Military roentgenology / War Department.

Date:
[1944]
Catalogue details

Licence: Public Domain Mark

Credit: Military roentgenology / War Department. Source: Wellcome Collection.

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    therefore a more accurate calibration. To adjust the ‘supply voltage for Item No. 96215 a line voltage __ compensator is provided on the side of the control ree! unit. The knob “G” on the control is set to zero nan and the main switch “A” is set on high (as indi- ACTUAL FOCAL | i cated by the red dot). The switch ‘‘B”’ is placed in SPOT | the radiographic position and knob “C” set on ee button ‘3.’ With a key or coin the line adjuster is regulated until the voltmeter “‘D” reads in the red area on the scale. The unit will then be calibrated 5 Bige PIN POINT DIAPHRAGM for line conditions. i nM (.5MM. IN DIAMETER ) 85. DIMENSIONS OF EFFECTIVE FOCAL SPOT. nM A simple method to determine the dimensions of the effective focal spot is to use a lead diaphragm having 20 CMS. Ht a 0.5 mm opening beneath the portal of the X-ray I tube, and at one-third the distance between it and a dental film, figure 67. An exposure is made at 60 kvp for 40 ma-secs at 30 cm. An image of the PENUMBRA focal spot will appear on the film. Using calipers, measure across the area of uniform density, ignoring the peripheral lesser densities produced by penumbra. 5 With this measurement apply the followmg formula: ASS e FILM SHEET LEAD \\ \\ \\ PROJECTED FOCAL SPOT \\ 3 ; (Measuring effective focal spot) PENUMBRA projected dimension 3 x aperture dimension 2 2 Figure 67. Measuring focal spot. = effective focal spot dimension. FILM (IN CARDBOARD HOLDER) WHITE PAPER PRIMARY BEAM FOCAL SPOT TUBE HOUSING DISTANCE OF FOCAL SPOT a b BENEATH PORTAL OF EXIT FROM TUBE Figure 68(a) and (b). Determination of focal spot level.
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