Discrepancy with experimental value for production cross section of Zn 63 and Zn 65 due to nat Cu (p,n) reaction

Dear experts,

I am trying to reproduce the experimental total cross section for production of Zn 63 and Zn 65 due to p,n reaction on nat Cu target.

Simulation result:

for proton energy 4.32 MeV, sigma (Zn63): 45.82 mb and sigma (Zn 65): 49.595 mb
for proton energy 4.63 MeV, sigma (Zn63): 75.62 mb and sigma (Zn 65): 70.43 mb

The table II in the attached pdf shows large differences in sigma (Zn63) and sigma (Zn 65) for these above energies.

I am attaching the input file for your reference as well.

p_on_NatCu_4.63MeV.inp (5.8 KB)

Cu(p,n)_PR_1974.pdf (917.1 KB)

Is it missing any reaction channel?



The reaction channel is just (the indicated) one.

The point is that the experimental cross sections are (naturally) given on 63Cu and 65Cu, respectively, and not natural copper (despite the fact that natural copper was actually used). This means that you should more conveniently run two separate simulations, with pure isotopic composition of 63Cu and 65Cu, respectively.

This way, you should rather find about 65 mb (63Zn) and 160 mb (65Zn) at 4.32 MeV and 110 mb (63Zn) and 230 mb (65Zn) at 4.63 MeV. The discrepancy with the reported measurements can be easily understood looking at the huge gradient displayed by the excitation functions in Figs. 2 and 3 up to about 6 MeV.


Thank you @ceruttif for the detailed explanation.



Dear @ceruttif ,

  1. I gave a run with pure Cu 63 and I got 81.55 mb (63 Zn) for 4.32 MeV; and 95.63 mb for 4.63 MeV. The statistical error is below 1%. Then is there any reason for getting slightly different value than yours ?

Similarly I am getting different values for pure Cu 65

p_on_Cu65_4.63MeV.inp (5.4 KB)

p_on_Cu63_4.63MeV.inp (5.4 KB)

  1. I also tested at other energies, but the simulated results are much different from the quoted experimental value:

At 6.16 MeV, prod cross section for Zn 63: 48.114 mb (simulated), experiment: 205 mb
At 7.23 MeV, prod cross section for Zn 63: 72.901 mb (simulated), experiment: 262 mb


At 6.16 MeV, prod cross section for Zn 65: 226.157 mb (simulated), experiment: 422 mb
At 7.23 MeV, prod cross section for Zn 65: 272.710 mb (simulated), experiment: 492 mb

Can you please let me know if I am making any mistake while calculating total production cross section from the output?


The problem is a miscommunication glitch between Flair and FLUKA, triggered by the use of AIR as alternate material for ionisation processes and affecting your material selection in the USRYIELD card, which turns out to be AIR instead of single isotope copper. You can realize this by looking at the output file, where the material index retained in the last field of the USRYIELD card actually corresponds to the air one (as in the material list). As temporary solution before dedicated Flair fixing, please move the AIR definition before the copper definition.

For 65Cu(p,n)65Zn, FLUKA gives 450 mb (vs 422 mb) at 6.16 MeV and 550 mb (vs 492 mb) at 7.23 MeV.
For 63Cu(p,n)63Zn, 92 mb and 142 mb, respectively. Here the energy gradient looks more pronounced and the discrepancy lowers below 30% above 9 MeV.

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