Isotopes of americium

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Americium (Am) has no stable isotopes. A standard atomic mass cannot be given.

File:Americium.jpg
Sample of Americium

19 radioisotopes of americium have been characterized, with the most stable being 243Am with a half-life of 7370 years, and 241Am with a half-life of 432.7 years. All of the remaining radioactive isotopes have half-lives that are less than 51 hours, and the majority of these have half-lives that are less than 100 minutes. This element also has 8 meta states, with the most stable being 242mAm (t½ 141 years). The isotopes of americium range in atomic weight from 231.046 u (231Am) to 249.078 u (249Am).

Table

nuclide
symbol
Z(p) N(n)  
isotopic mass (u)
 
half-life nuclear
spin
excitation energy
231Am 95 136 231.04556(32)# 30# s
232Am 95 137 232.04659(32)# 79(2) s
233Am 95 138 233.04635(11)# 3.2(8) min
234Am 95 139 234.04781(22)# 2.32(8) min
235Am 95 140 235.04795(13)# 9.9(5) min 5/2-#
236Am 95 141 236.04958(11)# 3.6(1) min
237Am 95 142 237.05000(6)# 73.0(10) min 5/2(-)
238Am 95 143 238.05198(5) 98(2) min 1+
238mAm 2500(200)# keV 35(10) µs
239Am 95 144 239.0530245(26) 11.9(1) h (5/2)-
239mAm 2500(200) keV 163(12) ns (7/2+)
240Am 95 145 240.055300(15) 50.8(3) h (3-)
241Am 95 146 241.0568291(20) 432.2(7) y 5/2-
241mAm 2200(100) keV 1.2(3) µs
242Am 95 147 242.0595492(20) 16.02(2) h 1-
242m1Am 48.60(5) keV 141(2) a 5-
242m2Am 2200(80) keV 14.0(10) ms (2+,3-)
243Am 95 148 243.0613811(25) 7.37(4)E+3 a 5/2-
244Am 95 149 244.0642848(22) 10.1(1) h (6-)#
244mAm 86.1(10) keV 26(1) min 1+
245Am 95 150 245.066452(4) 2.05(1) h (5/2)+
246Am 95 151 246.069775(20) 39(3) min (7-)
246m1Am 30(10) keV 25.0(2) min 2(-)
246m2Am ~2000 keV 73(10) µs
247Am 95 152 247.07209(11)# 23.0(13) min (5/2)#
248Am 95 153 248.07575(22)# 3# min
249Am 95 154 249.07848(32)# 1# min

Notes

  • Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses - ( ).
  • Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.

References


Isotopes of plutonium Isotopes of americium Isotopes of curium
Index to isotope pages · Table of nuclides



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