1 in the region of interest, [1][2][3][4][5][6] keV, amounting to less than 0.01% of the background [12].…”

“…6 Upper limit to 222 Rn concentration of the radon-free air provided by the LSC The laboratory has installed a radon abatement system (RAS), built by the company Apparatuses Technologies Construction (ATEKO a. s.) from Czech Republic, that can provide 220 m 3 h −1 with ∼1 mBq m −3 of 222 Rn for the experiments hosted by the LSC [6]. Though this 222 Rn concentration is very low to be detected by our HPGe detector, we have tested the 222 Rn content from the RAS as we did for the nitrogen purging ANAIS-112 (see section 5).…”

“…The posterior actions to provide a very low radioactive background to the experia e-mail: puimedon@unizar.es ments in the laboratory depend on their requirements. The experiments can be purged with nitrogen (from compressed nitrogen or evaporated from a liquid nitrogen dewar) or with radon-free air provided that the laboratory has an adequate system to satisfy this demand, see for instance [6]. Monitoring the 222 Rn level is also very important to avoid the plateout of the 222 Rn daughter, specially 210 Pb and its descendants, during the assembly of the components of an experiment [7].…”

“…We address three items in this article: monitoring the 222 Rn concentration inside the LSC and its correlation with the internal and external temperature, pressure and relative humidity; the measurement of the residual 222 Rn concentration of the evaporated nitrogen that was used to purge the ANAIS-112 experiment during 2017-2018 [11,12] and, finally, a similar measurement of the air provided by the radon abatement system [6] that supplies radon-free air to the experiments in the LSC [13][14][15][16][17][18][19]. Our data add very useful information to the published results of other background sources at LSC: the rock radioactivity [20], the neutron flux [21,22] and the cosmic-ray muon flux [23].…”