Isotopes of fermium
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Fermium (Fm) is a synthetic element, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be discovered (in fallout from nuclear testing) was 255Fm in 1952. 250Fm was independently synthesized shortly after the discovery of 255Fm. There are 20 known radioisotopes ranging in atomic mass from 241Fm to 260Fm (260Fm is unconfirmed), and 2 nuclear isomers, 250mFm and 251mFm. The longest-lived isotope is 257Fm with a half-life of 100.5 days, and the longest-lived isomer is 250mFm with a half-life of 1.8 seconds.
Table
nuclide symbol |
Z(p) | N(n) | isotopic mass (u) |
half-life | decay mode(s)[1][n 1] |
daughter isotope(s) |
nuclear spin |
---|---|---|---|---|---|---|---|
excitation energy | |||||||
241Fm | 100 | 141 | 241.07421(32)# | 730(60) µs | SF(>78%) | (various) | 5/2#+ |
α (<14%) | 237Cf | ||||||
242Fm | 100 | 142 | 242.07343(43)# | 0.8(2) ms | SF | (various) | 0+ |
α (rare) | 238Cf | ||||||
243Fm | 100 | 143 | 243.07447(23)# | 231(9) ms | α (91%) | 239Cf | 7/2−# |
SF (9%) | (various) | ||||||
β+ (rare) | 243Es | ||||||
244Fm | 100 | 144 | 244.07404(22)# | 3.12(8) ms | SF (99%) | (various) | 0+ |
α (1%) | 240Cf | ||||||
245Fm | 100 | 145 | 245.07535(21)# | 4.2(13) s | α (95.7%) | 241Cf | 1/2+# |
β+ (4.2%) | 245Es | ||||||
SF (.13%) | (various) | ||||||
246Fm | 100 | 146 | 246.075350(17) | 1.54(4) s | α (85%) | 242Cf | 0+ |
β+ (10%) | 246Es | ||||||
β+, SF (10%) | (various) | ||||||
SF (4.5%) | (various) | ||||||
247Fm | 100 | 147 | 247.07695(12)# | 31(1) s | α (>50%) | 243Cf | (7/2+) |
β+ (<50%) | 247Es | ||||||
248Fm | 100 | 148 | 248.077186(9) | 35.1(8) s | α (93%) | 244Cf | 0+ |
β+ (7%) | 248Es | ||||||
SF (.10%) | (various) | ||||||
249Fm | 100 | 149 | 249.078928(7) | 1.6(1) min | β+ (85%) | 249Es | (7/2+)# |
α (15%) | 245Cf | ||||||
250Fm | 100 | 150 | 250.079521(9) | 30.4(15) min | α (90%) | 246Cf | 0+ |
EC (10%) | 250Es | ||||||
SF (6.9×10−3%) | (various) | ||||||
250mFm | 1199.2(10) keV | 1.92(5) s | IT | 250Fm | (8−) | ||
251Fm | 100 | 151 | 251.081540(16) | 5.30(8) h | β+ (98.2%) | 251Es | (9/2−) |
α (1.8%) | 247Cf | ||||||
251mFm | 200.09(11) keV | 21.1(16) µs | (5/2+) | ||||
252Fm | 100 | 152 | 252.082467(6) | 25.39(4) h | α (99.99%) | 248Cf | 0+ |
SF (.0023%) | (various) | ||||||
β+β+ (rare) | 252Cf | ||||||
253Fm | 100 | 153 | 253.085185(4) | 3.00(12) d | EC (88%) | 253Es | (1/2)+ |
α (12%) | 249Cf | ||||||
254Fm | 100 | 154 | 254.0868544(30) | 3.240(2) h | α (99.94%) | 250Cf | 0+ |
SF (.0592%) | (various) | ||||||
255Fm | 100 | 155 | 255.089964(5) | 20.07(7) h | α | 251Cf | 7/2+ |
SF (2.4×10−5%) | (various) | ||||||
256Fm | 100 | 156 | 256.091774(8) | 157.6(13) min | SF (91.9%) | (various) | 0+ |
α (8.1%) | 252Cf | ||||||
257Fm[n 2] | 100 | 157 | 257.095106(7) | 100.5(2) d | α (99.79%) | 253Cf | (9/2+) |
SF (.21%) | (various) | ||||||
258Fm | 100 | 158 | 258.09708(22)# | 370(14) µs | SF | (various) | 0+ |
259Fm | 100 | 159 | 259.1006(3)# | 1.5(3) s | SF | (various) | 3/2+# |
260Fm[n 3][n 4] | 100 | 160 | 260.10281(55)# | 4 ms | 0+ |
- ↑ Abbreviations:
EC: Electron capture
IT: Isomeric transition
SF: Spontaneous fission - ↑ Heaviest nuclide produced via neutron capture
- ↑ Discovery of this isotope is unconfirmed
- ↑ Not directly synthesized, occurs as decay product of 260Md
Notes
- Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
- Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC, which use expanded uncertainties.
- The isotopes denoted by an isotope number with an "m" are metastable isomers.
Chronology of isotope discovery
Isotope | Discovered | Reaction |
---|---|---|
241Fm | 2008 | 204Pb(40Ar,3n) |
242Fm | 1975 | 204Pb(40Ar,2n), 206Pb(40Ar,4n) |
243Fm | 1981 | 206Pb(40Ar,3n) |
244Fm | 1967 | 233U(16O,5n) |
245Fm | 1967 | 233U(16O,4n) |
246Fm | 1966 | 235U(16O,5n) |
247Fm | 1967 | 239Pu(12C,4n) |
248Fm | 1958 | 240Pu(12C,4n) |
249Fm | 1960 | 238U(16O,5n) |
250Fm | 1954 | 238U(16O,4n) |
251Fm | 1957 | 249Cf(α,2n) |
252Fm | 1956 | 249Cf(α,n) |
253Fm | 1957 | 252Cf(α,3n) |
254Fm | 1954 | Neutron capture |
255Fm | 1954 | Neutron capture |
256Fm | 1955 | Neutron capture |
257Fm | 1964 | Neutron capture |
258Fm | 1971 | 257Fm(d,p) |
259Fm | 1980 | 257Fm(t,p) |
260Fm? | 1992? | 254Es+18O, 22Ne — transfer (EC of 260Md)[2] |
260Fm? was not confirmed in 1997.
References
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ see mendelevium
- Isotope masses from:
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- Isotopic compositions and standard atomic masses from:
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- Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
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Isotopes of einsteinium | Isotopes of fermium | Isotopes of mendelevium |
Table of nuclides |
Isotopes of the chemical elements | |||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 H |
2 He |
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3 Li |
4 Be |
5 B |
6 C |
7 N |
8 O |
9 F |
10 Ne |
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11 Na |
12 Mg |
13 Al |
14 Si |
15 P |
16 S |
17 Cl |
18 Ar |
||||||||||
19 K |
20 Ca |
21 Sc |
22 Ti |
23 V |
24 Cr |
25 Mn |
26 Fe |
27 Co |
28 Ni |
29 Cu |
30 Zn |
31 Ga |
32 Ge |
33 As |
34 Se |
35 Br |
36 Kr |
37 Rb |
38 Sr |
39 Y |
40 Zr |
41 Nb |
42 Mo |
43 Tc |
44 Ru |
45 Rh |
46 Pd |
47 Ag |
48 Cd |
49 In |
50 Sn |
51 Sb |
52 Te |
53 I |
54 Xe |
55 Cs |
56 Ba |
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72 Hf |
73 Ta |
74 W |
75 Re |
76 Os |
77 Ir |
78 Pt |
79 Au |
80 Hg |
81 Tl |
82 Pb |
83 Bi |
84 Po |
85 At |
86 Rn |
87 Fr |
88 Ra |
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104 Rf |
105 Db |
106 Sg |
107 Bh |
108 Hs |
109 Mt |
110 Ds |
111 Rg |
112 Cn |
113 Uut |
114 Fl |
115 Uup |
116 Lv |
117 Uus |
118 Uuo |
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57 La |
58 Ce |
59 Pr |
60 Nd |
61 Pm |
62 Sm |
63 Eu |
64 Gd |
65 Tb |
66 Dy |
67 Ho |
68 Er |
69 Tm |
70 Yb |
71 Lu |
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89 Ac |
90 Th |
91 Pa |
92 U |
93 Np |
94 Pu |
95 Am |
96 Cm |
97 Bk |
98 Cf |
99 Es |
100 Fm |
101 Md |
102 No |
103 Lr |
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