Proceedings of the international conference on nuclear physics, August 24-30, 1980, Berkeley, California. Volume 1. Abstracts. [Berkeley, California, August 24-30, 1980 (abstracts only)] Page: 456 of 975

                                
MEASUREMENT OF PARTICLE    SPECTRA OF a INDUCED NON-EQUILIBRIUM REACTIONS FOR
206-212po
B. Bochev, R.M. Lieder, J.P. Didelezt, T. Kutsarova, H. Beuscher, D.R. Haenni,
T. Morek, M. MUller-Veggian, A. Neskakis, and C. Mayer-Bbricke
Institute fur Kernphysik
Kernforschungsanlage Julich
D-5170 JUlich, W. Germany
In order to study the reaction mechanism of the 209Bi(a,charged particle
xny) reactions at incident energies of 45 MeV and 75 MeV spectra of p, d, and
t have been investigated. The charged particles were measured in coincidence
with y rays characteristic of the resultant Po nuclei. The a beams were provi-
ded by JULIC. The coincidences were measured by placing the particle detector
telescope at angles of 450, 900 and 1350.
As result of the 45-MeV experiment at 450 three spectra of protons coin-
cident with y rays in 2 ipo(41), 21Po(#2) and 212Po($3) are shown in fig. 1.
The maxima of the spectra are at 15.0 MeV, 22.5 MeV and 26.5 MeV for the
(a,p2n), (u,pn) and (a,p) channels, respectively.
The width of the respective peaks are 7.5 MeV, 6.7 MeV  350
and 3.9 MeV. The low energy tails seen in the spec-
tra 4 2 and 4 3 are most probably not real but due
to incomplete background subtraction. This notion       175   ,
results from an analysis in which gates have been
set on 2.5-MeV portions of the proton spectrum in
order to produce the corresponding y spectra. The y   n 0            -
lines resulting from the (a,p) and (a,pn) reactions  ~                     2
are in the y spectra corresponding to the maxima of  z 35
the respective p peaks at least a factor of 10 more  =V
intense then in the y spectra corresponding to proton O
energies outside the peak region. Similar spectra as c a   .
in fig. 1 have been obtained for d and t. The angu-     70                 3
lar distributions for all channels in the 45-MeV ex-
periment are shown in fig. 2. It can be seen that       35
the (a,p), (a,d) and (a,t) reactions are strongly       35      L
forward peaked. The angular distributions are less
pronounced for reactions in which one or two additi-     0
onal neutrons are emitted. For 75 MeV incident ener-         10   20  30   4
gy a similar decomposition of the inclusive p spec-
tra as in case of 45 MeV has been obtained. The ma-             Ep (MeV)
xima (widths) of the proton peaks are 20.5 MeV                 F    1
(13.0 MeV), 28.6 MeV (12.0 MeV), 38.9 MeV (10.0 MeV),          F    1
48.2 MeV (6.0 MeV) and 55.0 MeV (4.0 MeV) for the
(a,p4n), (a,p3n), (a,p2n), (a,pn) and (a,p) reac-       10 ar
tions, respectively.                                      Io.d2n -.
The energies of the proton peaks for the va-         Ad"
rious (a,pxn) channels can be understood assuming     r   atn
that the protons populate directly the entry lines    4   a
of the respective final nuclei. This implies that     E I ao-d
the neutrons carry along only a small kinetic ener-   -
gy. It may be concluded, therefore, that the protons 3
are emitted at first after the formation of the fused " a'
system and that the neutrons are emitted subsequent-
ly.                                                      o'    &s'  o    1s
*Institut de Physique Nucleaire, F-91406 Orsay,                  'ab
France                                                        Fig. 2

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