| 摘要 |
<p>An electron multiplier (12) having a voltage divider circuit (10) for applying predetermined voltages to the dynodes (14-28) of the electron multiplier (12). One of the dynodes (18) is for attenuating an output of the electron multiplier. The voltage divider circuit (10) is made up of two networks, the first of which is a normal resistor chain (32-46) which is connected to the dynodes except the attenuating dynode (18) for applying predetermined biasing voltages to those dynodes. The second network is also made up of resistances (50, 52, 54) and applies an attenuating voltage to the attenuating dynode (18). It furthermore includes a switch (58) which is operative to vary the resistance in the second network by a discrete amount to thereby vary the attenuating voltage in a discrete step. The first network is connected between an extra-high tension voltage (EHT) supply (48) and earth (49) and the second network Is connected between the voltage supply (48) and a second voltage supply (56) which is connected to the dynode (20) following the attenuating dynode (18) for controlling the gain of the following multiplier stages. The use of two voltage sources (48, 56) ensures that the attenuation voltage is variable in discrete steps independently of the pre-determined biasing voltages applied to the remaining dynodes.</p> |
