Verlag des Forschungszentrums Jülich
JUEL-3701
Nesaraja, Caroline Delini
Excitation funcitons and isomer ratios of fast neutron induced reactions on zinc, gallium and germanium
203 S., 1999
Excitation functions of fast neutron induced reactions are of considerable
significance in testing nuclear reaction models. Of special interest are studies
of the (n,p),(n,a) and (n,2n) reactions on some isotopes of Ge (70, 72, 73, 74
Ge), Ga (69, 71Ga) and Zn (67,68,70Zn). Neutrons in the energy
range of 6 to 12 MeV were produced via the D-D reaction on D2 gas target
at the compact cyclotron CV28 at Jülich, Germany. Use was made of the activation
technique in combination with HPGe detector [gamma]- ray spectrometry. In a few cases
low-level [beta]- counting was also applied and occasionally radiochemical separations
were performed. In this work, the following reactions; 70Ge(n,p)70Ga,
72Ge(n,[alpha]) 69m,gZn, 74Ge(n,p)74gGa,
74Ge(n,[alpha])71m,gZn, 69Ga(n,p) 69m,gZn,
71Ga(n,p) 71m,gZn, 71Ga(n,2n) 70Ga,
67Zn(n,p) 67Cu and 70Zn(n,2n)69gZn
were investigated in the neutron energy range of 6 to 12 MeV. Prior to this work
almost no data existed in this energy range. The measurements provided substantial
new information on the investigated process. Measurements were also done on the
reactions of 73Ge(n,p) 73Ga, 68Zn(n,[alpha])
65Ni and 70Zn(n,2n) 69mZn where some
information existed. Theoretical model calculations using the STAPRE code
employing the Hauser Feshbach and the exciton model formalism were
undertaken to describe the cross sections of all these reactions. In most
of the cases, the calculated values fit fairly well with the experimental
results and it is seen that the calculation is strongly influenced by the
level structure of the product. Attempts were made to adjust the input
parameters within the limited error to achieve a degree of agreement between
the experimental and calculated cross section values. Special emphasis was
made on the isomeric cross section ratio namely the isomeric pair
69m,gZn and 71m,gZn. The isomeric cross section ratios
show increasing trends which indicate that the yields of the high spin isomers
increase with the increasing incident neutron energies. The ratio of the
69m,gZn isomer pair was studied in three different reaction
channels (n,[alpha]), (n,p) and (n,2n) reactions and the (n,p) and (n,[alpha])
reactions in the 71m,gZn isomer ratio. In both cases the population
of the high spin isomer is higher in the (n,p) than in the (n,[alpha]) processes.
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