ray Interactions with Matter

1
Types of Ionizing Radiation x-rays and ?-rays
electromagnetic waves a particles ionized 4He
atoms ß particles - electrons neutrons
2
Radioactive Materials Materials that give off
ionizing radiation These are unstable atomic
nuclei which decay and emit ionizing radiation
such as x-rays. The type of radiation they emit
depends on the particular atomic nucleus.
3
Ionizing Radiation is all around us
Some comes from the sky cosmic rays Soil,
plants, people contain radioactive elements This
is called background radiation. It gives all of
us an annual radiation dose. We are also exposed
medically from x-rays, CT scans etc
4
Ionizing Radiation is all around us
Soil, plants, people contain radioactive
elements Naturally occurring radioactive
elements include 40K, 14C and elements in decay
chains that start with uranium and thorium
5
US Geological Survey
6
US Geological Survey
7
US Geological Survey
8
Relative Decay of 28Al and 36Cl
Ni(t) N0e-?t
9
Relative Decay of 28Al and 36Cl
Ni(t) N0e-?t
N is the number of radioactive atoms t is the
time ? is the decay constant it is the
probability that one radioactive atom will decay
per unit time
10
Half-Life

• For radioactive decay, we consider the The
  half-life, t½, is the time at which Ni(t)N0/2
• N0/2N0e-?t
• ?t ln(2)
• t½ ln(2)/?

Decay of Al-28