The document discusses different types of radioactive decay: - Radioactive decay occurs when an unstable atomic nucleus transforms spontaneously through emission of radiation. If the daughter nucleus is stable, decay ends, but it can continue with further unstable daughters until stability. - Rutherford discovered two types of radiation, alpha and beta rays, emitted from uranium that differed from X-rays in penetrating power. - There are five main types of radioactive decay: alpha, beta-minus, beta-plus, electron capture, and isomeric transition. Alpha decay involves emitting a helium nucleus. Beta decay involves converting a neutron to a proton with electron emission. Gamma emission does not change proton or neutron number but involves releasing energy from an excited

2. As mentioned previously, when
an unstable (i.e., radioactive)
atomic nucleus undergoes the
spontaneous transformation,
called radioactive
decay, radiation is emitted.

3. If the daughter nucleus is
stable, this spontaneous
transformation ends. If the
daughter is also unstable, the
process continues until a stable
nuclide is reached.

4. At Cambridge, Rutherford started
to work with J. J. Thomson on the
conductive effects of X-rays on
gases, work which led to the
discovery of the electron which
Thomson presented to the world in
1897.

5. Hearing of Becquerel's experience with
uranium, Rutherford started to explore
its radioactivity, discovering two types that
differed from X-rays in their penetrating
power. Continuing his research in Canada,
he coined the terms alpha ray and beta
ray in 1899 to describe the two distinct
types of radiation.

6. Most radionuclides decay in one or
more of the following ways:
(1) alpha decay,
(2) beta-minus emission,
(3) beta-plus (positron) emission,
(4) electron capture, or
(5) isomeric transition.

8. Alpha emission –emission of helium
nucleus or alpha particle from an
unstable nucleus.
Example:

9. A helium nucleus, the alpha particle, of 2 protons and
2 neutrons is emitted at high speed/kinetic energy
from the nucleus.
The residual atom (sometimes referred to as the
politically incorrect 'daughter nuclide'!*) has a mass
number of 4 less, and an atomic number of 2 less, than
the 'parent' or original atom.
Most atoms with an atomic number of over 82 (Pb)
usually undergo alpha decay.

10. * apart from Marie Curie, in
the late 19thC/early 20thC,
nuclear physics was
dominated by male
scientists!

11. Nuclear Transformation : Beta decay
Beta emission( β ) -emission of a high- speed electron
from an unstable nucleus.
Beta emission is the equivalent to the conversion of a
neutron to a proton.
Example :

12. •A neutron in the nucleus changes
spontaneously into a proton and a high
kinetic energy electron forms the emitted
beta particle.
•Since the proton and neutron have a mass
of 1 and the electrons mass is negligible, the
mass number stays the same but the atomic
(proton) number rises by 1.

13. •This tends to happen with isotopes
with too many neutrons to be stable
(too high an n/p ratio) and lies above
the stability curve shown in a previous
graph. By changing a neutron to a
proton the n/p ratio is reduced to an
isotope lying in the stability band.

14. Gamma emission
• The emission of gamma radiation from a nucleus does
not involve any change in the atomic (proton) number
or mass number.
– When a 'new' nucleus is formed it tends to have
excess energy making it potentially unstable.
– To become more 'nuclear stable' the nucleus loses
some energy as a burst of gamma radiation but the
proton and neutron numbers do not change.

15. Gamma Emission- emission from an excited
nucleus of a gamma photon, corresponding
radiation with a wavelength of about
10 -12 m. Meta-stable nucleus- a nucleus on
an excited stage with a lifetime of at least
nanosecond (10-9 s). In a meta-stable stage,
nucleus decay by gamma.

16. to be continued …
Thank You!