Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A pot of gold at the end of the cosmic "raynbow"?   We critically review the common belief that ultrahigh energy cosmic rays are
protons or atomic nuclei with masses not exceeding that of iron. We find that
heavier nuclei are indeed possible, and discuss possible sources and
acceleration mechanisms for such primaries. We also show detailed simulations
of extensive air showers produced by ``superheavy'' nuclei, and discuss
prospects for their detection in future experiments.

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The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
28
The categories of this paper are: alg-geom
7
The categories of this paper are: hep-th
8
The categories of this paper are: hep-ex
3
The categories of this paper are: physics
4
The categories of this paper are: cond-mat
1
The categories of this paper are: cs
19
The categories of this paper are: eess
14
The categories of this paper are: math-ph
35
The categories of this paper are: mtrl-th
24
The categories of this paper are: dg-ga
27
The categories of this paper are: comp-gas
11
The categories of this paper are: hep-lat
13
The categories of this paper are: quant-ph