1、EIA TEPL70 72 m 3234600 O008476 I m _ _- July 1972 RECOMMENDED PRACTICE ON X - RADIATION DETECTION AND MEASUREMENTS FOR MICROWAVE TUBES FORMULATED BY JEDEC ELECTRON TUBE COUNCIL Y - _- .JEDE PUBLICATION NO. 70-A ii EIA TEP170 72 W 3234b00 0008477 3 W Published by ELECTRONIC INDUSTRIES ASSOCIATION En
2、gineering Department 2001 Eye Street, N. W., Wlshington, D, C. 20006 -. P a - i- ,a EIA TEP170 72 - 3234600 0008478 5 - JEDEC PUBLICATION NO. 70 -A ON X-RADIATION DETECTION AND MEASUREMENTS FOR MICRWAVE TUBES Formulated by JEDEC Electron Tube Council July 1972 Electronic Industries Association Engin
3、eering Department 2001 Eye Street, N.W. Washington, D.C. 20006 -i- EIA TEP170 72 3234600 0008479 7 FOREWORD The material in this Publication was formulated under the cogni- zance of the JT-13 Committee on Microwave Devices and approved by the JEDEC Electron Tube Coun- cil. - ii - r -J f 1.1 1.2 1.3
4、1.4 EIA TEPL70 72 m 3234600 0008480 3 m RECOMMENDED PRACTICE ON X-RADIATION DETECTION AND MEASUREMENTS FOR MICROWAVE TUBES A. X-RADIATION FROM MICROWAVE TUBES 1.0 Introduction The demand for higher power output from microwave tubes has lead the tube designer to the use of higher voltages and current
5、s to achieve these demands. and currents makes it possible for the device to generate unwanted x-radiation. The use of high voltages The user, test personnel, equipment technicians, and maintenance personnel may be over-exposed to the radiation if adequate protection is not provided and if adequate
6、precaution is not observed. likelihood of over-exposure to the general public arising from these devices. In-plant personnel are not likely to be over-exposed because, (I) the design engineers will have established the magnitude of the problem, and (2) state and local statutes and insurance regulati
7、ons provide adequate controls. There is normally little Linear beam devices, such as traveling wave tubes and klystrons, can have x-radiation emission generally from the gun and collector ends of the tube. Linear beam amplifier devices generally show greater x-radiation generation with RF drive appl
8、ied than the FU? off. High power versions of magnetrons, klystrons, TWTs, and crossed field amplifiers can have x-radiation emitting from the cathode bushing and rf output window. also been detected coming through the anode walls on some high power devices. X-radiation has X-radiation arises from el
9、ectron bombardment of a target. The x-radiation intensity is proportional to average tube current, accelerating voltage quared, and the atomic number of the target element. The energy, or “hardness“ of x-radiation is usually specified in terms of electron volts. X-rays can penetrate solid matter. Th
10、e penetrating power is proportional to the energy of radiation Since it is generally accepted that peak voltages in excess of 15 kilovolts can cause significant x-radiation, measurements should be made of its intensity. EIA TEP170 72 m 3234b00 000848L 5 m B. MEASUREMENT OF X-RADIATION FROM MICROWAVE
11、 TUBES 1.0 Purpose and Scope 1.1 Purpose - To obtain the x-radiation characteristics of micro- wave tubes in order to determine the levels emitted by the tubes when they are operated at high voltages with integral tube shielding in place but without external shielding. 1.2 Scope - This test method a
12、pplies to the measurement of x-radiation emitted from microwave tubes. 2. O Apparatus Survey Meter - A dose-rate meter (electrostatically shielded) for probing or rapid surveying of a radiation field (Victoreen Model 440 RF/C, or equivalent.) This meter is intended to be the principal measuring inst
13、rument. Note: Other detectors of low energy x-radiation may also be used; such as Geiger-Mueller counters, proportional counters, scintillation counters, or solid-state counters, provided the calibration is known over the energy ranges being measured. 2.2 Ionization Chamber - 4k inch (11.43 cm) dime
14、ter and 4 inch (10.6 cm) length cylindrical ionization chamber (Victoreen 208A, or equivalent),used in combination with minometer. This chamber is meant ta be a secondary measuring instrument, but can be utilized as a reference standard. 2.3 Minometer - A device for charging the ionization chamber a
15、nd reading the residual charge after exposure (Victoreen II: Model 687C, or equivalent). 2.4 Timer - A stop-watch or equivalent device for measuring or controlling exposure time to an accuracy of at least 51.0%. 2.5 Test Equipment - To provide normal operation of the tube. Note: Test equipment shall
16、 be so designed as to shield operators to well below acceptable personnel safety levels. 2.6 Ionization Chamber Support - A holder for supporting the ionization chamber during exposure. of wood or plastic and shall not lie. the tube. It shall be constructed between the chamber and EIA TEP170 72 m 32
17、34600 0008482 7 2.7 Film Mount - A holder for x-ray sensitive film which has been from exposure to light (and heat designed to shield the film if necessary). Note: The mount often includes a series oftthicknesses of aluminum so that an expert (usually a film reader service)using a densitometer can d
18、etermine both energy and intensity. 3. O Calibra tion 3.1 The survey meter and/or ionization chamber and minometer combination must be calibrated by exposure to sources which bracket the intensity and energy to be measured. These standard source(s) shall be traceable to the National Bureau of Standa
19、rds. Note 1: Calibration shall be made in accordance with the three reading techniques f Section 5.2.4. Note 2: A large variety of microwave tubes emit x-rays with an effective energy between 7 keV and 21 keV, so these levels are recommended for calibration purposes when beam energy is in this range
20、. layers of alumm are 0.1 mm and 0.9 mm. For higher energy levels, the half value layers are as follows: Corresponding half value keV (effective) mJ; keV (effective) HVL J; 35 40 80 3.5 mm Al 1.0 mm Cu 4.8 mm AI 100 0.24 mm Pb 125 0.27 mm Pb 15 O 0.30 mm Pb half value layer Note 3 : To insure accura
21、te instrumentation, consideration should be given to correction factors for extreme variations in tempe rature and barometric pressur e. Note 4: If two or more individual laboratories require comparative radiation measurements, it is suggested that all chambers and minometers be calibrated by using
22、a common standard and by using the same standards laboratory (Victoreen instruments Company, or equivalent). 3.2 Stability of the calibration may be checked periodically by using an appropriate radioactive source. 4.0 Test Conditions 4.1 The tube under test shall be in a position to receive to the t
23、est The tube shall be operated at all equipment so that measurements will be made at the point where maximum radiati0n.s observed. conditions specified in the Tube Specification Sheet, - - EIA TEPL70 72 9 3234600 0008483 9 9 4.2 A warm-up period to minimize drift shall be provided for both the tube
24、and test equipment before proceeding with measurements. 4.3 It is recommended a group of tubes be measured to obtain worst condition data. It is also recommended that tubes nearing the end of life test also be measured as x-radiation may increase with life. 4,4 It is recommended that tubesbe measure
25、d while operating under pur- posely introduced unstable condttions as x-radiation may increase under non-normal operations 5. O Procedures 5.1 Survey Meter Method 5.1.1 The background radiation or leakage of the ionization chamber shall be verified at the test position for the test exposure period a
26、nd corrections to the observed data shall be applied as required (See Precautions). 5.1.2 The specified voltages of Section B.4 shall be applied. 5.1.3 The detectors specified for this measurement are normally calibrated to read the radiation level at the center of the detecting chamber. Therefore,
27、the distance from any readily accessible surface of the tube under test to the center of the chamber shall be 12 inches, This corres- ponds to 10 inches from the external surface of the tube under test to the window of the Victoreen Model 440 RF/C Survey Meter. mensions, the tube- to-window dis tanc
28、e will change. The tube- to-center-of-chamber distance remains constant. For equivalent equipment with different di- 5.1.4 Radiation measurements shall be made at the location of This point may be found by rotating maximum intensity. the tube or moving the survey meter. 5.1.5 Readings - At the point
29、 of maximum radiation, record the mximum stable radiation observed in mR/h. 5.2 Ionization Chamber Method 5.2.1 The background radiation or leakage of the ionization chamber shall be verified at the test position for the test exposure period and corrections to the observed data shall be applied as r
30、equired (See Precautions). 5.2.2 Radiation measurements shall be taken with the center of the Victoreen 208A ionization chamber 12 inches from any readily accessible surface of the tube under test. This corresponds to a distance of 9 inches between the window of the 208A and the external surface of
31、the tube under test. For equiva- lent equipment with different dimensions, the tube-to-window distance will change. The tube-to-center-of-chamber distance remains constant. EIA TEP170 72 I 3234b00 0008484 O 5.2.3 The measurements shall be made at the location of maximum intensity. mined with a surve
32、y meter. Readings - Atleast three successive readings shall be taken and averaged for each ionization chamber position. The location of maximum intensity may be deter- 5.2.4 5.3 X-Ray Film 5 .3.1 X-ray film can be used to define the source, measure the intensity, and determine the spatial pattern of
33、 the radiation, and to locate very small arearadiation sources such as leaks. It is recommended x-ray film be used on initial surveys to verify the point of grealrest radiation found hy the survey and ionization chamber methods. It can also be used for record purposes. Typical film types used are: K
34、odak type NS-2T No Screen Medical 5.3.1.1 X-ray Film, duplitized size 8“ x 10“ (optional) or equivalent. 5.3.1.2 Kodak Industrial X-ray Film type A A Estar Base size 8“ x 10“ (optional) or equivalent. 5.3.2 When film is used for record purposes, the film shall be positioned at a distance of 12 inche
35、s from readily accessible surfaces of the tube under test. Note: This method may be the only safe one to use when measuring x-radiation from very high voltage tubes. 6.0 Recorded Information The recorded information shall contain the following: 6.1 Identifiaction of the tube specimen, 6.2 Test date,
36、 laboratory and pertinent information on test equi-pment, including .model and serial numbers of chambers, minometers, and survey meters. Exposure time, minometer readings, average anode voltage and current, and any other test equipment data necessary to interpret results. 6.3 6.4 Report of readings
37、 per Sections B.5.1.5 and/or B.5.2.4. 6.5 Position of radiation measuring device. 7. O Precautions 7.1 When operating a tube with integral tube shielding in place but with- out external shielding, the x-radiation may be very great and hazard- ous. Adequate precautions must be taken to protect person
38、nel from _ _ EIA TEP170 72 W 3234600 0008485 2 W these hazards. When these conditions occur, film survey techniques are recommended in place of the survey meter. Assign film badges and dosimeters to all personnel involved in sur- vey operation. 7.2 7.3 High power tubes may emit large amounts of x-ra
39、diation . techniques should always be used in a preliminary survey to avoid accidental exposure to test personnel. Film badge. 7.3.1 Special coating cprovisions on film badges may be necessary if errors due to heat are to be avoided. Consult your film reader service. 7.4 7.5 It is desirable to keep
40、chambers fully charged when not in use. Chambers that have been fully discharged for an extended period may show an “insulation soakage“ Shen recharged. It may be avoided by repeated re-charging over a short period of 1.5 minutes or more. This leads to a drift. 7.6 It is desirable to keep a daily re
41、cord of the spontaneous discharge rate of ionization chambers due to natural radiation background of approximately 0.01 mRlh and to electrical leakage. If chmbers are recharged each day before use, (or during periods when not in use), the discharge rate can be determined. can be detected. In this wa
42、y excessive leakage 7.7 It is desirable to keep the protective cap on except when charging or reading to minimize the possibility of contaminating the end of the stem, but this protective cap must be removed before the instru- ment is used. 7.8 The exposed insulator et the end of the stem should not
43、 be contami- nated by touching, since body fluids may cause electrical leakage. 7,9 If necessary, the end of the stem may be cleaned by wiping with a soft cloth saturated with pure ethyl alcohol. 7.10 The same surface of the chamber should always be toward the tube to be measured, 7.11 The chamber s
44、hould be inserted in the minometer well with the same rotational orientation each time, 7.12 Radiation bursts (probably cosmic rays) produce transient deflections of the survey meter needle. tude. assure that the indication is a steady one due only to the tube being measured. They occur randomly.and
45、 vary in magni- Before a reading is recorded, precautioncshould be taken to 7.13 All radiation measuring devices have some degree of energy depend- ence. This is most.critica1 between 6 and 50 keV (the area of in- terest for microwave devices), where a small shift in the energy of the radiation bein
46、g measured may have a profound difference in the instrument response ckaracteristics. Therefore, instrument calibrations must be obtained against known radiation of the same EIA TEPL70 72 3234b00 000848b 4 spectral quality as that being measured. Readings made with survey instruments calibrated with
47、out regard to spectral responsecould read high (or low) by as much as a factor of 10 from the true exposure. (See section B.3.1). C. X-RADIATION CAUTION 1.0 2.0 3.0 Maximum X-Radiation Level- If the x-radiation level is below certain limits, the tube is consjidered safe. To determine the safe levels
48、, tube manufacturers shall consult state and local statutes, U.S. Government regulations, The National Council on Radiation Protection and Measurements, and the International Commission on Radiological Protection. Warnings - If the x-radiation level is in excess of that recommended in C.1.0 above, i
49、t is recommended that all the cautionmechanisms described below be used: 2.1 Tags and Decals - A decal shall be attached to each tube shipped. Recommended deslgn is shown if Fig. 1. If the size of the tube or specification prohibits or makes a decal impractical, it is recom- mended the same design be used on a tag which shall be attached to each tube shipped. 2.2 Application Notes, Bulletins and Tube Specification Sheets (TSS) Application Notes, Bulletins and TSS include the following reconmended paragraph: “THIS DEVICE MAY PRODUCE X-RADIATION WHEN ENERGIZED. CAUTION S
