Strontium-99

Properties and data of the isotope ⁹⁹Sr.

Contents

General data

Name of the isotope:Strontium-99; Sr-99Symbol:⁹⁹Sr or 9938SrMass number A:99 (= number of nucleons)Atomic number Z:38 (= number of protons)Neutrons N:61Isotopic mass:98.932881(5) u (atomic weight of Strontium-99)Nuclide mass:98.9120358 u (calculated nuclear mass without electrons)Mass excess:-62.52095 MeVMass defect:0.893030092 u (per nucleus)Nuclear binding energy:831.85217252 MeV (per nucleus)
8.4025472 MeV (average binding energy per nucleon)Separation energy:S_N = 4.170(6) MeV (first neutron)
S_P = 15.441(17) MeV (first proton)Half-life:269(1) msDecay constant λ:2.5767553180667 s^-1Specific activity α:1.583426886427 × 10⁺²² Bq g^-1
427953212547.95 Ci g^-1Spin and parity:
(nuclear angular momentum)3/2+Magnetic dipole moment:μ(μ_N) = -0.261(5)Quadrupole moment Q:0.84(8) barn (100 fm²)Nuclear g-factor:g_l = -0.174Charge radius:4.4495(225) femtometer fmYear of discovery:1975

Radioactive Decay

Half-life T_½ = 269(1) ms respectively 2.69 × 10^-1 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β^-	⁹⁹Y	99.9 %	8.128(8) MeV
β^-, n	⁹⁸Y	0.1 %	1.702(9) MeV

Parent Nuclides

Direct parent isotope is: ⁹⁹Rb.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 61) and isobaric (same nucleon number A = 99) with Strontium-99. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 61	Isobar A = 99
34	⁹⁵Se
35	⁹⁶Br
36	⁹⁷Kr	⁹⁹Kr
37	⁹⁸Rb	⁹⁹Rb
38	⁹⁹Sr	⁹⁹Sr
39	¹⁰⁰Y	⁹⁹Y
40	¹⁰¹Zr	⁹⁹Zr
41	¹⁰²Nb	⁹⁹Nb
42	¹⁰³Mo	⁹⁹Mo
43	¹⁰⁴Tc	⁹⁹Tc
44	¹⁰⁵Ru	⁹⁹Ru
45	¹⁰⁶Rh	⁹⁹Rh
46	¹⁰⁷Pd	⁹⁹Pd
47	¹⁰⁸Ag	⁹⁹Ag
48	¹⁰⁹Cd	⁹⁹Cd
49	¹¹⁰In	⁹⁹In
50	¹¹¹Sn	⁹⁹Sn
51	¹¹²Sb
52	¹¹³Te
53	¹¹⁴I
54	¹¹⁵Xe
55	¹¹⁶Cs
56	¹¹⁷Ba
57	¹¹⁸La
58	¹¹⁹Ce