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Isotopes of the Element Cesium

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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.

Isotopes With A Known Natural Abundance

Mass Number	Natural Abundance	Half-life
133	100%	STABLE

Known Isotopes

Mass Number	Half-life	Decay Mode	Branching Percentage
112	0.5 milliseconds	Proton Emission	100.00%
113	16.7 microseconds	Proton Emission	100.00%
		Alpha Decay	No Data Available
114	0.57 seconds	Electron Capture	99.98%
		Electron Capture with delayed Proton Emission	8.70%
		Electron Capture with delayed Alpha Decay	0.19%
		Alpha Decay	0.02%
115	1.4 seconds	Electron Capture	100.00%
		Electron Capture with delayed Proton Emission	~ 0.07%
116	0.70 seconds	Electron Capture	100.00%
		Electron Capture with delayed Proton Emission	2.80%
		Electron Capture with delayed Alpha Decay	0.05%
116_m	3.85 seconds	Electron Capture	100.00%
		Electron Capture with delayed Proton Emission	0.51%
		Electron Capture with delayed Alpha Decay	8.0×10^-3%
117	8.4 seconds	Electron Capture	100.00%
117_m	6.5 seconds	Electron Capture	No Data Available
118	14 seconds	Electron Capture	100.00%
		Electron Capture with delayed Proton Emission	< 0.04%
		Electron Capture with delayed Alpha Decay	< 2.4×10^-3%
118_m	17 seconds	Electron Capture	100.00%
		Electron Capture with delayed Proton Emission	< 0.04%
		Electron Capture with delayed Alpha Decay	< 2.4×10^-3%
119	43.0 seconds	Electron Capture	100.00%
119_m	30.4 seconds	Electron Capture	100.00%
120	61.3 seconds	Electron Capture	100.00%
		Electron Capture with delayed Alpha Decay	2.0×10^-5%
		Electron Capture with delayed Proton Emission	7.0×10^-6%
120_m	57 seconds	Electron Capture	100.00%
121	155 seconds	Electron Capture	100.00%
121_m	122 seconds	Isomeric Transition	17.00%
		Electron Capture	83.00%
122	21.18 seconds	Electron Capture	100.00%
122_m	0.36 seconds	Isomeric Transition	100.00%
122_m1	3.70 minutes	Electron Capture	100.00%
123	5.88 minutes	Electron Capture	100.00%
123_m	1.64 seconds	Isomeric Transition	100.00%
124	30.9 seconds	Electron Capture	100.00%
124_m	6.3 seconds	Isomeric Transition	100.00%
125	46.7 minutes	Electron Capture	100.00%
125_m	0.90 milliseconds	Isomeric Transition	100.00%
126	1.64 minutes	Electron Capture	100.00%
127	6.25 hours	Electron Capture	100.00%
128	3.66 minutes	Electron Capture	100.00%
129	32.06 hours	Electron Capture	100.00%
130	29.21 minutes	Electron Capture	98.40%
		Beta-minus Decay	1.60%
130_m	3.46 minutes	Isomeric Transition	99.84%
		Electron Capture	0.16%
131	9.689 days	Electron Capture	100.00%
132	6.480 days	Electron Capture	98.13%
		Beta-minus Decay	1.87%
133	STABLE	-	-
134	2.0652 years	Beta-minus Decay	100.00%
		Electron Capture	3.0×10^-4%
134_m	2.912 hours	Isomeric Transition	100.00%
135	2.3×10⁺⁶ years	Beta-minus Decay	100.00%
135_m	53 minutes	Isomeric Transition	100.00%
136	13.04 days	Beta-minus Decay	100.00%
136_m	17.5 seconds	Beta-minus Decay	No Data Available
		Isomeric Transition	> 0.00%
137	30.08 years	Beta-minus Decay	100.00%
138	33.41 minutes	Beta-minus Decay	100.00%
138_m	2.91 minutes	Isomeric Transition	81.00%
		Beta-minus Decay	19.00%
139	9.27 minutes	Beta-minus Decay	100.00%
140	63.7 seconds	Beta-minus Decay	100.00%
141	24.84 seconds	Beta-minus Decay	100.00%
		Beta-minus Decay with delayed Neutron Emission	0.04%
142	1.684 seconds	Beta-minus Decay	100.00%
		Beta-minus Decay with delayed Neutron Emission	0.09%
143	1.791 seconds	Beta-minus Decay	100.00%
		Beta-minus Decay with delayed Neutron Emission	1.64%
144	0.994 seconds	Beta-minus Decay	100.00%
		Beta-minus Decay with delayed Neutron Emission	3.03%
144_m	< 1 seconds	Beta-minus Decay	No Data Available
145	0.587 seconds	Beta-minus Decay	100.00%
		Beta-minus Decay with delayed Neutron Emission	14.70%
146	0.321 seconds	Beta-minus Decay	100.00%
		Beta-minus Decay with delayed Neutron Emission	14.20%
147	0.230 seconds	Beta-minus Decay	100.00%
		Beta-minus Decay with delayed Neutron Emission	28.50%
148	146 milliseconds	Beta-minus Decay	100.00%
		Beta-minus Decay with delayed Neutron Emission	25.10%
149	> 50 milliseconds	Beta-minus Decay	No Data Available
		Beta-minus Decay with delayed Neutron Emission	No Data Available
150	> 50 milliseconds	Beta-minus Decay	No Data Available
		Beta-minus Decay with delayed Neutron Emission	No Data Available
151	> 50 milliseconds	Beta-minus Decay	No Data Available
		Beta-minus Decay with delayed Neutron Emission	No Data Available

This page is maintained by Steve Gagnon.

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