-particles on the
angular
correlation in Mass-8
M. Beck, L. De Braeckeleer and K. B. Swartz
We developed a Monte Carlo program for the beta-decay part of
the Mass-8 experiment (see Section 1.1) in order to investigate
the effect of a threshold for detecting the
-particles. The threshold
arises from the finite thickness of the windows of the
-counters
and the thickness of the catcher foil. The simulated
angular
correlation used the allowed GT form for the
angular correlation
of 
and includes the kinematic boost by the recoiling 8Be. Other
weak form-factors were included by a generic a2-coefficient of
a2=k · E
with E
the kinetic -energy and
K=0.0033/MeV for 8Li.1
The thicknesses of the windows and catcher foils were approximately
200 µg/cm2 and
100 µg/cm2
for the 8Li measurements and
140 µg/cm2
and 90 µg/cm2
for the 8Be measurements.
These correspond to a total energy loss of 0.74 MeV and 0.6 MeV
for an -particle that passes
through the window and the entire
catcher foil.
In Fig. 1.3-1 the result of the simulation together with measured
data (see Ref. 1) for the kinematic coefficient a1 is displayed
for
8Li for different energy thresholds. The two data sets correspond
to two different
-counters.
It can be clearly seen that for higher
-energies the simulated
a1 with energy threshold deviates systematically
from the a1 without energy threshold. This deviation seen in the
simulation corresponds to the measured deviation of
the a1 coefficient
and lies in between the deviation of the two detectors. The reason
for the difference of the a1 coefficients for the
two -counters
is not yet understood (see Ref. 1).
In the future we plan to include a realistic
-energy loss computation
in the catcher foil and the window instead of applying an energy
cut.
Fig. 1.3-1. Measured and simulated
a1-coefficients.
u -
n is the a1
extracted from the upstream
-counter,
d -
n
for the downstream -counter.
The simulation shows a systematic deviation of the a1 depending
on the -energy threshold in the data.
angular correlation
in the decay of 8Li,
Ph.D. Thesis, University of Washington (1996).