Radium-208

Properties and data of the isotope ²⁰⁸Ra.

Content

General data

Name of the isotope:Radium-208; Ra-208Symbol:²⁰⁸Ra or 20888RaMass number A:208 (= number of nucleons)Atomic number Z:88 (= number of protons)Neutrons N:120Isotopic mass:208.001855(10) u (atomic weight of Radium-208)Nuclide mass:207.953586 u (calculated nuclear mass without electrons)Mass excess:1.72792 MeVMass defect:1.726537736 u (per nucleus)Nuclear binding energy:1608.25954186 MeV (per nucleus)
7.73201703 MeV (average binding energy per nucleon)Separation energy:S_N = 9.89(5) MeV (first neutron)
S_P = 2.717(2) MeV (first proton)Half-life:1.3(2) sDecay constant λ:0.53319013889227 s^-1Specific activity α:1.543724096893 × 10⁺²¹ Bq g^-1
41722272889.014 Ci g^-1Spin and parity:
(nuclear angular momentum)0+Charge radius:5.5850(183) femtometer fmYear of discovery:1967

Radioactive Decay

Half-life T_½ = 1.3(2) s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²⁰⁴Rn	95 %	7.273(5) MeV
EE/β⁺	²⁰⁸Fr	5 %	4.394(15) MeV

Parent Nuclides

Direct parent isotopes are: ²¹²Th, ²⁰⁸Ac.

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
^208mRa	2147.4(4) KeV	270(21) ns	(8+)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 120) and isobaric (same nucleon number A = 208) with Radium-208. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 120	Isobar A = 208
73	¹⁹³Ta
74	¹⁹⁴W
75	¹⁹⁵Re
76	¹⁹⁶Os
77	¹⁹⁷Ir
78	¹⁹⁸Pt	²⁰⁸Pt
79	¹⁹⁹Au	²⁰⁸Au
80	²⁰⁰Hg	²⁰⁸Hg
81	²⁰¹Tl	²⁰⁸Tl
82	²⁰²Pb	²⁰⁸Pb
83	²⁰³Bi	²⁰⁸Bi
84	²⁰⁴Po	²⁰⁸Po
85	²⁰⁵At	²⁰⁸At
86	²⁰⁶Rn	²⁰⁸Rn
87	²⁰⁷Fr	²⁰⁸Fr
88	²⁰⁸Ra	²⁰⁸Ra
89	²⁰⁹Ac	²⁰⁸Ac
90	²¹⁰Th	²⁰⁸Th