San José State University 

appletmagic.com Thayer Watkins Silicon Valley & Tornado Alley USA 

in Terms of the Quarks They Contain 
A proton consists of two up quarks and one down quark. A neutron, on the other hand, consists of one up quark and two down quarks. If n and p are the numbers of neutrons and protons, respectively, then the numbers of up quarks, #u, and down quarks, #d, are given by
The 2931 nuclides can be tabulated in terms of their values of #u and #d. Incremental binding energies can be computed but this means something different for quarks than for nucleons. A single down quark cannot be added to a nuclide.
The Set of Nuclides and their Characteristics which have 80 up Quarks  

Nuclide  Protons  Neutrons  Binding Energy  up Quarks  down Quarks 
52Ni  28  24  420.46  80  76 
53Co  27  26  449.296  80  79 
54Fe  26  28  471.7587  80  82 
55Mn  25  30  482.0703  80  85 
56Cr  24  32  488.506  80  88 
57V  23  34  486.45  80  91 
58Ti  22  36  482.5  80  94 
59Sc  21  38  470.9  80  97 
In order to increase #d but keep #u constant it is necessary decrease the number of protons by one and increase the number of neutrons by two. The decrease in the number of protons by one reduces the number of up quarks by two; the increase in the number of neutrons brings the number of up quarks back up by two. The decrease in the number of protons by one decreases the number of down quarks by one but the increase of two neutrons adds four down quarks for a net increase of three.
An incremental binding energy of a triplet of down quarks can be computed. Here is a graph of the incremental binding energy of a triplet of down quarks.
It is downward sloping indicating the interaction of one thriplet of down quards with the previous one is a repulsion. The second differences in binding energy with respect to the number of down quarks are shown below.
The interaction of a triplet of down quarks with the previous triplet is 6.7393 MeV or, since the interaction of triplets involves 9 interactions, 0.7488 MeV per down quark. The negativity of the value indicates that it is an interaction involving repelling.
The data and graphs for the incremental binding energies of up quarks are shown below.
The Set of Nuclides and their Characteristics which have 80 down Quarks  

Nuclide  Protons  Neutrons  Binding Energy  up Quarks  down Quarks  Incremental Binding Energy  Second Difference 
48S  16  32  362.8  64  80  
49Ar  18  31  398  67  80  35.2  
50Ca  20  30  427.491  70  80  29.491  5.709 
51Ti  22  29  444.1525  73  80  16.6615  12.8295 
52Cr  24  28  456.3451  76  80  12.1926  4.4689 
53Fe  26  27  458.3802  79  80  2.0351  10.1575 
54Ni  28  26  453.15  82  80  5.2302  7.2653 
55Zn  30  25  435.38  85  80  17.77  12.5398 
The interaction of a triplet of up quarks with the previous triplet is 8.8283 MeV or, since the interaction of tiplets involves 9 interactions, 0.9809 MeV per up quark. Again the negativity of the value indicates that it is an interaction involving repelling.
The increment with respect to one particle of the increments with respect to the other particle is called the cross difference. The binding energy to the interaction of the last particle of one type with the last particle of the other type is equal to the cross difference with respect to the numbers of the two particles. The cross difference is also the slope of the relationship between the incremental binding energy with respect to the numbers of one particle plotted versus the number of particles of the other type. Here are the data for establishing some of the cross differences.
The Incremental Binding Energies of Triplets of Down Quarks as a Function of the Numbers of Up and Down Quarks in the Nuclide 


Number of Up Quarks  
Number of Down Quarks  74  77  80  83  86 
73  28.357  
76  21.4971  31.874  
79  10.7967  19.3371  28.836  
82  6.1202  13.4332  22.4627  32.487  
85  2.661  3.4597  10.3116  19.5585  30.382 
88  5.5  0.776  6.4357  12.9944  21.7718 
91  14.2  7.52  2.056  4.5801  10.8543 
94  9.5  3.95  0.8  8.0369  
97  11.6  5.88  0.845  
100  7.5  1.7  
103  10.6 
Here is a graph of such a relationship for nuclides containing 85 down quarks.
The positive slope indicates that a triplet of up quarks are attracted to a triplet of down quarks. The amount for the graph shown is 8.26075 MeV. Since there are nine interactions of quarks involved in the interactions of triplets the amount per quark interaction is 0.9179 MeV.
First the above estimates of the interaction binding energies can be put together:
The Binding Energies Involved in the Various Interactions of Up and Down Quarks 


Interaction  Binding Energies MeV 
uu  −0.9809 
dd  −0.7488 
ud  +0.9179 
Now consider the binding energy for the interaction of two protons. This is the interaction of the two up quarks and one down quark in one proton with the two up quarks and one down quark in the other proton. First consider the interaction of one up quark with the quarks in the other proton. This 2uu+ud which equals −1.0439 MeV. This doubled for the two up quarks of the first proton is −2.0878 MeV. The interaction of the down quard of the first proton with the quarks of the second proton is 2ud+dd or +1.087 MeV. Combined the interaction total −1.0008 MeV.
For the binding energy of the interaction of two neutrons the separate components are as follows. The up quark of the first neutron with the quarks of the second neutron has an interaction of 2ud+uu, which totals +0.8549 MeV. One down quark in the first neutron has interactions with the quarks of the second neutron of ud+2dd, which amounts to −0.5797 MeV. Doubled this is −1.1594 MeV and this combined with the interaction of the up quark is −0.3045 MeV.
The interaction of a proton with a neutron involves the interactions of one up quark with the quarks of neutron. These are 2ud+uu, or +0.8549 MeV, which doubled is +1.7098 MeV. The interaction of the down quark of the proton with the quarks of the neutron is −0.5797 MeV. The total is then +1.1301 MeV. Notably the interaction of the unlike nucleons is opposite in sign to those of the interaction of like nucleons.
If the nucleonic charge of a proton is taken to be unity and that of a neutron is denoted as q then the interaction of two neutrons is proportional to q². Then the ratio of the interaction of neutrons to the interaction of protons should be equal to q². The square root of the ratio (0.3045)/(1.0008) is ±0.5516. The sign is established as () by the difference in the signs of the interaction of the unlike particles to those of the like particle. This differs significantly from the value of −2/3 found by other methods but it is definitely of the right order of magnitude .
There was an alternation in the previous displays of the incremental binding energies between negative slopes and less negative slopes. For nuclides with more quarks the less negative slope could be a small positive slope, as shown in the case below.
Such anomalies do not alter the fact that generally the relationships are downward sloping, indicating that the force between two like quarks is repulsion.
The data on incremental binding energies confirm that like quarks repel each other and unlike quarks are attracted to each other.
HOME PAGE OF Thayer Watkins 