Isotopes of americium

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Template:Short description Template:Infobox americium isotopes Americium (95Am) is an artificial element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no known stable isotopes. The first isotope to be synthesized was 241Am in 1944. The artificial element decays by ejecting alpha particles. Americium has an atomic number of 95 (the number of protons in the nucleus of the americium atom). Despite Template:Chem/link being an order of magnitude longer lived than Template:Chem/link, the former is harder to obtain than the latter as more of it is present in spent nuclear fuel.

Eighteen radioisotopes of americium, ranging from 229Am to 247Am with the exception of 231Am, have been characterized; another isotope, 223Am, has also been reported but is unconfirmed. The most stable isotopes are 243Am with a half-life of 7,370 years and 241Am with a half-life of 432.2 years. All of the remaining radioactive isotopes have half-lives that are less than seven days, the majority of which are shorter than two hours. This element also has fourteen meta states, with the most stable being 242m1Am (half-life 141 years). This isomer is unusual in that its half-life is far longer than that of the ground state of the same isotope.

List of isotopes

Script error: No such module "anchor". Template:Isotopes table |-id=Americium-223 | 223AmTemplate:Refn | style="text-align:right" | 95 | style="text-align:right" | 128 | 223.04584(32)# | Script error: No such module "val". | α | 219Np | 9/2–# |-id=Americium-229 | 229Am | style="text-align:right" | 95 | style="text-align:right" | 134 | 229.04528(11) | Script error: No such module "val". | α | 225Np | 5/2–# |-id=Americium-230 | rowspan=2 | 230Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 135 | rowspan=2 | 230.04603(15)# | rowspan=2 | Script error: No such module "val". | β+ (<70%) | 230Pu | rowspan=2 | 1–# |- | β+, SF (>30%) | (various) |-id=Americium-232 | rowspan=3 | 232Am | rowspan=3 style="text-align:right" | 95 | rowspan=3 style="text-align:right" | 137 | rowspan=3 | 232.04661(32)# | rowspan=3 | Script error: No such module "val". | β+ (97%) | 232Pu | rowspan=3 | 1–# |- | α? (3%) | 228Np |- | β+, SF (0.069%) | (various) |-id=Americium-233 | rowspan=2 | 233Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 138 | rowspan=2 | 233.04647(12)# | rowspan=2 | Script error: No such module "val". | β+? (95.5%) | 233Pu | rowspan=2 | 5/2–# |- | α (4.5%) | 229Np |-id=Americium-234 | rowspan=3 | 234Am | rowspan=3 style="text-align:right" | 95 | rowspan=3 style="text-align:right" | 139 | rowspan=3 | 234.04773(17)# | rowspan=3 | Script error: No such module "val". | β+ (99.95%) | 234Pu | rowspan=3 | 0–# |- | α (0.039%) | 230Np |- | β+, SF (0.0066%) | (various) |-id=Americium-235 | rowspan=2 | 235Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 140 | rowspan=2 | 235.04791(6) | rowspan=2 | Script error: No such module "val". | β+ (99.60%) | 235Pu | rowspan=2 | 5/2−# |- | α (0.40%) | 231Np |-id=Americium-236 | rowspan=2 | 236Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 141 | rowspan=2 | 236.04943(13)# | rowspan=2 | Script error: No such module "val". | β+ | 236Pu | rowspan=2 | 5− |- | α (4×10−3%) | 232Np |-id=Americium-236m | style="text-indent:1em" | 236mAm | colspan=3 style="text-indent:2em" | 50(50)# keV | Script error: No such module "val". | β+ | 236Pu | (1−) |-id=Americium-237 | rowspan=2 | 237Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 142 | rowspan=2 | 237.05000(6)# | rowspan=2 | Script error: No such module "val". | β+ (99.975%) | 237Pu | rowspan=2 | 5/2− |- | α (0.025%) | 233Np |-id=Americium-238 | rowspan=2 | 238Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 143 | rowspan=2 | 238.05198(6) | rowspan=2 | Script error: No such module "val". | β+ | 238Pu | rowspan=2 | 1+ |- | α (1.0×10−4%) | 234Np |-id=Americium-238m | style="text-indent:1em" | 238mAm | colspan="3" style="text-indent:2em" | 2500(200)# keV | Script error: No such module "val". | SF | (various) | |-id=Americium-239 | rowspan=2 | 239Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 144 | rowspan=2 | 239.0530227(21) | rowspan=2 | Script error: No such module "val". | EC (99.990%) | 239Pu | rowspan=2 | 5/2− |- | α (0.010%) | 235Np |-id=Americium-239m | style="text-indent:1em" | 239mAm | colspan="3" style="text-indent:2em" | 2500(200) keV | Script error: No such module "val". | SF | (various) | (7/2+) |-id=Americium-240 | rowspan=2 | 240Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 145 | rowspan=2 | 240.055298(15) | rowspan=2 | Script error: No such module "val". | β+ | 240Pu | rowspan=2 | (3−) |- | α (1.9×10−4%) | 236Np |-id=Americium-240m | style="text-indent:1em" | 240mAm | colspan="3" style="text-indent:2em" | 3000(200) keV | Script error: No such module "val". | SF | (various) | |- | rowspan=2 | 241Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 146 | rowspan=2 | 241.0568273(12) | rowspan=2 | Script error: No such module "val". | α | 237Np | rowspan=2 | 5/2− |- | SF (3.6×10−10%) | (various) |-id=Americium-241m | style="text-indent:1em" | 241mAm | colspan="3" style="text-indent:2em" | 2200(200) keV | Script error: No such module "val". | SF | (various) | |-id=Americium-242 | rowspan=2 | 242Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 147 | rowspan=2 | 242.0595474(12) | rowspan=2 | Script error: No such module "val". | β− (82.7%) | 242Cm | rowspan=2 | 1− |- | EC (17.3%) | 242Pu |- | rowspan=3 style="text-indent:1em" | 242m1Am | rowspan=3 colspan="3" style="text-indent:2em" | 48.60(5) keV | rowspan=3 | Script error: No such module "val". | IT (99.55%) | 242Am | rowspan=3 | 5− |- | α (0.45%) | 238Np |- | SF (<4.7×10−9%) | (various) |-id=Americium-242m2 | rowspan=2 style="text-indent:1em" | 242m2Am | rowspan=2 colspan="3" style="text-indent:2em" | 2200(80) keV | rowspan=2 | Script error: No such module "val". | SF | (various) | rowspan=2 | (2+, 3−) |- | IT | 242Am |- | rowspan=2 | 243Am | rowspan=2 style="text-align:right" | 95 | rowspan=2 style="text-align:right" | 148 | rowspan=2 | 243.0613799(15) | rowspan=2 | Script error: No such module "val". | α | 239Np | rowspan=2 | 5/2− |- | SF (3.7×10−9%) | (various) |-id=Americium-243m | style="text-indent:1em" | 243mAm | colspan="3" style="text-indent:2em" | 2300(200) keV | Script error: No such module "val". | SF | (various) | |-id=Americium-244 | 244Am | style="text-align:right" | 95 | style="text-align:right" | 149 | 244.0642829(16) | Script error: No such module "val". | β− | 244Cm | (6−) |-id=Americium-244m1 | rowspan=2 style="text-indent:1em" | 244m1Am | rowspan=2 colspan="3" style="text-indent:2em" | 89.3(16) keV | rowspan=2 | Script error: No such module "val". | β− (99.96%) | 244Cm | rowspan=2 | 1+ |- | EC (0.0364%) | 244Pu |-id=Americium-244m2 | style="text-indent:1em" | 244m2Am | colspan="3" style="text-indent:2em" | 2000(200)# keV | Script error: No such module "val". | SF | (various) | |-id=Americium-244m3 | style="text-indent:1em" | 244m3Am | colspan="3" style="text-indent:2em" | 2200(200)# keV | ~Script error: No such module "val". | SF | (various) | |-id=Americium-245 | 245Am | style="text-align:right" | 95 | style="text-align:right" | 150 | 245.0664528(20) | Script error: No such module "val". | β− | 245Cm | 5/2+ |-id=Americium-245m | style="text-indent:1em" | 245mAm | colspan="3" style="text-indent:2em" | 2400(400)# keV | Script error: No such module "val". | SF | (various) | |-id=Americium-246 | 246Am | style="text-align:right" | 95 | style="text-align:right" | 151 | 246.069774(19)# | Script error: No such module "val". | β− | 246Cm | 7− |-id=Americium-246m1 | style="text-indent:1em" | 246m1Am | colspan="3" style="text-indent:2em" | 30(10)# keV | Script error: No such module "val". | β− | 246Cm | 2(−) |-id=Americium-246m2 | style="text-indent:1em" | 246m2Am | colspan="3" style="text-indent:2em" | 2000(800)# keV | Script error: No such module "val". | SF | (various) | |-id=Americium-247 | 247Am | style="text-align:right" | 95 | style="text-align:right" | 152 | 247.07209(11)# | Script error: No such module "val". | β− | 247Cm | 5/2# Template:Isotopes table/footer

Actinides vs fission products

Template:Actinidesvsfissionproducts

Notable isotopes

Americium-241

File:Americium button hd.jpg
Americium-241 is used in ionization smoke detectors.

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Americium-241 is the most common isotope of americium in nuclear waste.[1] It is the isotope used in an americium smoke detector based on an ionization chamber. It is a potential fuel for long-lifetime radioisotope thermoelectric generators.

Parameter Value
Atomic mass Script error: No such module "val".
Mass excess 52930 keV
Beta decay energy −767 keV
Spin 5/2−
Half-life 432.6 years
Spontaneous fissions 1200 per kg s
Decay heat 114 watts/kg

Possible parent nuclides: beta from 241Pu, electron capture from 241Cm, alpha from 245Bk.

241Am alpha decays, with a by-product of gamma rays. Its presence in plutonium is determined by the original concentration of 241Pu and the sample age. Due to the low penetration of alpha radiation, 241Am only poses a health risk when ingested or inhaled. Older samples of plutonium containing plutonium-241 contain a buildup of 241Am. A chemical removal of americium from reworked plutonium (e.g. during reworking of plutonium pits) may be required.

Americium-242m

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Transmutation flow between 238Pu and 244Cm in LWR.[2]Script error: No such module "string".Fission percentage is 100 minus shown percentages.Script error: No such module "string".Total rate of transmutation varies greatly by nuclide.Script error: No such module "string".245Cm–248Cm are long-lived with negligible decay.
242mAm decay modes (half-life: 141 years)Template:NUBASE2020
Probability Decay mode Decay energy Decay product
99.55% isomeric transition 0.049 MeV 242Am
  0.45% alpha decay 5.64 MeV 238Np
Script error: No such module "val".Template:Tsp[3] spontaneous fission ~200 MeV fission products

Americium-242m has a mass of 242.0595492 g/mol. It is one of the rare cases, like 108mAg, 166mHo, 180mTa, 186mRe, 192mIr, 210mBi, 212mPo and others, where a higher-energy nuclear isomer is more stable than the ground state, americium-242.[4]

242mAm is fissile with a low critical mass, comparable to that of 239Pu.[5] It has a very high fission cross section, and is quickly destroyed if it is produced in a nuclear reactor. It has been investigated whether this isotope could be used for a novel type of nuclear rocket.[6][7]

242Am decay modes (half-life: 16 hours)Template:NUBASE2020
Probability Decay mode Decay energy Decay product
82.7% beta decay 0.664 MeV 242Cm
17.3% electron capture 0.751 MeV 242Pu

Americium-243

File:Am243.png
A sample of Am-243

Americium-243 has a mass of 243.06138 g/mol and a half-life of 7350 yearsTemplate:NUBASE2020, the longest lasting of all americium isotopes. It is formed in the nuclear fuel cycle by neutron capture on plutonium-242 followed by beta decay.[8] Production increases exponentially with increasing burnup as a total of 5 neutron captures on 238U are required. If MOX-fuel is used, particularly MOX-fuel high in Template:Chem/link and Template:Chem/link, more americium overall and more Template:Chem/link will be produced.

It decays by either emitting an alpha particle (with a decay energy of 5.27 MeV)[8] to become 239Np, which then quickly decays to 239Pu, or rarely, by spontaneous fission.[9]

As for the other americium isotopes, and more generally for all alpha emitters, 243Am is carcinogenic in case of internal contamination after being inhaled or ingested. 243Am also presents a risk of external irradiation associated with the gamma ray emitted by its short-lived decay product 239Np. The external irradiation risk for the other two americium isotopes (241Am and 242mAm) is less than 10% of that for americium-243.[1]

References

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  1. ↑ a b "Americium" Template:Webarchive. Argonne National Laboratory, EVS. Retrieved 25 December 2009.
  2. ↑ Script error: No such module "Citation/CS1".
  3. ↑ Script error: No such module "Citation/CS1". (halflife (9.5±3.5)×1011 years)
  4. ↑ 95-Am-242 Template:Webarchive
  5. ↑ Script error: No such module "citation/CS1".
  6. ↑ Script error: No such module "citation/CS1".
  7. ↑ Script error: No such module "Citation/CS1".
  8. ↑ a b "Americium-243" Template:Webarchive. Oak Ridge National Laboratory. Retrieved 25 December 2009.
  9. ↑ "Isotopes of the Element Americium". Jefferson Lab Science Education. Retrieved 25 December 2009.

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Sources

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