Answers

1.  Why are neutrons such good projectiles for producing nuclear reactions?

 

     ð  Because they are neutral and they are massive. 

     ð  If you want a particle to hit the nucleus with a lot of energy, a more massive particle is the better choice. 

     ð  A light electron would not be as effective.  

     ð  Using a positively charged projectile like an alpha or a proton means that the projectile will have to overcome the large electrical repulsion from the

          positively charged nucleus. 

     ð  Neutrons can penetrate directly to the nucleus and cause nuclear reactions.

2.  The energy from nuclear fission appears in the form of thermal energy. The thermal energy of what?

      ð  It appears in the kinetic energy of the fission products (daughter nuclei and neutrons). 

     ð  In other words, the fission products are moving very fast (especially the neutrons, due to the conservation of momentum).

 3.  Why would a porous block of uranium be more likely to explode if kept under water rather than in air?

     ð  For a nuclear chain reaction to occur in a block of porous uranium (which would lead to an explosion), the neutrons being emitted by the decays must be

            slowed down.

     ð  If the neutrons are too fast, they will pass through the block of uranium without interacting, effectively prohibiting a chain reaction. 

     ð  Water contains a much higher density of protons and neutrons than does air, and those protons and neutrons  will slow down (moderate) the neutrons,

           enabling them to take part in nuclear reactions. 

     ð  Thus, if water is filling all of the porous cavities, the water will slow the neutrons, allowing them to be captured by other uranium nuclei, and allow the

           chain reaction to continue, which might lead to an explosion.

 4.  Why must the fission process release neutrons if it is to be useful?

      ð  To get nuclei to fission, they must be bombarded by neutrons. 

     ð  This can be done using an external source, but then there is a large input of energy into the system, making it less efficient and so less useful. 

     ð  To make the fission reaction useful, it needs to be self-sustaining. 

     ð  To create such a chain reaction, each time a nuclei captures a neutron and fissions, one or more neutrons must be emitted in order to sustain the process.

 

5.  Why are neutrons released in a fission reaction?

 

     ð  A heavy nucleus decays because it is neutron-rich, especially after neutron capture. 

     ð  With too many neutrons, when compared to protons, the nucleus is unstable and  will fission into two daughter nuclei. 

     ð  These two daughter nuclei would still be neutron-rich and relatively unstable, and so the fission process is always accompanied by the emission of

            neutrons to alleviate this imbalance. 

     ð  Lighter nuclei are more stable with approximately equal numbers of protons and neutrons.

 

6.  Why do gamma particles penetrate matter more easily than beta particles do?

 

     ð  Gamma particles penetrate better than beta particles because they are neutral and have no mass. 

     ð  Thus, gamma particles do not interact with matter as easily or as often as beta particles, allowing them to better penetrate matter.

 

7.  What is the basic difference between fission and fusion?

 

     ð  Fission is the process in which heavier, less-stable nuclei break apart into two or more lighter, more-stable nuclei, which releases particles and energy. 

     ð  Fusion is the process in which lighter, less-stable nuclei combine with each other to create heavier, more-stable nuclei, which releases particles and energy.