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Properties and data of the isotope 243Am.


Americium-243 is the radioisotope of the element Americium, whose atomic nucleus has 148 neutrons in addition to the element-specific 95 protons, resulting in a mass number of 243: 243 Am.

See also: list of Americium isotopes.


General data

Name of the isotope:Americium-243; Am-243Symbol:243AmMass number A:243Atomic number Z:95 (= number of protons)Neutrons N:148Isotopic mass:243.0613799(15) u (atomic weight of Americium-243)Nuclide mass:243.009272 u (calculated nuclear mass without electrons)Mass excess:57.17501 MeVMass defect:1.964405708 u (per nucleus)Nuclear binding energy:1829.83213057 MeV (per nucleus)
7.53017338 MeV (average binding energy per nucleon)
Separation energy:SN = 6.3643(12) MeV (first neutron)
SP = 4.8309(14) MeV (first proton)
Half-life:7353(10) aDecay constant λ:2.984744350686 × 10-12 s-1Spin and parity:5/2-Charge radius:5.9048(35) femtometer fmYear of discovery:1950


Radioactive Decay

(Note: For the value of the half-life: cf. [1] ).

Half-life T½ = 7353(10) a respectively 2.3223 × 1011 seconds s.

Decay modeDaughterProbabilityDecay energyγ energy
α239Npca. 100 %5,4391(9) MeV


Americium-243 radioactive decay chain


Parent Nuclides

Direct parent isotopes are: 247Bk, 243Cm, 243Pu.



Comparison of the natural Americium isotopes including isotopic abundance (proportion of the isotope mixture):


Atomic Mass maQuantityHalf-lifeSpin
Isotopic mixture
243,061382541 u100 %
Isotope 243Am243,0613799(15) u100 %7353(10) a5/2-


NMR data

243Am belongs to the NMR active Nuclides.

Isotope:243Am-NMRQuantity:100 %Spin:5/2-Nuclearmagnetic moment
+ 1,50(1)Gyromagnetic ratio
107 rad T-1 s-1:
1,54Quadrupole moment
Q fm-2:
420,0(1300)Resonance frequency
v0 at 1 T:
4,6Relative Sensitivity:0,01446 (H0 = const.)
1,2532 (v0 = const.)
[related to 1H = 1,000]


Radiation Protection

The German Radiation Protection Ordinance, for example, specifies the following limit values for the isotope Americium-243 (exemption limits, clearance values and other values as a radioactive or highly radioactive source of radiation (HASS)):

Isotope:Am-243+Exemption level:103 BqExemption level per gram:0,1 Bq/g
Unrestricted handling of solids and liquids.
Activity HASS:0,2 TBqSurface contamination:0,1 Bq cm-2Half-life:7400 a


Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 148) and isobaric (same nucleon number A = 243) with Americium-243. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.


OZIsotone N = 148Isobar A = 243


External data and identifiers

CAS:14993-75-0InChI Key:LXQXZNRPTYVCNG-IGMARMGPSA-NSMILES:[243Am]PubChem:ID 105139Adopted Levels, Gammas:NuDat 243Am


Literature and References

[1] - M. Marouli, S. Pommé, V. Jobbágy et al.:
Absolute and relative measurement of the 243Am half-life.
In: Journal of Radioanalytical and Nuclear Chemistry, (2020), DOI 10.1007/s10967-020-07450-9.


Category: Isotopes

Last update: 26.11.2022

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