ENVIRO Station Aerosol
A walk-in measuring cabin that manages two months without a visit: a fresh filter every day from a magazine of sixty, with alpha, beta and gamma spectrometry at the filter.
A station that looks after itself
The building is part of the instrument. The electronics never see the weather — outside −30 to +50 °C, inside a controlled 5 to 35 °C.
- Cabin
- ISO 10′ · 2991 × 2438 × 2591 mm
- Mass
- about 2.6 t
- Flow
- 6.0 m³/h nominal
- Service interval
- 60 days
Five stages between outside air and result
Intake head
Omnidirectional, with louvres and heated so that icing cannot close it.
Sample line
Heated above the dew point, with a condensate separator at the lowest point.
Filter
Round filter of 47 mm diameter from the magazine, with an NFC chip.
Blower
Controlled; holds 6.0 m³/h even when the filter begins to clog.
Gas meter
Volume referred to 0 °C and 1013 hPa, collection efficiency 0.99.
Alpha and beta at the filter
PIPS detector with 1700 mm², 55 keV alpha and 30 keV beta, separated spectrally.
Gamma spectrometry
Scintillator or germanium in a lead chamber with 50 mm wall thickness, all round, lined with copper and tin.
Activity concentration
Per nuclide in Bq/m³, with uncertainty, decision threshold and detection limit to ISO 11929.
Both detectors sit at the filter, not behind it. Alpha and beta are counted while the air keeps flowing; the gamma detector looks out of the lead chamber at the same filter. All three results therefore belong to the same sample and the same time slice.
Fig. 1 — Measuring cabinet inside the cabin. Screen at eye level, keyboard drawer beneath it.
Fig. 2 — Design view of the cabinet. Filter magazine in the drawer, detectors in the base.
Radon sets the real limit
It is not the counting statistics that limit the station, but the natural background. Iodine-131 emits at 364.489 keV, the strongest radon line — lead-214 — at 351.932 keV. On a sodium iodide detector both arrive as one peak, and that peak consists predominantly of radon.
Fig. 3 — Separation of the two lines at three resolutions, schematic. Each curve referred to its own maximum.
| Compensation route | How it works | Robustness |
|---|---|---|
| Trapezoid method | Two empirical side windows | weak at the edge of the evaluation window |
| Reference to bismuth-214 | A different nuclide as the reference | the equilibrium drifts |
| Lead-214 at 295.2 keV | The same nuclide, fixed ratio 1.933 | invariant in time |
We take the third route. Both lines come from lead-214, so their intensity ratio cannot drift — it is a constant of the decay scheme and not a calibration.
One station, two detectors
The cabin and the air path are the same in both versions. Alpha and beta likewise: the same silicon detector with 1700 mm², the same component as in the ENVIRO GO.
Scintillator
- NaI(Tl) 3″ × 3″ with photomultiplier
- Resolution about 7 % at 662 keV
- No cooling, ready to measure at once
- Library of 10 to 15 nuclides
- Lower connected load, simpler maintenance
High-purity germanium
- Coaxial HPGe, 50 % relative efficiency
- 1.90 keV at 1.33 MeV
- Electric cooler, no liquid nitrogen
- Library of more than 50 nuclides
- Separates lines that a scintillator draws together
What the station can still detect
To ISO 11929 at 95 %, at 6.0 m³/h and a radon level of 40 Bq/m³.
| Nuclide | S · 1 h | G · 1 h | S · 24 h | G · 24 h |
|---|---|---|---|---|
| Cs-137 | 0.50 Bq/m³ | 0.10 Bq/m³ | 25 mBq/m³ | 5.0 mBq/m³ |
| Cs-134 | 0.44 Bq/m³ | 0.085 Bq/m³ | 22 mBq/m³ | 4.2 mBq/m³ |
| I-131 · at the filter | 0.48 Bq/m³ | 0.092 Bq/m³ | 24 mBq/m³ | 4.6 mBq/m³ |
| Co-60 | 0.52 Bq/m³ | 0.11 Bq/m³ | 26 mBq/m³ | 5.3 mBq/m³ |
| Total alpha | 0.40 Bq/m³ | 0.40 Bq/m³ | 20 mBq/m³ | 20 mBq/m³ |
| Total beta | 0.60 Bq/m³ | 0.60 Bq/m³ | 30 mBq/m³ | 30 mBq/m³ |
Alpha and beta are the same in both versions. I-131 here means the particle-bound fraction on the filter — for gaseous iodine there is the Station Iodine. The figures lie deliberately within the range that comparable stations show in the field, and nowhere beyond the best published value.
The cycle buys time, integration buys sensitivity
| Cycle | Cs-137, one window | What it is good for |
|---|---|---|
| 2 minutes | 3 to 15 Bq/m³ | Plant status and early warning |
| 5 minutes | 1.7 to 6 Bq/m³ | Plume tracking during an event |
| 10 minutes | 1.2 to 3 Bq/m³ | the standard value for reporting |
| 1 hour | 0.50 Bq/m³ · design value | nested window, always carried along |
| 24 hours | 25 mBq/m³ · design value | Monitoring limit |
Cycle and integration are decoupled: every report carries the nested windows over 10 minutes, 1 hour and 24 hours with it. A short cycle therefore buys response time, not sensitivity. The ranges cover the two Poisson regimes, 1/t and 1/√t; the version with germanium improves every limit by roughly a factor of five.
The factor of two comes from sampling and counting running at the same time: the filter only fills up during the measurement, so the mean activity on it is half the final value.
Desert heat, alpine winter
The cabin is the housing of the instrument. A split unit on the roof and an electric reheater hold 5 to 35 °C inside while −30 to +50 °C prevail outside. The intake head is heated so that icing cannot close it; the sample line stays above the dew point so that nothing condenses out.
The version with germanium is the reason why the cabin air has to stay below 40 °C: the cooler is specified for a 40 °C ambient, not for the 55 °C that the electronics tolerate.
- Outside
- −30 to +50 °C
- Inside, controlled
- 5 to 35 °C
- Foundation
- Concrete slab
Fig. 4 — The same cabin, two climate zones. Design view.
Who gets in, and who hears about it
| Area | How it is solved | What is reported |
|---|---|---|
| Door | Steel, three-point locking, mechanical key as fallback | State in the header of every screen |
| Access | RFID card and PIN at the door, role-based | every entry in the audit log |
| Door contact | Monitored reed contact with tamper line | DOOR OPEN in the message stream |
| Intervention | Tamper contacts on the cabinet front and the roof hatch | Alarm, remote within one minute |
| Climate control | An open door suspends the air conditioning | Notice if open longer than set |
An unattended station is only as good as its door. Every opening carries a card identifier and a time stamp; an opening outside an announced maintenance visit raises an alarm. The components are at design stage and not yet selected.
One screen, four questions answered
Is it working correctly right now? What is in the air? What happened while I was away? What do I have to do next?
On the left, position, days remaining and the four-step change assistant. On the right the station reports on itself: every delivery to EURDEP, IRIX and N42.42 with a time stamp, together with the backfill status after an interruption.
Fig. 5 to 9 — Screenshots from the station software. Operating language English, values are examples, not measurements.
Half an hour every two months
| Task | Interval | Duration |
|---|---|---|
| Exchange the filter magazine | every 60 days | 20 minutes |
| Check source and energy calibration | automatic, daily | none |
| Flow calibration against a standard | annually | 1 hour |
| Efficiency calibration on site | annually | 2 hours |
| Maintenance of the air conditioning | annually | 1 hour |
The daily check source measurement runs without anyone present. If it drifts out of its window, the station says so in the same message stream as the measured values — the problem reaches you before the data go wrong.
What sets the versions apart
| Parameter | Station A — S | Station A — G |
|---|---|---|
| Gamma detector | NaI(Tl) 3″ × 3″, PMT | HPGe, 50 % relative efficiency |
| Energy resolution | about 7 % at 662 keV | 1.90 keV at 1.33 MeV |
| Cooling | none | electric cooler |
| Ready to measure | at once | after 5 to 8 h cool-down time |
| Nuclide library | 10 to 15 nuclides | more than 50 nuclides |
| Connected load | about 0.9 kVA | about 1.6 kVA |
| Mass, ready for operation | about 2.6 t | about 2.6 t |
What both share
controlled 3 to 12 m³/h
55 keV alpha, 30 keV beta
Magazine for 60, 60 days
Precipitation and wind, on the roof
Lining of copper and tin
Collection efficiency 0.99
external UPS recommended
5 to 35 °C inside, controlled
2991 × 2438 × 2591 mm
Control areas from 20 mm
N42.42, EURDEP, IRIX, Modbus TCP
Ring buffer at least 3 years
Detector figures come from the data sheets of the component manufacturers. All other figures are design values.
What comes with it and what can be added
Included
- Cabin with cabinet, fully wired
- Intake head, mast and sample line
- Air conditioning and heating
- Weather station on the roof
- Filter magazine with 60 filters
- Factory calibration certificate
- Efficiency calibration on site
- Interface description and test client
On request
- Germanium detector, version G
- Intake head for PM2.5
- External uninterruptible power supply, recommended
- Cellular router
- Spare filter magazines
- Stack probe to ISO 2889
The cabin exists; the measuring chain inside it has not yet passed a type test. Cabins of this design have been built and can be seen in the photographs. Every performance figure on this page is a design value or an experience value from comparable systems; detector figures come from the data sheets of the component manufacturers.
On the standards we write “design to follow” — IEC 60761-1 and -2, ISO 2889 and ISO 11929. “Tested to” appears only where the type test has been passed. As an aerosol monitor this station falls under IEC 60761-2; iodine measurement to -4 is the business of the Station Iodine. CE marking to EN 61326 and EN 61010 through an external test house.
Aerosol or iodine — which question are you asking?
If gaseous iodine is your question, the Station Iodine answers it: a prefilter, a cartridge changer and radon subtraction are its entire design. This station stays what it is — the complete particle chain, with nothing bolted on.
