### Nuclei

goals
Nuclear fusion reactions at the center of the sun produce gamma ($\gamma$-ray) ray photons with energies of the order of $1MeV(10^{6} eV)$. By contrast what we see emanating from the sun's surface are visible radiations of wavelength $500 nm$. A simple model that explains this difference in wavelength is that a photon undergoes compton scattering many times (about $10$$^{26}$ times), as suggested by models of the solar interior, as it travels from the sun to its surface.
The neutral ion $\pi$ is an unstable particle produced in high energy particle collisions. Its mass is about $264$ times the mass of electron. Note that its average life time is $8.4\times10^{-17}$ $s$ before decaying into two gamma ray photons. Using the energy mass relationship between rest mass and energy, one can find uncertainty in the mass.
All nuclei consist of two types of particles - protons and neutrons. The nuclear force is the strongest force. Stability of nucleus is determined by the neutron-proton ratio or mass defect or binding energy per nucleus or packing fraction. The shape of the nucleus is calculated by quadrupole moment. Spin of a nucleus depends on even or odd mass number. The volume of the nucleus depends on the mass number. The whole mass of the atom (nearly 99%) is centered at the nucleus. The magnetic moment of the nucleus is measured in terms of the nuclear magnetons.
A certain nucleus A (mass number $238$ and atomic number $92$) is radioactive and becomes a nucleus B (mass number $234$ and atomic number $90$) by the loss of a particle.
Which of the following is the radio isotope in each pair?