Polonium-191

Properties and data of the isotope ¹⁹¹Po.

Content

General data

Name of the isotope:Polonium-191; Po-191Symbol:¹⁹¹Po or 19184PoMass number A:191 (= number of nucleons)Atomic number Z:84 (= number of protons)Neutrons N:107Isotopic mass:190.994558(8) u (atomic weight of Polonium-191)Nuclide mass:190.9484827 u (calculated nuclear mass without electrons)Mass excess:-5.06919 MeVMass defect:1.5898907 u (per nucleus)Nuclear binding energy:1480.97364771 MeV (per nucleus)
7.75378873 MeV (average binding energy per nucleon)Separation energy:S_N = 8.576(15) MeV (first neutron)
S_P = 1.758(24) MeV (first proton)Half-life:22(1) msDecay constant λ:31.506690025452 s^-1Specific activity α:9.986196071770 × 10⁺²² Bq g^-1
2698971911289.3 Ci g^-1Spin and parity:
(nuclear angular momentum)(3/2-)Year of discovery:1993

Radioactive Decay

Half-life T_½ = 22(1) ms respectively 2.2 × 10^-2 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	¹⁸⁷Pb	99.0(10) %	7.493(5) MeV

Parent Nuclides

Direct parent isotope is: ¹⁹⁵Rn.

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
^191mPo	40(15) keV	93(3) ms	(13/2+)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 107) and isobaric (same nucleon number A = 191) with Polonium-191. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 107	Isobar A = 191
65	¹⁷²Tb
66	¹⁷³Dy
67	¹⁷⁴Ho
68	¹⁷⁵Er
69	¹⁷⁶Tm
70	¹⁷⁷Yb
71	¹⁷⁸Lu
72	¹⁷⁹Hf
73	¹⁸⁰Ta	¹⁹¹Ta
74	¹⁸¹W	¹⁹¹W
75	¹⁸²Re	¹⁹¹Re
76	¹⁸³Os	¹⁹¹Os
77	¹⁸⁴Ir	¹⁹¹Ir
78	¹⁸⁵Pt	¹⁹¹Pt
79	¹⁸⁶Au	¹⁹¹Au
80	¹⁸⁷Hg	¹⁹¹Hg
81	¹⁸⁸Tl	¹⁹¹Tl
82	¹⁸⁹Pb	¹⁹¹Pb
83	¹⁹⁰Bi	¹⁹¹Bi
84	¹⁹¹Po	¹⁹¹Po
85	¹⁹²At	¹⁹¹At
86	¹⁹³Rn