Americium-239

Properties and data of the isotope ²³⁹Am.

Content

Americium-239 is the radioisotope of the element Americium, whose atomic nucleus has 144 neutrons in addition to the element-specific 95 protons, resulting in a mass number of 239: ²³⁹Am.

General data

Name of the isotope:Americium-239; Am-239Symbol:²³⁹Am or 23995AmMass number A:239 (= number of nucleons)Atomic number Z:95 (= number of protons)Neutrons N:144Isotopic mass:239.0530228(21) u (atomic weight of Americium-239)Nuclide mass:239.0009149 u (calculated nuclear mass without electrons)Mass excess:49.39042 MeVMass defect:1.938103144 u (per nucleus)Nuclear binding energy:1805.33145002 MeV (per nucleus)
7.55368808 MeV (average binding energy per nucleon)Separation energy:S_N = 7.10(5) MeV (first neutron)
S_P = 4.0618(17) MeV (first proton)Half-life:11.9(1) hDecay constant λ:1.617990617553 × 10^-5 s^-1Specific activity α:4.076890129273 × 10⁺¹⁶ Bq g^-1
1101862.1971009 Ci g^-1Spin and parity:
(nuclear angular momentum)(5/2)-Year of discovery:1948

Radioactive Decay

Half-life T_½ = 11.9(1) h (hours) respectively 4.2840 × 10⁴ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²³⁵Np	0.010(1) %	5.9224(14) MeV
EE	²³⁹Pu	99.990(1) %	0.801(23) MeV

Parent Nuclides

Direct parent isotopes are: ²³⁹Cm, ²⁴³Bk.

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
^239mAm	2500 keV	163(12) ns	(7/2+)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 144) and isobaric (same nucleon number A = 239) with Americium-239. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 144	Isobar A = 239
85	²²⁹At
86	²³⁰Rn
87	²³¹Fr
88	²³²Ra
89	²³³Ac
90	²³⁴Th
91	²³⁵Pa	²³⁹Pa
92	²³⁶U	²³⁹U
93	²³⁷Np	²³⁹Np
94	²³⁸Pu	²³⁹Pu
95	²³⁹Am	²³⁹Am
96	²⁴⁰Cm	²³⁹Cm
97	²⁴¹Bk	²³⁹Bk
98	²⁴²Cf	²³⁹Cf
99	²⁴³Es
100	²⁴⁴Fm
101	²⁴⁵Md