DD237721A1

DD237721A1 - RADON DIFFUSION CHAMBER

Info

Publication number: DD237721A1
Application number: DD27669085A
Authority: DD
Inventors: Gunter Pretzsch; Elke Boerner; Rainer Lehmann; Olaf Sarenio
Original assignee: Univ Dresden Tech
Priority date: 1985-05-28
Filing date: 1985-05-28
Publication date: 1986-07-23

Abstract

Die Erfindung betrifft eine Vorrichtung zum Nachweis von Alphastrahlung emittierenden radioaktiven Gasen, wie beispielsweise Radon und Thoron sowie deren alpha-aktiven Folgeprodukte. Die erfindungsgemaesse Loesung sieht eine Kammer vor, in die das Gas beispielsweise durch eine Oeffnung mit Filter hineingelangt. In der Kammer befindet sich ein einseitig metallisierter Elektret mit negativer Polaritaet und ein ihm zugewandter passiver Detektor, wobei der Abstand zwischen beiden hoechstens der Reichweite der Alphateilchen der Radonfolgeprodukte entspricht. Der Elektret sammelt die positiv geladenen Folgeprodukte und wirkt somit als Flaechenquelle. Dadurch erhoeht sich der Messeffekt des Detektors und die Messzeit kann verringert werden.The invention relates to a device for detecting alpha-emitting radioactive gases, such as radon and thoron and their alpha-active secondary products. The solution according to the invention provides a chamber into which the gas enters, for example through an opening with a filter. In the chamber is a one-sided metallized electret with negative polarity and a passive detector facing it, wherein the distance between the two corresponds at the most to the range of the alpha particles of the Radonfolgeprodukte. The electret collects the positively charged secondary products and thus acts as a surface source. This increases the measuring effect of the detector and the measuring time can be reduced.

Description

Der Elektret sammelt die positiv geladenen Folgeprodukte und wirkt somit als Flächenquelle. Dadurch lagern sich die Folgeprodukte nicht Undefiniert an den Kammerwänden ab, sondern bestrahlen den Detektor von der Elektretöberfläche her. Somit wird der Meßeffekt erhöht und die erforderliche Bestranlungszett verkürzt. Weitere Vorteile einer solchen Kammer gegenüber anderen Meßsystemen bestehen im einfachen Aufbau und den geringen Herstellungskosten sowie in der einfachen und sicheren Auswertung ohne merkliche Beeinflussung durch Umgebungseinflüsse. Nach erfolgter Auswertung kann der Elektret neu formiert und wiederverwendet werden.The electret collects the positively charged secondary products and thus acts as a surface source. As a result, the secondary products do not deposit undefined on the chamber walls, but instead irradiate the detector from the electretoberfläche. Thus, the measuring effect is increased and the required Bestranlungszett shortened. Other advantages of such a chamber over other measuring systems consist in the simple structure and low production costs and in the simple and reliable evaluation without noticeable influence of environmental influences. After evaluation, the electret can be reformed and reused.

Ausführungsbeispie!

Die Erfindung soll nachfolgend an einem Ausführungsbeispiel näher erläutert werden. Die erfindungsgemäße Vorrichtung ist in Fig. 1 dargestellt. Sie besteht aus einem Kammergehäuse 1 mit einer Diffusionsöffnung 2 in Form eines Filters, das Radon durchläßt und die Folgeprodukte zurückhält, einem einseitig metallisierten Polymerelektreten 3 mit einem Oberflächenpotential von — 1,5kV, einem im Abstand 4cm von Elektreten befindlichen Festkörperspurdetektor 4 und dem Kammervolumen 5. Die Diffusionskammer wurde über mehrere Stunden einer Atmosphäre mit erhöhter Radonkonzentration ausgesetzt. Ohne Elektret ergab sich nach Auswertung des Festkörperspurdetektors eine Empfindlichkeit von 0,4 Spuren -cm~²/(8q Γ¹ · h). Mit Elektret erhöhte sich die Empfindlichkeit auf 1,6 Spuren · cm~²/(Bq Γ¹ · h). Dadurch wird mit Elektret der gleiche Meßeffekt bereits in einer um den Faktor 4 kürzeren Zeit erhalten. Experimente mit einer größeren Entfernung des Eiektreten vom Festkörperspurdetektor als der Reichweite der Alphateilchen der Folgeprodukte ergaben keine Erhöhung der Empfindlichkeit.The invention will be explained in more detail below using an exemplary embodiment. The device according to the invention is shown in FIG. It consists of a chamber housing 1 with a diffusion opening 2 in the form of a filter that transmits radon and retains the secondary products, a one-sided metallized Polymerelektreten 3 with a surface potential of - 1,5kV, located at a distance of 4cm electret solid-state detector 4 and the chamber volume. 5 The diffusion chamber was exposed to an atmosphere of increased radon concentration over several hours. Without electret a sensitivity of 0.4 lanes ² / (8q Γ ¹ · h) resulted -cm after evaluation of solid state track detector ~. With electret the sensitivity increased to 1.6 tracks · cm ~ ² / (Bq Γ ¹ · h). As a result, the same measuring effect is already obtained with electret in a time shorter by a factor of 4. Experiments with a larger distance of the solid from the solid-state tracker than the reach of the alpha particles of the derived products did not increase the sensitivity.

Claims

Invention claim:

1. Radondiffusionskammer with a passive integrating detector, preferably a solid-state track detector in a chamber with a diffusion opening, characterized in that above the passive detector (4) facing it a negative electret (3) is arranged.

2. radon diffusion chamber according to item 1, characterized in that the distance between the detector and electret corresponds at most to the range of the alpha particles of the secondary products in air.

3. Radondiffusionskammer according to the points 1 and 2, characterized in that a cylindrical detector is arranged concentrically around a cylindrical electret.

For this 1 page drawing

Field of application of the invention

The invention relates to a device for detecting alpha radiation emitting radioactive gases, such as radon and thoron, and their alpha-active secondary products. It is particularly suitable for registration of alpha-active secondary products.

Characteristic of the known technical solutions

Devices are known for the detection of radon and / or thoron and their alpha-active secondary products which contain a chamber.

The radioactive gas is transported by a pump into the chamber. The inlet and / or outlet of the chamber contain filters which retain the alpha-active secondary products. After a collection time of, for example, a few minutes, the filter is removed and measured with an active detector, for example a semiconductor detector. From the knowledge of the Samrnel- and measuring conditions as well as the physical decay laws the concentration of Radon and / or Thoron and their alpha-active secondary products in the air can be determined.

Furthermore, chambers are known which contain an active detector and thus permit direct registration of the emitted alpha particles. In order to increase the counting efficiency and thus reduce the measuring time, an electric field was installed in the chamber by means of a battery or an electret, whereby a collection of the alpha-active secondary products, which are about 70% positively charged, on the sample to be measured or the active detector takes place. An additional acceleration by a pump is also known. With this method, a separate detection of radon and the alpha-active secondary products can be carried out. In order to save the active detector in the chamber for direct detection, an electret ionization chamber with pulse evaluation circuit has been proposed (G01 T 265673/8). There are also known devices without a pump in which the radioactive gas passes through natural diffusion through a chamber opening, which may for example contain a filter for the alpha-active secondary products, into the chamber. In the chamber are passive detectors, such as solid state track detectors (DE 1764686), thermoluminescence detectors or electret detectors that register the alpha radiation. From the measurement effect of these detectors and the measurement conditions, the concentration of radon and / or thoron and their alpha-active secondary products in air can be determined. However, the use of an electret detector is not favorable, since the measuring effect is additionally influenced by beta-emitting secondary products and the charged secondary products themselves and thus large uncertainties arise. In order to shorten the long measurement times of several weeks to months in environmental measurements, passive detectors were wrapped in aluminum foil and negatively charged by approaching electrets. As a result, the alpha-active secondary products are attracted and cause an increase in the measuring effect ("Health Physics", Vol.43, No. 3, 1982, pages 399-404.) A disadvantage of this method is that the Influenzladungen on the aluminum foil freely movable and at the slightest contact with soil, for example via a condensed water droplet, flow off immediately.The disadvantage is furthermore the poor reproducibility of the charge as well as the slowing down of the alpha particles in the aluminum foil before they reach the detector.

Object of the invention

The aim of the invention is to detect alpha-emitting radioactive gases, such as radon and / or thoron and / or their alpha-active secondary products with a passive detector in a chamber in a short time.

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Explanation of the essence of the invention

The object of the invention is to collect the alpha-active secondary products in the chamber and thereby achieve effective irradiation of the passive detector.

According to the invention, this object is achieved in that in a diffusion chamber with a passive integrating detector, preferably a solid-state detector above the passive detector a negative-oriented electret facing it is arranged, wherein the distance corresponds at most to the range.der alpha particles of the secondary products in air.