Download In 1896, Henri Becquerel was working with compounds containing

Nuclear Chemistry Notes
In 1896, _______________________ discovered radioactivity. _______________ is the
______________________________________________________________________by
atoms of certain elements producing new elements. Materials that emit this
kind of radiation are said to be _____________ and to undergo radioactive decay.
In 1899, _______________________ discovered that uranium compounds produce
three different kinds of radiation. He separated the radiations according to
their penetrating abilities and named them __________, __________, and
__________ radiation, after the first three letters of the Greek alphabet.
Alpha decay
In alpha decay, the ___________ emits an alpha particle; an alpha particle is
essentially a __________ nucleus, so it is a group of two __________ and two
_________. A helium nucleus is very ________. Alpha radiation can be stopped by
______________.
An example of an alpha decay involves uranium-238:

Beta decay
A beta particle is ____________. In beta decay an electron is involved. The
number of ___________ in the nucleus ____________ by one and the number of
__________ ___________ by one. ____ millimeters of aluminum are needed to stop
most beta particles
An example of such a process is:

Gamma decay
The third class of radioactive decay is gamma decay, in which the nucleus
changes from ____________________________________________________________.
Several millimeters of _______________ are needed to stop gamma rays.
Half-Life
The _________ required for _________ of the atoms in any given quantity of a
radioactive isotope to decay is the half-life of that isotope. Each particular
isotope has its own half-life.
For example, the half-life of 238U is ____________________. That is, in
_________________________, half of the 238U on Earth will have decayed into other
elements. In another ____________________, half of the remaining 238U will have
decayed. ____________________________ of the original material will remain on
Earth after 9 billion years.
Summary of Radioactive Decay
Fill in the chart:
Type of Decay
Symbol
What occurs
Stopped by
Half-Life Problems
1. Phosphorus-32 has a half-life of 14.3 days. How many days will it take
for a radioactive sample to decay to 1/8 its size?
2. Iodine-131 has a half-life of 8.0 days. How many grams of an original
160 mg sample will remain after 40 days?
3. How many days must elapse for a 0.80 mg sample of iodine-131 in the
thyroid to decay to 0.10 g.