Alpha nuclide

An alpha nuclide is a nuclide that consists of an integer number of alpha particles. Alpha nuclides have equal, even numbers of protons and neutrons; they are important in stellar nucleosynthesis since the energetic environment within stars is amenable to fusion of alpha particles into heavier nuclei.^[1][2] Stable alpha nuclides, and stable decay products of radioactive alpha nuclides, are some of the most common metals in the universe.

Alpha nuclide is also shorthand for alpha radionuclide, referring to those radioactive isotopes that undergo alpha decay and thereby emit alpha particles.^[3]

List of alpha nuclides

The entries for ³⁶Ar and ⁴⁰Ca are theoretical: they would release energy on decay, but the process has never been observed, and the half-lives are probably extremely long. Likewise, the chains for masses 64, 84, 92, and 96 theoretically can continue one more step by double electron capture (to ⁶⁴Ni, ⁸⁴Kr, ⁹²Zr, and ⁹⁶Mo respectively), but this has never been observed.

Alpha number	nuclide	Stable/radioactive	decay mode	half-life[4]	product(s) of decay (bold is stable)	alpha decay energy[5]
1	4 2He	Stable
2	8 4Be	Radioactive	α	8.19(37)×10−17 s	4 2He	+0.09184MeV
3	12 6C	Stable				-7.36659MeV
4	16 8O	Stable				-7.16192MeV
5	20 10Ne	Stable				-4.72985MeV
6	24 12Mg	Stable				-9.31656MeV
7	28 14Si	Stable				-9.98414MeV
8	32 16S	Stable				-6.94766MeV
9	36 18Ar	Observationally Stable	(ECEC)	never seen	(36 16S)	-6.64092MeV
10	40 20Ca	Observationally Stable	(ECEC)	never seen	(40 18Ar)	-7.03978MeV
11	44 22Ti	Radioactive	EC	60.0(11) y	44 21Sc → 44 20Ca	-5.1271MeV
12	48 24Cr	Radioactive	β+	21.56(3) h	48 23V → 48 22Ti	-7.698MeV
13	52 26Fe	Radioactive	β+	8.275(8) h	52m 25Mn → 52 24Cr	-7.936MeV
14	56 28Ni	Radioactive	β+	6.075(10) d	56 27Co → 56 26Fe	-8.0005MeV
15	60 30Zn	Radioactive	β+	2.38(5) min	60 29Cu → 60 28Ni	-2.6917MeV
16	64 32Ge	Radioactive	β+	63.7(25) s	64 31Ga → 64 30Zn	-2.566MeV
17	68 34Se	Radioactive	β+	35.5(7) s	68 33As → ... → 68 30Zn	-2.299MeV
18	72 36Kr	Radioactive	β+	17.16(18) s	72 35Br → ... → 72 32Ge	-2.176MeV
19	76 38Sr	Radioactive	β+	7.89(7) s	76 37Rb → ... → 76 34Se	-2.73MeV
20	80 40Zr	Radioactive	β+	4.6(6) s	80 39Y → ... → 80 36Kr	-3.70MeV
21	84 42Mo	Radioactive	β+	3.8(9) ms	84 41Nb → ... → 84 38Sr	-2.71MeV
22	88 44Ru	Radioactive	β+	1.3(3) s	88 43Tc → ... → 88 38Sr	-2.27MeV
23	92 46Pd	Radioactive	β+	1.1(3) s	92 45Rh → ... → 92 42Mo	-2.28MeV
24	96 48Cd	Radioactive	β+	1.003(47) s	96 47Ag → ... → 96 44Ru	-3.03MeV
25	100 50Sn	Radioactive	β+	1.1(4) s	100 49In → ... → 100 44Ru	-3.47MeV
26	104 52Te	Radioactive	α	<18 ns	100 50Sn → ... → 100 44Ru	+5.10MeV
27	108 54Xe	Radioactive	α	58+106 −23 μs	104 52Te → 100 50Sn → ... → 100 44Ru	+4.57MeV

As of 2024^[update], the heaviest known alpha nuclide is xenon-108.^[6]