Download Radioisotopes

Atomic structure
(N)
(Z)
A=Z+N
Isotope
• Isotopes are any of the different types of atoms
(Nuclides) of the same chemical element, each
having a different atomic mass (mass number)
• Isotopes of an element have nuclei with the
same number of protons (the same atomic
number) but different numbers of neutrons.
• Therefore, isotopes have different mass
numbers, which give the total number of
nucleons, the number of protons plus neutrons.
Isotope
• About 339 nuclides occur naturally on
Earth, of which 250 (about 74%) are
stable.
• Counting the radioactive nuclides not
found in nature that have been created
artificially, more than 3100 nuclides are
currently known
Isotope
• Elements are composed of one or more
naturally occurring isotopes, which are
normally stable.
• Some
elements
(radioactive) isotopes
have
unstable
Isotope
Elements in chemistry are represented by a symbol with two numbers
* Atomic number = number of protons or electrons
* Atomic mass = number of nucleons (protons + neutrons).
12
6
C
Change the atomic number = a different element.
Isotopes are atoms with identical atomic numbers but different mass numbers
1 2 3
12 13 14
32 31
131 127
1 1 1
6
6 6
15 15
53 53
H HH
C C C
P P
I I
Isotope
• Some isotopes are stable, others are
unstable or radioactive
• Radiation is emitted when an unstable
nucleus spontaneously changes, or
disintegrates into more stable one.
• Every element in the periodic table has at
least one radioactive isotope.
• Radioactivity is a form of nuclear
reaction
(nucleus)
not
chemical
reaction (electrons)
Nuclear and chemical reactions
• A nuclear reaction involves changes in an
atom’s nucleus, usually producing a different
element. Chemical reaction never changes the
nucleus, it only rearranges the outer shell
electrons.
– Different isotopes of an element have
essentially the chemical reactivity (same
electrons), but often have completely different
behavior in nuclear reactions.
Nuclear and chemical reactions
• The rate of nuclear reaction is not affected
by the change in temperature, pressure or
addition of a catalyst, or the chemical form
(compound or element).
• The energy change accompanying a
nuclear reaction can be several million
times greater than that of a chemical
reaction.
Radioactive decay
• Radioactive decay is the process in
which an unstable atomic nucleus loses
energy by emitting ionizing particles and
radiation.
• This decay, or loss of energy, results in an
atom of one type, called the parent nuclide
transforming to an atom of a different type,
called the daughter nuclide.
Radioactivity
Nuclear decay or Radioactivity is the
spontaneous emission of radiation from a
nucleus.
– One element can change into another element via
radioactive decay or transmutation
– Discovered by Henry Becquerel in 1896.
• He concluded that uranium gave off some
radiation.
Radioactivity
• The radiation or radioactivity was later shown to be separable
by electric (and magnetic) fields into three different types:
1. Alpha (a); a helium nucleus, He2+, emitted as alpha particle.
2. Beta (b); an electron emitted from the nucleus
3. Gamma (g); radioactivity consisting of high-energy light waves.
Radioactivity Half-Life
• Nuclear decay is a first order process 
dN
N
0.693

 N  Ln
 t  t1 / 2 
dt
N0

• Rates of nuclear decay are measured in units of half life (t1/2),
defined as the time required for one half of the radioactive
sample to decay.
Isotope
Particle type
Half life
3H
b-
12.3 yr
14C
b-
5570 yr
32P
b-
14 days
22Na
b- & g
15 hr
125I
g
60 days
131I
b-
8 days
238U
a
>billions yrs
Units of Radiation
• The SI unit of radioactive decay (the
phenomenon of natural and artificial
radioactivity) is the becquerel (Bq).
• One Bq is defined as one transformation
(or decay) per second.
Units of Radiation
• In the meteric system, radioactivity unit is
Becquerel (Bp); 1 Bp= 1 disintegration per
second (dps).
•The basic unit of radioactivity is Curie (Ci), and its
subdivisions: mCi, mCi
•The two units can be interconverted:
– 1 Ci= 3.7 x 1010 Bp or dps.
Units of Radiation
• Instruments (b or g counters) report
radiation as cpm or (count per minute).
cpm = dpm * (counting efficiency of
machine)
dpm= disintegration per minute