Thallium-205m2

Properties and data of the isotope ^205m2Tl.

Contents

Thallium-205m2 is an excited nuclear state of the nuclide ²⁰⁵Tl, characterized by a defined excitation energy (4835.6 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 Tl-205 in the ground state with a half-life of approximately 235 nanoseconds.

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

General data

Name of the isotope:Thallium-205m2; Tl-205m2Symbol:^205m2Tl or 205m281TlMass number A:205 (= number of nucleons)Atomic number Z:81 (= number of protons)Neutrons N:124Nucleon pairing (Z - N):odd - evenNuclear ratio (N/Z ratio):1.5308641975309 (= neutron-proton ratio)Neutron excess (N-Z):43Excitation energy:4835.6(15) keVIsotopic mass:204.974428(9) u (atomic weight of Thallium-205m2)Nuclide mass:204.929998 u (calculated nuclear mass without electrons)Mass excess:-23.82016 MeVMass defect:1.733849176 u (per nucleus)Nuclear binding energy:1615.07010435 MeV (per nucleus)
7.87839075 MeV (average binding energy per nucleon)Half-life:235(10) nsDecay constant λ:2949562.4704679 s^-1Specific activity α:8.7071964080 × 10⁺²⁷ Bq g^-1
2.353296326489 × 10⁺¹⁷ Ci g^-1Spin and parity:
(nuclear angular momentum)(35/2-)Year of discovery:2004

Radioactive Decay

Half-life T_½ = 235(10) ns respectively 2.35 × 10^-7 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
Iso	²⁰⁵Tl	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
²⁰⁵Tl		stable	1/2+
^205m1Tl	3290.61(17) keV	2.6(2) μs	25/2+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 124) and isobaric (same nucleon number A = 205) with Thallium-205m2. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 124	Isobar A = 205
75	¹⁹⁹Re
76	²⁰⁰Os
77	²⁰¹Ir	²⁰⁵Ir
78	²⁰²Pt	²⁰⁵Pt
79	²⁰³Au	²⁰⁵Au
80	²⁰⁴Hg	²⁰⁵Hg
81	²⁰⁵Tl	²⁰⁵Tl
82	²⁰⁶Pb	²⁰⁵Pb
83	²⁰⁷Bi	²⁰⁵Bi
84	²⁰⁸Po	²⁰⁵Po
85	²⁰⁹At	²⁰⁵At
86	²¹⁰Rn	²⁰⁵Rn
87	²¹¹Fr	²⁰⁵Fr
88	²¹²Ra	²⁰⁵Ra
89	²¹³Ac	²⁰⁵Ac
90	²¹⁴Th
91	²¹⁵Pa
92	²¹⁶U