Polonium-205

Properties and data of the isotope ²⁰⁵Po.

Contents

General Data

Radioactive Decay

Parent Nuclides

Isotones und Isobares

Literature

Polonium-205 is a radioisotope of the chemical element polonium, which has 121 neutrons in its atomic nucleus in addition to the element-specific 84 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 205. The very short-lived, only artificially produced, unstable and thus radioactive nuclide has no practical significance; the study of ²⁰⁵Po is exclusively for academic purposes.

A report on the first observation of the nuclide was published in 1951 [1].

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

General data

Name of the isotope:Polonium-205; Po-205Symbol:²⁰⁵Po or 20584PoMass 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):37Isotopic mass:204.981190(11) u (atomic weight of Polonium-205)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)Separation energy:S_N = 7.252(14) MeV (first neutron)
S_P = 4.164(14) MeV (first proton)Half-life:1.74(8) hDecay constant λ:0.00011065568016602 s^-1Specific activity α:3.266588690744 × 10⁺¹⁷ Bq g^-1
8828618.0830932 Ci g^-1Spin and parity:
(nuclear angular momentum)5/2-Magnetic dipole moment:μ(μ_N) = + 0.76(6)Quadrupole moment Q:+ 0.17 barn (100 fm²)Nuclear g-factor:g_l = 0.304Charge radius:5.5389(177) femtometer fmYear of discovery:1951

Radioactive Decay

Half-life T_½ = 1.74(8) h (hours) respectively 6.264 × 10³ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²⁰¹Pb	0.040(12) %	5.325(10) MeV
EC/β⁺	²⁰⁵Bi	99.960(12) %	3.544(11) MeV

Parent Nuclides

Direct parent isotopes are: ²⁰⁹Rn, ²⁰⁵At.

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+
^205m4Po	3087.2(4) keV	115(10) ns	29/2-

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-205. 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

External data and identifiers

Adopted Levels, Gammas:NuDat 205Po

Literature and References

[1] - D. G. Karraker, D. H. Templeton:
Polonium Isotopes Produced with High Energy Particles.
In: Physical Review, 81, 510, (1951), DOI 10.1103/PhysRev.81.510.