Thermochronology Laboratory
for Low Temperature (U-Th)/Helium Dating
Department of Neotectonics and Thermochronology
Institute of Rock Structure and Mechanics of the ASCR, v.v.i.

Rock samples of 1-2 kg are crushed, sieved and separated for specific density using our new facilities at the IRSM. We have a state of the art Retsch BB50 Jaw crusher, an automated Retsch AS200 sieving device and a Wilfley Shaking table to prepare our samples. Further density separation is done in our chemical lab by using heavy liquids such as Dimethylene Iodide and LST fastfloat (Sodium Heteropolytungstate).

Using our new Leica 8APS0 Binocular Microscope crystals are carefully selected from the mineral separates obtained in step 1 for analysis. Dimensions of each crystal are measured and recorded using the attached camera and PC system. Samples are packed in 1x1mm pure Pt or Nb envelopes and loaded into the Alphachron^TM.

In our new fully automated Alphachron^TM; gas extraction line the envelopes containing the sample crystals are heated to 900-1200°C using a high energy diode laser beam to release trapped Helium (α-particles from radioactive decay of U,Th and Sm) from the crystals. The Gas produced by this process is then analysed using the integrated Pfeiffer Quadrupol Mass Spectrometer to determine the naturally produced ⁴He concentration. This entire process is fully automated and controlled by the Alphachron PC.

After degassing, the samples are dissolved in nitric and hydrofluoric acid and spiked with standards containing known quantities of U and Th in our chemical laboratory. In addition to apatite dissolution facilities (fume hoods) we also have high pressure digestion vessels and a Memmert UN 160 oven for zircon digestion. Analysis of the parent isotopes ²³⁸U, ²³⁵U, ²³²Th and ¹⁴⁷Sm is conducted using a ThermoFisher Scientific ELEMENT 2 ICP-MS at our sister institute within the AVCR, the Institute of Geology.

The final step is to combine all results and calculate thermochronological ages using a standard radioactive decay equation and the obtained U/Th/Sm vs. He ratios.