This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440

Bonser, D.

Fatyga, M.

Kwiatkowski, K.

Rose, S.

Sobotka, L.G.

Stith, K.

Viola, V.E.

Wilson, W.

Woo, L.W.

English

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MASS DISTRIBUTIONS OF INTERMEDIATE-MASS FRAGMENTS IN LIGHT-ION-INDUCED REACTIONS 
K. Kwiatkowski, M. ~aty~at, K. Stith, W. Wilson, L. W. Woo, S.Rose, D. Bonser, and V. E. Viola 
Indiana University Cyclotron Facility, Bloomington, Indiana 47405 
L. G. Sobotka 
Washington University, St. Louis, Missouri 
Discrete nuclide distributions have been measured however, is consistent with values expected on the 
for intermediate-mass fragments produced in the basis of a simple touching-spheres model. Based on 
reaction of 270-MeV 3 ~ e  ions with nat~g and lg7Au earlier studies on this system at 200 MeV, it has been 
targets. Fragments were detected with a time-of-flight argued1 that both equilibrium and non-equilibrium 
telescope consisting of channel-plate fast-timing sources contribute to these yields. Using procedures 
detectors for start and stop signals. Particle Z described in Ref. 1, apparent temperatures have been 
identification was accomplished with a gridded gas derived for the non-equilibrium component as a function 
ionization chamber AE element and a 300 pm silicon of Z. These are plotted in Fig. 2 for both the 200-and 
surface barrier E element. These were backed up by a 270-MeV 3 ~ e  + nat~g data, showing a rather constant 
5 mm lithium-drifted silicon detector for detection of value of kT r 8 MeV for the IMFs. This analysis also 
energetic light ions. gives a value for the source velocity of f3 = 0.75PCN 
In Fig. 1 the energy spectrum for 12c fragments for the equilibrium components and i3 = 3PCN for the 
observed at a laboratory angle of 10 deg is shown. The non-equilibrium fragments. 
fragment energy spectra exhibit a Maxwellian-like In Fig. 3, spectra obtained for Be fragments at 20 
distribution which extends out to energies of 180 MeV. deg. and 160 deg. are compared for nat~g and lg7Au 
The maximum energies correspond to a momentum targets. These data demonstrate the importance of 
approximately 1.6 times that of the incoming beam, or target N/Z ratio (N/Z = 1.34 for Ag and 1.49 for Au) on 
nearly twice the momentum expected for Coulomb 
acceleration. The most probable emission energy, 
a 1 1 rn I I 1 
Figure 2. Apparent temperatures for the 
Figure 1. Energy spectrum observed for 12c fragments non-equilibrium component of IMFs produced in the 
emitted in the reaction of 270-MeV 3 ~ e  ions with naf.~g reaction of 200- (squares) and 270-MeV 3 ~ e  with nat~g 
at 10 deg. in the laboratory system. as a function of fragment atomic number. 
Be Fragments 
w 
w 
m 
V) - 
s 
the observed IMF isotropic ratios. Most evident is the 
change in the 7 ~ e / 9 ~ e  ratio for these two systems. On 
the other hand, the isotopic yields do not seem to 
depend strongly on angle. The energy spectra do, 
however, appear to depend on neutron number, as shown 
in Fig. 4 for 12c, 14c and 16c fragments observed at 20 
deg. with the Au target. These data suggest an 
evolution from Maxwellian to Gaussian with increasing 
neutron number, i.e. an increasingly steep slope is 
observed as a function of mass number. 
t~resent address: Brookhaven National Laboratory, 
Upton, NY 11973. 
1) K. Kwiatkowski et al., Phys. Lett. B171 41 (1986). 
Figure 3. Mass distributions for Be fragments emitted 
at 20 deg. and 160 deg. for 270-MeV 3'~e incident on 
nat~g and Au. 
E#BRrn(rnV) 
Figure 4. Energy spectra for carbon fragments observed at 20 deg. for the reaction of 270-MeV 3 ~ e  and lg7~u. 


Mass Distributions of Intermediate-Mass Fragments in Light-Ion-Induced Reactions

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Mass Distributions of Intermediate-Mass Fragments in Light-Ion-Induced Reactions

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