Biomedical Engineering Reference
In-Depth Information
EXAMPLE PROBLEM 15.1
Verify that the energy released by 1 amu is 931 MeV.
Solution
The conversion can be expressed by Einstein's equation
2
E
¼
mc
where
is the mass in grams, and
is the velocity of light in cm/sec. Then, the energy equivalent
m
c
(
) of one atomic mass unit is given by
E
10
24
gm
10
10
cm
2
E
¼ð
1
:
66
Þð
3
=
sec
Þ
10
3
gm-cm
2
sec
2
E
¼
1
:
49
=
The unit gm-cm
2
/sec
2
is frequently encountered in physics and is termed the
erg
,so
10
3
ergs
E
¼
1
:
49
An electron volt is defined as the amount
of kinetic energy acquired by an electron when it is accelerated in an electric field produced by a
potential difference of one volt. Since the work done by a difference of potential
Another convenient unit of energy is the
electron volt.
V
acting on a
10
19
coulombs, it is possible to calculate
charge
e
is
Ve
, and the charge on one electron is 1.6
the amount of energy in one electron volt as follows:
10
19
coulomb
1eV
¼
1
:
6
1 volt
10
19
joules
1eV
¼
1
:
6
or
10
12
ergs
Since the electron volt is a very small amount of energy, it is more commonly expressed in
thousands of electron volts (keV) or millions of electron volts (MeV):
1eV
¼
1
:
6
1 MeV
¼
1, 000, 000 eV
1 keV
¼
1, 000 eV
It is now possible to express the atomic mass unit in MeV:
10
3
ergs, and
1 amu
¼
1
:
49
10
6
ergs; therefore,
1 Mev
¼
1
:
60
1 amu
¼
931 MeV
Therefore, if one amu could be completely transformed into energy, 931 MeV would result.
To gain a concept of the magnitude of the electron volt, one million electron volts (MeV) is enough
to lift only a milligram weight one-millionth of a centimeter.
eventually comes to a stable
condition with the emission of ionizing radiation after a specific probability of life expec-
tancy. In general, there are two classifications of radionuclides: natural and artificial.
Naturally occurring radionuclides are those nuclides that emit radiation spontaneously
An unstable nuclide, commonly known as a
radionuclide,
