Polonium-205m4

Properties and data of the isotope ^205m4Po.

Contents

Polonium-205m4 is an excited nuclear state of the nuclide ²⁰⁵Po, characterized by a defined excitation energy (3087.2 keV). Its spin and parity quantum numbers differ from those of the ground state (gs). Simultaneously, this metastable nuclear isomer possesses an independent, experimentally measurable lifetime: decay occurs via an isomeric transition to Po-205 with a half-life of approximately 115 nanoseconds.

See also: List of individual Polonium isotopes (and general data sources).

General data

Name of the isotope:Polonium-205m4; Po-205m4Symbol:^205m4Po or 205m484PoMass number A:205 (= number of nucleons)Atomic number Z:84 (= number of protons)Neutrons N:121Nucleon pairing (Z - N):even - oddNuclear ratio (N/Z ratio):1.4404761904762 (= neutron-proton ratio)Neutron excess (N-Z):37Excitation energy:3087.2(4) keVIsotopic mass:204.981190(11) u (atomic weight of Polonium-205m4)Nuclide mass:204.9351147 u (calculated nuclear mass without electrons)Mass excess:-17.5214 MeVMass defect:1.724567524 u (per nucleus)Nuclear binding energy:1606.4243012 MeV (per nucleus)
7.8362161 MeV (average binding energy per nucleon)Half-life:115(10) nsDecay constant λ:6027366.7874778 s^-1Specific activity α:1.77929665728 × 10⁺²⁸ Bq g^-1
4.808909884564 × 10⁺¹⁷ Ci g^-1Spin and parity:
(nuclear angular momentum)29/2-Year of discovery:1985

Radioactive Decay

Half-life T_½ = 115(10) ns respectively 1.15 × 10^-7 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
Iso	²⁰⁵Po	100 %

Nuclear Isomers

Nuclear isomers or excited states with the activation energy in keV related to the ground state.

Nuclear Isomer	Excitation Energy	Half-life	Spin
^205m1Po	143.166(17) keV	310(60) ns	1/2-
^205m3Po	1461.21(21) keV	57.4(9) ms	19/2-
^205m2Po	880.31(7) keV	0.645(20) ms	13/2+
²⁰⁵Po		1.74(8) h	5/2-

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 121) and isobaric (same nucleon number A = 205) with Polonium-205m4. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 121	Isobar A = 205
73	¹⁹⁴Ta
74	¹⁹⁵W
75	¹⁹⁶Re
76	¹⁹⁷Os
77	¹⁹⁸Ir	²⁰⁵Ir
78	¹⁹⁹Pt	²⁰⁵Pt
79	²⁰⁰Au	²⁰⁵Au
80	²⁰¹Hg	²⁰⁵Hg
81	²⁰²Tl	²⁰⁵Tl
82	²⁰³Pb	²⁰⁵Pb
83	²⁰⁴Bi	²⁰⁵Bi
84	²⁰⁵Po	²⁰⁵Po
85	²⁰⁶At	²⁰⁵At
86	²⁰⁷Rn	²⁰⁵Rn
87	²⁰⁸Fr	²⁰⁵Fr
88	²⁰⁹Ra	²⁰⁵Ra
89	²¹⁰Ac	²⁰⁵Ac
90	²¹¹Th
91	²¹²Pa