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Percentage Deadtime Losses Percent Level Corrections Apply to All Measurements Deadtime Correction, % 10 9 8 7 6 5 4 3 2 1 0 At 1 μsec, 1% correction at 10Kcps, 5% at 50Kcps Deadtime Correction, Percentage At 2 μsec, 2% correction at 10Kcps, 10% at 50Kcps 6.00E-06 5.00E-06 4.00E-06 2.00E-06 1.00E-06 0 10000 20000 30000 40000 50000 Input Counts per second ~1.25 μsec UO EPMA Workshop 2008
Deadtime Relations Calculation of Deadtime Constant N = N i m [1− τ = m m τ ) N (1- N = c(1- Nmτ ) (Ν Ν m m / i ) / c] • N = true count rate, N m = measured count rate with deadtime losses (N m < N), and τ is the deadtime constant, which ranges from 1 to several μsec for WDS counting systems. It is necessary to know N m and N to calculate τ. We assume the proportionality of N to the probe current i is constant. This may not be true at low count rates. • N m / i = measured count rate in counts per second per nA, and c is the constant N / i Form: y = mx +b (N m / i) is y, x is N m , y-intercept b is constant c (= N / i). • Equivalent to τ = (1 – y / b) / x Measure x-ray intensity at increasing probe current Use count rate N m and N m / i to evaluate the deadtime constant τ over a range of intensity values UO EPMA Workshop 2008
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Page 9 and 10: Calibration of PHA Using Bias vs. l
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Page 13 and 14: Carbon Kα PHA Scans Graphite, Fe3C
Page 15 and 16: WDS Deadtime Issues in EPMA • Dea
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Page 21 and 22: Verification of Probe Current vs. A
Page 23 and 24: Deadtime Variation with Count Rate
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