system
Given the following post, respond as if you're commenting on Reddit:
human
In order to calculate relative atomic mass the masses of isotopes have to be taken into account. How did the scientists know (initially) what is the abundance of those isotopes?

Is it fixed (in an ore) or did they have to use some other method?
gpt
You use a mass spectrometer. The basic idea is that you use heat or a high voltage to strip one electron away from atoms, then you use an electric field or changing magnetic field to shoot the positively charged atoms (now ions) down a track. The track is curved, and at the end there is a detector that can tell you when an ion hits it. To make the corner and hit the detector, you have to bend the path the ion takes. You do this with an electric or magnetic field that crosses the track. The amount of bending depends on the strength of the field, which you control, the charge of the ion, which is +1, and the mass of the isotope. You do the math and vary the field to give the right bending for a specific isotope mass to hit the detector and count how many hits you get. Then change the field to give the right bending for a different isotope and count the hits. The ratios of hits for all your tests is the ratio of isotopes.
Same concept but different construction can be with one field and multiple detectors set up at different angles off the sriaight track.