1、- EIA TEP189 74 W 3234b00 0008519 4 W F E BRU ARY 1 974 ELECTRON TUBE RADIOACTIVITY CALCULATIONS IN MIC ROCURC E S/ T U BE FORMULATED BY JEDEC ELECTRON TUBE COUNCIL JEDEC PUBLICATION NO. 89 f r Publwle by ELECTRONIC INDUSTRIES ASSOCIATION Engineering Department 2001 Eye Street, N. W., Wrrhington, D.
2、 C. 20006 -_ I , t EIA TEP189 74 I 3234600 O008523 2 I -2- F O R E W O R D Minute quantities of radioactive isotopes are sometimes used to enhance the performance of electron tubes. Because of the Gery low level involved; it is impractical to directly measure the radioactivity. This Publication esta
3、blishes a recommended practice for calculation of these levels on a per tube basis. It was developed by the JEDEC JT-16 Committee on Government Specifications and Standards and approved for Publication by the JEDEC Electron Tube Council, EIA TEP189 74 W 3234b00 0008522 4 W 1 INTRODUCTION Radioactive
4、 isotopes are, on occasion, intentionally added by manufacturers of electron tubes to improve tube performance. may be required to determine the total radioactivity in microcuries per tube (pc/tube) to comply with existing Federal regulations. It is usually impractical to measure the radioactivity w
5、ith any degree of precision, The radionuclide is often surrounded by electrodes, spacers, and an envelope calibration of a measuring device; and the amount of radionuclide inten- tionally added in the tube is often so small that the amount of radiation is difficult to discern from the normal backgro
6、und radiation that exists in the atmosphere. For this reason, manufacturers such that the geometry considerations preclude a realistic Therefore, the radioactivity for electron tubes shall be determined by a calculation technique in terms of the known radionuclides which have been intentionally adde
7、d to the electron tube to either increase tube life or to improve the overall tube perforniance. BASIC THEORY The number of atoms (dN) in any one radioactive element that will disintegrate in a small interval dt is proportional to the number of atoms (N) present at the beginning of the time period d
8、t. The fundamental law of nature which describes the rate of disintegration or decay of a radioactive element is therefore as. follows: I i where A = a proportionality constant for the particular radioactive element; often called the decay or disintegration constant N = number of radioactive atoms o
9、f the element at any time t - dN dt = rate of disintegration (the rate change of N is negative because N is decreasing with time) Rearranging equation (1) gives : (3) - dN = -Adt N integrating equation (3) gives : !- - 5 - EIA TEP189 74 m 3234600 0008523 b m -4- (4) In N = -At + C at t = .O; N = No
10、therefore, equation (4) can be rewritten: In No = -A(O) + C or C = In No Referring to equation (4) again and replacing C: In N = -At + In No and In N - In No = -At (5) 1-1 natural logarithmic form to base E Rewriting equation (5) : r c (7) or, INt = No E -At 1 exponential foh Definitions: where No =
11、 original number of radioactive atoms of the element at time t = O N = Nt = number of radioactive atoms after a given decay time t X = a porportionality constant (decay constant) for a given radioactive element t = decay time Equations(5) (6)and(7)are written in tem of the natural logarithm to the b
12、ase E(Log Nt p log NO = log (F. -At -At) Nt f -At log F log - i NO Since: log E = ,4343 lyl c;oi logarithmic f om (base 10) common logarithmic QIX (base 10) or No (10 -.4343At) _ - At the half-life time: NT = 1/2 No due t half the atoms disintegrating andt = T Substituting in equation (9): - - _*-.
13、a. EIA TEPLBS 74 m 3234600 0008525 T m c 10 Theref ore: (13) 1.0 curie = 3.7 x 10 e disintegrations/second -6- 693 ,3010 .4343 AT=-= This expression for T (equation (11) is the same result that was derived from the exponential form (equation (8) using natural logarithms. (11) m/ For radioactive deca
14、y calculations the “half -life“ is a more convenient parameter to use than the decay constant A. can now be expressed in terms of the half-life T. The rate of disintegration from equation (2) - Substituting for X from equation (8): *693 NI rate of disintegration dt T Where A = atomic weight of the r
15、adioactive element Now the specific activity (S.A.) is the rate of decay of - one gram of the radioactive element or nuclide expressed in curies or microcuries. Therefore, 1 23 0.693 6.02 x 10 A 3.7 x loLu S.A. = - T (16) curies = curies/gram of radio- i/sec x atoms/gram x atom/sec (Specific = Activ
16、ity) active element EIA TEP189 74 m 3234600 O008526 L m E. i -7- (Specif i c Activity) element Reducing the Specific Activity equation (17) gives: 1.13 x 10 vc/gram of radio- for T = half-life in secondi TA active element S.A. = S.A. = 1.88 1017 TA 11 T = Ealf-life in minute! S,A, = 3.14 x 11 T = ha
17、lf -life in hours TA S.A. = 1.31 x1Ol4 I1 TA S.A. = 3.58 x 10l TA II 3: = half-life in days T = half-life in years To obtain the radioactivity in uc/tube: r I Radioactivity = S.A. above in pc/gm of radioactive element x actual mass in grams of the radioactive element used in the (w/ tube) tube I I I
18、f the radioactive element or nuclide is part of a mixture or a chemical compound, the specific-activity expression must be reduced by an amount corresponding.to the raction of the material which is radioactive since specific activity (S.A) is expressed per gram of radioactive element rather than the
19、 compound. Several.examples of the calculation of specific activity and ultimately the. radio- activity in pc/tube are included as follows: - EIA TEP189 74 W 3234600 0008527 3 W i. -8- EXAMPLES: RADIOACTIVE CALCULATIONS* A. For Pure Radioactive Element a 187 1. Re Known Factors 10 T = 4.3 x 10 years
20、 Reference Symbols T = half-life A = 187 A = atomic weight of radioactive gms of Re187 in tube = 0.1 S.A. = specific activity = rate of decay of 1 gram of pure radioactive element expressed in pc/gm of element Using equation (22): .3.58 x 10l1 S.A. = T A ; T in years the pure radioactive element (I.
21、ic/gm) -_ S.A. = 3.58 x 10l1 4.3 x 1O1O x 187 .S.A. = 0.0445 pc/gm of Re187 From equation (23): Radioactivity = S.A. (pc/gm) of radioactive element x gm of (IJ c/ tube ) radioactive element actually used per tube Radioactivity = 0.0445 x 0.1 gram of Re187 used in tube 1 Radioactivity = 0.00445 pc/tu
22、be of Re187 I From Vendor Information of ,002 pc/mm“/plated side compute pc level/Tab : Known Factors T = 92 years A = 63 I.ic/Tab = ,002 yc/m2 x 3mm2 x 2 plated 1 Tab of Nis3 material used/tube Area of each side of Ni63 tab = sides/Tab 3 m2 = .o12 Nis3 is plated on both sides of each tab Vendor Inf
23、ormation: .O02 pc/mm2/ plated side J: See Table 1 - Half-Life Values of Radioactive Elements EIA TEP189 74 3234600 0008528 5 m (24) -9 - - Radioactivity = .O12 yc/tube of NiG3 (26) I, I gms of Ni63/tube = 1.94 x Now using equation (22) : Radioactivity = ,012 ic/tube of Ni63 (27) S.A. = 3.58 x 10l1 9
24、2 x 63- OE 61.77 curies/ of Ni63 .k Dtvide equation (24) = .O12 pc/tube of Ni63 by equation (25) where the specific activity = 61,770,OQO pc/ of Ni63 to calculate the grams of Ni63 in the tube: ,012 pc/tube gms of Ni63/tube = - 61,770,000 pc/gm Ni63 Therefore, Repeating equation (23) : * This result
25、 not only shows the pc level/tube but also verifies the . pc/tube value obeained in equation (24) above, It also certifies that the calculated gm weight of Ni63 determined in equation (26) as 1.94 X 10-lo gm of Ni63/tube is likeiiise correct. The small amount of Ni63 used/tube (1.94 x infinitesimal
26、and.when multiplied by the large specific activity value for Ni63 (61,770,000 pc/gm of NiG3) gives an end product having an extremely low radioactivity level of . O12 ricltube. gms) is nearly EIA TEP189 7Y W 3234600 0008529 7 W + (28) -10- Radioactivity = 0.30 yc/tube of Co60 Known Factors T = 5.26
27、years A = 60 gms of Co60 in tube = 2.64 x Using equation (22): 305 = Fic/gm of c060 TA S.A. = = 3.58 x 10l1 5.26 (60) S.A. = 1,137 x lo9 vc/gm of Co60 Radioactivity = 1,137 x lo9 pc/gm of Co60 x 2.64 x .gms of Co60/tube 4. For Several Pure Radioactive Elements oz-Nuclides When more than one radioact
28、ive element or nuclide is present in an electron tube, then the radioactivity of each specie is determined (per Ai or A2 or A3 method above) and the radioactivity results can then be added to give the total radioactivity for the electron tube. For Radioactive Compounds 1. Thorium Tungsten Wire (ThW)
29、 Using equation (22) : 3*58 O1; T in years TA S.A. = W/gm 3.58 x 10l1 1.41 x lolo x 232 S.A. = S.A. = 0.1094 w/gm thorium Known Factors Th232 (radioactive thorium is the only radioactive compound T = 1.41 x lolo years A = 232 1.2% thoria in thoria tungsten (ThW) wire Wt of ThW wire used per tube = g
30、m of Th/tube = 0.00105 (see calculation of equation (31) on page 9) 0.1 gm EIA TEP183 74 m 3234b00 0008530 3 m -11- -F 5 t Radioactivity = 0,000115 pc/tube of Thorium From equation (23): Radioactivity pc/tube gmTh = S.A, x gm thorium actually used per tube Alternate Approach for B1, above 1 gm of Th
31、W wire contains 1.2% Th02 (Thoria) 1 gm of ThW wire contains 1 x ,012 = ,012 gms Th02 Atomic weight of Tho2 = 232 Molecular weight of Th02 = 232 + 32 = 264 Therefore, ratio of Th tb Th02 is: 232 (Th) = 0,879 264 (Th02) 232 Th 0.012 g Th02 264 Th02 = ,879 (-012) = 0.0105 gms Th/gm ThW wire gm ThW wir
32、e since 0.1 gm of ThW wire is used/tube, thefi: 0.0105 gm Th/gmThW wire x 0.1 gm ThW/tube = _ GmsTh Used = 0.00105 gm Th/tube The specific activity for thorium: S.A. Then: 0.1094 pc 0.0195 gm Th = 0.1094 wc/gm thorium (see pfevlous S.A. calculation equation (29) gmm gm ThW Wire = 0,00115 w/gm ThW wi
33、re since the weight of ThW wire used per tube = 0.1 gm Radioactivity = 0.00115 yc/gm ThW wire x 0.1 gm ThW wire/tube (w/ tube) adioactivity = .O00115 pc/tub& of Thorium For Several Radioactive Compounds in an Electron Tube When more than one radioactive compound is present in an electron tube, then
34、the radioactivity of each compound is determined and the radio- activity results can then be added to give the total radioactivity for O EIA TEP389 74 m 3234600 0008533 5 m c Radioactive Element 57 27“ 60 27“ 63 2 8Ni . 85 36“ 85m 3 gKr 187 75Re 226 88Ra o Th2 32 238 92 -12- Radi at ion Y - B- - 6 8
35、- - a 01 Energy (Hev) o. 122 O. 314 ,067 _ O. 67 O. 82 ,003 4.781 4.60 4.01 3.95 4.20 4.15 Hlf -Lif e Time -. . (0 270 days 5.26 yrs 92 yrs 10.76 yrs 4.4 hrs 4.3 x io10 .yrs 1602 yrs 1.41 x lO1O yrs 4.51 x LO9 yrs TABLE 1 HALF-LIFE VALUES OF RADIOACTIVE ELEMENTS* *Taken -from Radiological Health Han
36、dbook, U. S. Dept, of H. E.W. . Public Health Service Publication No. 2016, January 1970 * EIA TEP189 74 m 3234600 0008532 7 m 5 -13- BIBLIOGRAPHY 1, Reference Data for Radio Engineers, Fourth Edition, by International Telephone & Telegraph.Corpo-ration, 1956 2, Sourcebook on Atomic Energy by D. Van Nostrand Co.Inc., Princeton, New Jersey, 1970
