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Actinium-225

Properties and data of the isotope 225Ac.

 

Actinium-225 is the radioisotope of the element actinium, whose atomic nucleus has 136 neutrons in addition to the element-specific 89 protons, resulting in a mass number of 225.

See also: list of Actinium isotopes.

 

General data

Name of the isotope:Actinium-225; Ac-225Symbol:225AcMass number A:225Atomic number Z:89 (= number of protons)Neutrons N:136Isotopic mass:225.023229(5) u (atomic weight of Actinium-225)Nuclide mass:224.9744116 u (calculated nuclear mass without electrons)Mass excess:21.63767 MeVMass defect:1.851627424 u (per nucleus)Nuclear binding energy:1724.77983569 MeV (per nucleus)
7.66568816 MeV (average binding energy per nucleon)
Separation energy:SN = 6.668(6) MeV (first neutron)
SP = 4.478(5) MeV (first proton)
Half-life:9.9203(3) dDecay constant λ:8.086990123319 × 10-7 s-1Spin and parity:(3/2-)Year of discovery:1947

 

Radioactive Decay

Half-life T½ = 9.9203(3) d respectively 8.5711392 × 105 seconds s.

Decay modeDaughterProbabilityDecay energyγ energy
(intensity)
α221Fr> 99 %5,9351(14) MeV
CZ14C<< 1 %

 

The figure shows the radioactive decay cascade of the Ac-225 nuclide. The isotope is an unstable intermediate in the so-called neptunium series, which starts from Np-237 (complete decay series: see there).

 

Actinium-225 radioactive decay

 

Parent Nuclides

Direct parent isotopes are: 229Pa, 225Th, 225Ra.

 

Radiation Protection

The German Radiation Protection Ordinance, for example, specifies the following limit values for the isotope Actinium-225 (exemption limits, clearance values and other values as a radioactive or highly radioactive source of radiation (HASS)):

Isotope:Ac-225+Exemption level:104 BqExemption level per gram:10 Bq/g
Unrestricted handling of solids and liquids.
Half-life:10.0 d

 

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 136) and isobaric (same nucleon number A = 225) with Actinium-225. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

 

OZIsotone N = 136Isobar A = 225
80216Hg
81217Tl
82218Pb
83219Bi
84220Po225Po
85221At225At
86222Rn225Rn
87223Fr225Fr
88224Ra225Ra
89225Ac225Ac
90226Th225Th
91227Pa225Pa
92228U225U
93229Np225Np
94230Pu
95231Am
96232Cm
97233Bk

 

External data and identifiers

Adopted Levels, Gammas:NuDat 225Ac

 


Category: Isotopes

Last update: 26.11.2022



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