The RAD7 is able to measure both radon (222-Rn) and thoron (220-Rn) concentrations simultaneously and independently. The standard radon calibration is performed with a precision of better than 1% and we guarantee the RAD7 absolute accuracy for radon to be better than 5%. However thoron has a very short half life (about one minute) so that the concentration in the air will change during sample acquisition. For every minute the sample gas is in transit from the sampling point to the measurement chamber, the concentration of thoron in the sample will drop by half.

The RAD7 manual describes the standard setup for thoron sniffing. It is designed to minimize the transition time of the air sample from sampling point to measurement chamber. The pump runs continuously and the desiccant is in a small tube. In those conditions, the acquisition time is about one minute, so the default thoron sensitivity of the RAD7 is set at half the radon sniffing sensitivity. This setting is sufficient for most applications.

Occasionally a user requires more accurate thoron readings. For these applications DURRIDGE Company can provide, as an option, a specific thoron calibration for the setup used by the user. The detailed conditions of the calibration, including the air flow rate, may be chosen by the user and are clearly specified in the thoron calibration certificate issued by DURRIDGE. For any other setup, with a different flow rate or a different volume in the sample air path, that thoron calibration is no longer valid. For some projects, DURRIDGE Company has provided multiple thoron calibrations, each for a different setup of the RAD7 and air sample acquisition path.

The cost of the RAD7 Thoron Calibration Service is US $183 / GBP £143 / EUR €160.

RAD7 Thoron Calibration Service

$183.00Add to order

Shipping Information

1. You can send us your RAD7 at any time to either one of our Calibration facilities (USA and UK), listed below (see important, specific instructions for each below).

2. We need the RAD7 in house for 10 days, so the total time a RAD7 will be away from your facility will be 10 days plus the time the RAD7 spends in transit. If additional service or repair is required, this may delay the return of the instrument.

3. When sending your RAD7, please send the instrument only, without the cables and accessories. Pack the instrument upright in a box with one-inch (2.2cm) padding all around. A 14x14x14in (or 36x36x36cm) box is suitable. Pack the box well, and seal it carefully. Please include your contact info with the package.

4. International customers must be very careful, to avoid substantial extra shipping charges and delays, both for shipping to the nearest calibration facility, and for its subsequent return.

5. Commercial Invoice check-list:

  • For your courier or freight forwarder, you will need to provide a Commercial Invoice.
  • Please write only in English on the commercial invoice.
  • Please use the following description for RAD7: "Used RAD7 Electronic Radon Detector".
  • Insured value US$2,490.
  • Please state on the invoice that the instrument is MADE IN USA and that it is being "returned to the manufacturer temporarily for repair and recalibration".
  • Please use the HS (Commodity) code 9030.10.00.
  • Please mark the box with the serial number of the RAD7 (as the RMA – Return Merchandise Authorization).
  • Please add the phone number of the Calibration facility you choose, in case the Customs Office wants to call us.
  • Next, you must ensure that your courier (i.e. UPS, FedEX) or freight forwarder will deliver the package to our door. The formal "INCOTERM" for this is "DDP", which means "Delivered Duty Paid."
  • We will not pay or be responsible for USA or UK import duties, or Customs clearance charges. Your shipper must be told this when you arrange your shipment.
  • It is important to make sure you prepare all the documentation you need to reimport the goods back into your country without being charged.
  • For the Return to you: unless you instruct us otherwise, we will return your RAD7 via the same shipping method you used to deliver it to us, Freight Collect. DURRIDGE can pay for the return shipment CPT ("Carriage Paid To") to you, but our cost will be invoiced to you before shipment.

If we can help further, please email us at

Specific info for SHIPPING TO OUR USA FACILITY (from outside the USA)

DURRIDGE Company, Inc.
524 Boston Road
Billerica, MA 01821-2812, USA
Phone: +1 (978) 667-9556
Fax: +1 (978) 667-9557

Declaration Form

  • There needs to be documentation proving that the instrument was previously imported into your country, otherwise you may be charged import duties when the instrument is returned to your country.
  • Please fill out the declaration form provided below. Attach the completed declaration form to the commercial invoice. If the invoice is scanned and submitted electronically, please scan the declaration form and submit it electronically as well.
  • Foreign Shippers Declaration of US Goods Returned (PDF)

    Specific info for SHIPPING TO OUR UK FACILITY

    DURRIDGE UK Ltd.
    Sheffield Technology Park
    Cooper Buildings
    Arundel Street
    Sheffield S1 2NS, UK
    Phone: +44 (0)114 221 2003

    For Customers inside the EU:
    No special paperwork is required for shipping within the EU Customs Union.

    For Customers Outside the EU:
    Our UK office has a special authorisation from the UK tax authority (HMRC) to “import RAD7s temporarily for calibration and repair”, without them being assessed for UK import duty. So when sending your RAD7 to our UK office, please state on the commercial invoice that the instrument is being imported using our Inward Processing Authorisation reference IP/0920/142/18. Please also include our EORI number GB219670885000 and the Customs Procedure Code (CPC) 5100001 on the commercial invoice. Failure to do so may result in import duty being charged, for which you will be responsible.

    Related Article

    Technical Note: Thoron Calibration (HTML)