Consumer radon monitor showed impossible 25-hour spike (peak 19,100 Bq/m³ / 516 pCi/L) in an empty closed house with a 56 Bq/m³ baseline sensor malfunction or real event?
Hi everyone, I’m posting here about a problem I’m experiencing with my radon monitor, and I’d like to know from you how likely it is that this is an instrument error rather than a real event.
Device: Forensics Detectors continuous radon monitor (semiconductor alpha sensor, 6-hour reading blocks), running continuously for about 3-4 weeks.
House: old stone house (1950s or older) in a small hilltop village in southern Italy. Geology is sedimentary flysch — not volcanic, not granitic, low uranium content. 80 cm thick stone/brick walls, ventilated crawl space under the ground floor, 3 floors. It’s a vacation home, empty most of the year. Important detail: the house is very humid (documented rising damp in one wall) and was fully closed during the event.
Baseline data (verified over 3 weeks):
• 14-day average with the house closed: 55-57 Bq/m³ (about 1.5 pCi/L)
• Daily averages while closed: 52-70 Bq/m³ (1.4-1.9 pCi/L)
• Historical maximum peaks while closed: 117-140 Bq/m³ (3.2-3.8 pCi/L)
• With windows open: 12-39 Bq/m³ (0.3-1.1 pCi/L)
The anomaly — house EMPTY and fully closed, nobody entered for days. Five consecutive 6-hour readings, then an instant return to baseline: • Jun 30, 15:59 → 5,154 Bq/m³ (139 pCi/L) • Jun 30, 21:59 → 14,203 Bq/m³ (384 pCi/L) • Jul 1, 03:59 → 4,870 Bq/m³ (132 pCi/L) • Jul 1, 09:59 → 4,859 Bq/m³ (131 pCi/L) • Jul 1, 15:59 → 3,578 Bq/m³ (97 pCi/L) • Jul 1, 21:59 → 47 Bq/m³ (1.3 pCi/L) ← back to baseline
The Accumulated Peak stored by the device is 19.1 kBq/m³ = 19,100 Bq/m³ (516 pCi/L). Total duration about 25 hours: sharp rise, plateau, sharp fall. The Total Count jumped from ~109 to 2,964, so the chamber physically registered roughly 2,600 pulses during the event — internally consistent with the displayed concentrations, so it doesn’t look like a pure display/software glitch. The cumulative session average is now “poisoned” at 430-530 Bq/m³ even though 83 of the 88 readings average about 60 Bq/m³.
My questions:
1. Has anyone seen this exact failure mode (multi-hour spike to thousands, spontaneous recovery) on Forensics Detectors or similar semiconductor-based consumer monitors?
2. Does the Total Count behavior (real pulses counted) fit the humidity/condensation failure hypothesis?
3. Is there any plausible physical mechanism for a REAL 25-hour radon excursion of this magnitude in sedimentary geology? No earthquake reported; I’m checking weather archives.
4. Planned next steps: outdoor test of the unit, session reset, and a 3-month CR-39 passive dosimeter as an independent referee. Anything else you’d do?
For what it’s worth, I was NOT in the house during the event (zero personal exposure), so this is about understanding the instrument and the house, not panic. Thanks!