Astatine-195

Properties and data of the isotope ¹⁹⁵At.

Contents

General data

Name of the isotope:Astatine-195; At-195Symbol:¹⁹⁵At or 19585AtMass number A:195 (= number of nucleons)Atomic number Z:85 (= number of protons)Neutrons N:110Isotopic mass:194.996274(10) u (atomic weight of Astatine-195)Nuclide mass:194.9496503 u (calculated nuclear mass without electrons)Mass excess:-3.47075 MeVMass defect:1.62199448 u (per nucleus)Nuclear binding energy:1510.87812615 MeV (per nucleus)
7.74809295 MeV (average binding energy per nucleon)Separation energy:S_N = 10.821(27) MeV (first neutron)
S_P = -245(16) MeV (first proton)Half-life:290(20) msDecay constant λ:2.390162691586 s^-1Specific activity α:7.41953423035 × 10⁺²¹ Bq g^-1
200527952171.86 Ci g^-1Spin and parity:
(nuclear angular momentum)(1/2+)Year of discovery:1999

Radioactive Decay

Half-life T_½ = 290(20) ms respectively 2.90 × 10^-1 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
α	¹⁹¹Bi	100 %	7.344(6) MeV

Parent Nuclides

Direct parent isotope is: ¹⁹⁹Fr.

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
^195mAt	33.0(10) keV	143(3) ms	(7/2-)

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 110) and isobaric (same nucleon number A = 195) with Astatine-195. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 110	Isobar A = 195
69	¹⁷⁹Tm
70	¹⁸⁰Yb
71	¹⁸¹Lu
72	¹⁸²Hf
73	¹⁸³Ta
74	¹⁸⁴W	¹⁹⁵W
75	¹⁸⁵Re	¹⁹⁵Re
76	¹⁸⁶Os	¹⁹⁵Os
77	¹⁸⁷Ir	¹⁹⁵Ir
78	¹⁸⁸Pt	¹⁹⁵Pt
79	¹⁸⁹Au	¹⁹⁵Au
80	¹⁹⁰Hg	¹⁹⁵Hg
81	¹⁹¹Tl	¹⁹⁵Tl
82	¹⁹²Pb	¹⁹⁵Pb
83	¹⁹³Bi	¹⁹⁵Bi
84	¹⁹⁴Po	¹⁹⁵Po
85	¹⁹⁵At	¹⁹⁵At
86	¹⁹⁶Rn	¹⁹⁵Rn