DE681487C - Dosimeter for cathode rays with Lenard catcher and capacitor connected in parallel - Google Patents

Description

Cathode ray dosimeter with Lenard interceptor and parallel to it switched capacitor For measuring the intensity and amount of cathode rays one uses. according to L e -n a r d interceptor consisting of a conductive collecting plate exist that can be hit by the cathode radiation to be measured and for protection against discharge by secondary electrons and air conduction with a layer is surrounded by a preferably solid insulator, which is generally a grounded external occupancy. The amount of electricity collected by the disk Charge carriers are measured with an electrometer. The smaller the capacity of the Lenard interceptor. and the electrometer, the greater the voltage that occurs.

On the other hand, the greater the amount of residue, the higher the formation of residues Isolating agent. occurring voltage is. It has therefore been suggested that the Lenard catcher to connect a capacitor in parallel, which as possible no residue formation and whose capacitance is large compared with the capacitance of the Lenard capacitor. However, this arrangement has the disadvantage that the voltage appearing on the electrometer is very small, so that relatively delicate instruments are used that are not well suited for use in practical operation.

This difficulty can occur with a cathode ray dosimeter with Lenard collector and capacitor connected in parallel, its voltage is measured, can be avoided according to the invention in that the capacitance of the capacitor has a large value during collection and a small value during measurement, and that a switch is provided in the supply line to the collecting plate, each of which closed before the radiation is absorbed and before the capacity is reduced of the variable capacitor is opened. After opening the switch, Idie The capacitance of the capacitor connected in parallel is considerably reduced, so that the Tension rises to values that are already relatively insensitive, mechanically very resistant instruments can be measured. In some cases it is it is advisable to take care of this by means of a mechanical coupling or locking mechanism contribute to the reduction of the capacitance of the parallel capacitor only made after opening the switch in the supply line to the collecting plate will can. There are already known charging devices for ionization meters which charging by means of low voltage with artificially increased system capacity before, is taken and after charging the system capacity in order to increase the voltage is reduced again. A mechanical coupling is also used in the known arrangement between the switch located in the supply line from the supply current source and the to change the capacity of the ionization chamber serving mechanism.

The figure shows a schematic representation of an embodiment the invention. The cathode ray K first penetrates the earthed occupancy of the Lenard-Auffängers L, in the interior of which is embedded in the insulation material Auff, angpiatte is located on the switch S with the variable capacitor C is connected. The occupancy of the Lenard interceptor is just like the other Pole of the capacitor and the electric motor grounded. In the dotted line shown closed position of the switch S is the irradiation of the Lendard interceptor made by the cathode rays K. When the ratio of the capacity of the Lenard interceptor small enough for the capacitance of the capacitor C connected in parallel there is only a very low voltage at the insulator of the Lenard interceptor, and the electric charge bound in the receiver is only proportionate small, easily calculable part of the total collected by the collecting electrode Charge.

When charging is complete, switch S is opened first and then the capacitance of the variable capacitor C to such a small value decreased so that the voltage at the electrometer E rises to a measurable value. By the dash-dotted connecting line M is intended to be a mechanical coupling or lock + g are shown that when the switch S is closed, a reduction in capacitance C prevents the reduction in size or automatically immediately after the switch S is opened the capacitance of the variable capacitor C.

It may be useful to use the clutch or lock set up so that after opening the switch the capacity of the parallel connected Capacitor is automatically reduced to its smallest value and after closing of the switch is automatically regulated to its maximum value. Through this it is achieved that both during the irradiation and during the measurement the variable Capacitor has the correct capacity in each case.

Claims (4)

P A T E N T A N S P R Ü C H E: I. Dosimeter for cathode rays with Lenard collector and capacitor connected in parallel, its voltage is measured, characterized in that the capacitance of the capacitor during the interception has a large value, while the measurement has a small value, and that in the supply line to the collecting plate a switch is vorgesehlell, each closed before collecting the radiation and before reducing the capacity of the variable capacitor is opened. 2. Dosimeter according to claim I, characterized in that a lock is provided, through which a reduction in capacity when the switch is closed the parallel capacitor is prevented. 3. Dosimeter according to claim 1 and 2, characterized in that a Coupling is provided through which automatically after opening the switch Capacity of the parallel capacitor is reduced. 4. Dosimeter according to claim 3, characterized in that a mechanical Coupling between the switch and the variable parallel con! capacitor provided is, through which automatically the capacity on their after closing the switch largest and automatically regulated to their smallest value after opening the switch will.