Which particle loses energy each time ionization occurs, has a short range, and cannot penetrate a sheet of paper?

The particle described in the question is characterized by its ability to lose energy during ionization, its short range in matter, and its inability to penetrate a sheet of paper. Alpha particles fit this description perfectly.

Alpha particles are composed of two protons and two neutrons, making them relatively heavy and positively charged. Due to their mass and charge, they interact strongly with matter, resulting in significant ionization as they pass through materials. This strong interaction leads to the rapid loss of energy, causing them to have a very limited range. In fact, alpha particles can typically travel only a few centimeters in air and are stopped by materials such as paper or skin.

In contrast, beta particles, which are electrons or positrons, have a longer range and can penetrate materials more effectively than alpha particles. Gamma particles, being electromagnetic radiation, can penetrate much further, while neutrons, though neutral, can also traverse significant distances depending on the material they encounter.

Thus, the attributes of losing energy with each ionization, having a short range, and being unable to penetrate a sheet of paper make alpha particles the correct answer in this context.