Physics Department, Yarmouk University, Irbid Jordan
Phys. 649 Nuclear Techniques
Dr. Nidal M. Ershaidat
Appendix 1
Units
MKS is no more appropriate when studying physics at the microscopic
level (atom, nucleus, nucleons, quarks, etc …). The MLT dimensions are
replaced by a new "scale" based on energy and distance, whose basic
units are the electron-volt (eV) and the Fermi (F or fm)).
1eV = 1.6×10-19 J
Using the values of h, Planck’s constant and c, the speed of light1
(1)
(2)
h = 6.62606957×10-34 J.s, c = 2.99792458×108 m/s
we have in this new system:
hc = 1.9864457 × 10 −25 J ⋅ m
= 1.2415 × 10 − 5 eV ⋅ m
= 1241.5 eV ⋅ nm
= 1241.5 MeV ⋅ F
(3)
For simplicity we shall consider that
and
hc = 1240 eV.nm = 1240 MeV.F
(4)
hc = 197.0 eV.nm = 197.0 MeV.F
(5)
The fine structure constant (α), Bohr radius and the electron Compton
wavelength are respectively given by equations 6, 7 and 8.
Fine structure constant
Bohr radius
Electron Compton wavelength
(
k e2
9 × 10 9 1.6 × 10 −19
α=
=
hc
3.16153 × 10 − 26
a0 =
λ0 =
)
2
≈
1
137
(6)
197.0 × 137.3
°
≈ 0.53 A
0.510
(7)
h
hc
1240
=
= 243 F
=
me c me c 2
0.511
(8)
hc
αµc
2
=
2
Where µc is the Hydrogen atom reduced mass.
1
http://physics.nist.gov/constants [Friday, 03-Feb-2012]. National Institute of
Standards and Technology, Gaithersburg, MD 20899.
Table 1 gives the values of the rest mass of the electron, proton, neutron and
2
alpha particle in MeV/c units.
me = 0.511 MeV/c2
9-a
mp = 938.3 MeV/c2
9-b
mn = 939.573 MeV/c2
9-c
mα = 3727.4 MeV/c2 = 3.7274 GeV/c2
9-d
Table 1: Rest mass for some particles