Thulium-155

Properties and data of the isotope ¹⁵⁵Tm.

Contents

General data

Name of the isotope:Thulium-155; Tm-155Symbol:¹⁵⁵Tm or 15569TmMass number A:155 (= number of nucleons)Atomic number Z:69 (= number of protons)Neutrons N:86Isotopic mass:154.939210(11) u (atomic weight of Thulium-155)Nuclide mass:154.9013614 u (calculated nuclear mass without electrons)Mass excess:-56.62552 MeVMass defect:1.345899984 u (per nucleus)Nuclear binding energy:1253.6977597 MeV (per nucleus)
8.08837264 MeV (average binding energy per nucleon)Separation energy:S_N = 10.270(17) MeV (first neutron)
S_P = 1.310(11) MeV (first proton)Half-life:21.6(2) sDecay constant λ:0.032090147248146 s^-1Specific activity α:1.254879136002 × 10⁺²⁰ Bq g^-1
3391565232.4403 Ci g^-1Spin and parity:
(nuclear angular momentum)11/2-Year of discovery:1971

Radioactive Decay

Half-life T_½ = 21.6(2) s respectively 2.16 × 10¹ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
EC/β⁺	¹⁵⁵Er	99.11(24) %	5.583(12) MeV
α	¹⁵¹Ho	0.89(24) %	4.572(5) MeV

Parent Nuclides

Direct parent isotopes are: ¹⁵⁵Yb, ¹⁵⁹Lu.

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
^155mTm	41(6) keV	45(3) s	1/2+

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 86) and isobaric (same nucleon number A = 155) with Thulium-155. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 86	Isobar A = 155
48	¹³⁴Cd
49	¹³⁵In
50	¹³⁶Sn
51	¹³⁷Sb
52	¹³⁸Te
53	¹³⁹I
54	¹⁴⁰Xe
55	¹⁴¹Cs
56	¹⁴²Ba
57	¹⁴³La	¹⁵⁵La
58	¹⁴⁴Ce	¹⁵⁵Ce
59	¹⁴⁵Pr	¹⁵⁵Pr
60	¹⁴⁶Nd	¹⁵⁵Nd
61	¹⁴⁷Pm	¹⁵⁵Pm
62	¹⁴⁸Sm	¹⁵⁵Sm
63	¹⁴⁹Eu	¹⁵⁵Eu
64	¹⁵⁰Gd	¹⁵⁵Gd
65	¹⁵¹Tb	¹⁵⁵Tb
66	¹⁵²Dy	¹⁵⁵Dy
67	¹⁵³Ho	¹⁵⁵Ho
68	¹⁵⁴Er	¹⁵⁵Er
69	¹⁵⁵Tm	¹⁵⁵Tm
70	¹⁵⁶Yb	¹⁵⁵Yb
71	¹⁵⁷Lu	¹⁵⁵Lu
72	¹⁵⁸Hf	¹⁵⁵Hf
73	¹⁵⁹Ta	¹⁵⁵Ta
74	¹⁶⁰W
75	¹⁶¹Re
76	¹⁶²Os