Q Value for spontaneous fission and neutron induced fission

In summary, the Q value in units of MeV for each of the following processes is: i) spontaneous fission of 232U92 to 145La57 and 87Br35 is 87.5 MeV ii) neutron induced fission of 232U92 to 146La57 and 87Br35 is 87.5 MeV. Heavy nuclei such as 232U92 do not usually undergo fission because the Q value for fission is usually not large enough to overcome the repulsive forces between the protons in the nucleus.
  • #1
bmarson123
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0

Homework Statement


What is the Q value in units of MeV in each of the following processes?

i) The spontaneous fission of 232U92 to 145La57 and 87Br35

ii) The neutron induced fission of 232U92 to 146La57 and 87Br35

Explain why heavy nuclei such as 232U92 do not usually undergo fission.

[Masses given in atomic mass units are 232U92 232.0372; 145La57 144.9217; 146La57 145.9255; 87Br35 86.9203; n 1.0087]

Attempt

There are loads of equations for different Q values depending on the type of decay it undergoes. I'm not sure which to use.

Also, I think I need to convert the atomic mass units into something else but I'm not entirely sure what?

I basically don't know where to start with it!
 
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  • #2
bmarson123 said:
There are loads of equations for different Q values depending on the type of decay it undergoes. I'm not sure which to use.
Use what is given to you. You call these decays, but are they really that? What is a better name for the process in which a uranium nuclide becomes a lanthanum and a bromine nuclide?
bmarson123 said:
Also, I think I need to convert the atomic mass units into something else but I'm not entirely sure what?
Why convert? Use what is given to you.
bmarson123 said:
I basically don't know where to start with it!
Start by writing an equation for a given process, then make sure it conserves energy.
 

1. What is the Q value for spontaneous fission?

The Q value for spontaneous fission is the difference in energy between the initial nucleus and the two resulting fission fragments. It can be calculated using the equation Q = (M_initial - M_1 - M_2)c^2, where M_initial is the mass of the initial nucleus and M_1 and M_2 are the masses of the fission fragments.

2. How is the Q value for neutron induced fission determined?

The Q value for neutron induced fission is determined in a similar way to spontaneous fission, but with the addition of the energy of the incident neutron. The equation for Q in this case is Q = (M_initial + m_n - M_1 - M_2)c^2, where M_initial is the mass of the initial nucleus, m_n is the mass of the neutron, and M_1 and M_2 are the masses of the fission fragments.

3. What is the significance of the Q value for fission reactions?

The Q value for fission reactions is significant because it determines whether a reaction will be exothermic (releasing energy) or endothermic (requiring energy). A positive Q value indicates an exothermic reaction, while a negative Q value indicates an endothermic reaction.

4. How does the Q value affect the stability of a nucleus?

The Q value is directly related to the stability of a nucleus. If the Q value is high, meaning there is a large difference in energy between the initial nucleus and the fission fragments, the nucleus is more likely to be unstable and undergo fission. On the other hand, a low Q value indicates a more stable nucleus.

5. Can the Q value be used to predict the products of a fission reaction?

Yes, the Q value can be used to predict the products of a fission reaction. Since the Q value is dependent on the masses of the initial nucleus and the fission fragments, it can be used to determine the specific isotopes that will be formed in a fission reaction.

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