Thorium-232

Properties and data of the isotope ²³²Th.

Contents

General Data

Radioactive Decay

Parent Nuclides

Occurrence

Use

Isotones und Isobares

Literature

Thorium-232 is the radioisotope of the element Thorium, whose atomic nucleus has 142 neutrons in addition to the element-specific 90 protons, resulting in a mass number of 232.

General data

Name of the isotope:Thorium-232; Th-232Symbol:²³²Th or 23290ThMass number A:232 (= number of nucleons)Atomic number Z:90 (= number of protons)Neutrons N:142Isotopic mass:232.03806(2) u (atomic weight of Thorium-232)Nuclide mass:231.9886942 u (calculated nuclear mass without electrons)Mass excess:35.45266 MeVMass defect:1.896610952 u (per nucleus)Nuclear binding energy:1766.68172212 MeV (per nucleus)
7.61500742 MeV (average binding energy per nucleon)Separation energy:S_N = 6.4404(11) MeV (first neutron)
S_P = 7.605(13) MeV (first proton)Cross section:σ(n.γ) = 7.37(4) barn (thermal neutron capture cross-section)
σ(n.f) = 3 μb (gap cross-section)
σ(n.α) < 1 μbHalf-life:1.40(1) × 10¹⁰ aDecay constant λ:1.569968064977 × 10^-18 s^-1Specific activity α:4075.2451865942 Bq g^-1
1.101417617998 × 10^-7 Ci g^-1Spin and parity:
(nuclear angular momentum)0+Charge radius:5.7848(124) femtometer fmYear of discovery:1898

Radioactive Decay

Half-life T_½ = 1.40(1) × 10¹⁰ a respectively 4.41504 × 10¹⁷ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	²²⁸Ra	> 99 %	4.0816(14) MeV
SF	div	<< 1 %

Parent Nuclides

Direct parent isotopes are: ²³⁶U, ²³²Ac, ²³²Pa.

Occurrence

Thorium-232 is the only primordial isotope of thorium and effectively makes up all natural thorium; other thorium isotopes occur only in traces as relatively short-lived decay products of uranium and thorium. Some minerals that contain the thorium isotope in very small amounts are apatite, sphene, zircon, allanite, monazite, pyrochlore, thorite, and xenotime.

Comparison of the natural Thorium isotopes including isotopic abundance (mole fraction of the isotope mixture in percent):

	Atomic Mass m_a	Quantity	Half-life	Spin
Thorium Isotopic mixture	232.0377 u	100 %
Isotope ²³⁰Th	230.0331323(2) u	0.02(2) %	7.54(3) × 10⁴ a	0+
Isotope ²³²Th	232.03806(2) u	99.98(2) %	1.40(1) × 10¹⁰ a	0+

Use

Thorium-232, which is more abundant in nature than uranium, is used to artificially produce fissile Uranium-233. Th-232 is able to absorb neutrons and thus transmute them into U-233. The isotope is at the forefront of the uranium-thorium fuel cycle.

Concerns about the limits of the world's available uranium resources initially sparked interest in the thorium fuel cycle. It was envisaged that when uranium reserves were depleted, thorium could be used to produce it. However, uranium was relatively abundant in most countries ... and research into the thorium fuel cycle quickly waned. A notable exception was India's three-stage nuclear energy program. In the 21st century, thorium's potential to improve proliferation resistance and decay characteristics led to renewed interest in the thorium-based nuclear fuel cycle [1].

Th and U isotopes are technical products and parameters that need to be determined analytically in areas such as environmental monitoring or nuclear emergencies. A research group led by Youyi Ni et al. reports on a newer analytical method for the simultaneous determination of these radioactive nuclides in different types of real water samples with good practicability at the same time [2].

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 142) and isobaric (same nucleon number A = 232) with Thorium-232. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 142	Isobar A = 232
84	²²⁶Po
85	²²⁷At
86	²²⁸Rn
87	²²⁹Fr	²³²Fr
88	²³⁰Ra	²³²Ra
89	²³¹Ac	²³²Ac
90	²³²Th	²³²Th
91	²³³Pa	²³²Pa
92	²³⁴U	²³²U
93	²³⁵Np	²³²Np
94	²³⁶Pu	²³²Pu
95	²³⁷Am	²³²Am
96	²³⁸Cm	²³²Cm
97	²³⁹Bk
98	²⁴⁰Cf
99	²⁴¹Es
100	²⁴²Fm