Aston 1922
ISOTOPES[1]
F. W. ASTON, M.A., D.Sc, A.I.C., F.R.S.
Fellow of Trinity College, Cambridge
LONDON
EDWARD. ARNOLD & CO.
1922
[All rights reserved]
Printed in Great Britain
PREFACE
I have undertaken the preparation of this book on isotopes in response to many requests made to me by teachers of physics and chemistry and others working in these subjects that I should publish the results obtained by means of the mass spectrograph in a form more convenient to the public than that in which they first appeared. This is one of the reasons why the space allotted to the inactive isotopes may appear, in the light of the general title of the book, somewhat disproportion- ately large. Another is that the subject of radioactive isotopes really requires a book to itself, and I am in the hope that the inadequacy of my account may stimulate the production of such a volume by hands more competent than mine to deal with this very special and remarkable field of modern science. The logical order of exposition of a scientific subject is to start with the simple and from that build up the more complex. Unfortunately the sequence of events in experimental research is the exact opposite of this so that a compromise must be effected, unless one is content to sacrifice historical treatment altogether. The latter seems very undesirable in a new subject. I have endeavoured in Chapters I, II and IV, and elsewhere when possible, to adhere strictly to the historical order of events even at the cost of some reiteration.
I wish to take this opportunity of expressing my indebted- ness to Mr. C. G. Darwin for his timely criticism and unfailing assistance throughout the work, and also to Mr. R. H. Fowler for help with the proofs. My thanks are also due to Professor Soddy for his diagram of the radioactive isotopes, to Mr. A. J. Dempster for kindly sending me the illustrations of his work, to the proprietors of the Philosophical Magazine and to the Council of the Chemical Society for permission to use the plates and figures of my original papers, and to Messrs. Macmillan & Co., for the diagram of the radioactive trans- formations.
- F. W. Aston
- Cambridge,
- January, 1922.
CONTENTS
CHAPTER I - INTRODUCTION
CHAPTER II - THE RADIOACTIVE ISOTOPES
CHAPTER III - POSITIVE RAYS
CHAPTER IV - NEON
CHAPTER V - THE MASS-SPECTROGRAPH
CHAPTER VI - ANALYSIS OF THE ELEMENTS
CHAPTER VII - ANALYSIS OF THE ELEMENTS (Continued)
CHAPTER VIII - THE ELECTRICAL THEORY OF MATTER
CHAPTER IX - ISOTOPES AND ATOMIC NUMBERS
CHAPTER X - THE SPECTRA OF ISOTOPES
108. The Spectra of isotopes. As has already been stated^ the first experimental work on the spectra of isotopes was that of Russell and Rossi in 1912 who failed to distinguish=
any difference between the spectrum of thorium and that of a mixture of thorium and ionium containing a considerable percentage of the latter. The same negative result was obtained by Exner and Haschek.^ During the fractional diffusion of neon^ no spectroscopic difference was detected between the heaviest and the lightest fraction, though as the separation was small this negative evidence was not very strong. In 1914 Soddy and Hyman showed that the spectrum of lead derived from thorium was identical with that of ordinary=
lead.* Furthermore in the same year the experiments of Richards and Lembert,^ Honigschmidt and HoroAvitz,*^ and Merton proved the same result. Merton concluded from his 1914 experiments that the difference in wave-length for the A 4058 line must be less than 0-003 A. Before going on to consider the more recent results it will be as well to discuss = the magnitude of the difference to be expected from theory.
109. The magnitude of the Gravitational effect. In
the Bohr theory of spectra the planetary electrons of the atom rotate round the central positively charged nucleus in various
1 F. p. 9.
2 Exiier and Haschek, Sitz. Akad. Wiss. Wien, iia, 121, 175, = 1912.
3 V. p. 39.
- Soddy and Hyman, Jour. Chem. Soc, 105, 1402, 1914.
^ Richards and Lembert, Jour. Amer. Chem. Soc, 36, 1329, 1914.=
^ Honigschmidt and Horowitz, Sitz. Akad. Wiss. Wien, iia, = 123, 1914.
' Merton, Proc. Roy. Soc, 91A, 198, 1914.
121
122 ISOTOPES
stable orbits. The frequencies of the spectral lines emitted by the element are associated in an absolutely definite manner with the rotational frequencies of these orbits which are calculated by what is known as a " quantum " relation. Without going further into the theory it will be seen at once that if we alter the force acting between the central nucleus and its planetary electrons these orbits will change and with them the frequency of the light emitted. It is therefore of interest to examine the magnitude of the change, to be expected=
from this theory, when we alter the mass of the nucleus without=
changing its charge, and so pass from one isotope to another.
The difference in the system which will first occur to one is that although the electrical force remains the same the gravi- tational force must be altered. The order of magnitude of the change expected in the total force will clearly be given by=
considering the ratio between the electrical and gravitational forces acting, to take the simplest case, between the protou and the electron in a neutral hydrogen atom.
Assuming the law of force to be the same in both cases, this ratio is simply e^/GMm ; where e is the electronic charge 4-77 X 10~i", G the universal gravitational constant 6-6 x 10"^,=
M the mass of the proton 1-66 x lO"^*^ and m the mass of the=
electron 9-0 x 10~ 2^. Putting in these numerical values we obtain the prodigious ratio 2-3 x 10 ^9. In other words the effect of doubling the mass of the nucleus without altering its=
charge would give the same percentage increase in the total pull on the planetary electron, as would be produced in the pull between the earth and the moon by a quantity of meteoric dust weighing less than one million millionth of a gramme falling upon the surface of the former body. The gravitational effect may therefore be dismissed as entirely negligible.
110. Deviation of the Bohr orbits due to change in the position of the centre of gravity of the rotating system. Although we may neglect the gravitational effect there is another, of quite a different order, which arises in th= e following manner. The mass of the electron compared with that of the nucleus is small but not absolutely negligible, hence=
it will not rotate about the nucleus as though that were a
THE SPECTRA OF ISOTOPES 123
fixed point, but both will rotate about their common centre of gravity. The position of this centre of gravity will be shifted by any alteration in the mass of the nucleus. If E, M=
and e, m are the respective charge and mass of the nucleus and=
the rotating electron, the equation of motion is
rM , Ee
M + m r^
where r is the distance between the two charges and w the angular velocity. Bohr ^ introduced this effect of the mass of the nucleus in order to account for the results obtained by Fowler. 2 The Bohr expression for the frequency then becomes
where e, E and m, M are the charges and masses of the electron=
and nucleus respectively. If we suppose that the atomic weight of lead from radium to be one unit less than that of ordinary lead, this theory predicts a difference in wave-length, for the principle line, of 000005 A between the two, a quantity=
beyond the reach of the most delicate methods of spectrum analysis used up to the present.
111. Later experiments of Aronberg and Merton.
In 1917 Aronberg,^ applying the extremely high dispersion derived from the spectrum of the sixth order of a Michelson 10-inch grating to the line A 4058 emitted from a specimen of radio-lead of atomic weight 206-318, observed a difiference of 0-0044 A between this and ordinary lead, of atomic weight 207-20. This remarkable result has been since confirmed by Merton of Oxford* who gives the difference of wave-length between radio-lead from pitchblende and ordinary lead as 0-0050^2 0-0007, Merton made use of a totally different optical system, namely a Fabry and Perot etalon, so that the agreement is very striking.
It is to be noticed that the effect observed was not a mere
1 Bohr, Nature, 92, 231, 1913.
2 Fowler, Nature, 92, 95, 1913.
3 Aronberg, Proc. Nat. Acad. Sci., Z, 710, 1917, and Ast= rophys, Jour., 47, 96, 1918.
4 Merton, Proc. Boy. Soc, 96A, 388, 920.
124
ISOTOPES
broadening of the line but a definite shift, and that, though
of the same sign, it is about one hundred times greater than
that predicted by the Bohr theory, Merton also found a shift
of 0-0022 =C2=B10-0008 A between the wave-length of thorite-lead
and ordinary lead, differing in atomic weight by about 0-6.
The heavier atom shows the higher frequency in all cases.
This remarkable discrepancy between the shift predicted by
theory and that actually observed has been discussed by
Harkins and Aronberg.^
At a recent discussion on isotopes at the Royal Society ^ Merton commented upon the line 6708 A emitted by the element lithium, which consists of two components 0-151 A apart. If lithium is accepted as a mixture of isotopes 6 and 7,= ^ he calculated that each of these components should be accom- panied by a satellite, some sixteen times as faint, displaced by=
0-087 A. So far he had not been able to observe such satellites= . Previous experiments of Merton and Lindemann* on the expected doubling in the case of neon had given no conclusive results on account of the physical width of the lines. It was hoped that this difficulty could be overcome by the use of liquid hydrogen temperatures.
StiU more recently Merton^ has repeated his experiments on lead, using a very pure sample of uranium lead from Australian Carnotite. His final results are indicated in the following table :
A
(Carnotite lead)"! . ^(ordinary lead) J
r Wave niimber (ordinary lead) ' . Wave-number (Carnotite lead).
4058 3740 3684 3640 3573
0-011 =C2=B10-0008 0-0074=C2=B10-0011 0-0048=C2=B10-0007 0-0070=C2=B10-0003 0-0048=C2=B10-0005
0-065=C2=B10-005 0-053=C2=B10-008 0-035=C2=B10-005 0-C52=C2=B10-002 0-037=C2=B10-004
1 Harkiiis and Aronberg, Jour. Am. Chem. Soc, 42, 1328,
Merton, Proc. Roy. Soc.=C2=BB 99A, 87, 1921.
=C2=BB V. p. 86.
- Lindemann, ibid.
Merton, Roy. Soc. Proc, lOOA, 84, 1921.
1920.
THE SPECTRA OF ISOTOPES 125
It will be noticed that the shift for the line A 4058 is rathe= r more than twice that obtained before. Merton suggests that the most probable explanation of this difference is evidently that the Carnotite lead used is a purer sample of uranium lead=
than that obtained from the pitchblende residues. It is also apparent that the differences are not the same for different lines, an interesting and somewhat surprising result.
112. "Isotope" effect on the Infra-red spectrum of molecules. The extreme smaUness of the isotope " shift "=
described above in the case of line spectra emitted by atoms is=
due to the fact that one of the particles concerned in the vibration is the electron itself, whose mass is minute compared with that of the nucleus. Very much larger effects should be expected for any vibration in which two atoms or nuclei are concerned, instead of one atom and an electron. Such a vibration would be in the infra-red region of the spectrum.
This effect was first observed by Imes^ when mapping the fine structure of the infra-red absorption bands of the halogen acids. In the case of the HCl " Harmonic " band at 1-76^, mapped with a 20,000 line grating, the maxima were noticed to be attended by satellites. Imes remarks : " The apparent tendency of some of the maxima to resolve into doublets in the=
case of the HCl harmonic may be due to errors of observation, but it seems significant that the small secondary maxima are all on the long-wave side of the principal maxima they accom- pany. It is, of course, possible that still higher dispersion applied to the problem may show even the present curves to be composite."
Loomis^ pointed out that these satellites could be attributed to the recently discovered isotopes of chlorine. In a later paper ^ he has shown that, if mi is the mass of the hydrogen nucleus, and ma the mass of the charged halogen atom, the
difference should be expressed by the quanity ^ = ~ the
square root of which occurs in the denominator of the expression=
^ Imes, Astrophysical Journal, 50, 251, 1919.
2 Loomis, Nature, Oct. 7, 179, 1920.
^ Loomis, Astrophysical Journal, 52, 248, 1920.
126 ISOTOPES
for frequency. " Consequently the net difference between the spectra of isotopes will be that the wave-lengths of lines in the spectrum of the heavier isotope will be longer than the=
corresponding lines for the lighter isotope in the ratio 1 + 1/1330 : 1 for chlorine and 1 -f 1/6478 : 1 for bromine.=
Since the average atomic weight of chlorine is 35-46 the amounts=
of CP^ and CP' present in ordinary chlorine must be as 1-54 : 0-46 or as 3-35 : 1 and, if the lines were absolutely = sharp and perfectly resolved, the absorption spectrum of ordinary HCl should consist of pairs of lines separated by 1/1330 of their frequency and the one of shorter wave-length should have about 3-35 the intensity of the other. The average atomic weight of bromine is 79-92, hence the two isotopes are present in nearly equal proportions and the absorption spectrum of HBr should consist of lines of nearly equal intensity separated by 1/6478 of their frequency."
The latter will be too close to be observed with the dispersion=
employed. In the case of the HCl band at IIQ ju the difference=
of wave number on this view should be 4-3. The mean differ- ence of wave number given by Loomis' measurements of 13 lines on Imes' original curves for this band is 4-5 ^ 0-4 corre= - sponding to 14 A in wave-length.
The spectroscopic confirmation of the isotopes of chlorine has also been discussed by Kratzer,! who considers that the oscillation-rotation bands of hydrogen chloride due to Imes^ are in complete accordance with the theory.
1 H. Ivratzer, Zeit. Physik., 3, 60, 1920.
- Loc. cit.
CHAPTER XI - THE SEPARATION OF ISOTOPES
APPENDIX I
Table of atomic weights and isotopes of the elements.
The elements are given in order of their atomic= numbers. The
different periods are indicated by gaps after the inert gases. A curious relation, pointed out by Rydberg, is that the atomic numbers of all the inert gases are given by taking the series 2 (P + 2^ + 22 + 3^ + 3^ + 4^ + = ) and stoppmg the summation at any term. This gives the numbers used by Langmuir (p. 95).
The atomic weights given are the International ones except in the cases marked with an asterisk, where the figures are taken f= rom some of the recent determinations given below.
The isotopes where known are given in order of their atomic masses. The proportion of an isotope in a complex element is indicated by the index letters a, 6, c ... in descending order.=
In the case of isotopes of the radioactive elements 81-92 the ro= man numeral gives the number of them believed to exist. The nomen- clature of some of the rare earths 69-72 is not yet standardised.=
The names here are those used by Moseley. Some of these elements= , though detected by their X-ray spectra, have never been isolated.=
The elements corresponding to atomic numbers 43, 61, 75, 85, 87=
(all odd) have not yet been discovered.
Recent atomic weight determinations. The following is a list of some of the elements whose atomic weights have been re-=
determined quite recently, together with references to the papers in which they were published. Where more than one value is given different methods were used :
Fluorine 19-001. Moles and Batuecas, Jour. Chim. Phys., 18, 35= 3,
1920. Aluminium 26*963. Richards and Krepelka, Journ. Am. Chem. Soc,=
42, 2221, 1920.
Silicon 28-111. Baxter, Weatherelland Holmes, ibid., 42, 1194, =
1920.
Scandium 45-10. Honigschmid, Zeit. Electrochem., 25, 93, 1919.=
Tin 118-703. Baxter and Starkweather, Journ. Am. Chem. Soc, 42,=
905, 1920.
118-699. Brauner and Krepelka, ibid., 42, 917, 1920.
141
142
APPENDIX I
Tellurium 127-73, 127-79. Bruylants and Michielsen, Bull=
. Acad.
Bdg., 119, 1919. Samarium 150 "43. Owens, Balke and Kremers, Journ. Am. Chem= .
Soc, 42, 515, 1920. Thtdium 169-44, 169-66. James and Stewart, ibid., 42, 2022, = 1920. Bismuth 209-02. Honigschmid, Zeit. Electrochem., 26, 403, 1920= .
208-9967. Classen and Wey, Ber., 53, 2267, 1920. Antimony 121-773. Willard and McAlpine, Jouryi. Am. Chem. Soc, = 43,
797, 1921. Lanthanum 138-912. Baxter, Tani and Chapin, Journ. Am. Chem.=
Soc, 43, 1085, 1921.
Germanium 72-418. Miller, Journ. Am. Chem. Soc, 43, 1085, 19=
21.
Zinc 65-38. Baxter and Hodges, i&id., 43, 1242, 1921.
Cadmium 112-411. Baxter and Wilson, ibid., 43, 1230, 1921.
-Q
" m
o^
Element.
2
a
if
Masses of isotopes.
=C2=A3 -2 *^ Hydrogen . .
H
1
1-008
1
1-008
f^^'o Helium . . .
He
2
4-00
1
4
&> 1"
00 Lithivim .
Li
3
6-94
2
-
" Beryllium
Be
4
91
1
9
r^ Boron
B
5
10-9
2
10=C2=BB 11"
3 Carbon .
C
6
12-00
1
12
S Nitrogen .
N
7
14-008
1
14
^ Oxygen . . .
0
8
16-00
1
16
0 Fluorine .
F
9
19-00
1
19
^ Neon ....
Ne
10
20-20
2
20" 22* 23
oQ Sodium .
Na
11
2300
1
^ Magnesium .
Mg
12
24-32*
3
24-=3D 25* 26^
Aluminium .
Al
13
26-96*
_o Silicon
Si
14
28-3
2
28" 29* (30)
3 Phosphorus .
P
15
31-04
1
31
^ Sulphur . . .
s
16
3206
1
32
'S Chlorine . . .
CI
17
35-46
2
35" 37* (39)
^ Argon . . .
A
18
39-9
2
36* 40" 39" 41*
Potassium
K
19
39-10
2
Calcium .
Ca
20
40-07
(2)
40 (44)
Scandium
Sc
21
45-1*
Titanium .
Ti
22
48-1
Vanadium
V
23
510
0
2 Chromium .
Cr
24
52-0
H Manganese .
Mn
25
54-93
' Iron ....
Fe
26
55-84
n
^ Cobalt . . .
Co
27
58-97
J Nickel
Ni
28
58-68
2
58" 60*
P
n Copper .
Cu
29
63-57
J
=3D Zinc ....
Zn
30
65-37
(4)
(64=C2=B0 66* 68 7O<0
- Galliimi . . .
Ga
31
70-10
Germanivmi .
Ge
32
72-5
Arsenic .
As
33
74-96
1
75
Seleniima .
Se
34
79-2
Bromine .
Br
35
79-92
2
79" 81*
Krypton .
Kr
36
82-92
6
78/ 80 82'^ 83-^ 84=C2=BB
86*
APPENDIX I
143
"S .
^
o *^
O^i
o ^^
Element
o
X!
E >,
00
Masses of Isotopes.
Rubidium
Rb
37
85-45
2
85" 87*
Strontium
Sr
38
87-63
Yttrium .
Y
39
89-33
Zirconium
Zr
40
90-6
Niobium .
Nb
41
93-1
00 Molybdenum
Mo
42
96-0
- H _ ~
43
'-' Ruthenium .
Ru
44
101-7
'o Rhodium.
Rh
45
102-9
=C2=A7 Palladium
Pd
46
106-7
An Silver ....
Ag
47
107-88
X Cadmium
Cd
48
112-40
"O Indiimi .
In
49
114-8
Tin ... .
Sn
50
118-7
Antimony
Sb
51
120-2
Tellurium
Te
52
127-5
Iodine
I
53
126-92
1
127
L Xenon
X
54
130-2
(7)5
(128) 129" (130) 13P 132=C2=BB 134 136"
Caesium .
Cs
55
132-81
1
133
Barium .
Ba
56
137-37
Lanthanum .
La
57
139-0
Cerium
Ce
58
140-25
Praseodymium .
Pr
59
140-6
Neodymiimi .
Nd
60
144-3
61
Samarium
Sm
62
150-4
Europium
Eu
63
152-0
Gadolinium .
Gd
64
157-3
Terbium .
Tb
65
159-2
Dysprosium .
Ds
66
162-5
c
5 Holmium
Ho
67
163-5
J, Erbium .
Er
68
167-7
=C2=B0 Thulium . . .
Tu
69
168-5
1 Ytterbiiun . .
Yb
70
173-5
'C Lutecuim
Lu
71
175
Pm (Keltium) . .
(Kt)
72
ji Tantalum
Ta
73
181-5
<=C2=BB Tungsten.
W
74
1840
75
Osmium .
Os
76
190-9
Iridium .
Ir
77
193-1
Platinimi .
Pt
78
195-2
1
Gold ....
Au
79
197-2
Mercury .
Hg
80
200-6
(6)
(197-200) 202 204
Thallium . . .
Tl
81
204-0
IV
Lead ....
Pb
82
207-2
XI
Bismuth .
Bi
83
209-0*
V
Poloniuna
Po
84 85
z
VII
L Emanation
Em
86
222-0
III
i
87
.2 Radium . =C2=AE Actinium.
Ra
88
226-0
IV
Ac
89
II
^ Thorium . . .
Th
90
23215
VI
^ Uranium X .
UX
91
II
t_ Uranium
Ur
92
238-2
II
APPENDIX II
The Periodic Table of the Elements. The atomic numbers ar= e given in bold type, the atomic weights in italics and the isotopes, where = known, in ordinary numerals. The roman ntmierals indicate the chemical groups and the most important associated valencies are given below them. Elem= ents are placed to the left or to the right of the columns according= to their chemical properties, those in the same vertical line as each other have s= trong chemical similarities. The Rare Earth group is surrounded by a thick line.= Elements 59-72 have no properties pronounced enough to give them definite = places in the table. The properties of the missing elements can be p= redicted with
PERIODIC TABLE OF
IH
1-008
Valency
0
I
+ 1
II
+ 2
III
+ 3
IV
+ 4
2 He
4-00 4
3 Li
6-94 6, 7
4 Be
9-1
9
5B 10-9 10, 11
60
12-00 12
10 Ne
20-2 20, 22
11 Na
23-00 23
12 Mg
24-32
24, 25, 26
13 AI
26-96
14 Si 28-3 28,29
18 A
39-9 36, 40
19 K
39-1 39, 41
29 Cu
63-57
20 Ca
40-07
30 Zn
65-37
21 Sc 45-1
31 G
70-1
22 Ti 48-1
32 Ge
72-5
36 Kr
82-92
78, 80, 82, 83, 84, 86
37 Rb
85-45
85, 87
47 Ag 107-88
38 Sr
87-83
48 Cd 112-40
39 Y
89-33
49 In
114-8
40 Zr
90-6
50 Sn
118-7
54 Xe
130-2
129, 131, 132, 134, 136
55 Cs
132-81
133
56 Ba
137-37
57 La 58 Ce 139-0 140-25
59 Pr eONd 61 62 Sm 63 Eu =
64 Gd 65 Tb
140-6 144-3 150-4 152-0 =
157-3 159-2
66 Ds 67 Ho 68 Ev 69 Tu 70 Yb 7= 1 Lu 72 (Kt) 162-5 163-5 1677 168-5 173-5 =
175
79 Au
197-2
80 Hg
200-6 197-204
81 Tl
204-0
82 Pb
207-2
86 Em
222-0
87-
88 Ra
226-0
89 Ac
90 Th
232-15
144
considerable certainty from the positions of their atomic numbers. From the point of view of the construction of the atom the inert gas= es should mark the end of the periods as they are shown to do ua the hst of = atomic weights in Appendix I, on the other hand it is more usual in chemistry = to start with valency 0. From principles of general convenience of arrangement t= he latter plan is adopted in this table, which is intended to give = the maximum amount of chemical information. Hydrogen, which belongs equally wel= l to group I or group VII, is best omitted from the. table altoget= her.
THE ELEMENTS
V
VI
VII
VIII
3
2
-
-1
7N
80
9F
14-01
16-00
1900
14
16
19
15 P
16 S
17 CI
31-04
32-06
35-46
31
32
35, 37
23 V
24 Cr
25 Mn
26 Fe
27 Co
28 Ni
Sl-O
33 As
74-96 75
52-0
34 Se
79-2
54-93
35 Br
79-92 79, 81
55-85
58-97
58-68 58.60
41 Nb
42 Mo
43
44 Ru
45 Rh
46 Pd
93-5
51 Sb 120-2
96-0
52 Te 127-5
531
126-92 127
101-7
102-9
106-7
73 Ta
74 W
7&-
76 0a
77 Ir
78 Pt
181-5
83 Bi
209-0
184-0
84 Po
85
190-9
1931
195-2
91 UX
ii
92 U
238-2
145
Recent results obtained by Dempster. Thanks to a private=
communication the writer is able to include some further results=
obtained by Dempster and a diagram of his apparatus for obtaining=
Fig. 19. Diagram of Anode in Dempster's latest apparatus.=
positive rays from metals. A full account is to appear in the
Physical Review. Fig. 19 shows the new arrangement of
vaporising furnace A and ionising filament C. The analysing
apparatus has already been described on p, 31 and the results wi=
th
.4F
5-9
f
'
1
k
Lithium.
\
1
\
1
\
)
J
[
<=3D/
v..
^^
/
K
9
30
ZO
10
60
6-1
6-9
Atomic Weight.
7-0
7-1
Fig. 20. Curve for Lithium.
146
APPENDIX III
147
magnesium on p. 81. Fig. 20 shows one of the curves obtained
with lithium. It will be seen that the relative intensities of t=
he
isotopes is entirely different from that found by the writer (p. =
86)
and also disagrees very definitely with the chemical atomic weight= . Dempster describes these relative intensities as varying very considerably. This is a most remarkable phenomenon and further information upon it is very desirable. There seems just a possibi= lity that the 6 line is enhanced by doubly charged carbon but it is =
not
easy to see where such particles could be produced.
l/oltS 943 928 913-5 899-5 886 873 860 847-5=
J
\
Zinc.
1
t
\
1
\
1
\
f
\
r
\
\
1
1
\
\i
1
1
\
/
\
I
/
1
=C2=AE
l/
\
1
i^
\
^^
62 63 64 65 66 67 Atomic Weight.
Fig. 21. Curve for Zinc.
68 69
70
Fig. 21 gives a remarkable curve obtained from zinc. This
indicates three strong isotopes and a faint fourth. The absolute=
scale of atomic weight is not known with certainty, and the valu= es 63, 65, 67, 69 are given by Dempster as those in best agreement=
with the atomic weight 65-37. Considering that the error in th= e
148 APPENDIX III
mean atomic weight of lithium, when calculated on these lines, is about 5 per cent, it would appear possible that these might = be a unit too high or too low. The probability of this is strengthene= d very much by the rule given on p. 110 connecting even atomic number with even atomic weight.
Results with calcium show only one line. This makes it extremely=
probable that this is a simple element of atomic weight 40 and=
therefore an isobare of argon. ^
Note. In a still later communication Dempster states that =
he
has been successful in using an anode of calcium to which a sma= U quantity of zinc had been added. By this means he is able to compare the masses of the zinc isotopes with the strong calcium=
maximum, assumed as 40. This gives the atomic weights as 64, 66, 68 and 70. The intensities are quite different to those in = the curve given above for zinc. 64 is now the strongest, 66 and 68=
fainter, while 70 is very faint indeed. No explanation is yet advanced for these remarkable irregularities in relative intensity.=
He has also observed a small maximum at 44 invariably accom-
panying the strong calcium maximum 40. This he considers to be
probably due to an isotope of that element present in smaU quant=
ity
as suggested by the atomic weight 40 07.
The above values are included provisionally in the tables on pages 89 and 142.
" V. p. 88.
INDEX
Abnormal hydrides, 98
Abundance of the elements, 111
Accuracy of mass-spectrograph, 60
Actinivim chain, 14, 15
Additive law of mass, 99
Alkali metals, mass-spectra of, 83
Alpha ray changes, 13
Analysis of the elements, 63
Andrade and Rutherford, 11
Anode, composite, 80, 86
hot, 80, 83, 84
Anticathode, silica, 48
Antimony, 78
Argon, 66
Aronbeeg, 123
,, and Harkins, 124
Atmolysis, separation by, 127
Atomic number, 13, 93
theory, 2
,, volume of isotopes, 18
weights, tables of, 89, 141
weights of radio -elements, 13,
141
Atoms, structure of, 90
Balke, Owens and Kremers, 142 Barkla, 93
Batuecas and Moles, 141 Baxter and Hodges, 142 and Parsons, 113 and Starkweather, 141 and Wilson, 142 Tani and Chapin, 142 Weatherell and Holmes, 73, 142 Beryllium, 88 Beta ray change, 13 Bohr, 94, 95, 121, 122, 123
,, atom, 95 BOLTWOOD, 1, 7 Boron, 72
anomalous atomic weight of,
114
trifluoride, 73
Bracketing, method of, 59, 69 Brauner and Krepelka, 141 Broek, Van den, 93, 94, 116 Bromine, 76
Bronsted and Hevesy, 135, 136, 139
Brosslera, 102, 104
Bruylants and Michielson, 142
Caesium, 87
,, anomalous atomic weight of, 114 Calcium, 88, 148 Calibration curve, 55 Camera of mass-spectrograph, 51
positive ray, 26
Canalstrahlen, 22 Carbon, 63
Carnotite, lead from, 124 Cathode rays, 22, 24 Chadwick, 94
and Rutherford, 103
Chapin, Baxter and Tani, 142 Chapman, 130
and DooTSON, 130
Chemical action, separation by, 133
law of radioactive change,
11 Chlorine, 65, 113
separation of the isotopes
of, 136 Classen, 31
and Wey, 142 Claude, 35 Cleveite, lead from, 17 Coincidence, method of, 57 Composite anode, 80, 86 Constancy of chemical atomic weights,
22 Cosmical effect of change of mass, 103 Crookes, 3, 4, 24, 115, 117 ,, dark space, 24, 35
theory of the evolution of
elements, 117 Curie, Mlle. I., 113
M., 18
Dalton's hypothesis, 2 Darwin, 15
Davies and Horton, 68 Deflection of positive rays, 27 Dempster, 31, 80, 81, 86, 114, 146
149
150
INDEX
Dempster's method of analysis, 31,146
Density balance, 35
,, of isotopic leads, 17, 18 Diffusion of neon, 39
separation by, 127 velocity, determination of, 20 Disintegration theory of the evolu- tion of elements, 116 Distillation of neon, 37 Distribution of lines on mass-
spectrum, 64 DooTSON and Chapman, 130 Du Bois magnet, 61
Eddington, 104
Einstein's theory of relativity, 103 Electrical theory of matter, 90 Electric discharge in gases, 23
,, field of mass-spectrograph, 50 Electricity as an element, 115 Electrochemical properties of isotopes,
10 Electron, the, 91
Element, meaning of the word, 115 Enskog, 130 Epstein, 95 ExNER and Haschek, 121
Fa JANS, 11
First order lines, 61
Fleck, 12
Fluorine, 72, 97
Focussing positive rays, 44
FOWLEB, 123
and Aston, 45
Fractional distillation, separation by,
133 Fbanck and Knipping, 68
Gehrcke, 102
,, and Reichenheim, 80, 83, 88 Geigek and Nuttall, 10, 13 Goldstein, 22 Gravitation effect on spectra, 121
separation by, 131
Groh and Hevesy, 20, 135
Hahn, 8
and Meitner, 8
Halation effect, 60 Half-tone plates, 25 Hall and Harkins, 116 Harkins, 102, 111, 116, 129
and Aronberg, 124
and Hall, 116
,, and Wilson, 116 Haschek and Exner, 121 Helium, 67, 69, 106
Hevesy, 10, 12, 19
and Bronsted, 136, 136,
139
and Groh, 20, 135
and Paneth, 11
and Zechmeisteb, 20
Hodges and Baxter, 142 Holmes, Baxteb and Weathebell,
73, 141 Honigschmid, 17, 18, 141, 142
and Horovitz, 18,
121 Horovitz and Honigschmid, 18, 121 HoBTON and Davies, 68 Hot anode, 80, 83, 84 Hydrochloric acid, diffusion of, 129 Hydrogen, 67, 69, 106 Hyman and Soddy, 17, 121
Ibbs, 130
Imes, 125, 126
Indicators, radioactive, 19
Infra-red spectrum of isotopes, 125
Intensity of positive rays, 44
Iodine, 78
Ionic dissociation theory, proof of, 20
lonisation in discharge tube, 24
Ionium, 1, 7, 9, 18
,, atomic weight of, 18 Isobares, 12, 13, 97, 110 Isotopes, definition of, 12
diagrams of, 97
discovery of, 5
melting point of, 18
refractive index of, 18
separation of, 127
solubility of, 18
table of, 89, 141
James and Stewabt, 142 JoLY and Poole, 133
Keetman, 7
Kernel of atom, 98
Kibchoff, 116
Knipping and Franck, 68
kohlweiler, 116
Kratzer, 126
Kremers, Owens and Balke, 142
Krepelka and Bbaun, 141
,, and RiCHABDS, 141
Krypton, 70
,, anomalous atomic weight of, 114
Landaueb and Wendt, 70 Langmuib, 95, 96, 99 Lead, atomic weight of, 16
,, from carnotite, 124
,, from thorite, 17
isotopes of, 14, 15
INDEX
15)
Lembert and Richards, 17, 121
Lewis-Langmuir atom, 95
LmDEMANN, 102, 124, 134, 139
,, and Aston, 131
Lines of first and second order, 61, 76
of reference, 55, 64
Lithium, 86, 97, 146 LooMis, 125, 126
LUDLAM, 129
McAxpiNE and Willard, 142
Magnesimn, 80
Magnetic field of mass-spectrograph,
51 Marckwald, 7, 8 Mass, change of, 100
deduced from parabolas, 28
deduced from mass -spectrum,
55 Mass-spectrograph, 43 Mass-spectrum, 47, 54 Measurement of lines on mass-
spectrum, 59 Meitner, 21
,, and Hahn, 8 Melting point of isotopes, 18 Mercury, 72, 80
parabolas of, 30
separation of the isotopes
of, 134 Merton, 121, 123, 124, 125 Mesothorium, 8, 10 Meta-elements, 4
Metallic elements, mass-spectra of, 80 Meteoric nickel, 113 MiCHiELSON and Bruylants, 142 Microbalance for density, 35 MiLLIKAN, 22, 91
Molecular lines of second order, 75 Moles and Batuecas, 141 MOSELEY, 11, 93, 115 Mtjller, 142 Multiply charged rays, 30
Natural numbers and atomic weights,
111 Negatively charged rays, 29, 62 Negative mass-spectra, 62, 66 Neon, 1, 33, 64, 97 Neuberger, 21 Nickel, 79
meteoric, 113
Nitrogen, 67, 110 Nomenclature of isotopes, 61 Nucleus atom, 10, 92, 97, 125
structure of, 101
Ntjttall and Geiger, 10, 13
Order, lines of first and second, 61 Owens, Balke and Kremers, 142 Oxygen, 63
Packing effect, 100
Paneth and Hevesy, 11
Parabola method of analysis, 25
Parsons and Baxter, 113
Perforated electrodes, 22, 24
Periodic law, 11, 12, 34
table of the elements, 144,
145 Period of radio-elements, 13 Perrin, 104 Phosphonas, 77
Photochemical separation, 137 Photographic plates for positive rays,
25 Planck's quantum, 95 Planetary electrons, 92 Poole, 133
and JoLY, 133
Positive ray paraljolas, 28
rays, 22
separation by, 136
Potassium, 87 Pressure diffusion, 131 Proton, the, 92 Protyle, 90, 118 Prout's hypothesis, 2, 90, 100
Radioactive isotopes, 7, 14
classification of,
21
transformations, 13, 14,
15 Radium B and lead, 11
D and lead, 11
Ramsay, 115
and Collie, 39
and Travers, 33
Ratner, 24 Rayleigh, 127 Reference lines, 55, 64 Refractive index of isotopes, 18 Reichenheim and Gehrcke, 80, 83,
88 Renz, 139
Resolving power of mass-spectro- graph, 60 Richards 17
and Krepelka, 141
and Lembert, 17, 121
and Wads WORTH, 17
Richardson, 85 Rossi and Russell, 9, 120 Rubidium, 87 Russell, U
and Rossi, 9, 120
Rutherford, Sir E., 7, 9, 13, 92, 93, 102
and Chadwick, 103
and Andrade, 11
Rydberg, 141
162
INDEX
SCHUTZENBERGER, 3
Screens, willemite, 25
Secondary rays, 29
Second order, lines of the, 61
Selenium, 77
Separation of isotopes, 127
Silicon, 72
fluoride, 74
Skaupy, 139
Slit system of mass-spectrograph, 49 Smith and Van Haagen, 72 SoDDY, 6, 8, 10, 11, 12, 13, 14, 16, 17, 35
and Hyman, 17, 121
Sodium, 86 Solubility of isotopes, 18
SOMMERFEIiD, 95
Spectra of isotopes, 9, 121,
Spectrum lines, form of, 53
Spencer, 91
Starkweather and Baxter, 141
Stas, 91
Statistical relation of isotopes, 109
Stewart, 11, 12
and James, 142
Sulphur, 76
Tani, Baxter and Chapin, 142 Tellurium, 77 Thermal diffusion, 129 Third order line of argon, 67
lines of, 61
Thomson, G. P., 86, 88
Sir J. J., 1, 22, 29, 33, 62, 70, 72, 75, 84, 91, 129 Thorite, 17, 18 Thorium, 7, 9, 14, 15, 18, 120
Thorium, chain, 17, 18, 116
,, atomic weight of, 18
Tin, 78 Travers, 39
and Ramsay, 33
Triatomic hydrogen, 70
Unitary theory of matter, 90 Uranium, 10, 120 ,, chain, 15
Valency electrons, 98
Van Haagen and Smith, 72
Wadsworth and Richards, 17 Watson, 33
and Aston, 24, 35
Weatherell, Baxter and Holmes,
73, 141 Welsbach, 8
Wendt and Landaueb, 70 Wey and Classen, 142 Whole number rule, 90 WiEN, 22
WiLLARD and McAlpine, 142 Willemite screens, 25 Wilson and Baxter, 142
and Harkins, 116
Xenon, 70
- anomalous atomic weight of, 114
X-ray spectra of isotopes, 1 1
Zechmeister and Hevesy, 20 Zinc, 147
