The location (energy) of each peak indicates what is present and the height indicates how much!
A gamma-ray spectrum as it appears on the screen of a pulse-height analyzer. The gamma-ray peaks are marked with the name of the element whose radioactive isotope emits the gamma ray; two for cobalt and zinc and one for cesium.
There, on what looked like a small television screen, flashes of light appeared that gradually formed a curve with many peaks and valleys. After a few minutes the spectrometer was stopped and an electric typewriter automatically typed out rows and columns of numbers.
The chemist explained, “This curve, which you see on the screen, is a gamma-ray spectrum and tells us what elements are in the sample. The typed-out data give us an accurate measure of the shape of the curve on the screen. By measuring the gamma-rays’ energies we know what elements in the sample were made radioactive. The height of each gamma-ray peak tells us how much of that element is present in the sample.
“That gives us the information we need to calculate the concentrations of the small quantities of materials in our samples. We can do this because at the same time I irradiated a set of standards. Standards are materials that are just like the samples except that they contain known amounts of the impurities I am trying to measure.”
As the boys were leaving the laboratory, the chemist apologized for not having enough time to explain the activation analysis procedure more thoroughly, but he did give the boys a list of books to read on the subject of radioactivity and radioisotopes.[2] They thanked him for his help.
During the ride home, they discussed the paintings that were still unproven.
“It’s too bad that the method of activation analysis fingerprinting hasn’t been fully developed yet,” said Dad.
“Yes,” said Bill. “Then we could prove whether or not that last old painting was really by Aelbert Cuyp as the expert from the gallery believed. But what about those paintings that we found in the box that were not so old?”