Polonium-205m3

Properties and data of the isotope ^205m3Po.

Contents

Polonium-205m3 is an excited nuclear state of the nuclide ²⁰⁵Po, characterized by a defined excitation energy (1461.21 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 57.5 ms.

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

General data

Name of the isotope:Polonium-205m3; Po-205m3Symbol:^205m3Po or 205m384PoMass 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:1461.21(21) keVIsotopic mass:204.981190(11) u (atomic weight of Polonium-205m3)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:57.4(9) msDecay constant λ:12.075734852961 s^-1Specific activity α:3.564792954498 × 10⁺²² Bq g^-1
963457555269.97 Ci g^-1Spin and parity:
(nuclear angular momentum)19/2-Year of discovery:1973

Radioactive Decay

Half-life T_½ = 57.4(9) ms respectively 5.74 × 10^-2 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-
^205m2Po	880.31(7) keV	0.645(20) ms	13/2+
^205m4Po	3087.2(4) keV	115(10) ns	29/2-
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-205m3. 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