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.
Ac-225 decays by ɑ decay with a half-life of 9.918(3) days . Its 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) and Pb-209 (T1/2 = 3.2 h) leads to Bi-209. Including its short-lived decay chain, the cumulative ɑ emission is 400% per Ac-225 decay with an average ɑ energy of 6.88 MeV.
Ac-225 emits X-rays and γ-rays, notably 2.4% around 100 keV (+/-5%), its daughter Fr-221 emits γ-rays at 218.0 keV (11.44%) and its grand-grand-daughter Bi-213 γ-rays at 440.5 keV (25.94(15)%). These γ-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 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 production facility JRC Karlsruhe (JRC, Karlsruhe, International). Activity will be shipped from there to the users in dry form.
Examples of use
|Production route||Th-229→Ra-225→Ac-225 or Th-232(p,spallation)|
|Daughter||Decay chain involving radioactive Fr-221, At-217, Bi-213, Po-213, Pb-209 leading to quasi-stable Bi-209: cumulative 400% α, 200% β-|
|Processing||2-step purification process (cation exchange and extraction chromatography) or off-line mass separation|
|Primary Container||2.5 mL borosilicate glass V-vial with silicon rubber screw cap|
|Product Grade||GLP (JRC) or preclinical (MEDICIS), n.c.a.|
|Chemical Form||Dried nitric or chloridic form (JRC) or implanted into NaCl film (MEDICIS)|
|Radioactive Concentration (gamma spectrometry)||n.a.|
|Appearance||Dried solid (JRC) or thin NaCl layer on Au foil (MEDICIS CERN)|
|Radionuclide identification (gamma spectrometry)||100 keV (Ac-225), 218 keV (Fr-221) and 440 keV (Bi-213) gamma lines present|
|Radionuclidic Purity (gamma spectrometry)||JRC Karlsruhe: >99.98%; 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)
MEDICIS CERN: t.b.d.
|Chemical purity (ICP-OES)||n.a.|
|Molar activity (ICP-OES)||n.a.|
|Apparent Molar Activity||JRC Karlsruhe: e.g. up to 0.5 MBq/nmol (PSMA-617)|
|pH (pH strips)||n.a.|
|Activity available||JRC: max. 1000 MBq reserved for clinical studies every two months upon request, smaller amounts on request; MEDICIS CERN: 25 MBq few times per year|
|Activity limit for UN2910 (excepted package) shipment||6 MBq in dry state|