The 1.2 metre cyclotron of Shanghai Institute of Nuclear Research has been used as a high energy mass spectrometer for measurment of

3

H content in water sample collected from Mount Yuquan in the suburbs of Beijing.

The

3

H content was obtained by comparison with a sample containing known

3

H concentration. These two samples were concentrated electrolytically by a factor of several hundred. A blank sample containing no

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H was used to subtract the triton background due to the cyclotron interior contamination.

Three samples were alternatively introduced into the ion source in the form of gas. The

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H ions were identified and counted by a silicon detector telescope with a 100

µ

m Al foil inserted between the dE/dX and E detector. The cyclotron output was monitored by integrating the

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He counts in the dE/dX detector during the collection of

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H events in the E detector.

Our experimental results is in good agreement with the value obtained by beta-decay measurement done at Atomic Energy Institute in Beijing.