Method for effectively reducing adsorption and accumulation of tritium on ionization chamber wall

Abstract

The invention discloses a method for effectively reducing adsorption and accumulation of tritium on the wall of an ionization chamber. A non-metal hydrophobic coating is deposited on the surface of the wall of the ionization chamber. At present, the ionization chamber wall is mainly made of a metal material, tritium atoms enter metal lattices to accumulate, and therefore the tritium memory effect is caused, a layer of dense, uniform and firmly-combined hydrophobic coating is deposited on the chamber wall, and adsorption and accumulation of tritium on the chamber wall can be effectively reduced.

Description

Technical Field

[0001] The invention relates to the technical field of tritium measurement ionization chambers, and in particular to a method for effectively reducing the adsorption and accumulation of tritium on an ionization chamber wall. Background Art

[0002] Tritium is a radioactive isotope of hydrogen that emits beta rays when it decays spontaneously. In ambient air, it mainly exists in the form of tritiated water vapor HTO and tritium gas HT, and a very small amount exists in the form of tritiated methane CH 3 It exists in the form of T. For workplaces seriously involving tritium, when a large amount of tritium gas leaks, high activity concentrations of tritium of different components such as HTO and HT will exist in the local air. If it is inhaled into the body through the respiratory system, it may cause internal radiation damage. Therefore, high-precision measurement of tritium should be achieved, so as to provide a scientific and reasonable basis for radiation protection and environmental safety evaluation of tritium-related workers.

[0003] Currently, tritium is measured using an ionization chamber. The chamber is pressurized by electrodes so that charged ions entering the effective volume of the ionization chamber move toward the collecting electrode for measurement. Therefore, the chamber wall material needs to be conductive (otherwise, some charged particles on the outside of the wire mesh electrode may enter the wire mesh, resulting in an inflated measurement result). Therefore, the chamber wall material is usually stainless steel or gold-plated stainless steel. Since the chamber wall material is metal, tritium atoms will definitely enter the metal lattice after adsorption, which makes it difficult to remove and accumulate, affecting subsequent measurements.

[0004] Therefore, it is urgent to develop a method to effectively reduce the adsorption and accumulation of tritium on the walls of the ionization chamber. Summary of the invention

[0005] The present invention aims to solve the problem that when the ionization chamber wall material is metal material, tritium atoms will enter the metal lattice after adsorption, which makes it difficult to remove and accumulates, thus affecting subsequent measurements. A method for effectively reducing the adsorption and accumulation of tritium on the ionization chamber wall is provided.

[0006] In order to achieve the above technical objectives, the technical solution provided by the present invention is:

[0007] A method for effectively reducing the adsorption and accumulation of tritium on the wall of an ionization chamber is to deposit a non-metallic hydrophobic coating on the surface of the wall of the ionization chamber.

[0008] Furthermore, the deposition is carried out by plasma enhanced chemical vapor deposition.

[0009] Furthermore, the plasma enhanced chemical vapor deposition gas source is an organic silicon compound gas.

[0010] Furthermore, the organic silicon compound gas includes any one of hexamethyldisiloxane, ethyl orthosilicate, and silicon tetrahydride.

[0011] Furthermore, the plasma enhanced chemical vapor deposition uses continuous wave, with a power of 30W - 75W, a vacuum degree of 10 - 50 pa, a deposition time of 10 min - 15 min, and a deposition temperature of 20 - 400 degrees.

[0012] Furthermore, the plasma enhanced chemical vapor deposition uses pulsed wave, with a power of 6 - 10W, a frequency of 100 - 1000Hz, a duty cycle of 1 - 5%, a vacuum degree of 25 - 50 pa, and a deposition time of 15 - 20 min.

[0013] The present invention has the following beneficial effects:

[0014] 1. Currently, the ionization chamber wall is mainly made of metal materials, and tritium atoms will enter the metal lattice and accumulate, resulting in the tritium memory effect. The present invention deposits a dense, uniform, and firmly bonded hydrophobic coating on the chamber wall, which can effectively reduce the adsorption and accumulation of tritium on the chamber wall.

[0015] 2. For the hydrophobic coating prepared by the present invention, in terms of the adsorption amount comparison, Au / SS < pp-HMDSO / SS < SS, and in terms of the desorption rate comparison, pp-HMDSO / SS > SS > Au / SS. During the surface adsorption process of water vapor, the pp-HMDSO / SS sample has the fastest adsorption rate and reaches adsorption saturation earliest. Therefore, it can be seen from the performance that the tritium memory effect is effectively reduced. Description of the Drawings

[0016] Figure 1 It is a performance comparison diagram, where Figure A is the performance diagram of the SS (stainless steel) sample, Figure B is the performance diagram of the Au-SS sample (gold-stainless steel), and Figure C is the performance diagram of the Plasma polymerized (pp)-HMDSO / SS (plasma polymerized methyl diethoxysilane / stainless steel) sample;

[0017] Figure 2 It is a sample diagram;

[0018] Figure 3 It is a test data diagram. Detailed Embodiments

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0021] Example 1

[0022] After the surfaces of the chamber walls are cleaned and wiped with isopropyl alcohol and ultrapure water respectively, the surfaces of the parts that do not need to be deposited are covered with a mask. The sample is placed in a plasma-enhanced chemical vapor deposition chamber. The gas source is hexamethyldisiloxane, the carrier gas is oxygen, the heating temperature is 50 °C, the deposition is carried out using continuous wave, the power is 30 W, the vacuum degree is 50 Pa, and it can be obtained after depositing for 10 min.

[0023] Example 2

[0024] After the surfaces of the chamber walls are cleaned and wiped with isopropyl alcohol and ultrapure water respectively, the surfaces of the parts that do not need to be deposited are covered with a mask. The sample is placed in a plasma-enhanced chemical vapor deposition chamber. The gas source is hexamethyldisiloxane, the carrier gas is a mixture of oxygen and argon, the deposition temperature is room temperature, the deposition is carried out using continuous wave, the power is 75 W, the vacuum degree is 10 Pa, and it can be obtained after depositing for 15 min.

[0025] Example 3

[0026] After the surfaces of the chamber walls are cleaned and wiped with isopropyl alcohol and ultrapure water respectively, the surfaces of the parts that do not need to be deposited are covered with a mask. The sample is placed in a plasma-enhanced chemical vapor deposition chamber. The gas source is tetraethyl orthosilicate, the carrier gas is a mixture of oxygen and argon, the deposition temperature is room temperature, the deposition is carried out using pulsed wave, the power is 10 W, the frequency is 100 Hz, the duty cycle is 1%, the vacuum degree is 25 Pa, and it can be obtained after depositing for 20 min.

[0027] Example 4

[0028] After the surfaces of the chamber walls are cleaned and wiped with isopropyl alcohol and ultrapure water respectively, the surfaces of the parts that do not need to be deposited are covered with a mask. The sample is placed in a plasma-enhanced chemical vapor deposition chamber. The gas source is tetraethyl orthosilicate, the carrier gas is a mixture of oxygen and argon, the deposition temperature is room temperature, the deposition is carried out using pulsed wave, the power is 6 W, the frequency is 150 Hz, the duty cycle is 5%, the vacuum degree is 50 Pa, and it can be obtained after depositing for 15 min.

[0029] Example 5

[0030] After the surfaces of the chamber walls are cleaned and wiped with isopropyl alcohol and ultrapure water respectively, the surfaces of the parts that do not need to be deposited are covered with a mask. The sample is placed in a plasma-enhanced chemical vapor deposition chamber. The gas source is silane, the carrier gas is a mixture of oxygen and argon, the deposition temperature is 400 °C, the deposition is carried out using pulsed wave, the power is 6 W, the frequency is 150 Hz, the duty cycle is 5%, the vacuum degree is 50 Pa, and it can be obtained after depositing for 15 min.

[0031] Such as Figure 1As shown, the water vapor adsorption amount of the SS (stainless steel) sample is 2.19 μg·cm -2 , and the desorption rate is 0.109 μg·min -1 ; the water vapor adsorption amount of the Au-SS sample (gold-stainless steel) is 0.9375 μg·cm -2 , and the desorption rate is 0.0086 μg·min -1 ; the water vapor adsorption amount of the pp-HMDSO / SS (pp-hexamethyldisiloxane / stainless steel) sample is 1.875 μg·cm -2 , and the desorption rate is 0.324 μg·min -1 ; it can be seen from the test results that during the test, the water vapor adsorption and desorption on the gold surface are very slow, and at the same time, the adsorption amount on the gold surface is also very small. Therefore, gilding the inner wall of the ionization chamber may cause a large amount of tritium-containing water vapor to accumulate during long-term use, resulting in baseline drift.

[0032] Comparing from the adsorption amount, Au / SS < pp-HMDSO / SS < SS. Comparing from the desorption rate, pp-HMDSO / SS > SS > Au / SS. At the same time, it should be noted that during the surface adsorption process of water vapor, the pp-HMDSO / SS sample has the fastest adsorption rate and reaches adsorption saturation earliest. Therefore, it can be seen from the performance that the tritium memory effect is effectively reduced.

[0033] As Figure 2 shown, it can be seen that the pp-HMDSO sample treated by plasma has obvious hydrophobicity, while the gold and untreated stainless steel samples show hydrophilic characteristics, which may affect the water vapor adsorption on the sample surface.

[0034] As Figure 3 shown, the test results show that at room temperature, the water vapor adsorption and desorption amount (0.001%) of pp-HMDSO at low water vapor concentration (less than 50%) is 1 / 7 (0.007%) of that of gold and 1 / 22 (0.022%) of that of the stainless steel sample; at high water vapor concentration, the water vapor adsorption amount of the pp-HMDSO sample is comparable to that of the gold sample (0.008%) and is 28.6% of that of the stainless steel sample (0.028%). It is worth mentioning that at low water vapor concentration, the water vapor on the gold sample hardly desorbs, while the pp-HMDSO sample can desorb quickly. At high temperature, the water vapor adsorption amount of the pp-HMDSO sample is slightly higher than that of the gold sample, but is still much lower than that of the stainless steel sample.

[0035] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

[0036] The above specific embodiments are detailed descriptions of the present invention. It cannot be determined that the specific embodiments of the present invention are only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions and substitutions can still be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A method for effectively reducing the adsorption and accumulation of tritium on the wall of an ionization chamber, characterized in that: A non-metallic hydrophobic coating is deposited on the surface of the ionization chamber wall.

2. A method for effectively reducing the adsorption and accumulation of tritium on the wall of an ionization chamber according to claim 1, characterized in that: The deposition was performed by plasma enhanced chemical vapor deposition.

3. A method for effectively reducing the adsorption and accumulation of tritium on the wall of an ionization chamber according to claim 2, characterized in that: The plasma enhanced chemical vapor deposition gas source is an organic silicon compound gas.

4. A method for effectively reducing the adsorption and accumulation of tritium on the wall of an ionization chamber according to claim 3, characterized in that: The organic silicon compound gas includes any one of hexamethyldisiloxane, ethyl orthosilicate and silicon tetrahydride.

5. A method for effectively reducing the adsorption and accumulation of tritium on the wall of an ionization chamber according to claim 2, characterized in that: Plasma enhanced chemical vapor deposition uses continuous wave, power is 30W-75W, vacuum degree is 10-50pa, deposition time is 10min-15min, and deposition temperature is 20-400 degrees.

6. A method for effectively reducing the adsorption and accumulation of tritium on the wall of an ionization chamber according to claim 2, characterized in that: Plasma enhanced chemical vapor deposition uses a pulse wave with a power of 6-10W, a frequency of 100-1000Hz, a duty cycle of 1-10%, a vacuum degree of 25-50Pa, and a deposition time of 15-20min.

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