Development of an electrolysis system for tritium enrichment in superficial water samples.
Tritium present in the environment gradually decreased in the last decades and nowadays it has reached extremely low activity concentrations. The purpose of the present work is the implementation of a tritium enrichment system in water samples using electrolytic techniques and pure nickel and iron electrodes. In the present work a mean tritium enrichment factor of 13.0 +/- 3.2 was obtained. This result should allow to reach a minimum detectable activity of tritium in water samples of about 1 tritium unit (TU) or less. The present enrichment system necessitates further adjustments and improvements, such as a cooling system in order to reduce the tritium losses due to evaporation.
Electrolytic enrichment of tritium with Fe-Ni and Ni-Ni electrodes and estimation of tritium enrichment factor using Fe-Ni electrodes
The electrolytic separation factors of tritium, (T/H)water/(T/H)hydrogen, and the relationship between the tritium enrichment factor, Tf/Ti, and the final volume of water have been evaluated for Fe-Ni and Ni-Ni electrodes. The tritium separation factor for the Fe-Ni electrodes (25.9 ± 3.4) is systematically higher than that with the Ni-Ni electrodes (14.4 ± 4.4) when the electrolysis is conducted under similar conditions. The tritium separation factor with the Fe-Ni electrodes obtained in this study is similar to that obtained in previous studies. Chemically impure mild steel used in this study as a cathode material gives a high tritium separation factor as well as pure iron employed in previous studies. The tritium enrichment factor with the Ni-Ni electrodes shows a wide variation at a given final volume, depending upon the tritium separation factor. On the contrary, the tritium enrichment factor obtained with the Fe-Ni electrodes changes as a function of the final volume. When tritium in the sample is enriched 20–25 times with the Fe-Ni electrodes, a reliable tritium enrichment factor can be obtained directly from the final volume with an accuracy of ±3.5% (2σ) without measuring the deuterium or simultaneous electrolysis of a tritiated reference water.
IMPROVEMENT IN ENRICHMENT PROCEDURE FOR ANALYSIS OF TRITIUM IN NATURAL WATER. II.
天然水中のトリチウムの測定にさいして電解におけるトリチウムの分離係数 (β) を求めることが必要となるが, 多くの電極においてβは定数にならない。われわれは数種類の電極についてβを測定したところ100ml程度の試料の濃縮においてニッケル電極を用いるとβが非常に安定であることを見出した。この電極を用いれば重水素の分離係数 (α) を求めることなく, 水の容量の減少からただちにトリチウムの濃縮率を求めることができる。なお, この方法より求めた濃縮率の誤差は6%以下であった。10T.U.以下と推定される試料の濃縮に用いる大型電解槽についてはstlundの関係式を用いてαよりβを求めこれよりトリチウムの濃縮率を求めた。この方法により求められる濃縮率の誤差は10%以下であった。