Elements, Isotopes and Radioactivity

Authored by: Jane H. Hodgkinson , Frank D. Stacey

Practical Handbook of Earth Science

Print publication date:  September  2017
Online publication date:  September  2017

Print ISBN: 9781138552234
eBook ISBN: 9781315148038
Adobe ISBN:

10.1201/9781315148038-5

 

Abstract

Atomic No. z

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Elements, Isotopes and Radioactivity

3.1  Periodic Table of Elements: A Geochemical Classification (Figure 3.1)

A geochemical classification of the elements.

Figure 3.1   A geochemical classification of the elements.

3.2  Periodic Table of Elements: A Biological Classification (Figure 3.2)

A biological classification of the elements.

Figure 3.2   A biological classification of the elements.

3.3  Isotopes of the Naturally Occurring Elements

Table 3.1   Isotopic abundances and mean atomic weights

Atomic No. z

Element

Symbol (mean atomic wt., in units of u = 1.66053878 × 10−27 kg)

Isotopic Masses, with Abundances in Atomic % in Parentheses

0

Neutron

n a (1.0886)

1

Hydrogen

H (1.0079)

1 (99.985), 2 (0.015), 3 a (atmospheric trace from cosmic ray bombardment)

2

Helium

He (4.00260)

3 (0.00013), 4 (99.99987)

3

Lithium

Li (6.940)

6 (7.59), 7 (92.41)

4

Beryllium

Be (9.01218)

9 (100), 10 a (atmospheric trace from cosmic ray bombardment)

5

Boron

B (10.811)

10 (19.9), 11 (80.1)

6

Carbon

C (12.0107)

12 (98.93), 13 (1.07), 14 a (1.6 × 10−10 in atmosphere)

7

Nitrogen

N (14.0067)

14 (99.635), 15 (0.365)

8

Oxygen

O (15.9994)

16 (99.757), 17 (0.038), 18 (0.205)

9

Fluorine

F (18.99480)

19 (100)

10

Neon

Ne (20.1797)

20 (90.48), 21 (0.27), 22 (9.25)

11

Sodium

Na (22.9898)

23 (100)

12

Magnesium

Mg (24.3050)

24 (78.99), 25 (10.00), 26 (11.01)

13

Aluminium

Al (26.98154)

27 (100)

14

Silicon

Si (28.0855)

28 (92.22), 29 (4.69), 30 (3.09)

15

Phosphorus

P (30.97376)

31 (100)

16

Sulphur

S (32.065)

32 (94.93), 33 (0.76), 34 (4.29), 36 (0.02)

17

Chlorine

Cl (35.453)

35 (75.76), 37 (24.24)

18

Argon

Atmosphere

Ar (39.948)

36 (0.337), 38 (0.063), 40 (99.600)

Solar wind

Ar (36.67)

36 (75.3), 38 (14.2), 40 (10.5)

19

Potassium

K (39.0983)

39 (93.258), 40 a (0.01167), 41 (6.730)

20

Calcium

Ca (40.078)

40 (96.94), 42 (0.65), 43 (0.13), 44 (2.09), 46 (0.0041), 48 b (0.19)

21

Scandium

Sc (44.95591)

45 (100)

22

Titanium

Ti (47.867)

46 (8.25), 47 (7.44), 48 (73.72), 49 (5.41), 50 (5.18)

23

Vanadium

V (50.9415)

50 b (0.25), 51 (99.75)

24

Chromium

Cr (51.996)

50 (4.35), 52 (83.79), 53 (9.50), 54 (2.36)

25

Manganese

Mn (54.93804)

55 (100)

26

Iron

Fe (55.845)

54 (5.84), 56 (91.75), 57 (2.12), 58 (0.28)

27

Cobalt

Co (58.93319)

59 (100)

28

Nickel

Ni (58.6934)

58 (68.077), 60 (26.223), 61 (1.140), 62 (3.634), 64 (0.926)

29

Copper

Cu (63.546)

63 (69.2), 65 (30.8)

30

Zinc

Zn (65.409)

64 (48.27), 66 (27.98), 67 (4.10), 68 (19.02), 70 (0.63)

31

Gallium

Ga (69.723)

69 (60.108), 71 (39.892)

32

Germanium

Ge (72.63)

70 (20.38), 72 (27.31), 73 (7.76), 74 (36.72), 76 b (7.83)

33

Arsenic

As (74.9216)

75 (100)

34

Selenium

Se (78.96)

74 (0.89), 76 (9.37), 77 (7.63), 78 (23.77), 80 (49.61), 82 b (8.73)

35

Bromine

Br (79.904)

79 (50.69), 81 (49.31)

36

Krypton

Kr (83.798)

78 (0.35), 80 (2.29), 82 (11.59), 83 (11.50), 84 (56.99), 86 (17.28)

37

Rubidium

Rb (85.4678)

85 (72.165), 87 a (27.835)

38

Strontium

Sr (87.62)

84 (0.56), 86 (9.86), 87 (7.00), 88 (82.58)

39

Yttrium

Y (88.90585)

89 (100)

40

Zirconium

Zr (91.224)

90 (51.45), 91 (11.22), 92 (17.15), 94 (17.38), 96 b (2.80)

41

Niobium

Nb (92.90638)

93 (100)

42

Molybdenum

Mo (95.96)

92 (14.77), 94 (9.23), 95 (15.90), 96 (16.68), 97 (9.56), 98 (24.19), 100 a (9.67)

43

Technetium

Tc

No naturally occurring isotope

44

Ruthenium

Ru (101.07)

96 (5.44), 98 (1.87), 99 (12.76), 100 (12.60), 101 (17.06), 102 (31.55), 104 (18.62)

45

Rhodium

Rh (102.90550)

103 (100)

46

Palladium

Pd (106.42)

102 (1.02), 104 (11.14), 105 (22.33), 106 (27.33), 108 (26.46), 110 (11.72)

47

Silver

Ag (106.8682)

107 (51.839), 109 (48.161)

48

Cadmium

Cd (112.411)

106 (1.25), 108 (0.89), 110 (12.49), 111 (12.80), 112 (24.13), 113 b (12.22), 114 b (28.72), 116 b (7.49)

49

Indium

In (114.818)

113 (4.29), 115 b (95.71)

50

Tin

Sn (118.71)

112 (0.97), 114 (0.66), 115 (0.34), 116 (14.54), 117 (7.68), 118 (24.22), 119 (8.59), 120 (32.58), 122 (4.63), 124 (5.79)

51

Antimony

Sb (121.60)

121 (57.21), 123 (47.79)

52

Tellurium

Te (127.60)

120 (0.09), 122 (2.55), 123 (0.89), 124 (4.74), 125 (7.07), 126 (18.84), 128 b (31.74), 130 b (30.08)

53

Iodine

I (126.90448)

127 (100)

54

Xenon

Xe (131.293)

124 (0.095), 126 (0.089), 128 (1.910), 129 (26.401), 130 (4.071), 131 (21.232), 132 (26.909), 134 (10.436), 136 b (8.857)

55

Caesium

Cs (132.90552)

133 (100)

56

Barium

Ba (137.327)

130 b (0.106), 132 (0.101), 134 (2.417), 135 (6.592), 136 (7.854), 137 (11.232), 138 (71.698)

57

Lanthanum

La (138.90547)

138 a (0.090), 139 (99.910)

58

Cerium

Ce (140.116)

136 (0.190), 138 (0.251), 140 (88.450), 142 (11.114)

59

Praseodymium

Pr (140.90765)

141 (100)

60

Neodymium

Nd (144.242)

142 (27.2), 143 (12.2), 144 b (23.8), 145 (8.23), 146 (17.2), 148 (5.72), 150 b (5.60)

61

Promethium

Pm

No naturally occurring isotope

62

Samarium

Sm (150.36)

144 (3.07), 146 a (trace), 147 a (14.99), 148 b (11.24), 149 (13.82), 150 (7.38), 152 (26.75), 154 (22.75)

63

Europium

Eu (151.964)

151 b (47.81), 153 (52.19)

64

Gadolinium

Gd (157.25)

152 b (0.20), 154 (2.18), 155 (14.80), 156 (20.47), 157 (15.65), 158 (24.84), 160 (21.86)

65

Terbium

Tb (158.92535)

159 (100)

66

Dysprosium

Dy (162.500)

156 (0.056), 158 (0.095), 160 (2.329), 161 (18.889), 162 (25.475), 163 (24.896), 164 (28.260)

67

Holmium

Ho (164 93032)

165 (100)

68

Erbium

Er (167.259)

162 (0.139), 164 (1.601), 166 (33.503), 167 (22.869), 168 (26.978), 170 (14.910)

69

Thulium

Tm (168.9342)

169 (100)

70

Ytterbium

Yb (173.04)

168 (0.13), 170 (3.04), 171 (14.28), 172 (21.83), 173 (16.13), 174 (31.83), 176 (12.76)

71

Lutetium

Lu (174.967)

175 (97.41), 176 a (2.59)

72

Hafnium

Hf (178.49)

174 b (0.162), 176 (5.26), 177 (18.60), 178 (27.28), 179 (13.63), 180 (35.08)

73

Tantalum

Ta (180.9479)

180 (0.012), 181 (99.988)

74

Tungsten

W (183.84)

180 b (0.12), 182 (26.55), 183 (14.31), 184 (30.64), 186 (28.45)

75

Rhenium

Re (186.207)

185 (37.40), 187 a (62.60)

76

Osmium

Os (190.23)

184 (0.02), 186 b (1.59), 187 (1.96), 188 (13.24), 189 (16.15), 190 (26.26), 192 (40.78)

77

Iridium

Ir (192.217)

191 (37.3), 193 (62,7)

78

Platinum

Pt (195.089)

190 a (0.014), 192 (0.782), 194 (32.967), 195 (33.832), 196 (25.242), 198 (7.163)

79

Gold

Au (196.966569)

197 (100)

80

Mercury

Hg (200.592)

196 (0.15), 198 (9.97), 199 (16.87), 200 (23.10), 201 (13.18), 202 (29.86), 204 (6.87)

81

Thallium

Tl (204.3833)

203 (29.52), 205 (70.48)

82

Lead

Pb (207.21) (variable)

204 b (1.347), 206 (25.03). 207 (21.25), 208 (52.37) (averages in marine sediments)

83

Bismuth

Bi (208.9804)

209 b (100)

84

Polonium

Po

Intermediate daughters in uranium and thorium decay series

85

Astatine

At

86

Radon

Rn

87

Francium

Fr

88

Radium

Ra

89

Actinium

Ac

90

Thorium

Th (232.0381)

232 a (100)

91

Protactinium

Pa

Intermediate daughter in uranium decay

92

Uranium

U (238.0289)

234 a (0.0055), 235 a (0.7200), 238 a (99.2745)

Notes:

a  Radioactive isotopes.

b  Isotopes with half-lives exceeding the age of the universe.

3.4  Naturally occurring long-lived radioactive isotopes

This list recognises half-lives exceeding the age of the universe for isotopes that have generally been regarded as stable. The possibility that β decay rates are affected by neutrino flux is under consideration. It is not clear whether any of the following numbers are seriously affected.

Table 3.2    Decay mechanisms and half-lives

Isotope

% of Element

Decay Mechanism

Half-Life (years)

Decay Product

40K

0.01167

89.28% β 10.72% K 0.001% β+

1.248 × 109

40Ca40Ar40Ar

48Ca

0.19

4 × 1019

48Ti

50V

0.25

β

1.4 × 1017

50Cr

76Ge

7.83

1.8 × 1021

26Se

82Se

8.73

9.7 × 1019

82Kr

87Rb

27.835

β

4.92 × 1010

87Sr

96Zr

2.80

2 × 1019

96Mo

100Mo

9.67

8.5 × 1018

100Ru

113Cd

12.22

β

8.04 × 1015

113I

116Cd

7.49

2.8 × 1019

116Sn

115In

95.71

β

4.4 × 1014

115Sn

128Te

31.74

2.2 × 1024

128Xe

130Te

30.08

7.9 × 1020

130Xe

130Ba

0.106

2K

~1021

130Xe

136Xe

8.857

2.38 × 1021

136Ba

138La

0.090

33.6% β 66.4% β+

1.02 × 1011

138Ce138Ba

142Ce

11.05

α

5.0 × 1015

138Ba

144Nd

23.8

α

2.3 × 1015

140Ce

146Sm

trace

α

6.8 × 107

142Nd

147Sm

14.99

α

1.06 × 1011

143Nd

148Sm

11.24

α

7 × 1015

144Nd→140Ce

150Nd

5.6

6.7 × 1018

150Sm

151Eu

47.81

α, β

5 × 1018

147Pm→147Sm

152Gd

0.2

1.08 × 1014

148Sm→144Nd

156Dy

0.0524

α

2 × 1014

152Gd

174Hf

0.162

α

2.0 × 1015

170Yb

176Lu

2.59

β

3.85 × 1010

176Hf

180W

0.12

α

1.8 × 1018

176Hf

186Os

1.89

α

2 × 1015

182W

187Re

62.6

99.99% β 0.01% α

4.12 × 1010

187Os183Ta

190Pt

0.014

α

6.5 × 1011

186Os

204Pb

1.35

α

1.4 × 1017

200Hg

209Bi

100

α

1.9 × 1019

205Tl

232Th

100

6α + 4β

1.4010 × 1010

208Pb (final)

235U

0.7201

7α + 4β

7.0381 × 108

207Pb (final)

238U

99.2743

8α + 6 β 5.4 × 10−5% fission

4.4683 × 109

206Pb (final)

3.5  Some Extinct Isotopes

Table 3.3   Extinct isotopes with decay products that are identifiable in meteorites or provide isotopic clues to early solar system processes

Isotope

Decay Mechanism

Half-Life (years)

Decay Product

22Na

β+

2.603

22Ne

26Al

85% β+ 15% K

7.17 × 105

26Mg

60Fe

3 × 105

60Ni via 60Co

107Pd

β

6.5 × 105

107Ag

129I

β

1.6 × 107

129Xe

146Sm

α

1.03 × 108

142Nd

182Hf

8.9 × 106

182W via 182Ta

236U

α

2.4 × 107

208Pb via 232Th

244Pu

0.3% fission 99.7% α

8.3 × 107

0.3% fission products 99.7% 208Pb via 232Th

3.6  Short-Lived Isotopes

Table 3.4   Isotopes produced by cosmic rays or radioactive decay

Isotope

Decay Mechanism

Half-Life

Decay Product

Neutron

β

611 s (10.18 minutes)

1H

3H, tritium

β

12.32 years

3He

7Be

K

53.22 days

7Li

10Be

β

1.39 × 106 years

10B

14C

β

5730 years

14N

22Na

β

2.603 years

22Ne

32Si

153 years

32S via 32P

32P

β

14.263 days

32S

33P

β

25 days

33S

35S

β

87.5 days

35Cl

36Cl

98.1% β 1.9% K

3.01 × 105 years

36Ar36S

37Ar

K

35 days

37Cl

39Ar

β

270 years

39K

41Ca

K

1.02 × 105 years

41K

53Mn

K

3.7 × 106 years

53Cr

234U

α

2.47 × 105 years

230Th→206Pb

3.7  Fission Products

Nuclear fission, principally of 235U and 239Pu, results in fragments with unequal atomic masses in ranges 85–110 and 125–155. Statistics of the fragments depend somewhat on the fissioning isotopes and on conditions such as energies of incident neutrons. Each fission event also produces two or three neutrons and, in a few cases, other small fragments such as tritium (3H). The products are all neutron-rich, making them radioactive emitters of β particles (energetic electrons). There is a very wide range of radioactive fission products. Table 3.5 lists the ones of particular environmental concern on account of their abundances and likelihood of ingestion.

Table 3.5   Environmentally problematic fission products

Isotope

90Sr

137Cs

89Sr

3H

140Ba

131I

Half-life

28 years

30 years

15 days

13 years

128 days

8.05 days

Ingestion

30%

~100%

30%

High a

5%

100%

Notes:

a  Readily absorbed but also generally quickly excreted.

Releases from nuclear accidents also include isotopes of the actinides (elements close to thorium, uranium and plutonium in the periodic table), as well as unfissioned 235U and 239Pu (half-life 24,100 years).

The total intensity of radiation from fission products, R, decreases with time as a sum of numerous exponential decays, with complications arising from secondary decays. A rough empirical representation for fallout radiation at an open site, derived largely from Chernobyl data, is

3.1 R = R 1 t −1/2

where t is time in days, starting at day 1, when the intensity was R 1. This simple equation is a useful approximation for t = 1 day to 10,000 days (27.4 years). In the much longer term, this relationship will fail because fission products all have half-lives of either less than 100 years or more than 200,000 years and the half-life distribution of still active isotopes will change dramatically.

3.8  Radiogenic Heat

Table 3.6   Thermally important radioactive isotopes

Isotope

μW/kg

μW/kg of Element

Total Earth Content (kg)

Heat (1012 W)

Now

4.5 × 109 years ago

In 109 Years’ Time

238U

95.0

94.35

15.02 × 1016

14.25

28.6

12.2

235U

562.0

4.05

0.11 × 1016

0.60

50.1

0.22

232Th

26.6

26.6

55.98 × 1016

14.87

18.6

14.1

40K

30.0

0.00350

8.06 × 1020 (total K)

2.82

34.2

1.6

Total heat

31.2

132

28.1

Table 3.7   Average radiogenic heat in earth materials

Material

Concentration (ppm by mass)

K/U

Heat (10−12 W/kg)

U

Th

K

Igneous rocks

Granites

4.6

18

33,000

7000

1050

Alkali basalts

0.75

2.5

12,000

16,000

180

Tholeiitic basalts

0.11

0.04

1500

13,600

27

Eclogites

0.035

0.15

500

14,000

9.2

Peridotites

0.006

0.02

100

17,000

1.5

Meteorites

Carbonaceous Chondrites

0.020

0.070

400

20,000

5.2

Ordinary Chondrites

0.015

0.046

900

60,000

5.8

Iron Meteorites

Nil

Nil

Nil

<3 × 10−4

Moon

Apollo samples

0.23

0.85

590

2500

47

Global averages

Crust

1.2

4.5

15,500

13,000

293

Mantle

0.029

0.109

81

2800

5.7

Core

0

0

29

0.1

Whole Earth

0.025

0.093

135

5400

5.2

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