An open beam x-ray diffraction system and method are provided including modular x-ray heads for being detachably connected to a base unit having a common drive assembly that shifts the heads in an arcuate path during an x-ray diffraction measurement operation. Preferably, the resonator body is conical or a stepped cylinder. A 110-v, 20-w bulb 6 is putting on the bulb socket 5 inside of the heating tube 9. Switching noise within a desired passband can be reduced by switching at a rate that is greater than the desired passband. Such a resin composition improves stability of the polyacetal resin and inhibits formaldehyde emission.