Gold-198

Properties and data of the isotope ¹⁹⁸Au.

Content

General Data

Radioactive Decay

Formation

Isotones und Isobares

Literature

Gold-198 is the radioisotope of the chemical element Gold, which, in addition to the element-specific 79 protons, has 119 neutrons in the atomic nucleus, resulting in the mass number 198.

In medicine, ¹⁹⁸Au can be used in the form of appropriate radiopharmaceuticals for radiation therapy, for example to treat some types of cancer. The half-life (2.7 days) and low tissue penetration depth (about 4 mm) allows the β-emitter to destroy the tumor tissue without affecting the surrounding healthy tissue. Injectable ¹⁹⁸Au nanoparticles are also being investigated for similar applications. The European Pharmacopoeia (Ph. Eur) lists Gold-198 under the Latin name Auri[¹⁹⁸Au] colloidales solutio iniectabilis (injectable colloidal Au-198 solution).

Other applications: Au-198 can be used as a tracer for the study of sediments and water flows. In the coker units of oil refineries, the isotope is used to investigate the hydrodynamic behavior of solids in fluidized beds and to quantify the degree of contamination of the internals.

General data

Name of the isotope:Gold-198; Au-198Symbol:¹⁹⁸Au or 19879AuMass number A:198 (= number of nucleons)Atomic number Z:79 (= number of protons)Neutrons N:119Isotopic mass:197.9682437(6) u (atomic weight of Gold-198)Nuclide mass:197.9249106 u (calculated nuclear mass without electrons)Mass excess:-29.5808 MeVMass defect:1.681058832 u (per nucleus)Nuclear binding energy:1565.89621566 MeV (per nucleus)
7.90856675 MeV (average binding energy per nucleon)Separation energy:S_N = 6.51236(9) MeV (first neutron)
S_P = 6.4500(5) MeV (first proton)Half-life:2.6941(2) dDecay constant λ:2.977817012002 × 10^-6 s^-1Specific activity α:9.102961168221 × 10⁺¹⁵ Bq g^-1
246025.97751949 Ci g^-1Spin and parity:
(nuclear angular momentum)2-Magnetic dipole moment:μ(μ_N) = + 0.5934(4)Quadrupole moment Q:+ 0.64(2) barn (100 fm²)Nuclear g-factor:g_l = 0.2967Charge radius:5.4400(38) femtometer fmYear of discovery:1937

Radioactive Decay

Gold-198 decays radioactively with a half-life of 2.6941(2) days and the emission of beta radiation [0.31478(19) MeV; I = 98.990(9)%] and gamma radiation [0.41180205(17) MeV; I = 95.62(6)] and a total energy release of 1.3735(5) MeV to the stable isotope Mercury-198.

Half-life T_½ = 2.6941(2) d respectively 2.3277024 × 10⁵ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β^-	¹⁹⁸Hg	100 %	1.3735(5) MeV	0.41180205(17) MeV I = 95.62(6) %

Formation

Gold-198 is produced in nuclear reactors. The starting material is conventional, highly purified gold, which - as monoisotopic element - consists only of Au-197 exists. The gold target is placed in the neutron flux of the nuclear reactor, often embedded in a Pt capsule. The irradiation of Au-197 with thermal neutrons finally leads to the formation of gold-198 according to the following reaction scheme:

¹⁹⁷Au + ¹n → ¹⁹⁸Au + γ.

Nuclear Isomers

Nuclear isomers or excited states with the activation energy in keV related to the ground state.

Nuclear Isomer	Excitation Energy	Half-life	Spin
^198m1Au	312.2227(20) keV	124(4) ns	5+
^198m2Au	811.7(15) keV	2.272(16) d	(12-)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 119) and isobaric (same nucleon number A = 198) with Gold-198. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

OZ	Isotone N = 119	Isobar A = 198
73	¹⁹²Ta
74	¹⁹³W
75	¹⁹⁴Re	¹⁹⁸Re
76	¹⁹⁵Os	¹⁹⁸Os
77	¹⁹⁶Ir	¹⁹⁸Ir
78	¹⁹⁷Pt	¹⁹⁸Pt
79	¹⁹⁸Au	¹⁹⁸Au
80	¹⁹⁹Hg	¹⁹⁸Hg
81	²⁰⁰Tl	¹⁹⁸Tl
82	²⁰¹Pb	¹⁹⁸Pb
83	²⁰²Bi	¹⁹⁸Bi
84	²⁰³Po	¹⁹⁸Po
85	²⁰⁴At	¹⁹⁸At
86	²⁰⁵Rn	¹⁹⁸Rn
87	²⁰⁶Fr
88	²⁰⁷Ra
89	²⁰⁸Ac
90	²⁰⁹Th