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The Periodic Table of Elements

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Isotopes of the Element Fermium
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Most of the isotope data on this site has been obtained from the National Nuclear Data Center. Please visit their site for more information.

All Known Isotopes of the Element Fermium

Mass Number		Half-life		Decay Mode		Branching Percentage

242		0.8 milliseconds		Spontaneous Fission		<= 100.00

243		0.18 seconds		Alpha Decay		<= 100.00

				Spontaneous Fission		<= 0.40

244		3.3 milliseconds		Spontaneous Fission		<= 100.00

245		4.2 seconds		Alpha Decay		<= 100.00

				Spontaneous Fission		<= 0.10

246		1.1 seconds		Alpha Decay		92.00

				Spontaneous Fission		8.00

				Electron Capture		<= 1.00

247		35 seconds		Alpha Decay		>= 50.00

				Electron Capture		<= 50.00

247_m		9.2 seconds		Alpha Decay		<= 100.00

248		36 seconds		Alpha Decay		93.00

				Electron Capture		7.00

				Spontaneous Fission		0.10

249		2.6 minutes		Electron Capture		67.00

				Alpha Decay		33.00

250		30 minutes		Alpha Decay		> 90.00

				Electron Capture		< 10.00

				Spontaneous Fission		6.9E-3

250_m		1.8 seconds		Isomeric Transition		>= 80.00

				Alpha Decay		< 20.00

				Spontaneous Fission		<= 8.2E-5

				Electron Capture		No Data Available

251		5.30 hours		Electron Capture		98.20

				Alpha Decay		1.80

252		25.39 hours		Alpha Decay		100.00

				Spontaneous Fission		2.3E-3

253		3.00 days		Electron Capture		88.00

				Alpha Decay		12.00

254		3.240 hours		Alpha Decay		99.94

				Spontaneous Fission		0.06

255		20.07 hours		Alpha Decay		100.00

				Spontaneous Fission		2.4E-5

256		157.6 minutes		Spontaneous Fission		91.90

				Alpha Decay		8.10

257		100.5 days		Alpha Decay		99.79

				Spontaneous Fission		0.21

258		370 microseconds		Spontaneous Fission		<= 100.00

259		1.5 seconds		Spontaneous Fission		100.00

260		≈ 4 milliseconds		Spontaneous Fission		100.00

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