Ac 225
9.9 d
α 5,830, 5,797...
γ 100, (150...)

Chemical properties

Ac-225 is an actinide most often in trivalent state and chemically has analogies with the lanthanide series. The ionic radius of Ac3+ is 112 pm, suitable for many macrocyclic chelators used with other trivalent metallic ions, in particular DOTA.

Nuclear properties

Ac-225 decays with a half-life of 9.918(3) days by a decay chain involving Fr-221 (T1/2 = 4.8 min), At-217 (T1/2 = 32 ms), Bi-213 (T1/2 = 0.76 h), Po-213 (T1/2 = 3.7 µs), Pb-209 (T1/2 = 3.2 h) to Bi-209. Including its short-lived decay chain, the cumulative alpha emission is 400% per Ac-225 decay with an average alpha energy of 6.88 MeV.

Ac-225 emits X-rays and gamma rays, notably 2.4% around 100 keV (+/-5%), its daughter Fr-221 emits gamma rays at 218.0 keV (11.44%) and its grand-grand-daughter Bi-213 gamma rays at 440.5 keV (25.94(15)%). These gamma rays enable SPECT-imaging with high energy collimators .


Ac-225 is produced at JRC Karlsruhe by elution from Th-229 generators . Ac-225 is also produced by high energy proton induced spallation of thorium targets at MEDICIS at CERN. An off-line mass separation is performed at the PRISMAP production facility MEDICIS at CERN. The mass-separated ions are implanted into a solid matrix, e.g. a NaCl layer on a noble metal backing. Ra-225 is co-implanted at significant levels, while the co-produced Ac-227 is removed by the mass separation process. The implanted layer can be dissolved and used directly, but an additional radiochemical separation is used to obtain optimum radionuclidic purity.


Radiochemical separations are performed at the PRISMAP production facility JRC Karlsruhe (JRC, Karlsruhe, International). Activity will be shipped from there to the users in dry form.

Examples of use

  • Mass-separated Ac-225 produced at CERN has been used in preclinical studies since over 25 years .
  • Ac-225 labelled to antibodies or peptides has been used and is being used in several clinical trials and early clinical phases .

Purity grades available


No carrier added (n.c.a.)

Half-life9.92 d
DaughterDecay chain involving radioactive Fr-221, At-217, Bi-213, Po-213, Pb-209 leading to Bi-209
Branching Ratio/DecayCumulative 400% α, 200% β-
ProductionTh-229→Ra-225→Ac-225 or Th-232(p,spallation)
Purificationtwo step purification process (cation exchange and extraction chromatography) or off-line mass separation
Chemical Formnitric or chloridic form or implanted into NaCl film
Specific ActivityCarrier-free (2.16 TBq/mg theoretical specific activity)
Radionuclidic PurityJRC Karlsruhe: U-233/Th-229 < 90 ppm (limit of detection), Ra-225 < 20 ppm (limit of detection)
(Fr-221, At-217, Bi-213, Po-213, Pb-209 not considered)
Radiochemical PurityJRC Karlsruhe: e.g. up to 0.5 MBq/nM (PSMA-617); MEDICIS CERN: t.b.d.
Chemical PurityJRC Karlsruhe: >99.98%
Identification100 keV (Ac-225); 218 keV (Fr-221); 440 keV (Bi-213) gamma lines present
Appearancedried solid (JRC) or thin NaCl layer on Au foil (MEDICIS CERN)
Activity availableJRC: max. 1000 MBq reserved for clinical studies every two months upon request MEDICIS CERN: 25 MBq
AvailabilityJRC: every two months, smaller amounts for preclinical studies upon request
MEDICIS CERN: few times per year
GradeGLP (JRC) or preclinical (MEDICIS), n.c.a.


  • α-therapy

Point of supply

  • Karlsruhe, Germany

Involved production facilities

JRC, International
CERN, International