Jesse cuts a circular paper disk of radius $12$ along two radii to form two sectors, the smaller having a central angle of $120$ degrees. He makes two circular cones, using each sector to form the lateral surface of a cone. What is the ratio of the volume of the smaller cone to that of the larger?

$ \textbf{(A)}\ \frac{1}{8} \qquad\textbf{(B)}\ \frac{1}{4} \qquad\textbf{(C)}\ \frac{\sqrt{10}}{10} \qquad\textbf{(D)}\ \frac{\sqrt{5}}{6} \qquad\textbf{(E)}\ \frac{\sqrt{10}}{5} $
1. **Determine the arc lengths of the sectors:**
   - The circumference of the original circle is given by:
     \[
     2\pi \times 12 = 24\pi
     \]
   - The smaller sector has a central angle of \(120^\circ\), which is \(\frac{120}{360} = \frac{1}{3}\) of the full circle. Therefore, the arc length of the smaller sector is:
     \[
     \frac{1}{3} \times 24\pi = 8\pi
     \]
   - The larger sector has a central angle of \(240^\circ\), which is \(\frac{240}{360} = \frac{2}{3}\) of the full circle. Therefore, the arc length of the larger sector is:
     \[
     \frac{2}{3} \times 24\pi = 16\pi
     \]

2. **Form the cones:**
   - The arc length of each sector becomes the circumference of the base of the corresponding cone.
   - For the smaller sector:
     \[
     2\pi r_1 = 8\pi \implies r_1 = 4
     \]
   - For the larger sector:
     \[
     2\pi r_2 = 16\pi \implies r_2 = 8
     \]

3. **Determine the slant heights:**
   - Both sectors have a slant height equal to the radius of the original circle, which is \(12\).

4. **Calculate the heights of the cones:**
   - For the smaller cone:
     \[
     l_1 = 12, \quad r_1 = 4
     \]
     Using the Pythagorean theorem in the right triangle formed by the radius, height, and slant height:
     \[
     h_1 = \sqrt{l_1^2 - r_1^2} = \sqrt{12^2 - 4^2} = \sqrt{144 - 16} = \sqrt{128} = 8\sqrt{2}
     \]
   - For the larger cone:
     \[
     l_2 = 12, \quad r_2 = 8
     \]
     Using the Pythagorean theorem:
     \[
     h_2 = \sqrt{l_2^2 - r_2^2} = \sqrt{12^2 - 8^2} = \sqrt{144 - 64} = \sqrt{80} = 4\sqrt{5}
     \]

5. **Calculate the volumes of the cones:**
   - Volume of the smaller cone:
     \[
     V_1 = \frac{1}{3} \pi r_1^2 h_1 = \frac{1}{3} \pi (4^2) (8\sqrt{2}) = \frac{1}{3} \pi (16) (8\sqrt{2}) = \frac{128\sqrt{2}}{3} \pi
     \]
   - Volume of the larger cone:
     \[
     V_2 = \frac{1}{3} \pi r_2^2 h_2 = \frac{1}{3} \pi (8^2) (4\sqrt{5}) = \frac{1}{3} \pi (64) (4\sqrt{5}) = \frac{256\sqrt{5}}{3} \pi
     \]

6. **Determine the ratio of the volumes:**
   \[
   \frac{V_1}{V_2} = \frac{\frac{128\sqrt{2}}{3} \pi}{\frac{256\sqrt{5}}{3} \pi} = \frac{128\sqrt{2}}{256\sqrt{5}} = \frac{\sqrt{2}}{2\sqrt{5}} = \frac{\sqrt{2}}{2\sqrt{5}} \times \frac{\sqrt{5}}{\sqrt{5}} = \frac{\sqrt{10}}{10}
   \]

The final answer is \(\boxed{\frac{\sqrt{10}}{10}}\)