Atomic and nuclear constants

Masses, magnetic moments, radii and ratios for the electron, muon, tau, proton, neutron and light nuclei, plus α, R∞ and the Bohr radius.

Atomic & nuclear

a_{0}

Bohr radius 5.291 772 105 44(82) × 10⁻¹¹ m Atomic & nuclear

m_{e}

Electron mass 9.109 383 7139(28) × 10⁻³¹ kg Atomic & nuclear

α

Fine-structure constant 7.297 352 5643(11) × 10⁻³ Atomic & nuclear

E_{h}

Hartree energy 4.359 744 722 2060(48) × 10⁻¹⁸ J Atomic & nuclear

m_{n}

Neutron mass 1.674 927 500 56(85) × 10⁻²⁷ kg Atomic & nuclear

m_{p}

Proton mass 1.672 621 925 95(52) × 10⁻²⁷ kg Atomic & nuclear

R_∞

Rydberg constant 10 973 731.568 157(12) m⁻¹

General

Symbol	Quantity	Value (uncertainty)	Unit	Rel. unc.
$a_{0}$	Bohr radius	5.291 772 105 44(82) × 10⁻¹¹	m	1.5 × 10⁻¹⁰
$r_{e}$	Classical electron radius	2.817 940 3205(13) × 10⁻¹⁵	m	4.6 × 10⁻¹⁰
$λ_C$	Compton wavelength	2.426 310 235 38(76) × 10⁻¹²	m	3.1 × 10⁻¹⁰
$α$	Fine-structure constant	7.297 352 5643(11) × 10⁻³		1.5 × 10⁻¹⁰
$E_{h}$	Hartree energy	4.359 744 722 2060(48) × 10⁻¹⁸	J	1.1 × 10⁻¹²
$E_{h}$	Hartree energy in eV	27.211 386 245 981(30)	eV	1.1 × 10⁻¹²
$α^ − 1$	Inverse fine-structure constant	137.035 999 177(21)		1.5 × 10⁻¹⁰
$πℏ/mₑ$	Quantum of circulation	3.636 947 5467(11) × 10⁻⁴	m² s⁻¹	3.0 × 10⁻¹⁰
$h/mₑ$	Quantum of circulation times 2	7.273 895 0934(23) × 10⁻⁴	m² s⁻¹	3.2 × 10⁻¹⁰
$λ̄_C$	Reduced Compton wavelength	3.861 592 6744(12) × 10⁻¹³	m	3.1 × 10⁻¹⁰
$R_∞$	Rydberg constant	10 973 731.568 157(12)	m⁻¹	1.1 × 10⁻¹²
$R_∞c$	Rydberg constant times c in Hz	3.289 841 960 2500(36) × 10¹⁵	Hz	1.1 × 10⁻¹²
$R_∞hc$	Rydberg constant times hc in eV	13.605 693 122 990(15)	eV	1.1 × 10⁻¹²
$R_∞hc$	Rydberg constant times hc in J	2.179 872 361 1030(24) × 10⁻¹⁸	J	1.1 × 10⁻¹²
$σ_dp$	Shielding difference of d and p in HD	1.987 70(10) × 10⁻⁸		5.0 × 10⁻⁵
$σ_{tp}$	Shielding difference of t and p in HT	2.394 50(20) × 10⁻⁸		8.4 × 10⁻⁵
$σ_{e}$	Thomson cross section	6.652 458 7051(62) × 10⁻²⁹	m²	9.3 × 10⁻¹⁰

Electroweak

Symbol	Quantity	Value (uncertainty)	Unit	Rel. unc.
$G_F/(ℏc)³$	Fermi coupling constant	1.166 3787(6) × 10⁻⁵	GeV⁻²	5.1 × 10⁻⁷
$sin²θ_W$	Weak mixing angle	0.223 05(23)		1.0 × 10⁻³
$m_W/m_Z$	W to Z mass ratio	0.881 45(13)		1.5 × 10⁻⁴

Electron

Symbol	Quantity	Value (uncertainty)	Unit	Rel. unc.
$− e/mₑ$	Electron charge to mass quotient	−1.758 820 008 38(55) × 10¹¹	C kg⁻¹	3.1 × 10⁻¹⁰
$μₑ/μ_d$	Electron-deuteron magnetic moment ratio	−2143.923 4921(56)		2.6 × 10⁻⁹
$mₑ/m_d$	Electron-deuteron mass ratio	2.724 437 107 629(47) × 10⁻⁴		1.7 × 10⁻¹¹
$g_{e}$	Electron g factor	−2.002 319 304 360 92(36)		1.8 × 10⁻¹³
$γ_{e}$	Electron gyromagnetic ratio	1.760 859 627 84(55) × 10¹¹	s⁻¹ T⁻¹	3.1 × 10⁻¹⁰
$γₑ/2π$	Electron gyromagnetic ratio in MHz/T	28 024.951 3861(87)	MHz T⁻¹	3.1 × 10⁻¹⁰
$mₑ/mₕ$	Electron-helion mass ratio	1.819 543 074 649(53) × 10⁻⁴		2.9 × 10⁻¹¹
$μ_{e}$	Electron magnetic moment	−9.284 764 6917(29) × 10⁻²⁴	J T⁻¹	3.1 × 10⁻¹⁰
$a_{e}$	Electron magnetic moment anomaly	1.159 652 180 46(18) × 10⁻³		1.6 × 10⁻¹⁰
$μₑ/μ_B$	Electron magnetic moment to Bohr magneton ratio	−1.001 159 652 180 46(18)		1.8 × 10⁻¹³
$μₑ/μ_N$	Electron magnetic moment to nuclear magneton ratio	−1838.281 971 877(32)		1.7 × 10⁻¹¹
$m_{e}$	Electron mass	9.109 383 7139(28) × 10⁻³¹	kg	3.1 × 10⁻¹⁰
$m_{e} c^{2}$	Electron mass energy equivalent	8.187 105 7880(26) × 10⁻¹⁴	J	3.2 × 10⁻¹⁰
$m_{e} c^{2}$	Electron mass energy equivalent in MeV	0.510 998 950 69(16)	MeV	3.1 × 10⁻¹⁰
$m_{e}$	Electron mass in u	5.485 799 090 441(97) × 10⁻⁴	u	1.8 × 10⁻¹¹
$M(e)$	Electron molar mass	5.485 799 0962(17) × 10⁻⁷	kg mol⁻¹	3.1 × 10⁻¹⁰
$μₑ/μ_μ$	Electron-muon magnetic moment ratio	206.766 9881(46)		2.2 × 10⁻⁸
$mₑ/m_μ$	Electron-muon mass ratio	4.836 331 70(11) × 10⁻³		2.3 × 10⁻⁸
$μₑ/μₙ$	Electron-neutron magnetic moment ratio	960.920 48(23)		2.4 × 10⁻⁷
$mₑ/mₙ$	Electron-neutron mass ratio	5.438 673 4416(22) × 10⁻⁴		4.0 × 10⁻¹⁰
$μₑ/μₚ$	Electron-proton magnetic moment ratio	−658.210 687 89(19)		2.9 × 10⁻¹⁰
$mₑ/mₚ$	Electron-proton mass ratio	5.446 170 214 889(94) × 10⁻⁴		1.7 × 10⁻¹¹
$Aᵣ(e)$	Electron relative atomic mass	5.485 799 090 441(97) × 10⁻⁴		1.8 × 10⁻¹¹
$mₑ/m_τ$	Electron-tau mass ratio	2.875 85(19) × 10⁻⁴		6.6 × 10⁻⁵
$mₑ/m_α$	Electron to alpha particle mass ratio	1.370 933 554 733(32) × 10⁻⁴		2.3 × 10⁻¹¹
$μₑ/μₕ′$	Electron to shielded helion magnetic moment ratio	864.058 239 86(70)		8.1 × 10⁻¹⁰
$μₑ/μₚ′$	Electron to shielded proton magnetic moment ratio	−658.227 5856(27)		4.1 × 10⁻⁹
$mₑ/mₜ$	Electron-triton mass ratio	1.819 200 062 327(68) × 10⁻⁴		3.7 × 10⁻¹¹

Muon

Symbol	Quantity	Value (uncertainty)	Unit	Rel. unc.
$λ_C,μ$	Muon Compton wavelength	1.173 444 110(26) × 10⁻¹⁴	m	2.2 × 10⁻⁸
$m_μ/mₑ$	Muon-electron mass ratio	206.768 2827(46)		2.2 × 10⁻⁸
$g_μ$	Muon g factor	−2.002 331 841 23(82)		4.1 × 10⁻¹⁰
$μ_μ$	Muon magnetic moment	−4.490 448 30(10) × 10⁻²⁶	J T⁻¹	2.2 × 10⁻⁸
$a_μ$	Muon magnetic moment anomaly	1.165 920 62(41) × 10⁻³		3.5 × 10⁻⁷
$μ_μ/μ_B$	Muon magnetic moment to Bohr magneton ratio	−4.841 970 48(11) × 10⁻³		2.3 × 10⁻⁸
$μ_μ/μ_N$	Muon magnetic moment to nuclear magneton ratio	−8.890 597 04(20)		2.2 × 10⁻⁸
$m_μ$	Muon mass	1.883 531 627(42) × 10⁻²⁸	kg	2.2 × 10⁻⁸
$m_μc²$	Muon mass energy equivalent	1.692 833 804(38) × 10⁻¹¹	J	2.2 × 10⁻⁸
$m_μc²$	Muon mass energy equivalent in MeV	105.658 3755(23)	MeV	2.2 × 10⁻⁸
$m_μ$	Muon mass in u	0.113 428 9257(25)	u	2.2 × 10⁻⁸
$M(μ)$	Muon molar mass	1.134 289 258(25) × 10⁻⁴	kg mol⁻¹	2.2 × 10⁻⁸
$m_μ/mₙ$	Muon-neutron mass ratio	0.112 454 5168(25)		2.2 × 10⁻⁸
$μ_μ/μₚ$	Muon-proton magnetic moment ratio	−3.183 345 146(71)		2.2 × 10⁻⁸
$m_μ/mₚ$	Muon-proton mass ratio	0.112 609 5262(25)		2.2 × 10⁻⁸
$m_μ/m_τ$	Muon-tau mass ratio	5.946 35(40) × 10⁻²		6.7 × 10⁻⁵
$λ̄_C,μ$	Reduced muon Compton wavelength	1.867 594 306(42) × 10⁻¹⁵	m	2.2 × 10⁻⁸

Tau

Symbol	Quantity	Value (uncertainty)	Unit	Rel. unc.
$λ̄_C,τ$	Reduced tau Compton wavelength	1.110 538(75) × 10⁻¹⁶	m	6.8 × 10⁻⁵
$λ_C,τ$	Tau Compton wavelength	6.977 71(47) × 10⁻¹⁶	m	6.7 × 10⁻⁵
$m_τ/mₑ$	Tau-electron mass ratio	3477.23(23)		6.6 × 10⁻⁵
$m_τc²$	Tau energy equivalent	1776.86(12)	MeV	6.8 × 10⁻⁵
$m_τ$	Tau mass	3.167 54(21) × 10⁻²⁷	kg	6.6 × 10⁻⁵
$m_τc²$	Tau mass energy equivalent	2.846 84(19) × 10⁻¹⁰	J	6.7 × 10⁻⁵
$m_τ$	Tau mass in u	1.907 54(13)	u	6.8 × 10⁻⁵
$M(τ)$	Tau molar mass	1.907 54(13) × 10⁻³	kg mol⁻¹	6.8 × 10⁻⁵
$m_τ/m_μ$	Tau-muon mass ratio	16.8170(11)		6.5 × 10⁻⁵
$m_τ/mₙ$	Tau-neutron mass ratio	1.891 15(13)		6.9 × 10⁻⁵
$m_τ/mₚ$	Tau-proton mass ratio	1.893 76(13)		6.9 × 10⁻⁵

Proton

Symbol	Quantity	Value (uncertainty)	Unit	Rel. unc.
$e/mₚ$	Proton charge to mass quotient	9.578 833 1430(30) × 10⁷	C kg⁻¹	3.1 × 10⁻¹⁰
$λ_C,p$	Proton Compton wavelength	1.321 409 853 60(41) × 10⁻¹⁵	m	3.1 × 10⁻¹⁰
$mₚ/mₑ$	Proton-electron mass ratio	1836.152 673 426(32)		1.7 × 10⁻¹¹
$g_{p}$	Proton g factor	5.585 694 6893(16)		2.9 × 10⁻¹⁰
$γ_{p}$	Proton gyromagnetic ratio	2.675 221 8708(11) × 10⁸	s⁻¹ T⁻¹	4.1 × 10⁻¹⁰
$γₚ/2π$	Proton gyromagnetic ratio in MHz/T	42.577 478 461(18)	MHz T⁻¹	4.2 × 10⁻¹⁰
$μ_{p}$	Proton magnetic moment	1.410 606 795 45(60) × 10⁻²⁶	J T⁻¹	4.3 × 10⁻¹⁰
$μₚ/μ_B$	Proton magnetic moment to Bohr magneton ratio	1.521 032 202 30(45) × 10⁻³		3.0 × 10⁻¹⁰
$μₚ/μ_N$	Proton magnetic moment to nuclear magneton ratio	2.792 847 344 63(82)		2.9 × 10⁻¹⁰
$σ_{p}^{'}$	Proton magnetic shielding correction	2.567 15(41) × 10⁻⁵		1.6 × 10⁻⁴
$m_{p}$	Proton mass	1.672 621 925 95(52) × 10⁻²⁷	kg	3.1 × 10⁻¹⁰
$m_{p} c^{2}$	Proton mass energy equivalent	1.503 277 618 02(47) × 10⁻¹⁰	J	3.1 × 10⁻¹⁰
$m_{p} c^{2}$	Proton mass energy equivalent in MeV	938.272 089 43(29)	MeV	3.1 × 10⁻¹⁰
$m_{p}$	Proton mass in u	1.007 276 466 5789(83)	u	8.2 × 10⁻¹²
$M(p)$	Proton molar mass	1.007 276 467 64(31) × 10⁻³	kg mol⁻¹	3.1 × 10⁻¹⁰
$mₚ/m_μ$	Proton-muon mass ratio	8.880 243 38(20)		2.3 × 10⁻⁸
$μₚ/μₙ$	Proton-neutron magnetic moment ratio	−1.459 898 02(34)		2.3 × 10⁻⁷
$mₚ/mₙ$	Proton-neutron mass ratio	0.998 623 477 97(40)		4.0 × 10⁻¹⁰
$Aᵣ(p)$	Proton relative atomic mass	1.007 276 466 5789(83)		8.2 × 10⁻¹²
$r_{p}$	Proton rms charge radius	8.4075(64) × 10⁻¹⁶	m	7.6 × 10⁻⁴
$mₚ/m_τ$	Proton-tau mass ratio	0.528 051(36)		6.8 × 10⁻⁵
$λ̄_C,p$	Reduced proton Compton wavelength	2.103 089 100 51(66) × 10⁻¹⁶	m	3.1 × 10⁻¹⁰
$γ_{p^{'}}$	Shielded proton gyromagnetic ratio	2.675 153 194(11) × 10⁸	s⁻¹ T⁻¹	4.1 × 10⁻⁹
$γₚ′/2π$	Shielded proton gyromagnetic ratio in MHz/T	42.576 385 43(17)	MHz T⁻¹	4.0 × 10⁻⁹
$μ_{p^{'}}$	Shielded proton magnetic moment	1.410 570 5830(58) × 10⁻²⁶	J T⁻¹	4.1 × 10⁻⁹
$μₚ′/μ_B$	Shielded proton magnetic moment to Bohr magneton ratio	1.520 993 1551(62) × 10⁻³		4.1 × 10⁻⁹
$μₚ′/μ_N$	Shielded proton magnetic moment to nuclear magneton ratio	2.792 775 648(11)		3.9 × 10⁻⁹

Neutron

Symbol	Quantity	Value (uncertainty)	Unit	Rel. unc.
$λ_C,n$	Neutron Compton wavelength	1.319 590 903 82(67) × 10⁻¹⁵	m	5.1 × 10⁻¹⁰
$μₙ/μₑ$	Neutron-electron magnetic moment ratio	1.040 668 84(24) × 10⁻³		2.3 × 10⁻⁷
$mₙ/mₑ$	Neutron-electron mass ratio	1838.683 662 00(74)		4.0 × 10⁻¹⁰
$g_{n}$	Neutron g factor	−3.826 085 52(90)		2.4 × 10⁻⁷
$γ_{n}$	Neutron gyromagnetic ratio	1.832 471 74(43) × 10⁸	s⁻¹ T⁻¹	2.3 × 10⁻⁷
$γₙ/2π$	Neutron gyromagnetic ratio in MHz/T	29.164 6935(69)	MHz T⁻¹	2.4 × 10⁻⁷
$μ_{n}$	Neutron magnetic moment	−9.662 3653(23) × 10⁻²⁷	J T⁻¹	2.4 × 10⁻⁷
$μₙ/μ_B$	Neutron magnetic moment to Bohr magneton ratio	−1.041 875 65(25) × 10⁻³		2.4 × 10⁻⁷
$μₙ/μ_N$	Neutron magnetic moment to nuclear magneton ratio	−1.913 042 76(45)		2.4 × 10⁻⁷
$m_{n}$	Neutron mass	1.674 927 500 56(85) × 10⁻²⁷	kg	5.1 × 10⁻¹⁰
$m_{n} c^{2}$	Neutron mass energy equivalent	1.505 349 765 14(76) × 10⁻¹⁰	J	5.0 × 10⁻¹⁰
$m_{n} c^{2}$	Neutron mass energy equivalent in MeV	939.565 421 94(48)	MeV	5.1 × 10⁻¹⁰
$m_{n}$	Neutron mass in u	1.008 664 916 06(40)	u	4.0 × 10⁻¹⁰
$M(n)$	Neutron molar mass	1.008 664 917 12(51) × 10⁻³	kg mol⁻¹	5.1 × 10⁻¹⁰
$mₙ/m_μ$	Neutron-muon mass ratio	8.892 484 08(20)		2.2 × 10⁻⁸
$μₙ/μₚ$	Neutron-proton magnetic moment ratio	−0.684 979 35(16)		2.3 × 10⁻⁷
$mₙ − mₚ$	Neutron-proton mass difference	2.305 574 61(67) × 10⁻³⁰	kg	2.9 × 10⁻⁷
$(mₙ − mₚ)c²$	Neutron-proton mass difference energy equivalent	2.072 147 12(60) × 10⁻¹³	J	2.9 × 10⁻⁷
$(mₙ − mₚ)c²$	Neutron-proton mass difference energy equivalent in MeV	1.293 332 51(38)	MeV	2.9 × 10⁻⁷
$mₙ − mₚ$	Neutron-proton mass difference in u	1.388 449 48(40) × 10⁻³	u	2.9 × 10⁻⁷
$mₙ/mₚ$	Neutron-proton mass ratio	1.001 378 419 46(40)		4.0 × 10⁻¹⁰
$Aᵣ(n)$	Neutron relative atomic mass	1.008 664 916 06(40)		4.0 × 10⁻¹⁰
$mₙ/m_τ$	Neutron-tau mass ratio	0.528 779(36)		6.8 × 10⁻⁵
$μₙ/μₚ′$	Neutron to shielded proton magnetic moment ratio	−0.684 996 94(16)		2.3 × 10⁻⁷
$λ̄_C,n$	Reduced neutron Compton wavelength	2.100 194 1520(11) × 10⁻¹⁶	m	5.2 × 10⁻¹⁰

Deuteron

Symbol	Quantity	Value (uncertainty)	Unit	Rel. unc.
$μ_d/μₑ$	Deuteron-electron magnetic moment ratio	−4.664 345 550(12) × 10⁻⁴		2.6 × 10⁻⁹
$m_d/mₑ$	Deuteron-electron mass ratio	3670.482 967 655(63)		1.7 × 10⁻¹¹
$g_d$	Deuteron g factor	0.857 438 2335(22)		2.6 × 10⁻⁹
$μ_d$	Deuteron magnetic moment	4.330 735 087(11) × 10⁻²⁷	J T⁻¹	2.5 × 10⁻⁹
$μ_d/μ_B$	Deuteron magnetic moment to Bohr magneton ratio	4.669 754 568(12) × 10⁻⁴		2.6 × 10⁻⁹
$μ_d/μ_N$	Deuteron magnetic moment to nuclear magneton ratio	0.857 438 2335(22)		2.6 × 10⁻⁹
$m_d$	Deuteron mass	3.343 583 7768(10) × 10⁻²⁷	kg	3.0 × 10⁻¹⁰
$m_dc²$	Deuteron mass energy equivalent	3.005 063 234 91(94) × 10⁻¹⁰	J	3.1 × 10⁻¹⁰
$m_dc²$	Deuteron mass energy equivalent in MeV	1875.612 945 00(58)	MeV	3.1 × 10⁻¹⁰
$m_d$	Deuteron mass in u	2.013 553 212 544(15)	u	7.4 × 10⁻¹²
$M(d)$	Deuteron molar mass	2.013 553 214 66(63) × 10⁻³	kg mol⁻¹	3.1 × 10⁻¹⁰
$μ_d/μₙ$	Deuteron-neutron magnetic moment ratio	−0.448 206 52(11)		2.5 × 10⁻⁷
$μ_d/μₚ$	Deuteron-proton magnetic moment ratio	0.307 012 209 30(79)		2.6 × 10⁻⁹
$m_d/mₚ$	Deuteron-proton mass ratio	1.999 007 501 2699(84)		4.2 × 10⁻¹²
$Aᵣ(d)$	Deuteron relative atomic mass	2.013 553 212 544(15)		7.4 × 10⁻¹²
$r_d$	Deuteron rms charge radius	2.127 78(27) × 10⁻¹⁵	m	1.3 × 10⁻⁴

Triton

Symbol	Quantity	Value (uncertainty)	Unit	Rel. unc.
$mₜ/mₑ$	Triton-electron mass ratio	5496.921 535 51(21)		3.8 × 10⁻¹¹
$g_{t}$	Triton g factor	5.957 924 930(12)		2.0 × 10⁻⁹
$μ_{t}$	Triton magnetic moment	1.504 609 5178(30) × 10⁻²⁶	J T⁻¹	2.0 × 10⁻⁹
$μₜ/μ_B$	Triton magnetic moment to Bohr magneton ratio	1.622 393 6648(32) × 10⁻³		2.0 × 10⁻⁹
$μₜ/μ_N$	Triton magnetic moment to nuclear magneton ratio	2.978 962 4650(59)		2.0 × 10⁻⁹
$m_{t}$	Triton mass	5.007 356 7512(16) × 10⁻²⁷	kg	3.2 × 10⁻¹⁰
$m_{t} c^{2}$	Triton mass energy equivalent	4.500 387 8119(14) × 10⁻¹⁰	J	3.1 × 10⁻¹⁰
$m_{t} c^{2}$	Triton mass energy equivalent in MeV	2808.921 136 68(88)	MeV	3.1 × 10⁻¹⁰
$m_{t}$	Triton mass in u	3.015 500 715 97(10)	u	3.3 × 10⁻¹¹
$M(t)$	Triton molar mass	3.015 500 719 13(94) × 10⁻³	kg mol⁻¹	3.1 × 10⁻¹⁰
$mₜ/mₚ$	Triton-proton mass ratio	2.993 717 034 03(10)		3.3 × 10⁻¹¹
$Aᵣ(t)$	Triton relative atomic mass	3.015 500 715 97(10)		3.3 × 10⁻¹¹
$μₜ/μₚ$	Triton to proton magnetic moment ratio	1.066 639 9189(21)		2.0 × 10⁻⁹

Helion

Symbol	Quantity	Value (uncertainty)	Unit	Rel. unc.
$mₕ/mₑ$	Helion-electron mass ratio	5495.885 279 84(16)		2.9 × 10⁻¹¹
$g_{h}$	Helion g factor	−4.255 250 6995(34)		8.0 × 10⁻¹⁰
$μ_{h}$	Helion magnetic moment	−1.074 617 551 98(93) × 10⁻²⁶	J T⁻¹	8.7 × 10⁻¹⁰
$μₕ/μ_B$	Helion magnetic moment to Bohr magneton ratio	−1.158 740 980 83(94) × 10⁻³		8.1 × 10⁻¹⁰
$μₕ/μ_N$	Helion magnetic moment to nuclear magneton ratio	−2.127 625 3498(17)		8.0 × 10⁻¹⁰
$m_{h}$	Helion mass	5.006 412 7862(16) × 10⁻²⁷	kg	3.2 × 10⁻¹⁰
$m_{h} c^{2}$	Helion mass energy equivalent	4.499 539 4185(14) × 10⁻¹⁰	J	3.1 × 10⁻¹⁰
$m_{h} c^{2}$	Helion mass energy equivalent in MeV	2808.391 611 12(88)	MeV	3.1 × 10⁻¹⁰
$m_{h}$	Helion mass in u	3.014 932 246 932(74)	u	2.5 × 10⁻¹¹
$M(h)$	Helion molar mass	3.014 932 250 10(94) × 10⁻³	kg mol⁻¹	3.1 × 10⁻¹⁰
$mₕ/mₚ$	Helion-proton mass ratio	2.993 152 671 552(70)		2.3 × 10⁻¹¹
$Aᵣ(h)$	Helion relative atomic mass	3.014 932 246 932(74)		2.5 × 10⁻¹¹
$σ_{h}^{'}$	Helion shielding shift	5.996 7029(23) × 10⁻⁵		3.8 × 10⁻⁷
$γ_{h^{'}}$	Shielded helion gyromagnetic ratio	2.037 894 6078(18) × 10⁸	s⁻¹ T⁻¹	8.8 × 10⁻¹⁰
$γₕ′/2π$	Shielded helion gyromagnetic ratio in MHz/T	32.434 100 033(28)	MHz T⁻¹	8.6 × 10⁻¹⁰
$μ_{h^{'}}$	Shielded helion magnetic moment	−1.074 553 110 35(93) × 10⁻²⁶	J T⁻¹	8.7 × 10⁻¹⁰
$μₕ′/μ_B$	Shielded helion magnetic moment to Bohr magneton ratio	−1.158 671 494 57(94) × 10⁻³		8.1 × 10⁻¹⁰
$μₕ′/μ_N$	Shielded helion magnetic moment to nuclear magneton ratio	−2.127 497 7624(17)		8.0 × 10⁻¹⁰
$μₕ′/μₚ$	Shielded helion to proton magnetic moment ratio	−0.761 766 577 21(66)		8.7 × 10⁻¹⁰
$μₕ′/μₚ′$	Shielded helion to shielded proton magnetic moment ratio	−0.761 786 1334(31)		4.1 × 10⁻⁹

Alpha particle

Symbol	Quantity	Value (uncertainty)	Unit	Rel. unc.
$m_α/mₑ$	Alpha particle-electron mass ratio	7294.299 541 71(17)		2.3 × 10⁻¹¹
$m_α$	Alpha particle mass	6.644 657 3450(21) × 10⁻²⁷	kg	3.2 × 10⁻¹⁰
$m_αc²$	Alpha particle mass energy equivalent	5.971 920 1997(19) × 10⁻¹⁰	J	3.2 × 10⁻¹⁰
$m_αc²$	Alpha particle mass energy equivalent in MeV	3727.379 4118(12)	MeV	3.2 × 10⁻¹⁰
$m_α$	Alpha particle mass in u	4.001 506 179 129(62)	u	1.5 × 10⁻¹¹
$M(α)$	Alpha particle molar mass	4.001 506 1833(12) × 10⁻³	kg mol⁻¹	3.0 × 10⁻¹⁰
$m_α/mₚ$	Alpha particle-proton mass ratio	3.972 599 690 252(70)		1.8 × 10⁻¹¹
$Aᵣ(α)$	Alpha particle relative atomic mass	4.001 506 179 129(62)		1.5 × 10⁻¹¹
$r_α$	Alpha particle rms charge radius	1.6785(21) × 10⁻¹⁵	m	1.3 × 10⁻³