Francium-205

Properties and data of the isotope ²⁰⁵Fr.

Content

General data

Name of the isotope:Francium-205; Fr-205Symbol:²⁰⁵Fr or 20587FrMass number A:205 (= number of nucleons)Atomic number Z:87 (= number of protons)Neutrons N:118Isotopic mass:204.998594(8) u (atomic weight of Francium-205)Nuclide mass:204.9508734 u (calculated nuclear mass without electrons)Mass excess:-1.30968 MeVMass defect:1.704643872 u (per nucleus)Nuclear binding energy:1587.8655389 MeV (per nucleus)
7.74568556 MeV (average binding energy per nucleon)Separation energy:S_N = 9.988(26) MeV (first neutron)
S_P = 0.629(11) MeV (first proton)Half-life:3.92(4) sDecay constant λ:0.17682326034692 s^-1Specific activity α:5.219875397659 × 10⁺²⁰ Bq g^-1
14107771345.025 Ci g^-1Spin and parity:
(nuclear angular momentum)(9/2-)Year of discovery:1964

Radioactive Decay

Half-life T_½ = 3.92(4) s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²⁰¹At	≤ 100 %	7.0547(24) MeV

Parent Nuclides

Direct parent isotope is: ²⁰⁹Ac.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 118) and isobaric (same nucleon number A = 205) with Francium-205. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 118	Isobar A = 205
72	¹⁹⁰Hf
73	¹⁹¹Ta
74	¹⁹²W
75	¹⁹³Re
76	¹⁹⁴Os
77	¹⁹⁵Ir	²⁰⁵Ir
78	¹⁹⁶Pt	²⁰⁵Pt
79	¹⁹⁷Au	²⁰⁵Au
80	¹⁹⁸Hg	²⁰⁵Hg
81	¹⁹⁹Tl	²⁰⁵Tl
82	²⁰⁰Pb	²⁰⁵Pb
83	²⁰¹Bi	²⁰⁵Bi
84	²⁰²Po	²⁰⁵Po
85	²⁰³At	²⁰⁵At
86	²⁰⁴Rn	²⁰⁵Rn
87	²⁰⁵Fr	²⁰⁵Fr
88	²⁰⁶Ra	²⁰⁵Ra
89	²⁰⁷Ac	²⁰⁵Ac
90	²⁰⁸Th