The Natural Rock Sample system consists of a 21oz (600g) sample of granite gravel from a stone quarry, normally sold by the truckload as construction material. It is enclosed in a container that, by closing two ball valves, may be completely sealed.

Granite, in general, contains trace amounts of both uranium and thorium that has been in the rock since it was formed, millions if not billions of years ago. Therefore all the progeny of both the uranium and thorium decay chains are fully supported and in full equilibrium down to 226-Ra and 224-Ra.

The rock sample is dry and therefore constitutes a rock-steady emitter of both radon and thoron. It is possible to take advantage of that property to check the performance of a RAD7.

The device, as it stands, can provide a means for monitoring long-term changes in both radon and thoron sensitivity. After calibration at DURRIDGE Company, and with the optional Thoron Calibration Check Kit (sold separately), the device can be used for low-precision checking of both the RAD7’s radon sensitivity (monthly) and its thoron sensitivity (any time). A copy of the Durridge-issued Natural Rock Sample Calibration Form can be previewed here (PDF).

Natural Rock Sample Physical Specifications
Shipping Dimensions16″ x 8″ x 8″ (41 cm x 20 cm x 20 cm)
Shipping Weight5 pounds (2.3 kg)

$400.00Add to order

Natural Rock Sample Thoron Calibration

The Natural Rock Sample System comes already calibrated for radon. Thoron calibration is also offered as an option. Thoron calibration may be performed when the Natural Rock Sample System is purchased, or at any time thereafter.

$227.00Add to order

Thoron Calibration Check Kit

Check the thoron calibration of the RAD7 using the components in the Thoron Calibration Kit. The Thoron Calibration Check Kit consists of a Pump, Power Adaptors, Laboratory Drying Unit, Needle Valve, Custom Flow Meter, Tubing Set, and Carrying Case. (See photo and components diagram.) The Thoron Calibration Check Kit requires the Natural Rock Sample, which is not included.

$665.00Add to order

DURRIDGE Natural Rock Sample
DURRIDGE Natural Rock Sample



Thoron Calibration Check Kit for Natural Rock Sample
Thoron Calibration Check Kit for Natural Rock Sample (sold separately)