**Isotope Used for the Treatment of Brain Tumors and Cancer: Co-60**

The correct answer is option 'D' - Co-60. Cobalt-60 (Co-60) is an isotope used in the treatment of brain tumors and cancer. It is widely used in radiation therapy due to its high energy gamma rays.

**Explanation:**

Cobalt-60 is an artificial radioactive isotope of cobalt. It is produced by bombarding stable cobalt-59 with neutrons in a nuclear reactor. Here's why Co-60 is used in the treatment of brain tumors and cancer:

1. **High Energy Gamma Rays:** Cobalt-60 emits high-energy gamma rays, which are a form of ionizing radiation. These gamma rays can penetrate deep into the body and destroy cancer cells by damaging their DNA.

2. **Targeted Radiation Therapy:** In radiation therapy, Co-60 is used to deliver a precise dose of radiation to the tumor or cancer cells while minimizing damage to surrounding healthy tissues. This is achieved by using specialized equipment, such as a linear accelerator or a gamma knife, to direct the gamma rays towards the tumor site.

3. **Half-Life and Stability:** The half-life of Co-60 is approximately 5.27 years. This long half-life allows for the production and storage of Co-60 in medical facilities. It also ensures a consistent and reliable supply of the isotope for cancer treatment.

4. **Tissue Penetration:** The high-energy gamma rays emitted by Co-60 can penetrate deep into the body, making it suitable for the treatment of brain tumors and cancers located in deep tissues. This ability to penetrate through tissues ensures that the radiation reaches the target area effectively.

5. **Brachytherapy Applications:** Co-60 can also be used in brachytherapy, a type of radiation therapy where radioactive sources are placed directly into or near the tumor. Co-60 brachytherapy sources are commonly used for treating cervical, prostate, and breast cancers.

In summary, Cobalt-60 (Co-60) is widely used in the treatment of brain tumors and cancer due to its high-energy gamma rays, long half-life, tissue penetration capabilities, and its suitability for both external beam radiation therapy and brachytherapy applications.

Cobalt therapy  is the medical use  of gamma rays from the radioisotope cobalt -60 to theat conditions such as cancer. Beginning in the 1950s, cobalt -60 was widely used in external beam radiotherapy (teletherapy) machines, which produced a beam of gamma rays which was directed into the patient's body to kill tumor  tissue.