222Rn detection at the microBq/m3 range in nitrogen gas and a new Rn purification technique for liquid nitrogen

Area of Science:

• Nuclear Physics
• Particle Physics
• Experimental Physics

Background:

• The Borexino solar neutrino experiment requires extremely low background radioactivity.
• Radon-222 (222Rn) is a significant radioactive contaminant in noble gases.
• Effective methods for radon removal and detection are crucial for sensitive experiments.

Purpose of the Study:

• To construct a concentration line for radon-222 (222Rn) from large volumes of nitrogen gas.
• To achieve ultra-low radon concentrations in nitrogen for sensitive detection.
• To report on radon removal from liquid nitrogen and subsequent measurements.

Main Methods:

• Utilized cryo-adsorption in a charcoal trap with very low intrinsic 226Ra contamination.
• Employed proportional counters for the detection of 222Rn.
• Investigated radon removal from liquid nitrogen via direct adsorption in the liquid phase.

Main Results:

• Successfully constructed a radon concentration line for nitrogen gas.
• Achieved a very low blank for activity from the daughter nuclide 222Rn.
• Demonstrated the capability to detect radon at concentrations below the microBq/m3 level in gaseous nitrogen.
• Reported 222Rn measurements on evaporated nitrogen, both with and without prior purification.

Conclusions:

• The developed cryo-adsorption method is highly effective for removing radon from nitrogen gas.
• The technique enables ultra-low level detection of radon, crucial for background reduction in experiments like Borexino.
• Direct adsorption in the liquid phase is a viable method for radon removal from liquid nitrogen.