Things that don’t change
Question 10S: Short Answer		

Checking on conserved quantities 
Try these questions, which require you to notice quantities that are conserved. 

Change, and no change 
Here is the equation for the reaction in which a neutron decays to a proton p, an electron e and an antineutrino : 

1.	How does the equation show that the total number of nucleons remains the same?

 
2.	How does the equation show that the total electric charge remains the same?

 
3.	Which symbols show that the electron and antineutrino are not nucleons, but leptons with zero nucleon number?

 
4.	An electron is a lepton. An antineutrino is an antilepton. Explain how in this reaction the lepton number is conserved, even though it creates two leptons.

 
Here is the equation for an electron interacting with a proton to produce a neutron and a neutrino: 

5.	How does the equation show that the total number of nucleons remains the same?

 
6.	How does the equation show that the total electric charge remains the same?

 
7.	How does the equation show that the total lepton number remains the same? Why is this neutrino not an antineutrino?

 

The stable iron nucleus is . ‘Lightweight’ iron  decays emitting a positron and a neutrino. ‘Heavyweight’ iron  decays emitting an electron and an antineutrino. Here are the reactions: 

8.	In the first equation, what values show that the nucleon number stays the same?

 
9.	In the second equation, what values show that the nucleon number stays the same?

 
10.	How can you see from the first equation that charge is conserved?

 
11.	How can you see from the second equation that charge is conserved?

 
12.	In the first equation, the positive electron (positron) is an antilepton. How does the equation show that total lepton number is unchanged even though two are produced?

 
13.	In the second equation, why is an antineutrino emitted?

 
14.	In both equations, how does the reaction change the chemical element involved?