Nuclear PP.ppt

Radioactivity
 This is the process by which unstable isotopes
emit material.
 The instability in the atom is the result of an
unstable nucleus trying to become more stable.
 A radioisotope is defines as the nuclei of an
unstable isotope
 Example: C-14 radioactive dating process

Radiation
Is defined as the material and/ or energy that
are emitted from an unstable isotope.
Examples:
Alpha – this is a Helium ion He 4
2a
Beta – changes a neutron into a proton or a
proton into a neutron. 0
-1b
Gamma – is not a particle – it is energy (ray)
0
0g

Energy
In terms of the energy associated with each
type of radiation:
Increasing energy
a b g
Good news…………………………Bad news

Penetrating Ability
Depending upon its energy, different types of radiation
are stopped by different materials
a b g
Good News………………………Bad news

Radioactive Decay
The next step in the process of
becoming more stable

Nuclear Chemistry deals with the nuclei of
atoms breaking apart. Atoms are continually
undergoing decay. When studying nuclear
chemistry, there is a typical format used to
represent specific isotopes.
Copyright © Cengage Learning. All rights reserved 7

The nuclear reactions that we will cover in chemistry class
can be categorized as either an emission reaction or a
bombardment reaction.
Emission reactions: These are decay
reactions, in which an unstable isotope
decays into another element/isotope and
releases a particle. The particles we will
covering include:
 4
2a Alpha particle – helium nucleus
 0
-1b Beta particle – electron
 0
0g Gamma emission
1
1p Proton
1
0n Neutron

First type of Radioactive Decay –
Alpha Particle Production
 Alpha particle – helium nucleus
 Examples
 Net effect is loss of 4 in mass number and
loss of 2 in atomic number.

Where A is the parent isotope (the atom being
broken apart) B is the daughter isotope or the
isotope formed.
When an element is broken down in alpha decay it
loses two neutrons and two (2) protons. This means
that the name of the element will change as well,
moving back two (2) places on the periodic table.

Nuclear equations are typically written in the
format shown below.
Alpha decay follows the form:

Alpha decay is not very penetrating
because the He atoms capture electrons
before traveling very far. However it is very
damaging because the alpha particles can
knock atoms off of molecules.
Alpha decay is the most common in
elements with an atomic number greater
than 83.

Second type of Radioactive Decay –
Beta Particle Production
 Beta particle – electron
 Examples
 Net effect is to change a neutron to a
proton.

Beta negative decay
follows the form:
The beta emission
increases the atomic
number by one (1) by
adding one (1) proton. At
the same time, one (1)
neutron is lost so the mass
of the daughter isotope is
the same as the parent
isotope.

 Beta negative decay is more penetrating than
alpha decay because the particles are smaller,
but less penetrating than gamma decay.
 Beta electrons can penetrate through about one
(1) cm of flesh before they are brought to a halt
because of electrostatic forces.
 Beta decay is most common in elements with a
high neutron to proton ratio.

Gamma emission

Am
Z A 0
0g + A
Z B

(Isotopes are moving from an excited state
(m) to ground state)
Third type of Radioactive Decay –
Gamma Production

Gamma decay follows the form:
 In gamma emission, neither the atomic number or the
mass number is changed. A high energy gamma ray
is given off when the parent isotope falls into a lower
energy state.
 Gamma radiation is the most penetrating of all. These
photons can pass through the body and cause
damage by ionizing all the molecules in their way

Fourth type of Radioactive Decay –
Positron Production
 Positron – particle with same mass
as an electron but with a positive
charge
 Example
 Net effect is to change a proton to a
neutron.

Positron emission (also called Beta
positive decay) follows the form:
 In this reaction a positron is emitted.
 A positron is exactly like an electron in mass and
charge force except with a positive charge.
 It is formed when a proton breaks into a neutron with
mass and no charge and this positron with no mass
and the positive charge.
 Positron emission is most common in lighter
elements with a low neutron to proton ratio.

20
Fifth type of Radioactive Decay –
Electron Capture
 Process in which one of the inner-
orbital electrons is captured by the
nucleus.

Electron capture follows the form:
21
In this reaction a nucleus captures one (1) of
its own atom's inner shell electrons which
reduces the atomic number by one.
This captured electron joins with a proton in
the nucleus to form a neutron.
Electron capture is common in larger
elements with a low neutron to proton ratio.

Transuranium Elements
 Elements with atomic numbers greater
than 92 which have been synthesized.

Bombardment reactions
These are reactions that result from the
addition of a particle to an isotope, which
results in the formation of a new
element/isotope and occasionally another
particle. Isotopes can be bombarded with
any of the following particles:
 4
2a 0
-1b 0
0g 1
1p 1
0n
23

Bombardment reactions
 Alpha bombardment
 A
Z X + 4
2a A+4
Z+2 Y
 Beta bombardment
 A
Z X + 0
-1b A
Z-1 Y
 Gamma bombardment
 A
Z X + 0
0g Am
Z X
 Proton bombardment
 A
Z X + 1
1p A+1
Z+1 Y
 Neutron bombardment
 A
Z X + 1
0n A+1
Z X
24

25
Concept Check Transformation
If the bombardment of Am-243 with alpha
particles leads to the emission of a neutron, which
nuclide is formed in this nuclear transformation
process?
247
97
247
96
248
96
246
97
a) Bk
b) Cm
c) Cm
d) Bk The correct answer is d. Since a neutron is
emitted, the mass number goes up by 3
(not 4) and the atomic number goes up by
2 (from 95 to 97).

Nuclear PP.ppt

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