Lecture 5 Outline
HW3: Due Friday, Jan 25 (Quiz 2)
Recitation: Ch 24: Radioactive Decay.
Radiation Dosage, Nuclear Medicine
Binding Energy, Nuclear Power
Nuclear transmutation – transform 1 element into
another - like Alchemy
7N + 4
1H + 17
8O Rutherford, 1919
This led to the discovery of the neutron – like a gamma ray
(neutral charge), but heavy like a proton.
This approach is used to make the transuranium elements
And studied in accelerators
Radiation when it interacts with matter can cause two
Non-ionizing radation – causes atoms to vibrate matter
Ionizing radiation – causes loss of electron(s):
This type of radiation can be dangerous because it
causes reactive radical species.
Units of Radioactivity
Activity or disintegrations (transformations) per unit
of time is expressed in units of curies (Ci) or in the SI
unit of becquerels (Bq)
One becquerel = 1 disintegration per second (s-1
One curie = 3.7 x 1010
disintegrations per second
= 3.7 x 1010
Units of Dose
Not all types of radiation are absorbed to the same
extent. Different types of radiation deposit different
amounts of energy when absorbed by the body.
A Gray is the SI unit of absorbed dose.
gy = 1 joule / kg of body tissue
= 100 rads
Particle Relative energy deposited
Relative Biological Effectiveness
0n 1 - 100
rem = RBE x rads
1 gy = 1 J/kg
4 gy/ 1 g H2O raises the temperature by 4o
Radiation damage is not due to heating, it results
from breaking chemical bonds in a body
producing free radicals.
The body can handle and repair a certain amount of free
radical damage whether it is caused by radiation, drinking
alcohol, heavy labor, heavy exercise, eating slightly rancid
food, or from wounds. Radiation sickness is a free radical
disease just as a hang-over is.
The body can handle a certain amount of free radicals before
the free radicals overwhelm the body's free radical scavenging
system. When overwhelmed, part of the free radical damage
consists of damage to the body's free radical scavenging system
creating a vicious cycle.
Radiation kills by breaking cells DNA. As a consequence, cells
can no longer reproduce. LD50 is approximately 2.5 - 4 Gy
(250 – 400 rem) depending on length of exposure and
•uses radioactive substances (radiopharmaceuticals)
•radioactive substances are administered and the
radiation emitted is measured
•usually involves the formation of an image
•radionuclides are also administered to treat disease
or provide pain relief.
•iodine-131 is often used for the treatment of
thyrotoxicosis and thyroid cancer.
Mo → 99m
Tc + e- 99
Mo: t1/2 = 66 h
Tc → 99
Tc + γ 99m
Tc: t1/2 = 6 h
γ-rays behave like x-rays,
they pass through tissue.
Cardiolite distributes in the
heart proportionally to the
blood flow in the heart’s
Positron Emission, β+
Positron Emission: decay by loss of an a positron, a
particle with the same mass as an electron but with a
positive charge (a positive electron).
6C → 11
5B + 0
The positron interacts with an electron, and the two annihilate
each other. All of their mass is converted into energy––two
0.511 MeV gamma rays are produced.
–1e + 0
+1e → 2 γ (0.511 MeV each)
Positron Emission Tomography
→ 2 γ (0.511 MeV each, in opposite directions)