DE1032430B - Counter tube with a large measuring range - Google Patents

Description

GERMAN

In Dosisleistungsmeßgeräten, particularly in orientation devices for gamma rays, there is often the demand for a continuous over about four orders of magnitude range span, to be also detected as an upper limit while still 50 r / h = 1.4 x 20- ² r / s. With the Geiger-Müller counter tubes that have been used up to now, however, the upper limit value is around 10 ~ ⁴ r / s, provided that the operating point is in the trigger range of the counter shape characteristic. It is known that the counting speed can be increased by moving the operating point to the proportional range. The disadvantages of this measure are, on the one hand, the lower gas gain by about three powers of ten, and on the other hand, the need to stabilize the operating point as best as possible. The latter results in a considerable complication of the circuit complexity. Frequent calibration checks are also necessary because of the influence of temperature on the counter tube.

A counter tube design with a large measuring range is known in which a plurality of separately connectable cathode cylinders are arranged around a common gas space in the axial direction. These either have different wall thicknesses with the same diameter or graduated inner diameters]> with the same wall thicknesses. This arrangement ensures that different counting speeds occur in the individual counting tube volumes formed by the cathode cylinders. With such an arrangement, however, the limit value of about 1.4-ΙΟ " ² r / s mentioned at the beginning cannot be achieved. In addition, a counter tube of this type has considerable dimensions due to the axial alignment of the individual cathode cylinders that make it difficult or impossible to use it in small portable devices.

It is also known to increase the counting speed in the trigger area (Geiger plateau) to reduce the dead time of the counter tube by limiting the expansion of the ion tube will. This can be achieved by lined up insulating beads at certain intervals on the counting wire will. It has been found, however, that this proposal presents considerable manufacturing difficulties caused.

Another way to increase the counting speed in the Geiger Plateau is the Reduction of the "active volume" of the counter tube by applying the principle of the peak counter comes. However, this brings the disadvantage of a considerable shortening of the undesired manner Plateau length and a significant increase in the plateau slope with it. To face that has already been proposed, the top of the counter counter tube with a large measuring range

Applicant:

P. Gossen & Co. G. mb H.,
Erlangen, Nägelsbachstrasse. 25th

Harald Danklefsen, Erlangen,
has been named as the inventor

rounded off by a ball and this a spherical cap-shaped one Facing cathode. However, this proposal is difficult to achieve in practice realize because it is difficult to provide the ball with a sufficiently smooth surface. Namely there the effective surface of the sphere is only small, even the slightest surface unevenness is sufficient, as they are unavoidable with justifiable manufacturing effort, to ensure homogeneity of the electric field and the clean operation of the counter tube from the outset to question. In addition, peak counters cannot easily be compared with conventional counters higher sensitivity and cylinder cathodes constructively combine in a common gas space permit.

The counter tube according to the invention with a wide measuring range also has a counting room with a small active one for high counting speeds Volume, but does not have the disadvantages just mentioned. This is achieved in that the cathode of the system for high counting speeds is designed as a ring with a circular cross-section, the surrounds the counting wire. The cathode ring can also be easily in a normal Arrange the counter tube additionally.

The new counter tube is shown schematically in the drawing.

Both the ring-shaped metal cathode 2 is located inside the gas-tight insulating sheath 1 with a circular cross-section which, together with the counting wire 3, forms the system for high counting speeds forms, as well as the metal cylinder 4, which with the same ZälhMraiht the system for low Represents dose rate. The insulating bead 5 attached to the counting wire 3 has the purpose of being known

809 557/355

Assign the effect of distortion of the electric field in the edge zone of the cathode cylinder 4 eliminate.

The counter tube is connected via connections 6, 7 and 8 connected to the radiation meter. This itself is structured in such a way that when selecting a range the appropriate counting system is switched on.

The particular advantage of the ring-shaped cathode 2 lies in the fact that only a very small one of it active volume is enclosed, which by the geometric shape of the ring cross-section per se already has a good field-like homogeneity, and furthermore that the with a justifiable manufacturing effort possible surface unevenness has little influence on the homogeneity of the electrical Field, since the ring-shaped cathode has a comparatively large effective surface compared to these bumps. This ring-shaped cathode still has the advantage of relatively easy machinability of their effective surface.

Claims (1)

Claim: Geiger-Müller counter tube with two counting systems of different sizes of the cathode surface for high and low counting speeds and with counting wire common to both systems, characterized in that the cathode of the system for the high counting speed as Ring is formed with a substantially circular cross-section. Considered publications:
British Patent No. 681,468. 1 sheet of drawings © 809 557/355 6.58