DE2907974C2 - Method of making a thermoluminescent dosimeter element - Google Patents

Description

a) the thermoluminescent material is cooled to a ^{temperature which is 150 to 200 °} C. below the melting temperature of the thermoluminescent material, and

b) the cooled pill thus obtained is then chemically polished so that it has a surface roughness of at most 0.1 μΐη.

2. The method of claim 1, wherein the thermoluminescent dosimeter is produced on the basis of lithium fluoride, characterized in that that chemical polishing in a concentrated orthophosphorous acid with subsequent rinsing takes place in distilled water.

3. The method according to claim 1, characterized in that the melting temperature of the thermoluminescent material is exceeded ^{by 30 to 100 0 C for complete melting.}

The invention relates to a method for producing a thermoluminescent dosimeter element, wherein an ion compound as a thermoluminescent material placed in a crucible, under vacuum or in a Inert gas atmosphere heated above its melting temperature and thereby completely melted and then with a given cooling rate in the range of 0.5 to 2 ° C / min to a considerable is cooled below its melting temperature lying temperature.

A method of the type defined above is already known from DE-AS 13 02 393. According to this known Method is also an ionic compound for the production of a thermoluminescence dosimeter element, essentially lithium fluoride, as a thermoluminescent substance placed in a crucible, then under vacuum or in an equivalent manner in a Inert gas atmosphere heated above a melting temperature, and the melt then obtained is then cooled by the crucible containing the melt slowly at a controlled speed is lowered into a zone, the temperature of which is below the melting point of the melt, while the Temperature in the upper zone is kept above the melting point of the melt. When the crucible is in the lower zone has been lowered and all of the melt has solidified, the furnace is running at one speed cooled from about 0.17 to 0.83 ° C./min to room temperature. However, this known method is not used to do this, a thermoluminescent dosimeter element in To manufacture the shape of a pill; rather, it delivers one

Crystal bar, which is then pulverized.

From the journal "Radiation Therapy", Volume 132, 1967, No. 4, pages 553 to 558, a method for producing a thermoluminescence dosimeter element is known in which several LiF single crystal disks are powdered, the powder is mixed with tetrafluoroethylene powder and then pressed ^{at a pressure of 1300 kg / cm 2.} The columns thus obtained, 11 mm in diameter and 2 cm high, are then ^{sintered for 20 minutes at 360 °} C. and can then be machined, resulting in tablets from 03 to 1 mm thick.

From DD-PS 56 877 a method for the treatment of lithium fluoride single crystals is known which are used for dose measurements of ionizing radiation. The starting material here is a LiF single crystal, which is broken up into wafers, these wafers being additionally heated at 500 ^° C. for about 2 minutes before each use and then cooled for about 2 minutes at room temperature.

From DD-PS 42 614 a process for the production of lithium fluoride thermoluminescence dosimeters is known, in which a soft lithium salt is used as the starting substance. After carrying out various precipitation processes the Ausfällprodukt LiF and is annealed in air atmosphere between 600 ⁰ C to 750 ⁰ C, although at an annealing time of 10 to 100 minutes followed by quenching. If this known method is used for the production of pills, the thermoluminescent material thus obtained has to be additionally compressed with a binder or without a binder. Both the pressing and the use of a binder have the result that the product obtained has, on the one hand, a low thermal stability and, on the other hand, also has a reduced sensitivity

From DE-OS 15 92 901 a process for the production of thermoluminescent dosimeter elements in the form of pills is known. This known process is based on the use of a special compression technique, according to which powdery thermoluminescent material at a pressure of at least 703 kg / cm ² and a temperature at least room temperature and not higher than 815 ° C is pressed. This detector has no housing and is therefore from. the measurement errors caused by the housing. However, this detector only provides reliable results if it is used once, because microscopic damage to the structure of the detector, which is formed by mechanically connected powder particles, occurs during the thermal treatment process when the result is read. The presence of such mechanical micro-damage in the structure also leads to a decrease in the sensitivity of the detector.

Finally, DE-AS 15 39 894 discloses a method for producing thermoluminescent dosimeter elements known in which LiF is formed as a thermoluminescent material in an inert gas Atmosphere is compressed by mechanical pressure. The increased used in the pressing process Temperature is approximately half the melting temperature of lithium fluoride. Also this well-known The process leads to the change already described and, in particular, to a decrease in sensitivity of the elements.

The invention is therefore based on the object of further developing the method of the type defined at the outset.

denotes that it is a pill-shaped thermoluminescent dosimeter element with increased sensitivity that remains the same after repeated use.

Based on the method of the type mentioned at the outset, this object is achieved according to the invention solved that

a) the thermoluminescent material is cooled to a ^{temperature which is 150 to 200 °} C. below the melting temperature of the thermoluminescent material, and

b) the cooled pill thus obtained is then chemically polished so that it has a surface roughness having a maximum of 0.1 μπι.

In contrast to the known methods, the method according to the invention turns one into a solution Realized specific crystal structure particularly suitable for the stated task, with the sintering or compression with or without binders associated undesirable consequences are avoided.

If the thermoluminescent dosimeter element is made on the basis of lithium fluoride, takes place chemical polishing expediently in a concentrated orthophosphorous acid with subsequent Rinse in distilled water.

Finally, the method according to the invention can also experience an advantageous embodiment in that the melting temperature of the thermoluminescent material is exceeded ^{by 30 to 100 ° C. for complete melting.}

The invention is explained in more detail below with the aid of exemplary embodiments

The detector for thermolurninescence dosimetry produced by the method according to the invention represents a composed of a plurality of single-crystalline particles bonded together by molecular forces Pill based on an ionic compound.

The pill can have any desired shape and dimensions. Possible ionic compounds include KCl, LiNbO ₃ , CaF ₂ , LiF, Al ₂ O _3, among others.

The detector is manufactured as follows. A powdery ionic compound is used as the starting material. The powder is poured into a crucible in the shape of the pill and heated under vacuum or in an inert gas atmosphere (argon or helium) to a temperature of 30 to 100 ^° C. above the melting temperature of the starting material until the latter has completely melted for 15 to 45 min . The melt is then slowly cooled at a rate of 0.5 to 2 ° C / min to a temperature 150 to 200 ° C below the melting temperature of the starting material Molecular force-linked single-crystalline particles having pill corresponding to the shape of the crucible.

This pill has a surface roughness of at most 0.1 μm.

This surface quality of the pill is achieved by chemical polishing immediately after the pill has cooled down Manufacturing process realized immediately before the dosimeter element is used

As a result of the chemical polishing, no disturbed layer with a is formed on the surface of the pill distorted crystal structure, as is the case after mechanical processing. The detector with Such a surface has practically no background signal because it is resistant to chemiluminescence causing chemosorption of atmospheric vapors as well as causing anti-triboluminescence mechanical influences is and is characterized by increased reproducibility.

In the manufacture of the detector based on lithium fluoride, chemical polishing is concentrated in one orthophosphorous acid with subsequent rinsing of the detector in distilled water to realize.

In order to clarify the essence of the present invention, the following are specific procedures described.

ie is game 1

A powder of activated lithium fluoride with a grain size of 0.18 to 0.20 mm (melting temperature of 862 ° C.) was taken as the starting material, placed in a graphite crucible with 25 depressions 4 mm in diameter and 2 mm in height and in a vacuum at one temperature heated from 950 ⁰ C in the course of 15 min. The starting material melted completely. Then, the melt at a rate of 0.6 ° C / min to 700 ° C and further to room temperature at a rate of 10 ⁰ C / was cooled min. The pills obtained were used as thermoluminescent dosimeter elements. The tests of the dosimeter elements have shown their good dosimetric properties - lack of triboluminescence and ease of use.

Example 2

Pills, prepared as described in Example 1, were taken and subjected to chemical polishing in a concentrated orthophosphorous acid at a temperature of 130 ° C. for 1.5 to 3 minutes. Subsequently, the pellets were rinsed in hot (80 to 9O ⁰ C) and then in cold distilled water and dried in air.

The finished detectors were irradiated in a gamma radiation field with a dose of 0.01 rad and illuminated in a measuring system for the thermoluminescence detectors. After 40 similar measurements a mean square deviation of readings of the detector was not over on a detector ± 4% obtained.

When using unpolished detectors manufactured according to Example 1, reproducibility resulted of ± 10%, which can be attributed to their own smaller value of the signal-to-noise ratio is.

Example 3

A powder of lithium niobate with a melting temperature of 1260 ^° C., a grain size of 0.1 to 0.2 mm was taken ^{as the starting material, placed in a platinum crucible and heated at a temperature of 1290 °} C. until it completely melted cooled to room temperature at a rate below 50 ° C / min.

The obtained pills were chemically concentrated in 1 part by volume of hydrofluoric acid and 3 parts by volume Nitric acid-containing solvent at a temperature of 50 to 80 ° C in the course of 5 to

Polished for 8 min, whereupon the pills in distilled water rinsed and air dried.

The finished dosimeter elements were irradiated with a dose of gamma radiation of 10 ^-3 rad. The reproducibility of the measurements was ± 5%.

Example 4

As a starting material a powder of potassium chloride having a melting temperature of 770 ⁰ C and a particle size from 0.10 to 0.15 was taken mm, poured into a platinum crucible and heated in vacuum or an inert atmosphere at a temperature of 810 ° C until complete melting Cooling was then carried out first at a rate of 0.6 ° C./min to a temperature of 550 ° C., furthermore at a rate not exceeding 10 ° C./h to room temperature. The pills obtained were chemically polished in a solution of 0.5% by weight FeCb in 80 to 85% ethyl alcohol in the course of 3 to 5 minutes. The pills were then rinsed in 96% ethyl alcohol and dried in air

When the detectors were irradiated several times, the reproducibility was ± 10%.

The thermoluminescent dosimeter element produced by the method of the invention is for Dosimetry in medical radiology or for individual radiation protection monitoring in particular suitable

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Claims (1)

Patent claims: 1. A method of manufacturing a thermoluminescent dosimeter element, wherein an ion compound as a thermoluminescent material in a Crucible placed under vacuum or in an inert gas atmosphere above its melting temperature heated and thereby completely melted and then with a specified cooling rate in the range from 0.5 to 2 ° C / min to one that is considerably below its melting temperature Temperature is cooled, characterized in that