Spectrometer ROM scanning versus Step/Count Scanning
Note also the checkbox to utilize a “ROM” based spectrometer scan instead of the default step/count method for wavescans. The ROM scan option is only available on certain instruments, normally the JEOL 8900/8200/8500 and 8230 and 8530 and Cameca SX100/SXFive instruments. The difference is that a ROM spectrometer scan smoothly scrolls the spectrometer Bragg angle while counting x-rays as opposed to the normal wavescan which uses a defined spectrometer step size and count time interval method.
The ROM scan is more efficient at short count times due to low speed limitations, while the step/count method is more accurate because the spectrometer position is not “calculated” based on motor speed and also more sensitive because count time per step is not limited.
SX100 note: Be aware that because the Cameca ROM scan intensity digitization is limited to 18 bits of x-ray count data, very slow scans at high beam currents on pure samples may produce numerical intensity “wrapping” effects when the counters overflow (above 262144 counts) at the peak position intensity. The solution is to increase the scan speed, reduce the count time per point, decrease the beam current or use the step/count method for peakscan or wavescan acquisition.