Americium-238

Properties and data of the isotope ²³⁸Am.

Content

General data

Name of the isotope:Americium-238; Am-238Symbol:²³⁸Am or 23895AmMass number A:238 (= number of nucleons)Atomic number Z:95 (= number of protons)Neutrons N:143Isotopic mass:238.05198(5) u (atomic weight of Americium-238)Nuclide mass:237.9998721 u (calculated nuclear mass without electrons)Mass excess:48.41906 MeVMass defect:1.930481028 u (per nucleus)Nuclear binding energy:1798.2314947 MeV (per nucleus)
7.55559452 MeV (average binding energy per nucleon)Separation energy:S_N = 6.22(8) MeV (first neutron)
S_P = 3.96(5) MeV (first proton)Half-life:98(2) minDecay constant λ:0.00011788217356462 s^-1Specific activity α:2.982785941519 × 10⁺¹⁷ Bq g^-1
8061583.6257284 Ci g^-1Spin and parity:
(nuclear angular momentum)1+Year of discovery:1950

Radioactive Decay

Half-life T_½ = 98(2) min (minutes) respectively 5.880 × 10³ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²³⁴Np	0.0001 %	6.04(5) MeV
EE/β⁺	²³⁸Pu	ca. 100 %	2.26(5) MeV

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
^238mAm	2500 keV	35 μs

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 143) and isobaric (same nucleon number A = 238) with Americium-238. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 143	Isobar A = 238
84	²²⁷Po
85	²²⁸At
86	²²⁹Rn
87	²³⁰Fr
88	²³¹Ra
89	²³²Ac
90	²³³Th	²³⁸Th
91	²³⁴Pa	²³⁸Pa
92	²³⁵U	²³⁸U
93	²³⁶Np	²³⁸Np
94	²³⁷Pu	²³⁸Pu
95	²³⁸Am	²³⁸Am
96	²³⁹Cm	²³⁸Cm
97	²⁴⁰Bk	²³⁸Bk
98	²⁴¹Cf	²³⁸Cf
99	²⁴²Es
100	²⁴³Fm
101	²⁴⁴Md