Isotopes of francium

Francium (₈₇Fr) has no stable isotopes, thus a standard atomic weight cannot be given. Its most stable isotope is ²²³Fr with a half-life of 22 minutes, occurring in trace quantities in nature as an intermediate decay product of ²³⁵U.

Isotopes of francium (₈₇Fr)

Main isotopes[1] Decay abun­dance half-life (t1/2) mode pro­duct 212Fr synth 20.0 min β+ 212Rn α 208At 221Fr trace 4.801 min α 217At β− 221Ra 222Fr synth 14.2 min β− 222Ra 223Fr trace 22.00 min β− 223Ra α 219At

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Of elements whose most stable isotopes have been identified with certainty, francium is the most unstable, though astatine is the rarest in nature due to its naturally-occurring isotopes having even shorter half-lives and even smaller branching ratios.

The elements with atomic number of 106 (seaborgium) or greater have their longest known half-life of any isotope shorter than that of francium, but as those elements have only isotopes on the proton-rich side of beta stability discovered, there is a strong possibility that undiscovered isotopes of these elements will have longer half-lives that could exceed that of francium-223.

List of isotopes

Nuclide [n 1]	Historic name	Z	N	Isotopic mass (Da)[2] [n 2][n 3]	Half-life[1] [n 4]	Decay mode[1] [n 5]	Daughter isotope	Spin and parity[1] [n 6][n 4]	Isotopic abundance
		Excitation energy[n 4]
197Fr		87	110	197.01101(6)	2.3(19) ms	α	193At	(7/2−)
198Fr		87	111	198.01028(3)	15(3) ms	α	194At	3+#
198mFr[n 7]		0(50) keV			1.1(7) ms	α	194At	(10−)
199Fr		87	112	199.007269(15)	6.6(22) ms	α	195At	1/2+#
199m1Fr		45(13) keV			6.5(9) ms	α	195At	7/2−#
199m2Fr		250(50)# keV			2.2(12) ms	α	195At	13/2+#
200Fr		87	113	200.00658(3)	47.5(28) ms	α	196At	(3+)
200m1Fr[n 7]		50(60) keV			190(120) ms	α	196At	10−#
200m2Fr		150(50)# keV			790(360) ns
201Fr		87	114	201.003852(10)	62.8(19) ms	α	197At	9/2−
201m1Fr		129(10) keV			24(6) ms	α	197At	1/2+
201m2Fr		289.5(4) keV			720(40) ns	IT	201Fr	13/2+
202Fr		87	115	202.003330(6)	372(12) ms	α	198At	3+
202mFr		257(6) keV			286(13) ms	α	198At	10−
						IT (?%)	202Fr
203Fr		87	116	203.000941(7)	550(10) ms	α	199At	9/2−
203m1Fr		361(6) keV			43(4) ms	IT (80%)	203Fr	1/2+
						α (20%)	199At
203m2Fr		426.0(10) keV			370(50) ns	IT	203Fr	13/2+
204Fr		87	117	204.000652(26)	1.75(26) s	α (96%)	200At	3+
						β+ (4%)	204Rn
204m1Fr		50(4) keV			2.41(19) s	α (90%)	200At	7+
						β+ (10%)	204Rn
204m2Fr		326(4) keV			1.65(15) s	α (53%)	200At	10−
						IT (47%)	204Fr
205Fr		87	118	204.998594(8)	3.90(7) s	α (98.5%)	201At	9/2−
						β+ (1.5%)	205Rn
205m1Fr		544.0(10) keV			80(20) ns	IT	205Fr	13/2+
205m2Fr		609(6) keV			1.15(4) ms	IT	203Fr	(1/2+)
206Fr		87	119	205.998661(30)	~16 s	α (88.4%)	202At	3+
						β+ (11.6%)	206Rn
206m1Fr		200(40) keV			~16 s	α (84.7%)	202At	7+
						β+ (?%)	206Rn
						IT (?%)	206Fr
206m2Fr		730(40) keV			700(100) ms	IT (87%)	206Fr	10−
						α (13%)	202At
207Fr		87	120	206.996941(19)	14.8(1) s	α (95%)	203At	9/2−
						β+ (5%)	207Rn
208Fr		87	121	207.997139(13)	59.1(3) s	α (89%)	204At	7+
						β+ (11%)	208Rn
208mFr		826.3(5) keV			432(11) ns	IT	208Fr	10−
209Fr		87	122	208.995940(12)	50.5(7) s	α (89%)	205At	9/2−
						β+ (11%)	209Rn
209mFr		4659.8(7) keV			420(18) ns	IT	209Fr	45/2−
210Fr		87	123	209.996411(14)	3.18(6) min	α (71%)	206At	6+
						β+ (29%)	210Rn
210mFr		4417.2(10) keV			475(6) ns	IT	210Fr	(23)+
211Fr		87	124	210.995555(13)	3.10(2) min	α (87%)	207At	9/2−
						β+ (13%)	211Rn
211m1Fr		2423.16(24) keV			146(14) ns	IT	211Fr	29/2+
211m2Fr		4657.3(4) keV			124.5(12) ns	IT	211Fr	45/2−
212Fr		87	125	211.996225(9)	20.0(6) min	β+ (57%)	212Rn	5+
						α (43%)	208At
212m1Fr		1551.4(3) keV			31.9(7) μs	IT	212Fr	11+
212m2Fr		2492.2(4) keV			604(28) ns	IT	212Fr	15−
212m3Fr		5854.7(6) keV			312(21) ns	IT	212Fr	27−
212m4Fr		8533.4(11) keV			23.6(21) μs	IT	212Fr	34+#
213Fr		87	126	212.996184(5)	34.14(6) s	α (99.44%)	209At	9/2−
						β+ (0.56%)	213Rn
213m1Fr		1590.41(18) keV			505(14) ns	IT	213Fr	21/2−
213m2Fr		2537.62(23) keV			238(6) ns	IT	213Fr	29/2+
213m3Fr		8094.8(7) keV			3.1(2) μs	IT	213Fr	(65/2−)
214Fr		87	127	213.998971(9)	5.51(13) ms	α	210At	(1−)
214m1Fr		121(5) keV			3.35(5) ms	α	210At	(8−)
214m2Fr		638(5) keV			103(4) ns	IT	214Fr	(11+)
214m3Fr		6577(100)# keV			108(7) ns	IT	214Fr	(33+)
215Fr		87	128	215.000342(8)	90(4) ns	α	211At	9/2−
216Fr		87	129	216.003190(4)	700(20) ns	α	212At	(1−)
216mFr		219(6) keV			850(30) ns	α	212m1At[3]	(9−)
217Fr		87	130	217.004632(7)	22(5) μs	α	213At	9/2−
218Fr		87	131	218.007579(5)	1.4(5) ms	α	214At	1−
218mFr		87(4) keV			21.9(5) ms	α	214At	(8−)
219Fr		87	132	219.009251(7)	22.5(17) ms	α	215At	9/2−
220Fr		87	133	220.012327(4)	27.4(3) s	α (99.65%)	216At	1+
						β− (0.35%)	220Ra
221Fr		87	134	221.014254(5)	4.801(5) min	α	217At	5/2−	Trace[n 8]
						β− (0.0048%)	221Ra
						CD (8.8×10−11%)[n 9]	207Tl 14C
222Fr		87	135	222.017583(8)	14.2(3) min	β−	222Ra	2−
223Fr	Actinium K	87	136	223.0197342(21)	22.00(7) min	β−	223Ra	3/2−	Trace[n 10]
						α (0.006%)	219At
224Fr		87	137	224.023348(12)	3.33(10) min	β−	224Ra	1−
225Fr		87	138	225.025572(13)	3.95(14) min	β−	225Ra	3/2−
226Fr		87	139	226.029545(7)	48.5(7) s	β−	226Ra	1−
227Fr		87	140	227.031865(6)	2.47(3) min	β−	227Ra	1/2+
228Fr		87	141	228.035839(7)	38(1) s	β−	228Ra	2−
228mFr		1004(30) keV			180(110) s
229Fr		87	142	229.038291(5)	50.2(4) s	β−	229Ra	(1/2+)
230Fr		87	143	230.042391(7)	19.1(5) s	β−	230Ra	2+#
231Fr		87	144	231.045175(8)	17.6(6) s	β−	231Ra	(1/2+)
232Fr		87	145	232.049461(15)	5.5(6) s	β−	232Ra	(5)
233Fr		87	146	233.052518(21)	900(100) ms	β−	233Ra	1/2+#
This table header & footer: view

1. ^mFr – Excited nuclear isomer.
2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
4. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
5. Modes of decay:

   α:	Alpha decay
   β+:	Positron emission
   β−:	Beta decay
   CD:	Cluster decay
   IT:	Isomeric transition

6. ( ) spin value – Indicates spin with weak assignment arguments.
7. Order of ground state and isomer is uncertain.
8. Intermediate decay product of ²³⁷Np
9. The nuclide with the lowest atomic number known to undergo cluster decay
10. Intermediate decay product of ²³⁵U