GAS-FILLED DETECTOR Radiation DetectorsAs detector voltage is increased, the electric field has more influence upon electrons produced.Sufficient voltage causes a cascade effect that releases more electrons from the cathode. Forceson the electron are greater, and its mean-free path between collisions is reduced at this threshold.Calculating the change in the capacitor’s charge yields the height of the resulting pulse. Initialcapacitor charge (Q), with an applied voltage (V), and capacitance (C), is given by Equation 6-4.(6-4)QCVA change of charge (DQ) is proportional to the change in voltage (DV) and equals the height ofthe pulse, as given by Equation 6-5 or 6-6.(6-5)DQCDV(6-6)DVDQCThe total number of electrons collected by the anode determines the change in the charge of thecapacitor (DQ). The change in charge is directly related to the total ionizing events which occurin the gas. The ion pairs (n) initially formed by the incident radiation attain a great enoughvelocity to cause secondary ionization of other atoms or molecules in the gas. The resultantelectrons cause further ionizations. This multiplication of electrons is termed gas amplification.The gas amplification factor (A) designates the increase in ion pairs when the initial ion pairscreate additional ion pairs. Therefore, the height of the pulse is given by Equation 6-7.(6-7)DVAneCwhereDV = pulse height (volts)A = gas amplification factorn = initial ionizing eventse = charge of the electron (1.602 x 10^{-19} coulombs)C = detector capacitance (farads)IC-06 Page 12 Rev. 0

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