Spectrometers

A CMMS spectrometer is a magnet (or magnets) plus an array of counters to detect incoming muons and decay positrons. The magnets are of various types - Helmholtz, solenoid, or solid pole electromagnet; superconducting or not. In fact, most spectrometers have more than one magnet. The main magnet of an apparatus is usually oriented so the field is along the beam axis (z direction) which allows surface muons to enter the sample without being turned away. Other coils provide weaker fields in perpendicular directions either for zeroing the field or for applying weak fields (<10 mT) transverse (x,y directions) to the beam direction. Most of the counter systems are movable in various ways, and many follow a uniform standard design of multi-counter modules mounted on tracks on tables attached to the spectrometer. Some counter arrangements are partially built into the sample inserts. These are the low background apparatuses for small or thin samples which have veto counters to reject counts from anything but the sample itself. All apparatuses rest, and roll, on standardized rails so they can be reproducibly positioned in any beamline. They can be rolled back from the beam snout (to access collimators etc) at any time and accurately rolled back into position by one person. The four beam lines, M15, M20, M9B and M13 which are used for µSR have such rail systems. enter the text here