Boron-21

Properties and data of the isotope ²¹B.

Contents

Boron-21 is a radioisotope of the chemical element boron, which has 16 neutrons in its atomic nucleus in addition to the element-specific 5 protons; the sum of the number of these atomic nucleus building blocks results in a mass number of 21. The very short-lived, only artificially produced, unstable and thus radioactive nuclide has no practical significance; the study of ²¹B is exclusively for academic purposes.

²¹Boron was first artificially produced and characterized in 2018 [1].

General data

Name of the isotope:Boron-21; B-21Symbol:²¹B or 215BMass number A:21 (= number of nucleons)Atomic number Z:5 (= number of protons)Neutrons N:16Isotopic mass:21.08415(60) u (atomic weight of Boron-21)Nuclide mass:21.0814071 u (calculated nuclear mass without electrons)Mass excess:78.38522 MeVMass defect:0.093613816000001 u (per nucleus)Nuclear binding energy:87.20070792 MeV (per nucleus)
4.15241466 MeV (average binding energy per nucleon)Half-life:< 260 nsDecay constant λ:2665950.6944613 s^-1Specific activity α:7.645109813186 × 10⁺²⁸ Bq g^-1
2.066245895455 × 10⁺¹⁸ Ci g^-1Spin and parity:
(nuclear angular momentum)(3/2-)Year of discovery:2018

Radioactive Decay

Half-life T_½ = < 260 ns respectively 2.6 × 10^-7 seconds s.

Decay mode	Daughter	Probability	Decay energy	γ energy (intensity)
2n	¹⁹B

Isotones and Isobars

The following table shows the atomic nuclei that are isotonic (same neutron number N = 16) and isobaric (same nucleon number A = 21) with Boron-21. Naturally occurring isotopes are marked in green; light green = naturally occurring radionuclides.

Z	Isotone N = 16	Isobar A = 21
5	²¹B	²¹B
6	²²C	²¹C
7	²³N	²¹N
8	²⁴O	²¹O
9	²⁵F	²¹F
10	²⁶Ne	²¹Ne
11	²⁷Na	²¹Na
12	²⁸Mg	²¹Mg
13	²⁹Al	²¹Al
14	³⁰Si
15	³¹P
16	³²S
17	³³Cl
18	³⁴Ar
19	³⁵K
20	³⁶Ca
21	³⁷Sc
22	³⁸Ti