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Beryllium is unique as being the only monoisotopic element with both an even number of protons and an odd number of neutrons. There are 25 other monoisotopic elements but all have odd atomic numbers, and even numbers of neutrons. Of the 10 radioisotopes of beryllium, the most stable are 10 Be with a half-life of 1.387(12) million years [nb 1 ...
Thus, for high-energy neutrons, beryllium is a neutron multiplier, releasing more neutrons than it absorbs. This nuclear reaction is: [16] 9 4 Be + n → 2 4 2 He + 2 n. Neutrons are liberated when beryllium nuclei are struck by energetic alpha particles [15] producing the nuclear reaction 9 4 Be + 4 2 He → 12 6 C + n. where 4 2 He is an ...
Beryllium-8 (8 Be, Be-8) is a radionuclide with 4 neutrons and 4 protons. It is an unbound resonance and nominally an isotope of beryllium . It decays into two alpha particles with a half-life on the order of 8.19 × 10 −17 seconds.
Beryllium's most common isotope is 9 Be, which contains 4 protons and 5 neutrons. It makes up almost 100% of all naturally occurring beryllium and is its only stable isotope; however other isotopes have been synthesised. In ionic compounds, beryllium loses its two valence electrons to form the cation, Be 2+.
Of the 26 "monoisotopic" elements that have only a single stable isotope, all but one have an odd atomic number—the single exception being beryllium. In addition, no odd-numbered element has more than two stable isotopes, while every even-numbered element with stable isotopes, except for helium, beryllium, and carbon, has at least three.
No odd-neutron-number isotope is the most naturally abundant isotope in its element, except for beryllium-9 (which is the only stable beryllium isotope), nitrogen-14, and platinum-195. No stable nuclides have a neutron number of 19, 21, 35, 39, 45, 61, 89, 115, 123, or ≥ 127.
The only stable nuclides having an odd number of protons and an odd number of neutrons are hydrogen-2, lithium-6, boron-10, nitrogen-14 and (observationally) tantalum-180m. This is because the mass–energy of such atoms is usually higher than that of their neighbors on the same isobaric chain, so most of them are unstable to beta decay .
Two examples of isotopes that emit neutrons are beryllium-13 (decaying to beryllium-12 with a mean life 2.7 × 10 −21 s) and helium-5 (helium-4, 7 × 10 −22 s). [1] In tables of nuclear decay modes, neutron emission is commonly denoted by the abbreviation n.