Thallium-181m

Properties and data of the isotope ^181mTl.

Contents

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

General data

Name of the isotope:Thallium-181m; Tl-181mSymbol:^181mTl or 181m81TlMass number A:181 (= number of nucleons)Atomic number Z:81 (= number of protons)Neutrons N:100Nucleon pairing (Z - N):odd - evenNuclear ratio (N/Z ratio):1.2345679012346 (= neutron-proton ratio)Neutron excess (N-Z):19Excitation energy:835.9(5) keVIsotopic mass:180.98626(1) u (atomic weight of Thallium-181m)Nuclide mass:180.94183 u (calculated nuclear mass without electrons)Mass excess:-12.79873 MeVMass defect:1.514059192 u (per nucleus)Nuclear binding energy:1410.33705299 MeV (per nucleus)
7.79191742 MeV (average binding energy per nucleon)Half-life:1.40(3) msDecay constant λ:495.10512897139 s^-1Specific activity α:1.656440459523 × 10⁺²⁴ Bq g^-1
44768661068211 Ci g^-1Spin and parity:
(nuclear angular momentum)(9/2-)

Radioactive Decay

Half-life T_½ = 1.40(3) ms respectively 1.40 × 10^-3 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
Iso	¹⁸¹Tl	99.60(4) %
α	¹⁷⁷Au	0.40(6) %

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
¹⁸¹Tl		3.2(3) s	(1/2+)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 100) and isobaric (same nucleon number A = 181) with Thallium-181m. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 100	Isobar A = 181
58	¹⁵⁸Ce
59	¹⁵⁹Pr
60	¹⁶⁰Nd
61	¹⁶¹Pm
62	¹⁶²Sm
63	¹⁶³Eu
64	¹⁶⁴Gd
65	¹⁶⁵Tb
66	¹⁶⁶Dy
67	¹⁶⁷Ho
68	¹⁶⁸Er
69	¹⁶⁹Tm
70	¹⁷⁰Yb	¹⁸¹Yb
71	¹⁷¹Lu	¹⁸¹Lu
72	¹⁷²Hf	¹⁸¹Hf
73	¹⁷³Ta	¹⁸¹Ta
74	¹⁷⁴W	¹⁸¹W
75	¹⁷⁵Re	¹⁸¹Re
76	¹⁷⁶Os	¹⁸¹Os
77	¹⁷⁷Ir	¹⁸¹Ir
78	¹⁷⁸Pt	¹⁸¹Pt
79	¹⁷⁹Au	¹⁸¹Au
80	¹⁸⁰Hg	¹⁸¹Hg
81	¹⁸¹Tl	¹⁸¹Tl
82	¹⁸²Pb	¹⁸¹Pb