Publications [#132887] of G. Allan Johnson

Papers Published
  1. F O'Foghludha, GA Johnson, Voltage waveform effects on output and penetration of W- and Mo-anode mammographic tubes., Physics in medicine and biology, ENGLAND, vol. 26 no. 2 (March, 1981), pp. 291-303 .

    Abstract:
    The output and half-value thickness (HVT) for arbitrary voltage waveforms can be calculated if the variation of both quantities with voltage is known under constant-potential (ripple-free) conditions. An apparatus to study this variation is described. It permits measurements of output and HVT with a Si(Li) spectrometer under conditions equivalent to constant-potential operation; it uses mechanical or electronic gating to limit observations to constant-potential operation; it uses mechanical or electronic gating to limit observations to short periods near the peaks of a sinusoidal waveform. For W anodes both HVT and output are found to follow simple power laws, while polynomial functions of voltage are needed for Mo anodes. Calculations based on these data agree well with experiments in which various ripples are simulated by altering the gating interval. For Mo anodes, the output increases as the ripple decreases, but the HVT changes very little. For W anodes both quantities decrease when the ripple increases. The implications in mammography are briefly discussed.