Practical exercise 3: HOW DO THE ELEMENTS SYNTHESIZE IN STARS
The poster of the original exercise with pictures is given at Appendix 2.
Aim:
The process of nuclear reactions to be explained and demonstrated how the radiation of stars appear.
Necessary materials:
• a bowl with smaller marshmallows (or styrofoam balls), which can be one colored or several different colors,
• a bowl of raw pasta in the shape of tubes,
• a periodic table of chemical elements.
Optional: for older students, an illustration of the electromagnetic spectrum can be added, indicating the types of radiation and napkins for the candies / balls.
Instructions for the teacher:
This exercise shows how the chemical elements are formed in the Universe and where radiation comes from. The duration is about 5 to 10 minutes. Students must have a periodic table of chemical elements. You can conduct the exercise as A) independent work - students follow the instructions below and write down their answers, then discuss the results; B) You give the instructions below and ask the questions during the exercise that the students have to answer before the next step.
Instructions for students:
This exercise will show you how the chemical elements are formed and where the radiation comes from.
1. Take the periodic table. Indicate on the table the elements hydrogen H and helium He. These are the elements that are most abundant in the stars.
2. Remove one from the bowl of candies / balls. Let it be a proton. The number of protons in the nucleus determines the chemical element. Hydrogen has 1 proton. Then how many hydrogen atoms will the candy / ball illustrate? [Answer: One]
3. Each student should take two candies / balls that represent two hydrogen nuclei. Usually in nuclear reactions, the nuclei merge two by two.
4. Which element has two protons in its nucleus? Indicate it on the table. [Answer: Helium]
5. Let's see how the star forms helium: Squeeze the candies / balls together in your hands. Imagine that your clasped hands represent the core of a star. There the temperature and pressure are so high that the atoms move very fast and collide constantly with other atoms. And sometimes the nuclei of two atoms merge (For older students: At such high pressures and temperatures, the atoms in the nuclei of stars have lost their electronic shells and consist only of nuclei (protons and neutrons), and the electrons in the shells have become independent particles). Can you merge your cores? Crush the candies / balls so that they form a new core. This is a nuclear reaction! The two hydrogen nuclei merged to form the nucleus of which element? [Answer: Helium]
6. Take one pasta from the pasta bowl. Let it represent a gamma ray. (For older students: Indicate in the picture of the electromagnetic spectrum where the gamma rays are. What is their energy compared to other types of radiation? [Answer: Highest]) Put the new core on the table and pasta next to it. This is what a two-core fusion scheme looks like, in which energy is released in the form of a gamma ray.
7. Make another helium core by taking two more candies and merging them together. Place the new core on the table. What else do you need to complete the process? [Answer: Gamma ray (pasta)] What is the process called? [Answer: Nuclear reaction]
8. Repeat step 7. How many cores do you have now and on which element? [Answer: Three nuclei of helium] And how many protons? [Answer: Six]
9. Take two of the helium nuclei and crush them together. Take out one more pasta. What did you do? [Answer: Nuclear reaction]
10. To the fused helium nuclei, add the third. How many protons does the newest nucleus have? [Answer: Six]. What is this element? Find it and indicate it on the periodic table [Answer: Carbon]
11. For older students: In step 9, by merging two helium nuclei, a beryllium Be nucleus (with four protons in the nucleus) was obtained. Beryllium is a rather unstable element and would disintegrate in less than 1 second. But if we add another helium nucleus to it first, the next element is formed (with 6 protons in the nucleus). Scientists call helium nuclei "alpha particles" and the process of forming carbon from three helium nuclei "triple alpha process."