Thorium-221

Properties and data of the isotope ²²¹Th.

Content

General data

Name of the isotope:Thorium-221; Th-221Symbol:²²¹Th or 22190ThMass number A:221 (= number of nucleons)Atomic number Z:90 (= number of protons)Neutrons N:131Isotopic mass:221.018186(9) u (atomic weight of Thorium-221)Nuclide mass:220.9688202 u (calculated nuclear mass without electrons)Mass excess:16.94015 MeVMass defect:1.821170876 u (per nucleus)Nuclear binding energy:1696.40974397 MeV (per nucleus)
7.67606219 MeV (average binding energy per nucleon)Separation energy:S_N = 5.821(16) MeV (first neutron)
S_P = 4.093(10) MeV (first proton)Half-life:1.74(3) msDecay constant λ:398.36044859767 s^-1Specific activity α:1.085512549539 × 10⁺²⁴ Bq g^-1
29338177014586 Ci g^-1Spin and parity:
(nuclear angular momentum)(7/2+)Year of discovery:1970

Radioactive Decay

Half-life T_½ = 1.74(3) ms respectively 1.74 × 10^-3 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²¹⁷Ra	100 %	8.625(4) MeV

Parent Nuclides

Direct parent isotope is: ²²⁵U.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 131) and isobaric (same nucleon number A = 221) with Thorium-221. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 131	Isobar A = 221
79	²¹⁰Au
80	²¹¹Hg
81	²¹²Tl
82	²¹³Pb
83	²¹⁴Bi	²²¹Bi
84	²¹⁵Po	²²¹Po
85	²¹⁶At	²²¹At
86	²¹⁷Rn	²²¹Rn
87	²¹⁸Fr	²²¹Fr
88	²¹⁹Ra	²²¹Ra
89	²²⁰Ac	²²¹Ac
90	²²¹Th	²²¹Th
91	²²²Pa	²²¹Pa
92	²²³U	²²¹U