Meitnerium

Meitnerium

Meitnerium is a chemical element with the symbol Mt and atomic number 109. It is placed as the heaviest member of group 9 in the periodic table but a sufficiently stable isotope is not known at this time which would allow chemical experiments to confirm its position, unlike its lighter...

(Mt) 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 synthesized was ²⁶⁶Mt in 1982 (this is also the only isotope directly synthesized, all other isotopes are decay product

Decay product

In nuclear physics, a decay product is the remaining nuclide left over from radioactive decay. Radioactive decay often involves a sequence of steps...

s of heavier element

Chemical element

A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

s). There are seven known isotopes, from ²⁶⁶Mt to ²⁷⁸Mt. There may also be two isomers

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...

. The longest-lived of the known isotopes is ²⁷⁸Mt 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 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)	daughter isotope(s)	nuclear spin
	excitation energy
266Mt	109	157	266.13730(37)#	1.2(4) ms	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...	262Bh
268MtNot directly synthesized, occurs as decay product Decay product In nuclear physics, a decay product is the remaining nuclide left over from radioactive decay. Radioactive decay often involves a sequence of steps...  of 272Rg	109	159	268.13873(34)#	21(+8-5) ms	α	264Bh	5+#,6+#
268mMtThis isomer is unconfirmed	0+X keV			0.07(+10-3) s	α	264Bh
270MtNot directly synthesized, occurs in decay chain Decay chain In nuclear science, the decay chain refers to the radioactive decay of different discrete radioactive decay products as a chained series of transformations... of 278Uut	109	161	270.14066(58)#	2# s	α	266Bh
270mMt					α	266Bh
274MtNot directly synthesized, occurs in decay chain of 282Uut	109	165	274.14749(60)#	20# s	α	270Bh
275MtNot directly synthesized, occurs in decay chain of 287Uup	109	166	275.14865(64)#	9.7(+460-44) ms	α	271Bh
276MtNot directly synthesized, occurs in decay chain of 288Uup	109	167	276.15116(73)#	0.72(+87-25) s	α	272Bh
278MtNot directly synthesized, occurs in decay chain of 294Uus	109	169	278.15481(90)#	7.6 s	α	274Bh

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