Astatine-191m

Properties and data of the isotope ¹⁹¹At.

Content

General data

Name of the isotope:Astatine-191m; At-191mSymbol:¹⁹¹At or 19185AtMass number A:191 (= number of nucleons)Atomic number Z:85 (= number of protons)Neutrons N:106Isotopic mass:191.004148(17) u (atomic weight of Astatine-191m)
Excitation energy: 55(30)keVNuclide mass:190.9575243 u (calculated nuclear mass without electrons)Mass excess:3.86384 MeVMass defect:1.579460816 u (per nucleus)Nuclear binding energy:1471.25827334 MeV (per nucleus)
7.7029229 MeV (average binding energy per nucleon)Half-life:ca. 2.1 msDecay constant λ:330.07008598093 s^-1Specific activity α:1.040695576664 × 10⁺²⁴ Bq g^-1
28126907477411 Ci g^-1Spin and parity:
(nuclear angular momentum)(7/2-)

Radioactive Decay

Half-life T_½ = ca. 2.1 ms respectively 2.1 × 10^-3 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	¹⁸⁷Bi	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
¹⁹¹At		ca. 1.7 ms	(1/2+)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 106) and isobaric (same nucleon number A = 191) with Astatine-191m. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 106	Isobar A = 191
64	¹⁷⁰Gd
65	¹⁷¹Tb
66	¹⁷²Dy
67	¹⁷³Ho
68	¹⁷⁴Er
69	¹⁷⁵Tm
70	¹⁷⁶Yb
71	¹⁷⁷Lu
72	¹⁷⁸Hf
73	¹⁷⁹Ta	¹⁹¹Ta
74	¹⁸⁰W	¹⁹¹W
75	¹⁸¹Re	¹⁹¹Re
76	¹⁸²Os	¹⁹¹Os
77	¹⁸³Ir	¹⁹¹Ir
78	¹⁸⁴Pt	¹⁹¹Pt
79	¹⁸⁵Au	¹⁹¹Au
80	¹⁸⁶Hg	¹⁹¹Hg
81	¹⁸⁷Tl	¹⁹¹Tl
82	¹⁸⁸Pb	¹⁹¹Pb
83	¹⁸⁹Bi	¹⁹¹Bi
84	¹⁹⁰Po	¹⁹¹Po
85	¹⁹¹At	¹⁹¹At