English experiment
Vocabulaire :
- Accurately: exactement/ Average : moyenne
- Beaker: bécher/ Bounce: rebondir
- Decay : décroissance
- Fleeting: le fugitif
- Plastic bowl: cuvette en plastique/ Poured: versé
- Slight: légère/ Set aside: écarter
- Tasty: délicieux
To understand about half life
Some elements have forms (called isotopes) with unstable atomic nuclei that have a tendency to change, or decay.
For example, U-235 is an unstable isotope of uranium that has 92 protons and 143 neutrons in the nucleus of each atom.
Through a series of changes within the nucleus, it emits several particles, ending up with 82 protons and 125 neutrons.
This is a stable condition, and there are no more changes in the atomic nucleus.
During 704 million years, half the U-235 atoms that existed at the beginning of that time will decay to Pb-207.
This is known as the half-life of U- 235.
A tasty way for students to understand about half-life is to give each team 100 pieces of « regular » M&M’s candy
Material:
- a beaker large enough for…
- 100 pieces of « regular » M&M’s candy
- a cleaned large plastic bowl
- hydroalcoholic gel
- a cleaned table
Method:
- Wash your hand before starting
- On your table each piece should be placed with the printed M facing down
The printed M facing down represents the parent isotope
- The candy should be poured into a beaker large enough for them to bounce around freely
- It should be shaken thoroughly
- Then poured back onto your table so that it is spread out instead of making a pile
This first time of pouring represents one half life.
And all those pieces of candy that have the printed M facing up represent a change to the daughter isotope
The printed M facing up represents the daughter isotope
- The team should pick up and set aside ONLY those pieces of candy that have the M facing up
- Then, count the number of pieces of candy left with the M facing down (parents isotopes)
- These are the parent isotopes that did not change during the first half-life
The teacher should have each team report how many pieces of parent isotope remain.
And the first row of the decay table (figure 1) should be filled in by students and the average number calculated.
- The same procedure of shaking, counting the « survivors », and filling in the next row on the decay table should be done seven or eight more times
Each time represents a half-life
- After the results of the final « half life » of the M&M’s are collected, the candies are no longer needed
Each team should plot on a graph (figure 2) the number of pieces of candy remaining after each of their « shakes » and connect each successive point on the graph with a light line
On the same graph each team should plot the AVERAGE VALUES for the class as a whole and connect that by a heavier line
AND, on the same graph, each group should plot points where, after each « shake » the starting number is divided by exactly two and connect these points by a differently colored line
- This line begins at 100;
- the next point is almost 100/ 2, or 50;
- the next point is 50/2, or 25 and so on.
Éléments de correction
Then eat the candy’s if you like !
Découvrez maintenant comment on utilise la désintégration d’éléments radioactifs pour déterminer l’âge d’un objet
TP suivant : déterminer l’âge d’un objet
Le coin du labo
- Il faut acheter ces deux types de M&M’s car ils ont une face marquée m et pas l’autre.
- Environ 2,50€ pour 400 bonbons.
