A constant contact side bearing assembly for a railcar including a housing with wall structure defining a central axis for the side bearing assembly and a multipiece cap. And, there are upper and lower horizontal plates set between the first and second slant faces so as keep LED modules properly spaced. The average particle diameter of Sendust is in the range of 30 to 100 \u03bcm. A transfer mechanism is disposed below the vacuum lock chamber to receive the measured dose of source material from the lower dose cup and to transfer the source material to a downstream deposition head while isolating the deposition conditions and sublimated source material within the deposition head. The second portion of the fluorescence X-rays released by the at least one aperture have known directional information based on a position of the collimator.