Nuclear Physics and Medicine

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Nuclear Physics and Medicine
Introduction - general Master course Medical
Physics Students in Medical Sciences - Transport
phenomena through neutral membranes -
Electrocardiogram and biomagnetism - Feedback and
control - Atoms and light - Medical use of X
rays - Nuclear physics and medicine - Nuclear
imaging Literature Russell K.
Hobbie, Intermediate Physics for Medicine and
Biology (3rd ed., 1997, Springer)
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Nuclear Physics and Medicine

• Introduction - today
• Nuclear physics and its interdisciplinary use.
• - You will calculate the rest energy of an
  isotope.
• - You will discuss if a certain radioactive decay
  is possible.
• You will calculate the age of a bone fragment
  from its radioactivity.
• You will discuss what application you imagine
  for medical sciences.

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Nuclear Physics and Medicine
Introduction Nuclear binding energies Radioactiv
e decays Half-live and decay rate Radioactive
dating Summary Following lecture Tomography
Carbon dating of the remains of a sea-turtle can
tell when humans inhabited the site of an ancient
man-made stone circle (pictures from book of
Giancoli).
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Nuclear binding energies - 1
The total mass ( in kg, eV/c2, or atomic mass
units) of a stable nucleus is always less than
the sum of the masses of its separate protons (p)
and neutrons (n). Isotopes are indicated by AZX,
where A is the sum of the number of protons Z and
neutrons N of element X. The rest energy E0 m
c2 is in J (joule) or eV (electronvolt). 1 kg of
material with E0 1.(3.108)2 9.1016 J,
acquires EK 9.8 J over 1 m from gravity when it
falls.
?
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Nuclear binding energies - 2
The average binding energy per nucleon is the
total binding energy divided by A, the total
number of nucleons (protons and
neutrons). Question What element will most
probable remain after nuclear burning inside
stars ?
8 4 0
Answer Iron (Fe) The elements that form the core
of the earth are believed to be ejected by a
supernova explosion at the end of the life of a
burning star.
0 50 100 150
200
A (mass number)
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Radioactive decays
Transmutation of elements occur when a nucleus
decays by ß decay. Electrons (and positrons)
emitted by atomic nuclei are often called ß
particles. They are not orbital electrons, but
are created in the nucleus. Example. How much
energy is released in 14C decay ? Solution. Look
up the atomic masses, including 6 electrons
before and 7 electrons after decay. Mass
difference ?m m(14C) - m(14N) 0.000168
a.m.u. 0.156 MeV/c2. Energy release ?E 0.156
MeV. Questions. How much energy is needed for
the change of 13C to 12C ? Look at slide 4. Is
such radioactive decay possible ?
m(14C) 14.003242 a.m.u. m(14N) 14.003074
a.m.u.,
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Half-live and decay rate
Decay probability ? Decay rate dN/dt Number of
survivors N Half-life T½
? 3.8 1012 s1 (8300 yr)1 dN/dt N ? N
N0 e ? t N0 e ? T½ 0.5 N0 e ? T ½ 2
? ? T½ ln 2 T½ 0.693 / ? 5730 yr
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Radioactive dating of bone of 200 g carbon with
16 decays s1
Constant production of 14C in the
atmosphere. Ratio 14C / 12C is R 1.3
1012. Absorption of CO2 by living
plants Number of 14C atoms in 200 g carbon, N0
Original decay rate Present rate Question
How many years (T ) old is the bone?
? 3.8 1012 s1 N0 R 6.02 1023 w / A
1.3 1013 atoms dN/dt (0) N0 ? 50 s1 dN/dt
(T) 16 s1 9400 yr
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Nuclear Physics and Medicine
Summary - today Nuclear physics and its
interdisciplinary use. - You calculated the rest
energy of the 12C isotope. - You discussed if
radioactive decay of 13C to 12C is possible. -
You calculated the age of a 9400 year old bone
fragment from its 14C radioactivity. - You
suggested the following nuclear physics
applications for medical sciences
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Homework
Study section 42-10 about Radioactive
Dating. Answer the question in writing Can 14C
dating be used to measure the age of stone walls
and tablets of ancient civilizations ? Read
section 43-9 about Imaging by Tomography.