Ac-228

Actinium-228

Natural

β, γ radiation

Half-life: 6.15 hours

Main emission lines: 338, 911, 1588 keV

Decay chain: Th-232

Related lines: 238, 583, 727, 2614 keV

Advanced data

Decay mode Beta-

Beta-

Avg. En., keV	Intensity, %	Decay En., keV
385.0	29.9	(1165)
609.7	11.65	(1738)
181.0	7.6	(603)
747.0	7	(2076)
327.0	5.90	(1011)
315.7	5.8	(981)
142.8	4.19	(488)
310.2	3.11	(966)
364.7	3.11	(1111)
143.7	3.0	(491)
129.0	2.43	(446)
117.5	1.76	(410)
215.3	1.2	(702)
145.3	1.15	(496)
130.8	1.12	(451)
288.8	0.67	(907)
208.9	0.60	(684)
694.3	0.6	(1947)
609.3	0.59	(1806)
111.3	0.389	(390)
367.0	0.33	(1118)

‍

Gamma

Energy., keV	Intensity, %
911.204	25.8
968.971	15.8
338.320	11.27
964.766	4.99
463.004	4.40
794.947	4.25
209.253	3.89
270.245	3.46
1588.20	3.22
328.000	2.95
129.065	2.42
674.75	2.1
409.462	1.92
835.710	1.61
1630.627	1.51
772.291	1.49
99.509	1.26
755.315	1.00
840.377	0.91
562.500	0.87
1495.910	0.86
1459.138	0.83
904.20	0.77
214.85	0.76
153.977	0.722
726.863	0.62
1580.53	0.60
830.486	0.540
1247.08	0.50
782.142	0.485
1638.281	0.47
57.766	0.47
1501.57	0.46
508.959	0.45
332.370	0.40
340.96	0.369
199.407	0.315
1110.610	0.285
958.61	0.28

‍

X-rays

Energy., keV	Intensity, %
11.118 - 20.450	33.4
93.347	3.2
89.954	2.01
104.817 - 108.971	1.54
104.817 - 106.315	1.16
108.479 - 108.680	0.39

This isotope is almost always present in a mixture with other isotopes characteristic of the decay chain of thorium-232.

Actinium-228 (Ac-228) is a naturally occurring radioactive isotope of actinium, part of the thorium-232 decay series. It has a half-life of approximately 6.15 hours and undergoes beta decay, producing thorium-228. As a beta emitter, Ac-228 releases high-energy particles during its decay, contributing to the natural radiation present in the environment. Due to its short half-life and high radioactivity, it requires specialized handling and containment.

Actinium-228 is naturally found in trace amounts in minerals containing thorium, such as monazite and thorite. It is typically encountered in environments rich in thorium, as it forms part of the thorium decay chain. Due to its high radioactivity, Ac-228 is usually found only in controlled research settings or as a byproduct in facilities handling thorium-containing materials.

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