4 8 4 



Table 596 

 ISOTOPES. PACKING FRACTIONS 



(See Table 851) 



This table contains several sets of values. Those followed directly by figures in parentheses, 

 e.g., Sn, 118.72 ( — 7.13 ± 2), taken from Aston, Proc. Roy. Soc, 115A, 487, 1927, give 

 first the atomic mass referred to oxygen (Oi 6 + O17) determined by the mass spectroscope 

 and often of greater probable accuracy than the corresponding atomic weight determination 

 (see Birge, p. 81 ff.). The figures following in parentheses are "packing fractions". The 

 protons and electrons are so closely packed that their electromagnetic fields interfere and a 

 certain fraction of the combined mass is destroyed. The mass destroyed corresponds to 

 energy released. The greater this is the more tightly are the charges cemented and the more 

 stable the nucleus. The "fraction" measures the divergence from the "whole number" rule 

 divided by the mass number, expressed in parts per 10,000. The numbers in braces are 

 ordinary atomic weights from page 483. Numbers in brackets are % abundance. The other 

 numbers are the nearest whole numbers to the mass of the corresponding isotope. Aston, 

 Philos. Mag., 49, 1 199, 1925. See page 486 for the radioactive isotopes. 



1.00778(778 ± 1.5) Abundance of 2. 1/800 



4.00216(5.4 ± 1) 



6.012(20.0 ± 3), 7.012(17.0 ± 3) 



{9.02) (Aston) 



10.0135(13.5 ± 1.5), 11.0110(10.0 ± 1.5) 



12.0036(3.0 ± 1), 13 (Birge, 1929) [Relative abundance, 400-1] 



14.008(5.7 ± 2), 15 (Naude, 1929) [Relative abundance, 700-1] 



16.0000, 17, 18, (Giauque, Johnston, i929)[Abundance Oie/Oi7 = 8600, Oie/Ou = 1100] 



19.000(0.0 ± 1) 



20.0004(0.2 ± 1), 22.0048(2.2?) 



{22.997) (Aston) 



24, 25, 26 (Dempster) 



(26.97) (Aston) 



28, 29, 30 (Aston) 



30.9825(- 5-6 ± 1.5) 



32, 97 % of whole; 34, 33 (Aston) 



34.983(-4.8 ± 1.5), 36.98o( -5.0 ± 1.5) 



39.97i(-7.2 ± 1), 35.976(-6.6 ± 5), 1% of whole 



39, 41 (Aston) 

 2? 40, 44? (Dempster) 



(45.10I (Aston) 



(47.90 j (Aston) 



[50.96) (Aston) 



[52.011 )S2(- I0)[82], 53[io], 50[5], 54[3], Aston, 1930 



1 54-93) (Aston) 

 2? 56, 54? (Aston) 



58, 60 (Aston) 



(65.380) (- 9-9), 64U8], 66[26], 68[i7], 65(2], 67(5]. 6g[i], 7o[o. 4 ] 



74-934(~ 8.8 ± 1.5) 



80, 78, 76, 82, 77, 74 (Aston) 



78.929(- 9-0 ± 1.5). 8o.926(- 8.6 ± 1.5) 



83-928(- 8.5 ± 2)[57l, 85-929(- 8.2 ± 1.5M17]. 8l.927(- 8.8 ± I.5M12] 



82.927(- 8.17 ± I.5)[l2], 79,926(- 9-4 ± 2)[2], 77.926(- 9-4 ± 2H.4] 



85, 87 (Aston) 



88, 86 (Aston) 



(88.92) (Aston) 



( 91.22 j (Aston) 



95-97(- 5.5). 98(- 5-5)[23]. 96[l8], 95(15]. 92[i4l. 94[lo], ioo(- 5S)[io], 97[lo] 



102(30], 101(22], 104(17], 100(14], 99(i2J, 96(5], 98?, (Aston, 1931) 



( 1 14.8) (Aston) 



118. 72(— 7.3 ± 2), 120(27.0], 118(21], 116(14.1], 124(6.2], 119(11.0], 117(9.8], 122(5.0], 



121(3.0], 112(1.1], H4(.7], 115(0.4] (Probably all the same packing fraction.) 



121, 123 (Aston) 



128, 130, 126 (Aston) 



i26.932(- 5-13 ± 2) 



131. 27(- 5-3). 129(27.1], 132(26.4], 131(20.7], 134(10.3]. 136(8.8], 130(4.2], 128)2.3] 



I26[.i], I24(.i] (Probably all the same packing fraction.) 



1 132.81 j (Aston) 



(140.92) (Aston) 



142, 144, 146, (145) (Aston) 



190. 3i( — 1.0 ± 2.0), 192(42.6], 190(25.1], 189(17-3). 188(13.5], i86[i.o], 187(0.6] (Aston, 1931) 



200.62(+ .08), 202(29.27], 200(23.77], 199(16.4]. 198(10], 201(13.7], 204(6.8], I96[.i] (All 



same packing fraction.) 



207, 205, 211, 203, 201 , 209, 213, 215, Goslin, Allison 



238, 239, 240, 234, 237, 235, 233, 236, Goslin, Allison 



Corrections (Nature 192, 477, Mar. 26, 1932. 



Kr 83.7. Xe 131. 3- 



Calculation of atomic weights from mass spectra leads to the following: (O =16): Ratio isotopes O16: 

 Oi8:Oi7::630:i:o.2. 



Li 6.923, Cs 132.91, B 10.806, Ge 72.65, Se 78.96, Te 128.03, W 183.96, Br 79.916, Re 186.22, Ru 101.1, 

 Os 190.31. 



For isotopes of Pb (201 to 216), Bi (205 to 217, 219), Ra (226, 228, 230, 232), Th (229 to 236); Bishop, 

 Lawrenz, Dollins, Allison, Goslin, Phys. Rev. 43, 1933- 



Smithsonian Tables 



