RE: Rns28 Aug 2024 14:33
LLL
In the determination of the helium isotope ratio, achieving accurate results is primarily constrained by the 3He+ signal value. During the measurement, gas impurities are ionized by the ion source, generating charged ions with the same mass-to-charge ratio as the target ion. These ions will interfere with the measurement. The ion interfering with 3He+ is HD+, and that interfering with 4He+ is 12C3+. Typically, the resolution of a small mass spectrometer is too low to distinguish 3He+ and 4He+ from their corresponding interfering ions; only a large magnetic mass spectrometer can do this and thus accurately measure the helium isotope ratio. In the field, the measured 4He concentration is usually used to represent the total helium concentration due to the low resolution of portable instruments.
I guess they only have a small, portable, mass spectrometer in the field.