DE7918805U1 - DEVICE FOR ENERGY DISCRIMINATION OF CORE TRACES - Google Patents

Description

Sill · ·

Description:

The innovation relates to a device for energy discrimination of the nuclear tracks in nuclear track detector foils, the nuclear track detector foils by a chemical pre-etching are pretreated, the layer thickness corresponding to the individual | t-particle reaches is removed before the actual etching process to make the nuclear traces visible and Electrochemical etching for visualization only after the nuclear track detector foils have been irradiated the nuclear tracks is made.

A major contribution to natural radiation exposure can be traced back to the influence of radon / thoron and their secondary products. These ole-radionuclides occur in the free atmosphere and, after an oC fall, get into the lungs as free ions or stored in aerosols. According to the radium and thorium content in the soil and in the building material, the mean inhalation dose for the population as a result of radon and secondary products is 775 mrem / year based on the entire lungs. In closed residential buildings, but especially in mines, lo- to loo-times this lung burden can occur under certain circumstances. When measuring radon and secondary products, one is faced with the task of determining the radiation exposure primarily to secondary products

222

determine, since the noble gas radon Rn only lingers briefly in the lungs, while the aerosols accumulated short-lived by-products remain in the bronchial space (the following tables 1

4th .. .. • · · · · · • *
■> •
• • I · · · · •
fc ♦ »

and 2 give these decay series for radon and thoron):

Table 1:

Surname

isotope

radon

RaA

222 218 214 214 214 21o

Rn Po Pb Bi Po Pb

Half-life

Rays
art

3.823 d 3.o5 min 26.8 min 19.7 min 164 .us 21 a

MeV

5.49 6.OO

7.69

Table 2:

Surname

isotope

Half-life

MeV

Thoron
ThA
ThB
Th C
Th C '

Q

216 212 212 2o8,

Rn Po Pb Po Tl

55.65 s or 15 s io. 6 h ο. 3 .us 3.1 min

6.29 6.78

8.78

According to the current state of the art, the measurement of radon / thoron and secondary products is mainly carried out with battery-operated devices that suck in air through a filter and the air separated by the filter Eliminate secondary products. Here will be

• · * 4

Essentially three methods are used, in each of which a certain amount of air is passed through a filter is pumped (IAEA Safety Series No. 43, "Manual on Radiological Safety in Uranium and Thorium Mines and Mills "):

1. Kusnetz method

After an air throughput of Io liters (approx. 5 minutes pumping time) Radon products are collected on the filter and after a waiting time of 40 to 90 minutes the «(activity is measured. With the help of The Kusnetz correction curve is used to determine the potential eC energy of the radionuclides in WL (Working Level).

2. Instant working level ^ meter

The oi / ß activity of the filter is measured here immediately after sampling or after an air flow of around 5 liters.

3. Measurement of the oC energy concentration

After a short-term or long-term separation of the secondary products on a filter, the short-lived «(RaA and RaC« C emitters are detected separately by spectroscopy and, after a measuring time of approx. 2 hours after sampling, are displayed directly as vC energy concentration (B. Haider, W. Jacobi, BMBW-FB-K-72-14, 1972).

The construction of radon dosimeters with long-term integration is essentially limited to two embodiments. The active radon dosimeter pumps air through a filter and, in particular, measures the α -particles of the decay products with a thermoluminescent dosimeter or a nuclear track detector. The disadvantage is that a TLD also detects the gamma background radiation and dust particles are collected on the dosimeter surface, which can lead to incorrect measurements / 3/6 / ^f

If you are using Kodak LR-115 Cellulose Nitrate Sheets, you can because of the high absorption of the ο-particles behind in cover films different thickness covers in the nuclear track film three different α-energy groups, namely RaA, RaC and ThC detected separately will. In all of these cases, however, a battery-operated device with a pump must be used (IAEA Symp. On Advances in Radiotion Protection Monitoring, Stockholm, June 26-3o 1978, P. Duport et al).

One described by Frank et al (Radon Workshop, Feb. 1977, HASL-325, pp. 6-8) Diffusion chamber lets radon through a filter into the measuring volume, in which after about 5 hours equilibrium between Radon and its derivatives occur. This dosimeter measures essentially exclusively radon via the by-products after an equilibrium has been established between radon and its by-products. However, the determination is of interest for radiation protection lung exposure, especially from secondary products. In a living room or in a mine, the Indoor air or ventilation of the tunnel between radon and secondary products does not expect a balance. The measurement of the radon concentration Via the secondary products in a diffusion chamber, under unfavorable conditions (lo% equilibrium) a corresponding Overestimation of the lung burden up to a factor Io.

£ 47 J.Huber, B. Haider, W.Jacobi, Proc. of NEA Specialist Meeting Radon Monitoring, p. 139, 1978

G.M. Hassib, E. Piesch, Proc. of NEA Specialist Meeting Radon Monitoring, p. 35, 1978

• · ■ »» t

ι ι I ■ * · Il

The task set for the innovation is to develop a device of e.g. Kind of bidding with the Measuring influence of radon / thoron separately and exclusively Radon / thoron by-products are to be detected, which due to their different X-energies one different At brag for «energy concentration.

According to the innovation, this object is achieved as it is reproduced in the features of the claim.

The method used since then to separate different ot energy groups is based on the experimental one Finding that the range of ^ -particles in a nuclear track detector film, e.g. in Makrofol polycarbonate, is determined by the Ä energy. at conventional etching of the Kodak LR-Il5 detector, etching groups or nuclear traces are visible when the thin, red-colored detector layer is etched through, so that, on microscopic evaluation, bright Holes appear on a red background. To absorb the Si particles and discriminate between different The detector film is therefore ci energy groups in a known manner with plastic films of different thicknesses covered.

This method is not optimal, so that a device has been proposed according to the innovation that provides for a chemical pre-etching of the detector film, whereby a considerable part of the • (-particle range corresponding layer thickness before the actual etching process to make the core traces visible is replaced. Nuclear traces only become visible with a subsequent electrochemical etching.

The innovation is explained in the following on the basis of an execution J

For example, explained in more detail by means of FIGS. 1-2, the j

show an Ätzkcinmer. '|

In the case of the innovation, the use of a conventional pre-etching leads to a targeted removal of the surface layer. The etching time can be matched to the corresponding α-energy or the corresponding o-emitter. Some interesting ones The ratios for secondary products are listed in Table 3 below.

Table 3:

Preetch time isotopically removed

Detector layer in hours in .um

Ra A 8.4 3.56

Ra C 15.ο 6.36

Th C 25 ^ lo.6o

For example, if only these three energy groups are of interest, a single special etching chamber 14 can be used, as shown in Fig. 1 and 2 (the number of energy groups can be expanded). Fig. 1 shows in section the cylindrical etching cannon 14 with three bores 15 that are uniformly distributed around the axis of rotation 2ο and run parallel to it (see also FIG. 2). They can be filled with pre-treatment liquid for different etching times and / or in different concentrations. on one of the end faces 17 of the Xtzkammer 14 is a film 4 or 5 with the interposition of a seal 21 by means of a screw cap 16 brought into contact with all the bores 15 or the etching liquids contained therein at the same time. According to the Number of holes 15 is the number of simultaneously discriminable energy groups.

Claims (1)

Nuclear Research Center Karlsruhe, March 24th, 1981 Karlsruhe GmbH PLA 8116 Ga / he Protection claim: Device for the energy discrimination of the nuclear tracks in nuclear track detector foils, the nuclear track detector foils are pretreated by a chemical pre-etch that reaches the individual tf-particle corresponding layer thickness even before the actual etching process for visualization the nuclear track is detached and only after the irradiation of the nuclear track detector foils is an electrochemical one Etching to make the nuclear traces visible is carried out, characterized by an etching chamber (14) with several axially continuous bores (15) for receiving an etching liquid and by an end cap (16) with which the core track detector film (4 or 5) for etching on the an end face (17) of the etching chamber and with the etching liquid in the bores (15) in Is brought into contact.