Isotopes of fermium
Encyclopedia
Fermium
(Fm) is an artificial element, and thus a standard atomic mass
cannot be given. Like all artificial elements, it has no stable isotope
s. 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 19 known radioisotopes ranging in atomic mass
from 242Fm to 260Fm, and 2 nuclear isomer
s, 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.
Fermium
Fermium is a synthetic element with the symbol Fm. It is the 100th element in the periodic table and a member of the actinide series. It is the heaviest element that can be formed by neutron bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities,...
(Fm) is an artificial element, and thus a standard atomic mass
Atomic mass
The atomic mass is the mass of a specific isotope, most often expressed in unified atomic mass units. The atomic mass is the total mass of protons, neutrons and electrons in a single atom....
cannot be given. Like all artificial elements, it has no stable isotope
Stable isotope
Stable isotopes are chemical isotopes that may or may not be radioactive, but if radioactive, have half-lives too long to be measured.Only 90 nuclides from the first 40 elements are energetically stable to any kind of decay save proton decay, in theory...
s. The first isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
to be discovered (in fallout
Fallout
Fallout or nuclear fallout is the residual radiation hazard from a nuclear explosion.Fallout may also refer to:*Fallout , a 1997 post-apocalyptic computer role-playing game released by Interplay Entertainment...
from nuclear testing
Nuclear testing
Nuclear weapons tests are experiments carried out to determine the effectiveness, yield and explosive capability of nuclear weapons. Throughout the twentieth century, most nations that have developed nuclear weapons have tested them...
) was 255Fm in 1952. 250Fm was independently synthesized shortly after the discovery of 255Fm. There are 19 known radioisotopes ranging in atomic mass
Atomic mass
The atomic mass is the mass of a specific isotope, most often expressed in unified atomic mass units. The atomic mass is the total mass of protons, neutrons and electrons in a single atom....
from 242Fm to 260Fm, and 2 nuclear isomer
Nuclear isomer
A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons . "Metastable" refers to the fact that these excited states have half-lives more than 100 to 1000 times the half-lives of the other possible excited nuclear states...
s, 250mFm and 251mFm. The longest-lived isotope is 257Fm with a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
of 100.5 days, and the longest-lived isomer is 250mFm with a half-life of 1.8 seconds.
Table
| nuclide symbol |
Z(p Proton The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number.... ) |
N(n Neutron The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of... ) |
isotopic mass (u) |
half-life | decay mode(s)Abbreviations: EC: Electron capture Electron capture Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino... IT: Isomeric transition Isomeric transition An isomeric transition is a radioactive decay process that involves emission of a gamma ray from an atom where the nucleus is in an excited metastable state, referred to in its excited state, as a nuclear isomer.... SF: Spontaneous fission Spontaneous fission Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses... |
daughter isotope(s) |
nuclear spin |
|---|---|---|---|---|---|---|---|
| excitation energy | |||||||
| 242Fm | 100 | 142 | 242.07343(43)# | 0.8(2) ms | SF Spontaneous fission Spontaneous fission is a form of radioactive decay characteristic of very heavy isotopes. Because the nuclear binding energy reaches a maximum at a nuclear mass greater than about 60 atomic mass units , spontaneous breakdown into smaller nuclei and single particles becomes possible at heavier masses... |
(various) | 0+ |
| α Alpha decay Alpha decay is a type of radioactive decay in which an atomic nucleus emits an alpha particle and thereby transforms into an atom with a mass number 4 less and atomic number 2 less... (rare) |
238Cf | ||||||
| 243Fm | 100 | 143 | 243.07435(23)# | 210(60) ms [0.18(+8-4) s] |
α (60%) | 239Cf | 7/2-# |
| β+ (40%) | 243Es | ||||||
| SF (.57%) | (various) | ||||||
| 244Fm | 100 | 144 | 244.07408(30)# | 3.3(5) ms | SF (99%) | (various) | 0+ |
| α (1%) | 240Cf | ||||||
| 245Fm | 100 | 145 | 245.07539(30)# | 4.2(13) s | α (95.7%) | 241Cf | 1/2+# |
| β+ (4.2%) | 245Es | ||||||
| SF (.13%) | (various) | ||||||
| 246Fm | 100 | 146 | 246.07530(4) | 1.1(2) s | α (85%) | 242Cf | 0+ |
| β+ (10%) | 246Es | ||||||
| β+, SF (10%) | (various) | ||||||
| SF (4.5%) | (various) | ||||||
| 247Fm | 100 | 147 | 247.07685(15)# | 29(1) s | α (50%) | 243Cf | (7/2+) |
| β+ (50%) | 247Es | ||||||
| 248Fm | 100 | 148 | 248.077195(13) | 36(2) s | α (99%) | 244Cf | 0+ |
| β+ (1%) | 248Es | ||||||
| SF (.05%) | (various) | ||||||
| 249Fm | 100 | 149 | 249.07903(11)# | 2.6(7) min | β+ (85%) | 249Es | (7/2+)# |
| α (15%) | 245Cf | ||||||
| 250Fm | 100 | 150 | 250.079521(13) | 30(3) min | α (90%) | 246Cf | 0+ |
| EC Electron capture Electron capture is a process in which a proton-rich nuclide absorbs an inner atomic electron and simultaneously emits a neutrino... (10%) |
250Es | ||||||
| SF (6×10−4%) | (various) | ||||||
| 250mFm | 1500(300)# keV | 1.8(1) s | IT Isomeric transition An isomeric transition is a radioactive decay process that involves emission of a gamma ray from an atom where the nucleus is in an excited metastable state, referred to in its excited state, as a nuclear isomer.... |
250Fm | 7,8# | ||
| 251Fm | 100 | 151 | 251.081575(9) | 5.30(8) h | β+ (98.2%) | 251Es | (9/2-) |
| α (1.8%) | 247Cf | ||||||
| 251mFm | 191(2) keV | 15.2(23) 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 | 254.0868542(30) | 3.240(2) h | α (99.94%) | 250Cf | 0+ |
| SF (.06%) | (various) | ||||||
| 255Fm | 100 | 155 | 255.089962(5) | 20.07(7) h | α | 251Cf | 7/2+ |
| SF (2×10−5%) | (various) | ||||||
| 256Fm | 100 | 156 | 256.091773(8) | 157.6(13) min | SF (91.9%) | (various) | 0+ |
| α (8.1%) | 252Cf | ||||||
| 257FmHeaviest nuclide produced via neutron capture Neutron capture Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with one or more neutrons and they merge to form a heavier nucleus. Since neutrons have no electric charge they can enter a nucleus more easily than positively charged protons, which are repelled... |
100 | 157 | 257.095105(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 | 100 | 160 | 260.10268(54)# | 1# min | 0+ | ||