Along with colleague Bruce Rude, Felicia is working on an analytical technique to scan inside beamline vacuum chambers. This process, called a Residual Gas Analysis (RGA) scan, detects the presence of unwanted gases, which could disrupt a beam of x rays as it travels down a beamline to an experiment. Even a minute amount of gas can coat and distort the specialized optics required to guide x rays down a beamline, so the gas must be detected, analyzed, and removed before a beamline can be used.Below is the result of an RGA scan on Beamline 7.3 at the ALS (you can take a virtual tour of this beamline), and some possible contaminating compounds. Take a look at the peaks of the spectrum below, and see if the Atomic Mass Units (AMU) match up to any of the possible contaminants. Also, can you guess how some of the contaminants got into the chamber?
Symbol Mass (AMU) Possible Compounds ------------------------------------------------------------- Hydrogen H 1 HO, H20 Carbon C 12 C, CH, CH2, CH3, CO2, etc. Nitrogen N 14 N, N2, NH, NH2, etc. Oxygen O 16 O2, Argon Ar 40 ArExample: Take a look at the peak at 15 AMU, and figure out what compounds could be present.
CH3 = 1(C=12) + 3(H=1) = 12+3 = 15 AMU, and
NH = 1(N=14) + 1(H=1) = 14+1 = 15 AMU
So either or both of these compounds could be contaminating the vacuum chamber. Try to figure out what contaminants may be causing the peaks at 16 AMU and 28 AMU.This month's winner was Yevgenya Shevtsov of Los Angeles, California. We also received correct answers from several other readers, but Yevgenya answered first. Congratulations, Yevgenya!