Measurement of the French national tritiated-water standard by helium-3 mass spectrometry

• A solution was prepared by gravimetric dilution of a tritiated water primary standard.
• The solution was measured by 3He mass spectrometry and liquid scintillation counting.
• Both methods give consistent results within their standard uncertainties.
• All results are consistent with the calculated value of the solution.

The 3He ingrowth technique is based on the detection of the tritium radioactive daughter, 3He, by mass spectrometry. Over the last three decades it has been used extensively in oceanography and groundwater studies for measurements of very low to ultra-low levels of tritium. To compare it with the best available methods of radioactive counting, we applied this method to measure the massic activity of a tritiated-water primary standard prepared by the French Laboratoire National Henri Becquerel (LNHB). One liter of a low-level tritium solution was prepared from a small aliquot of the LNHB standard by two-step gravimetric dilution with tritium-free groundwater. Sixteen samples of this solution were analyzed at the LSCE-Saclay noble gas facility, using the 3He ingrowth method. The massic activity of the prepared solution was also measured by Liquid Scintillation Counting using the Quantulus LNHB counter and an internal calibration method with the LNHB tritiated water standard. All results agree within their standard uncertainty.