Radon monitor logs at SuperK

Plot from the handwritten logs

Two identical electronic radon monitors (made by Sun Nuclear Corp.) are set up inside the SuperK system. The locations are:

inside the water purification hallway (outside the SK dome).
inside the SuperK dome, near electronics hut 3.

One of the regular shift duties is to check these monitors and write down the current reading into a logbook, along with date and time.

inside the SuperK dome vs. water system

Here is the resulting plot of the entries from January 1, 1997, until August 20, 1997:

Obviously, there is a strong seasonal variation, i.e. whether the outside temperature is higher or lower than the relatively constant temperature inside the tunnel system.

Also, the red curve shows that the system in the radon hut is indeed keeping the radon level inside the dome lower than outside. The periods with rising levels indicate that the system was turned off once in a while for several days - and thus radon-rich air sneaked into the dome through the entrance doors.

Here is a zoomed plot for the 3-month observation period from June 20 until August 20, 1997 with additional information:

The blue curve (o) is from the monitor at the water system.
The red curve (*) from the monitor at hut 3 inside the SuperK dome.
The green curve(+) from a third monitor inside the air intake chamber of the radon hut (i.e. the air that was pushed through the tunnel pipe in bypass mode). [Unfortunately, there's no data available from this monitor for the times before July 23, 1997].
Power on and off periods of the system in the radon hut (bypass or filter-without regeneration mode).

Clearly, as soon as the system in the radon hut is turned off the radon concentration is rising at a rate of about 150-200 Bq/m^3 per day (37 Bq/m^3 = 1 pCi/l). When the system is turned back on again, the concentration then seems to go down by approx. 200-300 Bq/m^3 until about reaching a similar (but somewhat higher) level than at the fresh air intake of the radon hut. There also seems to be a noticeable response delay of about 24 hours in either direction.

Alternative monitors at SuperK (from our Japanese colleagues)

Alternatively, our Japanese colleagues have installed a bunch of more radon monitors. I didn't have the chance to check them out while I was in the mine, though. So, I can't tell how comparable the results are. Obviously, they only agree in part with the logs electronic monitors mentioned above.

Here are the plots of the 3 sensors of interest for us:

SK Dome air: This is supposedly setup near the center hut inside the dome.
Duct air: Air sampled at the outlet end of the air duct right above the SuperK dome entrance. So, this is the air that directly came from the system in the radon hut. [This monitor was not installed before January 1997].
Mine air: Supposedly setup in the water system area, at the very end of the hallway (with very low airflow from the rest of the tunnel system).

1996 data (mid May until December 31, 1996):

1997 data (January 1 until August 30, 1996):

HGB, 9/05/97