A(t) = Ao EXP(-t/1.44 t1/2)
where A(t) is the amount at any time = t
Ao is the starting amount at t=0
t = time
t1/2 = the half life of the isotope.
The factor of 1.44 links the natural log of 2 into the equation (really 1/ln2) Question 1
True of False:
The higher the activity in counts per second the smaller the half life value of the radioactive
material.
True
False
Question 2
A Radium - 226 atom decays by emitting an alpha particle. Determine the new element and/or
isotope type that the atom has become.
Francium - 222
Radon - 224
Radon – 222
Radium - 222
Radium - 224
Question 3
A carbon - 14 atom decays by emitting a Beta particle. Determine the new element that the atom
has become.
boron
carbon
nitrogen
fluorine
oxygen Question 4
A Ba-137m (unstable) nucleus emits a gamma ray. What does it now become?
La-137
Ba-137
Xe-133
La-138
La-133
Question 5
A radioactive material has a half line of 15 minutes. It starts off with 100 grams. Determine the
amount of grams present of the radioactive material after exactly 3 hours.
1.5625 grams left
0.0244 grams left
0.1953 grams left
0.0459 grams left
0.1278 grams left
0.7836 grams left
Question 6
Tritium has a half life of 12.3 years. Bill buys a 10.0 gram sample of tritium on Ebay for $ 1,000.
Assuming that the amount of tritium follows the same equation form as the activity equation
shown on page 126 in our lab procedure, determine the amount of tritium left over at the end of 5
years. The Ao value would be the 10 grams and t1/2 = 12.3 years. Don't forget the 1.44 in the
denominator.
7.93 grams
8.41 grams
7.54 grams
7.37 grams
8.23 grams Question 7
A piece of charcoal from a tree killed by the volcanic eruption that formed Crater Lake in
Oregon gave 7.0 disintegrations of Carbon-14 nuclei per minute per gram of total carbon as its
activity. Present day carbon 14 (in living matter) gives 15.3 disintegrations per minute per gram of total carbon (because it has more carbon-14 in it). Using this information determine the date
of the volcanic eruption. State the year. Take half life of C-14 as 5,730 years. about 6,400 AD
about 4,200 BC
about 4,000 BC
about 4,900 BC
about 4,400 BC
about 5,600 BC
Question 8
The radioactive isotope Mt - 277n named after Austrian scientist Lisa Meitner, was first detected August 29, 1982 by a German research team when they bombarded a target of Bi 208 with accelerated nuclei of iron (Links to an external site.)­58. If exactly 1.00 grams of the material was placed in a test chamber and 1 minute later only 0.00024 grams was left, determine the half life of the material. Assume that its decay follows the same equation as the activity in our lab procedure on page 126. Don't forget the 1.44 in the denominator. (Links to an external site.) Half-life = 3.33 seconds
Half-life = 2.75 seconds
Half-life = 5.00 seconds
Half-life = 1.25 seconds
Half-life = 7.60 seconds Question 9
When the activity from a radioactive half life experiment was plotted in EXCEL the resultant
TRENDINE was seen as:
y = 2,877 EXP (-0.37 x) What was the activity in counts per minute at t = 0?
0.0036
2.702
1.876
0.37
2,877
Question 10
When the activity from a radioactive half life experiment was plotted in EXCEL the resultant
TRENDINE was seen as:
y = 2,877 EXP (-0.37 x)
Determine the half life of this isotope. The X axis (representing time) is plotted in minutes.
0.37 minutes
0.644 minutes
1.876 minutes
3.06 minutes
2.63 minutes

 

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