Radon daughter removal from PTFE surfaces and its application in liquid xenon detectors

Long-lived radon daughters are a critical background source in experiments searching for low-energy rare events. Originating from radon in ambient air, radioactive polonium, bismuth and lead isotopes plate-out on materials that are later employed in the experiment. In this paper, we examine cleaning procedures for their capability to remove radon daughters from PTFE surfaces, a material often used in liquid xenon TPCs. We find a large difference between the removal efficiency obtained for the decay chains of $$^{222}$$ 222 Rn and $$^{220}$$ 220 Rn. This indicates that the plate-out mechanism has an effect on the cleaning success. While the long-lived $$^{222}$$ 222 Rn daughters can be reduced by a factor of 2, the removal of $$^{220}$$ 220 Rn daughters is up to 10 times more efficient depending on the treatment. Furthermore, the impact of a nitric acid based PTFE cleaning on the liquid xenon purity is investigated in a small-scale liquid xenon TPC.

Monitoring rain rate with proximal gamma-ray spectroscopy

<p>We present an exhaustive study of the gamma activity increase measured at ground level for the atmospheric radon daughter <sup>214</sup>Pb. We demonstrate the effectiveness of proximal gamma-ray spectroscopy in continuously gathering reliable measurements of rain-induced <sup>214</sup>Pb gamma signal related to the rain intensity and amount. Since every impulse of rain produces a sudden increase of gamma signal, we study such transient activity to obtain information on precipitations and rain formation.</p><p>A novel spectroscopic instrument specifically tailored for gathering reliable and unbiased estimates of atmospheric and terrestrial gamma emitters has been developed. After seven months of continuous acquisition, we analyze the temporal evolution of the <sup>214</sup>Pb net count rate with an innovative and reproducible mathematical model for extracting information on this radon daughter’s content in the rain water. The effectiveness of the model is proved by an excellent coefficient of determination (r<sup>2</sup> = 0.91) between measured and reconstructed <sup>214</sup>Pb count rates. We observe that the impulsive increase of <sup>214</sup>Pb count rates ΔC is clearly related to the rain rate R by the power law dependence ΔC = A·R<sup>0.50 ± 0.03</sup>, where the parameter A is equipment dependent. This means that the expected increase of atmospheric <sup>214</sup>Pb activity measured at ground level during a rain event is proportional to the square root of the rain rate √R.</p><p>We observe that the <sup>214</sup>Pb abundance (G) of the rain water is inversely related to the rain rate G ∝ 1/R<sup>0.48 ± 0.03</sup> and to the rain median volume diameter λ<sub>m</sub> with G ∝ 1/ λ<sub>m</sub><sup>2.2</sup>.  We proved that, for a fixed rainfall amount, the longer is the rain duration (i.e. the lower is the rainfall intensity and the smaller is the mean raindrop volume), the higher is the <sup>214</sup>Pb content of the rain water.</p><p>Since the developed algorithm is detector independent, it can be used for analysing the data collected by the networks of thousands of gamma sensors distributed around the Earth, typically utilised for monitoring the air radioactivity in case of a nuclear fallout. From this spectroscopic technique we shall learn a lot more about the rain formation and scavenging mechanisms which are responsible for the attachment of <sup>214</sup>Pb to rain droplets in-cloud. Finally, our research provides a comprehensive characterization of the background radiation assessments relevant for radioprotection, earthquake predictions, cosmic rays research and anthropic radiation monitoring.</p>

Improvement of the detection limit by radon background reduction method

This paper describes a simple method to reduce the radon background component applied in environmental studies using gamma spectrometry. The radon component can be reduced by introducing either nitrogen gas or clean air into the detector chamber in order to create a positive pressure and further minimize radon intrusion from outside. This method shows that we can minimize the influence of radon daughter background such as 214Pb, 214Bi and 210Pb (from 238U), 212Pb, 212Bi and 208Tl (from 232Th). By the way, the detection limit of the gamma spectrometry is discussed.