GOST 22720.2-77

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  ГОСТ 22720.2-77

GOST 22720.2−77 Rare metals and alloys on their basis. Method for the determination of oxygen (with Change No. 1)

GOST 22720.2−77

Group B59

STATE STANDARD OF THE USSR

RARE METALS AND ALLOYS ON THEIR BASIS

Method of determining oxygen

Rare metals and their alloys. Method for the determination of oxygen

AXTU 1709*

______________
* Introduced advanced Edit. N 1.

Date of introduction 1979−01−01

The decision of the State standards Committee of the Council of Ministers of the USSR from September 29, 1977 N 2341 introduction installed from 01.01.79

Proven in 1983 by the Decree of Gosstandart from 27.07.83 3511 N validity extended to 01.01.89*

________________

* Expiration removed by Protocol No. 3−93 Interstate Council for standardization, Metrology and certification (ICS No. 5/6, 1993). — Note the manufacturer’s database.

REPRINTING. November 1983

The Change N 1, approved and put into effect by the Decree of the USSR State Committee for standards from 02.03.88 N 427 with 01.01.89

Change No. 1 made by the manufacturer of the database in the text IUS N 5, 1988

This standard applies to rare metals and alloys on their basis, in which the content of fluorine, boron and naturally radioactive isotopes in the amount does not exceed the oxygen content more than two times, and sets of neutron-activation method for the determination of oxygen (when oxygen mass fraction of from 5·10% or more).

The method is based on nuclear reaction O (, )N, occurring during the irradiation of sample by fast neutrons with an energy of 14.5 MeV. The decay of the formed radioisotope N, the half-life of 7.14, is accompanied by the emission of electrons and gamma rays high energy, which allows to identify N in the presence of other radioisotopes. The oxygen content is determined by comparing activity of the test sample with the activity sample comparison.

1. GENERAL REQUIREMENTS

1.1. General requirements for method of analysis according to GOST 22720.0−77.

1.2. When the mass fraction of oxygen in the analyzed sample >0.01% of the analysis is performed without removing the surface of the metal layer after irradiation; when the mass fraction of oxygen of 0.01% the analysis is performed with the obligatory removal of the surface layer of the test sample after its irradiation with the aim to eliminate the influence of surface contamination on results of analysis.

2. APPARATUS, MATERIALS AND REAGENTS

The installation of «Giredmet-2081» neutron activation determination of oxygen (Fig.1). Allowed other equipment, not inferior to the main analytical parameters (repeatability, limit of detection, background noise) of the facility.

1 — neutron generator NG-150; 2 — pneumatic conduit transport system with loading and unloading device; 3 — unit rapid removal of surface contaminants; 4 — detector for measuring the activity of the test sample and reference sample; 5 — measuring apparatus with a multi-channel analyzer; 6 — computing device (WU); 7 — automatic control unit installation; 8 monitor neutron flux; 9 — device for measuring neutron flux; 10 — detector device for measurement of neutron flux

Damn.1

In the install kit includes: neutron generator of the type NG-150, providing a neutron flux of at least 1−2·10on natural hair./with; pneumatic conveying system (PTS), including the irradiation unit, providing a flux density of neutrons with energy 14.5 MeV to 1−2·10on natural hair./cm·with the pneumatic conduit and a loading and unloading device for the withdrawal of the sample from the pneumatic conduit; block rapid removal of surface contamination of the analyzed sample; a detector for measuring the activity of the test sample and reference sample; instrumentation: three single channel analyzer with scalar devices PP-9−2M, a multichannel analyzer number of channels 128 (for example, AI-128); computing unit (IU); the block of automatic control unit; a detector for monitoring neutron flux; a device for measuring neutron flux.

The source of radioactive co (OSGI).

A set of sample comparison of titanium in the form of cylinders with a diameter of (6±0,2) to (30±1,0) mm and a height of (4±0,1) to (10±0,5) mm and diameter 2 mm and height 1 mm (each size not less than 5 PCs) or similar size samples comparison of polymethylmethacrylate.

Generator NG-150 is installed in the chamber, ensuring radiation safety. NG-150 is adjacent the irradiation unit connected by pneumatic conduit with the loading and unloading device, located in the analytical area outside the location of the NG-150. TCP performs the task of transporting a self-extracting capsules from the sample loading and unloading unit to the irradiation unit and back for no more than 2−3 C. title reproduces the conditions and the geometry of irradiation of a test sample and reference sample, producing automatic opening of the capsule and extraction of the irradiated sample with its direction into the block for rapid removal of surface contaminants with the subsequent installation of the sample into the detector for the registration of induced activity. Submission of samples to the irradiation position is successively the pneumatic conduit NTS.

The unit for removal of surface contaminants provides for 2.5−7.5 sec, the etching of the metal layer from fractions of a micrometer to tens of micrometer.

Measuring the activity of the irradiated sample is made using two blocks of scintillation crystals Na1 (T1) with a diameter of 150 mm and a height of 100 mm, placed in a lead protection with thickness of 50 mm. the detector Signals are served by two single-channel analyzer and then through the adder to a scalar device. The third single channel analyzer connected to the detector for monitoring neutron flux, which is necessary to measure the flow of neutrons with energy 14.5 MeV for sequential irradiation of the reference sample and a test sample.

WU makes the calculation for a given algorithm and outputs the result of the analysis on the light Board. The calculation of the mass fraction of oxygen in the analyzed sample () in percent is done automatically by the formula

,

where  — mass fraction of oxygen in the reference sample, %;

, is the mass of the reference sample and test sample, respectively, g;

, is the number of pulses from the reference sample and test sample, respectively;

,  — monitor the neutron flux of the reference sample and test sample, respectively;

that is the background in the measurement signal from the reference sample and test sample, respectively;

 — coefficient taking into account the difference of the self-absorption of quanta in the analyzed sample and the reference sample.

The amount injected into the memory of WU before analysis. The automatic control unit is the device that sets the exposure time (10−20 s), etching (2,5−7,5), measuring the activity and background (20) and providing, together with WU on automatic analysis mode.

A device for measuring neutron flux is a detector located at the target NG connected with a separate single-channel analyzer and is designed for the continuous monitoring of neutron flux with energy of 14.5 MeV.

Analytical scale.

Nitric acid GOST 4461−77, h.d. a.

Hydrochloric acid by the GOST 3118−77, h.d. a.

Sulfuric acid GOST 4204−77, h.d. a.

Hydrofluoric acid (hydrofluoric acid) according to GOST 10484−78, h.d. a.

Acetone according to GOST 2603−79.

Rectified ethyl alcohol GOST 18300−87.

(Changed edition, Rev. N 1).

3. PREPARATION FOR ASSAY

3.1. Sample preparation for analysis

Compact samples are made in the form of cylinders, whose dimensions correspond to the size of the reference sample. The rounded edges of the samples.

Samples in the form of powders and granules Packed in polyethylene capsules with an inner diameter of 22 mm, a height of 7 mm and a wall thickness of 1 mm (similar to the size of the reference sample). The mass fraction of oxygen in the polyethylene should be 2·10%.

Before the analysis of compact samples were washed with acetone, alcohol, dried in air and weighed.

3.2. Preparation instrument to the analysis

Before starting the installation-2081 check the position of toggle switches and switches indicated in the table.1.

Table 1

Include power stabilizer, 2 min units high voltage (high voltage is 1.4 kV), 30 min — device for measuring neutron flux and sets the optimal mode of operation of the NG. The maximum neutron flux should be 1−2·10on natural hair./if you want to analyze samples with a mass fraction of oxygen of 5·10-1·10%.

The power of single-channel analyzers, the automatic control unit installation, the title and the compressor, VU and multi-channel analyzer.

Tune the single-channel analyzers. This is placed in the detector for measuring the activity of the sample source . Set handle «smoothly Gain» and «Amplification rudely» both single-channel analyzers in the middle position. Smoothly changing load resistance PMT, achieve equality of detector signals, controlling their size by observation on the screen of the analyzer. By adjusting the «Gain exactly» set the position of the line of 1.17 MeV With 60 channel — when using a 512-channel analyzer and the position of the line of 1.17 MeV in 15-channel 128-channel analyzer.

Loaded into the capsule pneumopathy sample comparison. By pressing the «start» button on the automatic control unit installation send the capsule to the irradiation (sample position is controlled by the light Board, «start NG», «Exposure», «start detector», «Etching», «Measurement»). After receipt of the irradiated reference sample to the detector is noted by the marker of the analyzer the position of the upper discrimination level corresponding to the upper boundary fotopic of 7.11 MeV. Then the test sample is irradiated and within 1 min after end of irradiation set the position of the lower discrimination level corresponding to the upper limit of the instrumental spectrum of the material test sample. Increase the «Gain roughly» twice, is input to the «Nozzles», analyzer, «discriminator» and the rotation of the handle «Lower level», «Top level» set the levels of discrimination on both single-channel discriminators. Return handle «strengthening the rough» to its original position. Open 20 with the flap NG, and then set the levels of discrimination spectrum monitor neutron flux so that the ratio of activity/background of the monitor was at least 10.

If the analysis lead to the removal of the surface layer of the sample after irradiation (p.1.2) pick the Etchant speeds the etching is not less than 0.6 µm/s. Pour 3 DMEtchant in the capacity of the unit remove surface dirt.

(Changed edition, Rev. N 1)

.

3.3. Check of correctness of setting of the equipment

Validate the setting and measuring apparatus. For this purpose, two reference sample of the same size, but with different oxygen content. Analyze them, taking conventionally, one for reference sample, another for the analyzed sample.

Introduced to the computing device constant , see sec. 2 (when checking the settings of factor 1).

Load one of the samples of the comparison in the capsule of the pneumatic conduit and press the button «start NG». After the end of the program and appearing on a digital display VU download their result of the second comparison sample and sent for irradiation. Record the result of the determination, transfer switch «Program» to position «II», press the «Zero VU» and again irradiated with the second reference sample. If two of the obtained result deviates in absolute value from the known oxygen content in the reference sample is not more than the magnitude of acceptable differences for oxygen content in the reference sample, the hardware configuration is correct. If this condition is not satised, reiterate the hardware configuration. Background in the analysis should not exceed 50 pulses. 20 s. the Test configuration of the instrument was repeated after every hour of operation.

4. ANALYSIS

Introduced in WU constant calculated for a test sample with an appropriate factor .

In the analysis of samples of all operations performed in the same sequence as when checking the setting of the equipment.

When the mass fraction of oxygen of 0.01% include block rapid removal of surface contamination. On contact thermometer, set the required temperature etching. The automatic control unit set the switch to position «etching»; «switch while etching» is set to the desired position and after 10 minutes needed to heat the Etchant, proceed to the analysis. After each definition control the thickness of the remote layer. Through two parallel determination count value with the new mass of the sample.

5. PROCESSING OF THE RESULTS

5.1. The results of the analysis according to the formula given in sect.2, is calculated in WU. The final result is calculated as the arithmetic mean of the results of two parallel measurements.

5.2. Allowable absolute differences between the results of two parallel measurements with a probability of 0.95 should not exceed the values given in table.2.

Table 2

The value is determined by the relation

,

where and  — coefficients of self-absorption of the detected flux N (gamma quanta with an energy of 6−7 MeV) in the reference sample and test sample.

The self-absorption coefficients for various materials is determined graphically (Fig.2).

The dependence of the coefficient of self-absorption of-rays from the macroscopic cross section interaction -rays (6−7 MeV) with the material of the sample for different volumes at a 2.5 (where is the radius, the height of the sample). The value is equal to: 1 — 0,3925 cm; 2 — 7,065 cm; 3 — 50,24 cm; 4 — 200 cm

Damn.2

The macroscopic cross section of some metals are given below.