# Radioactivity
at A2 Level

**A2 Level Radioactivity INDEX**

Radioactivity at 16+ level differs
from that at 14-16 level primarily in the application of
mathematical interpretation that is required. It is useful
to revise the subject at the lower level before beginning
this section of study. An extensive glossary of terms is accessible from this section this should

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**From radioactivity
studied at level (14-16) the following should be fully appreciated:**

**Symbols**

**Why
radioactivity occurs**

**Background
radiation**

**Half
Life**

**Uses**

**Safety**

The exponential
decay of a radioactive isotope requires the use of natural logarithms.
A section on the mathematical skills required for this section is included
so that you can revise the basic rules for manipulation of equations,
exponents and logarithms. Being able to 'speak mathematics' fluently is
very important at 16+ level

**Mathematical
skills**

**New material at 16+ level:**

**The equations relating
to radioactive decay are exponential in character. This causes problems
with calculations relating to half-life. See Mathematical
skills before continuing.**

**Radioactive
decay and half life calculations at 16+**

**When considering radioactive decay
as represented in equations you now have to also consider particle physics
and the balancing of lepton number and baryon number (from your AS syllabus!).**

**Balancing
Equations**

**The ****Feynman
diagrams** will also have to
be known for beta decay.

**Practical
knowledge is imperative at this level (see safety).**

**A Geiger-counter
meter only records the particles that interact with it. Students
often think that the true activity of a sample is measured by the instrument.
The count rate is always lower than the true activity.**

**Illustrative
question**

**In order to answer questions that
relate the number of atoms in a sample with its mass students must understand
what a mole is.**

**The
mole and the Avogadro number**

**Try this question:**
**The half-life of Pb 210
is 20 years. Find the initial number of disintegrations per second for
1.0g of this isotope of lead.**

**Try this question:** **A speck of uranium dust
contains 10**^{14} atoms. It has a mass of 3.95 x 10^{-8}g.
The half life of Uranium 238 is 4.5 x 10^{9} years. It is inhaled
and lodges in the lung. What is the initial rate of disintegration of
the dust spec?

**Carbon
14 dating is used to date artefacts that contain once living material. **

**Try this question:** **If the equilibrium concentration
of carbon 14 in living plants gives 16 disintegrations per minute per
gramme of carbon, estimate the age of a piece of timber if 2.0g of carbon
prepared from it gives 15 disintegrations per minute.**

**(The half-life of carbon 14 is 5.57 x 10**^{3}
years).

**Medical use of radioisotopes forms
an important part of Medical Physics content syllabuses. This makes
an understanding of the physiological effects off radioactive materials
important, but even if you are not studying that option this is 'good
for your soul'**

**Effects
of radiation exposure**

**When
a patient is injected with a radioactive tracer the bodily functions
expel the isotope from the body by natural processes such as excretion,
respiration and perspiration. Therefore the effective half-life of the
isotope is less that the physical isotope but also depends upon the
rate at which the body removes it: the biological half-life. The combination
of these is called the effective half-life.**

**Calculations
related to effective half-life**

**Choice of
tracer isotope**