Radon-222

Properties and data of the isotope ²²²Rn.

Contents

General Data

Radioactive Decay

Parent Nuclides

Radiation Protection

Isotones und Isobares

Radon-222 is a radioisotope of the chemical element radon, which has 136 neutrons in its atomic nucleus in addition to the element-specific 86 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 222.

See also: List of individual Radon isotopes (and general data sources).

General data

Name of the isotope:Radon-222; Rn-222Other names:Radon. Niton; Radium EmanationSymbol:²²²Rn or 22286RnMass number A:222 (= number of nucleons)Atomic number Z:86 (= number of protons)Neutrons N:136Nucleon pairing (Z - N):even - evenNuclear ratio (N/Z ratio):1.5813953488372 (= neutron-proton ratio)Neutron excess (N-Z):50Isotopic mass:222.0175760(21) u (atomic weight of Radon-222)Nuclide mass:221.9704038 u (calculated nuclear mass without electrons)Mass excess:16.37194 MeVMass defect:1.833805328 u (per nucleus)Nuclear binding energy:1708.1786602 MeV (per nucleus)
7.69449847 MeV (average binding energy per nucleon)Separation energy:S_N = 6.171(6) MeV (first neutron)
S_P = 7.700(14) MeV (first proton)Cross section:σ(n.γ) = 0.74(5) barn (thermal neutron capture cross-section)Half-life:3.8222(9) dDecay constant λ:2.098931717868 × 10^-6 s^-1Specific activity α:5.693721829005 × 10⁺¹⁵ Bq g^-1
153884.37375691 Ci g^-1Spin and parity:
(nuclear angular momentum)0+Charge radius:5.6915(203) femtometer fmYear of discovery:1899

Radioactive Decay

Half-life T_½ = 3.8222(9) d respectively 3.3023808 × 10⁵ seconds s.

Decay mode	Daughter	Probability	Decay energy	Details	γ energy (intensity)
α	²¹⁸Po	100 %	5.5904(3) MeV	α: 5.4895(3) MeV 99.92(1) %	0.510(2) MeV 0.076(1) %

Parent Nuclides

Direct parent isotope is: ²²⁶Ra.

Occurrence

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

	Atomic Mass m_a	Quantity	Half-life	Spin
Radon Isotopic mixture	222.017577269 u	100 %
Isotope ²²²Rn	222.0175760(21) u	100 %	3.8222(9) d	0+

Radiation Protection

The Radiation Protection Ordinance (European Union), for example, specifies the following limit values for the isotope Radon-222 (exemption limits, clearance values and other values as a radioactive or highly radioactive source of radiation (HASS)):

IARC group 1 (monography 43, 78, 100D, 2012).

Exemption level:10⁸ BqExemption level per gram:10 Bq/g
Unrestricted handling of solids and liquids.Half-life:3.8 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 = 222) with Radon-222. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 136	Isobar A = 222
80	²¹⁶Hg
81	²¹⁷Tl
82	²¹⁸Pb
83	²¹⁹Bi	²²²Bi
84	²²⁰Po	²²²Po
85	²²¹At	²²²At
86	²²²Rn	²²²Rn
87	²²³Fr	²²²Fr
88	²²⁴Ra	²²²Ra
89	²²⁵Ac	²²²Ac
90	²²⁶Th	²²²Th
91	²²⁷Pa	²²²Pa
92	²²⁸U	²²²U
93	²²⁹Np	²²²Np
94	²³⁰Pu
95	²³¹Am
96	²³²Cm
97	²³³Bk