Characterization of photons produced in solid films of organic molecules by the impact of Cf252-fission fragments

M. Wehofsky
D. Martin
Karsten Koch   Phone: +49-(0)441-798-3494   Fax: +49-(0)441-798-3201
Wilfried Tuszynski   Phone: +49-(0)441-798-3203   Fax: +49-(0)441-798-3201
Eberhard R. Hilf   Phone: +49-(0)441-798-2543   Fax: +49-(0)441-798-3201


Date: 1997

Article: published in Nuclear Instruments and Methods in Physics Research NIM B 125, pp. 71-76 (1997)

Experiments on photon production in solid films of organic molecules by the
impact of Cf252-fission fragments are presented. The samples were mainly 
prepared with Coronene or POPOP sprayed onto an aluminized polyester foil using
the nebulizer spray technique. It is demonstrated by scanning electron
micrographs that this technique is a suitable method to prepare homogeneous
solid films of organic compounds by producing layers of microcrystals. Time
profiles and photon spectra have been determined by bombarding these samples
with Cf252-fission fragments as well as, for comparision, by exciting with
light. The results give evidence that the photons induced by fission fragment
bombardment originate from molecular fluorescence in the solid sample.      
Approximately 500 photons per fission fragment have been produced within a
100 ns time window in about 2*10E-9 m thick POPOP samples. The photon yield has
been observed to increase linearly with the thickness of the sample up to about
16*10E-9 m. Only very few photons per fission fragment has been  obtained with
Rhodamine6G samples and the same low photon yield has been observed under the
bombardment with 2 keV electrons. These results probably indicate that the
excitation of molecular species by energetic delta-electrons is the necessary
step in the process of photon production by fast heavy ions. Photons which have
been additionally produced when extracting positive ions  come also from
molecular fluorescence in the samples. But this fluorescence is excited by
electrons which originate from impacts of fission fragments on components of
the acceleration system and which are accelerated back to the sample.

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