Thorium-225

Properties and data of the isotope ²²⁵Th.

Content

General data

Name of the isotope:Thorium-225; Th-225Symbol:²²⁵Th or 22590ThMass number A:225 (= number of nucleons)Atomic number Z:90 (= number of protons)Neutrons N:135Isotopic mass:225.023951(5) u (atomic weight of Thorium-225)Nuclide mass:224.9745852 u (calculated nuclear mass without electrons)Mass excess:22.31021 MeVMass defect:1.85006554 u (per nucleus)Nuclear binding energy:1723.32495012 MeV (per nucleus)
7.659222 MeV (average binding energy per nucleon)Separation energy:S_N = 5.755(11) MeV (first neutron)
S_P = 5.213(6) MeV (first proton)Half-life:8.75(4) minDecay constant λ:0.0013202803439237 s^-1Specific activity α:3.533739646984 × 10⁺¹⁸ Bq g^-1
95506476.945516 Ci g^-1Spin and parity:
(nuclear angular momentum)(3/2+)Year of discovery:1949

Radioactive Decay

Half-life T_½ = 8.75(4) min (minutes) respectively 5.25 × 10² seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²²¹Ra	ca. 90 %	6.9214(21) MeV
EE	²²⁵Ac	ca. 10 %	0.637(7) MeV

Parent Nuclides

Direct parent isotope is: ²²⁹U.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 135) and isobaric (same nucleon number A = 225) with Thorium-225. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 135	Isobar A = 225
80	²¹⁵Hg
81	²¹⁶Tl
82	²¹⁷Pb
83	²¹⁸Bi
84	²¹⁹Po	²²⁵Po
85	²²⁰At	²²⁵At
86	²²¹Rn	²²⁵Rn
87	²²²Fr	²²⁵Fr
88	²²³Ra	²²⁵Ra
89	²²⁴Ac	²²⁵Ac
90	²²⁵Th	²²⁵Th
91	²²⁶Pa	²²⁵Pa
92	²²⁷U	²²⁵U
93	²²⁸Np	²²⁵Np
94	²²⁹Pu
95	²³⁰Am