Project number: P05/02
Final scientific report
Project Title: Purazot
LNGS Access period: February 2002 – October 2003
Group Leader: M. Wojcik: M. Smoluchowski Institute of Physics, Jagellonian University, Cracow (PL)
Researchers: M. Wojcik, G. Zuzel, M. Misiaszek: M. Smoluchowski Institute of Physics, Jagellonian University, Cracow (PL)
Delivered access (filled by TARI administration): 116 man-days
Final scientific report (filled by group leader):
The main goal of our project was to develop a system able to permanently supply ultra-low background detectors (gamma spectrometers, dark mater detectors etc.) with Rn222-free nitrogen gas at flow rate higher than 2 m3/d. In a standard way concentration of Rn222 (Rn) is reduced in detector chambers by flushing them with nitrogen from the pressurized gas cylinders or with nitrogen gas evaporated directly from the liquid phase (boil-off nitrogen). According to our tests in both cases Rn concentration in used gas is not negligible and varies from 0.5 up to 1.8 mBq/m3.
In our approach boil-off nitrogen is additionally purified on a charcoal trap cooled by the liquid phase from which is evaporated. This makes the system very compact, easy in use, and what is most important Rn concentration is reduced in the gas by almost two orders of magnitude. Sincs Rn has very strong infuence on the beckground of very sensitive detectors, we should observe improvement in background for a choosen HPGe spectrometr.
A special Rn trap to be mounted in a 100 l dewar containing liquid nitrogen was designed and build. As an adsorber about 390 cm3 of activated charcoal (Merck) was used. Evaporated nitrogen passes through the trap where Rn is stopped and next (after purification) is led to the detector chamber to be flushed. To accelerate nitrogen gas generation an electrical heater was placed on the bottom inside the Dewar. It gives a possibility to change the evaporation rate from 0.2 m3/h (minimum production rate – freely evaporated N2) up to 2.5 m3/h (at maximum heating power). The maximum amount of gaseous nitrogen our system can produce reaches 50 m3. The design of the trap allows production of nitrogen with two qualities: standard boil-off N2 and low-Rn N2 (purified boil-off N2).
Using Rn detection system installed at the Gran Sasso laboratory we could test Rn content in generated gas at different production rates before and after purification. Measurements were performed in 2002 and in 2003. Rn from about 40 m3 of N2 at flow rate of about 1 m3/h has been accumulated and measured applying the LNGS Rn monitoring system. Both qualities of produced gas have been tested. The achieved ultra-low Rn concentration in N2 is nearly in agreement with our expectation and it was equal to (12+-3) microBq/m3. It means our system reduces Rn content in N2 by a factor 40. We foresee even lower Rn concentration at a lower production rate (e.g. 0.5 m3/h). Final tests with HPGe detectors supplied with our low-Rn nitrogen gas were not performed because of the formal situation at the LNGS laboratory (restriction concerning using liquids, LN2 as well).
Publications (quote also planned or in preparation) (filled by group leader):
M. Wojcik, G. Zuzel, “Low-222Rn nitrogen gas generator for ultra-low background counting systems”, in preparation, to be submitted to Nucl. Instr. Meth. in Phys. Research for publication
Evaluation by USP (October 2003)
The aim of this project was to develop a system able to permanently supply ultra-low background detectors with Rn free nitrogen gas. Substantial aspects have been achieved on the purification technique. Publication to be submitted to NIM
LNGS Access period: February 2002 – October 2003
Group Leader: M. Wojcik: M. Smoluchowski Institute of Physics, Jagellonian University, Cracow (PL)
Researchers: M. Wojcik, G. Zuzel, M. Misiaszek: M. Smoluchowski Institute of Physics, Jagellonian University, Cracow (PL)
Delivered access (filled by TARI administration): 116 man-days
Final scientific report (filled by group leader):
The main goal of our project was to develop a system able to permanently supply ultra-low background detectors (gamma spectrometers, dark mater detectors etc.) with Rn222-free nitrogen gas at flow rate higher than 2 m3/d. In a standard way concentration of Rn222 (Rn) is reduced in detector chambers by flushing them with nitrogen from the pressurized gas cylinders or with nitrogen gas evaporated directly from the liquid phase (boil-off nitrogen). According to our tests in both cases Rn concentration in used gas is not negligible and varies from 0.5 up to 1.8 mBq/m3.
In our approach boil-off nitrogen is additionally purified on a charcoal trap cooled by the liquid phase from which is evaporated. This makes the system very compact, easy in use, and what is most important Rn concentration is reduced in the gas by almost two orders of magnitude. Sincs Rn has very strong infuence on the beckground of very sensitive detectors, we should observe improvement in background for a choosen HPGe spectrometr.
A special Rn trap to be mounted in a 100 l dewar containing liquid nitrogen was designed and build. As an adsorber about 390 cm3 of activated charcoal (Merck) was used. Evaporated nitrogen passes through the trap where Rn is stopped and next (after purification) is led to the detector chamber to be flushed. To accelerate nitrogen gas generation an electrical heater was placed on the bottom inside the Dewar. It gives a possibility to change the evaporation rate from 0.2 m3/h (minimum production rate – freely evaporated N2) up to 2.5 m3/h (at maximum heating power). The maximum amount of gaseous nitrogen our system can produce reaches 50 m3. The design of the trap allows production of nitrogen with two qualities: standard boil-off N2 and low-Rn N2 (purified boil-off N2).
Using Rn detection system installed at the Gran Sasso laboratory we could test Rn content in generated gas at different production rates before and after purification. Measurements were performed in 2002 and in 2003. Rn from about 40 m3 of N2 at flow rate of about 1 m3/h has been accumulated and measured applying the LNGS Rn monitoring system. Both qualities of produced gas have been tested. The achieved ultra-low Rn concentration in N2 is nearly in agreement with our expectation and it was equal to (12+-3) microBq/m3. It means our system reduces Rn content in N2 by a factor 40. We foresee even lower Rn concentration at a lower production rate (e.g. 0.5 m3/h). Final tests with HPGe detectors supplied with our low-Rn nitrogen gas were not performed because of the formal situation at the LNGS laboratory (restriction concerning using liquids, LN2 as well).
Publications (quote also planned or in preparation) (filled by group leader):
M. Wojcik, G. Zuzel, “Low-222Rn nitrogen gas generator for ultra-low background counting systems”, in preparation, to be submitted to Nucl. Instr. Meth. in Phys. Research for publication
Evaluation by USP (October 2003)
The aim of this project was to develop a system able to permanently supply ultra-low background detectors with Rn free nitrogen gas. Substantial aspects have been achieved on the purification technique. Publication to be submitted to NIM