In the heart of the actinide series, americium sits between plutonium and curium and shows up in everything from smoke alarms to neutron sources. Its isotopes highlight how small changes in mass number affect radioactivity and practical use.
There are 5 Americium Isotopes, ranging from Am-241 to Am-244 (Am-241, Am-244 mark the endpoints). For each isotope, data are organized with Mass number (A),Half-life (yr/d/h/s),Decay mode(s), which you’ll find below.
Which Americium isotope is most commonly encountered and why?
Am-241 is the most commonly encountered because it emits alpha particles and has a half-life (about 432 years) suitable for long-term devices like smoke detectors and small neutron sources; its production and handling are well established for those uses.
How should I interpret the half-life and decay mode columns for these isotopes?
Half-life tells you how quickly the isotope decays (years, days, hours, or seconds), while decay mode(s) indicate the type of radiation emitted (alpha, beta, spontaneous fission, etc.), which together determine safety handling, applications, and expected activity changes over time.
Americium Isotopes
| Isotope | Mass number (A) | Half-life (yr/d/h/s) | Decay mode(s) |
|---|---|---|---|
| Am-241 | 241 | 432.2 yr | alpha |
| Am-242m | 242 | 141.00 yr | IT, alpha, beta- |
| Am-242 | 242 | 16.02 h | beta-, alpha |
| Am-243 | 243 | 7,370.00 yr | alpha |
| Am-244 | 244 | 10.10 h | beta-, alpha |
Images and Descriptions
Am-241
Commonly produced from decay of Pu-241 and in reactors; used in household smoke detectors, industrial gauging, and neutron sources; known for long-lived radioactivity and predominantly alpha decay, with small gamma emissions useful for detection.
Am-242m
A long-lived metastable isomer produced in reactors via neutron capture on Am-241/Am-242; notable for unusual nuclear properties and high neutron-induced fission probability, used mainly in research rather than practical applications.
Am-242
Ground-state Am-242 is formed in reactors from neutron capture chains; it decays relatively quickly to curium isotopes and is chiefly of interest in nuclear data studies and short-term radiochemistry experiments.
Am-243
Produced in reactors by successive neutron captures (and from Pu decay pathways); used as a reference in actinide research and considered in advanced fuel-cycle studies due to its long half-life and alpha emission.
Am-244
Formed in irradiated plutonium/americium mixtures in reactors; has short half-life and is primarily of interest in radiochemical experiments and decay-scheme studies rather than widespread practical use.
