Rubidium-87

Properties and data of the isotope ⁸⁷Rb.

Contents

General Data

Radioactive Decay

Parent Nuclides

NMR Data

Isotones und Isobares

Literature

Rubidium-87 is a very long-lived radioisotope of the chemical element rubidium, which has 50 neutrons in its atomic nucleus in addition to the element-specific 37 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 87.

The radioactive nuclide ⁸⁷Rb was first reported in 1921. The discovery was made using a so-called Cavendish mass spectrograph [1].

General data

Name of the isotope:Rubidium-87; Rb-87Symbol:⁸⁷Rb or 8737RbMass number A:87 (= number of nucleons)Atomic number Z:37 (= number of protons)Neutrons N:50Isotopic mass:86.909180529(6) u (atomic weight of Rubidium-87)Nuclide mass:86.8888839 u (calculated nuclear mass without electrons)Mass excess:-84.59779 MeVMass defect:0.81359145499999 u (per nucleus)Nuclear binding energy:757.85555878 MeV (per nucleus)
8.71098343 MeV (average binding energy per nucleon)Separation energy:S_N = 9.92212(20) MeV (first neutron)
S_P = 8.621097(5) MeV (first proton)Half-life:4.97(3) × 10¹⁰ aDecay constant λ:4.422445253458 × 10^-19 s^-1Specific activity α:3096.8125885681 Bq g^-1
8.369763752886 × 10^-8 Ci g^-1Spin and parity:
(nuclear angular momentum)3/2-Magnetic dipole moment:μ(μ_N) = +2.751324(74)Charge radius:4.1989(21) femtometer fmYear of discovery:1921

Radioactive Decay

Rubidium-87 is a primordial radioisotope with a half-life of 49,700,000,000 years, which means that the terrestrial ⁸⁷Rb deposits were already present when the earth was formed. The radioactive nuclide decays into the ground state of the stable isotope strontium-87, emitting an electron (β^--particle) with an energy of 0.08167(36) MeV and an antineutrino (0.1671(8) MeV).

Half-life T_½ = 4.97(3) × 10¹⁰ a respectively 1.5673392 × 10¹⁸ seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
β^-	⁸⁷Sr	100 %	0.282275(6) MeV

Formation and radioactive decay of rubidium-87

Parent Nuclides

Direct parent isotopes are: ⁸⁷Kr, ^87mSr.

Occurrence

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

	Atomic Mass m_a	Quantity	Half-life	Spin
Rubidium Isotopic mixture	85.4678 u	100 %
Isotope ⁸⁵Rb	84.91178974(3) u	72.17(2) %	stable	5/2-
Isotope ⁸⁷Rb	86.909180529(6) u	27.83(2) %	4.97(3) × 10¹⁰ a	3/2-

NMR data

Nuclear magnetic properties of the NMR active Nuclide ⁸⁷Rb

Isotope:⁸⁷Rb-NMRQuantity:27.83(2) %Spin:3/2-Nuclearmagnetic moment
μ/μ_N:+2.751324(74)Gyromagnetic ratio γ:8.7851 · 10⁷ rad T^-1 s^-1Nuclear g-factor:g_l = 1.834216Quadrupole moment Q:+ 0.1335(5) barn (100 fm²)Resonance frequency:v₀ = 13.9814 at 1 TFrequency ratio:Ξ(⁸⁷Rb) = 32.720454 %Relative Sensitivity:0.17704 (H₀ = const.)
1.6419 (v₀ = const.)
[related to ¹H = 1.000]Reference compound:
(conditions)Solution of 0.01M rubidium chloride (RbCl) in deuterium oxide (D₂O).

The two naturally occurring rubidium isotopes are quadrupolar and therefore NMR active. In contrast to rubidium-85, the ⁸⁷Rb nucleus produces less broad signals in the NMR spectrum and is more sensitive.

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 50) and isobaric (same nucleon number A = 87) with Rubidium-87. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 50	Isobar A = 87
28	⁷⁸Ni
29	⁷⁹Cu
30	⁸⁰Zn
31	⁸¹Ga	⁸⁷Ga
32	⁸²Ge	⁸⁷Ge
33	⁸³As	⁸⁷As
34	⁸⁴Se	⁸⁷Se
35	⁸⁵Br	⁸⁷Br
36	⁸⁶Kr	⁸⁷Kr
37	⁸⁷Rb	⁸⁷Rb
38	⁸⁸Sr	⁸⁷Sr
39	⁸⁹Y	⁸⁷Y
40	⁹⁰Zr	⁸⁷Zr
41	⁹¹Nb	⁸⁷Nb
42	⁹²Mo	⁸⁷Mo
43	⁹³Tc	⁸⁷Tc
44	⁹⁴Ru	⁸⁷Ru
45	⁹⁵Rh
46	⁹⁶Pd
47	⁹⁷Ag
48	⁹⁸Cd
49	⁹⁹In
50	¹⁰⁰Sn