Crystal nuclei are the initial building blocks of a crystal structure. They are formed when atoms or molecules come together in a specific arrangement that is repeated in a regular pattern to form a crystal lattice. These nuclei serve as the starting point for crystal growth, with additional atoms or molecules attaching to them to further expand the crystal structure. The size and shape of crystal nuclei can influence the overall growth and properties of the crystal. **

Energy is released when heavy nuclei split in a process called nuclear fission because the total mass of the resulting nuclei is less than the original nucleus, and this mass difference is converted into energy according to Einstein's famous equation E=mc^2. Similarly, energy is released when light nuclei fuse in a process called nuclear fusion because the resulting nucleus is more stable than the original nuclei, and the excess energy is released in the form of kinetic energy and radiation. Both nuclear fission and fusion involve changes in nuclear binding energies, leading to the release of energy. **

The number of decaying nuclei per second in radioactivity can vary widely depending on the specific radioactive material and its activity level. However, in general, the rate of decay is often measured in becquerels (Bq), where 1 Bq is equal to 1 decay per second. So, the number of decaying nuclei per second in radioactivity can range from a few Bq for low-level radioactive materials to millions or even billions of Bq for highly radioactive substances. **

Energy is released when heavy nuclei split (fission) because the resulting nuclei are more stable and have lower binding energy per nucleon. This excess energy is released in the form of kinetic energy and radiation. Similarly, energy is released when light nuclei fuse (fusion) because the resulting nucleus is also more stable and has a higher binding energy per nucleon. This excess energy is also released in the form of kinetic energy and radiation. **

Helium nuclei, also known as alpha particles, have a positive charge of +2. This means they have two protons, which are positively charged, and no electrons, which are negatively charged. As a result, helium nuclei are positively charged and are attracted to negatively charged particles. **

Atomic nuclei don't fall apart because of the strong nuclear force, which is one of the four fundamental forces of nature. This force is responsible for holding the protons and neutrons together in the nucleus, overcoming the electromagnetic repulsion between the positively charged protons. The strong nuclear force is much stronger than the electromagnetic force at short distances, which allows it to keep the nucleus stable. Additionally, the presence of neutrons in the nucleus also helps to stabilize it by adding to the attractive nuclear force without adding to the electromagnetic repulsion. **

Atomic nuclei are the central part of an atom, containing protons and neutrons. The number of protons in the nucleus determines the element's identity, while the number of neutrons can vary, creating different isotopes of the same element. Cations are positively charged ions that are formed when an atom loses one or more electrons. This loss of electrons creates an imbalance between the number of protons and electrons, resulting in a net positive charge. **

Atomic nuclei that undergo radioactive decay per second refers to the rate at which the nuclei of unstable atoms disintegrate and emit radiation. This process is random and cannot be predicted for any individual nucleus, but the overall rate of decay for a large sample of atoms can be measured and expressed as the number of decays per second. This rate is known as the activity of the radioactive substance and is measured in becquerels (Bq). The higher the activity, the more unstable the substance and the more rapidly it is decaying. **