Introduction:
Boron neutron capture therapy (BNCT) is a type of radiation therapy used for treating cancer. It involves the use of a boron compound that selectively accumulates in tumor cells and then irradiating the tumor with neutrons. The irradiated boron nuclei undergo a nuclear reaction, resulting in the release of high-energy particles that can damage the tumor cells.

Explanation:
The initial boron isotope used in boron neutron capture therapy is 10B. When the tumor is exposed to a neutron beam, the 10B nuclei capture a thermal neutron, resulting in the formation of an excited state of 11B (boron-11).

The 11B nucleus, in its excited state, undergoes a process called neutron capture, where it absorbs the neutron and forms an unstable compound nucleus. This compound nucleus then undergoes a process called nuclear fission, resulting in the release of high-energy particles.

The particle generated after neutron capture is a 7Li (lithium-7) particle. This particle is released along with an alpha particle (α) and a gamma ray (γ). The high-energy particles, particularly the alpha particle, are highly ionizing and can cause significant damage to the tumor cells.

The release of the alpha particle and gamma ray occurs within the tumor, leading to localized radiation damage and sparing the surrounding healthy tissues from significant radiation exposure.

The alpha particle and gamma ray released during the boron neutron capture reaction have a short range and deposit most of their energy within a few cell diameters, making BNCT an effective treatment for localized tumors.

Conclusion:
In boron neutron capture therapy, the initial boron isotope used is 10B, and the particle generated after neutron capture is a 7Li particle. This therapy exploits the ability of boron-10 to capture neutrons and release high-energy particles, which selectively damage tumor cells while sparing surrounding healthy tissues.