We have established the primary components that must be included in the scintillating mixture. Qualitative results have convinced us that PPO, POPOP, and a suitable scintillator are needed. POPOP is difficult to dissolve and a derivative may be

1
Developing an Aqueous Scintillator for Neutrino
Detectors Emily Baldwina, Stephen Wiggintona, Mr.
Paul Conrowa, and Professor Kevin McFarlandb
Scintillation occurs when a gamma ray interacts
with a molecule and through a series of steps
produces light. The ultimate goal of this project
is to make a water-based scintillator that can be
produced on a metric ton scale, at a reasonable
price. This scintillator will be used in a
detector in future high-energy particle
experiments. To make a water-based scintillator,
a surfactant is needed to keep hydrophobic
scintillator in solution with water. The
surfactant forms micelles that keep water and
scintillator apart while in solution. Organic
liquid scintillators and a commercial solid
scintillator have produced good preliminary
results. Organic scintillators xylene, toluene,
and 1,2,4 trimethylbenzene were used with PPO and
POPOP in solution. The only water-based solution
produced currently is a gel. The aqueous gel was
made without POPOP and has given encouraging
results. Future efforts will be concentrated on
making better aqueous solutions.
A method was developed to reliably compare
results from one sample to another. The peak
maximum is too broad and noisy to use. Instead,
the channel at half the peak maximum is used.
This channel, along the Compton edge, is effected
by the energy of the gamma source, the voltage of
the across the PMT, and the components of the
scintillating mixture.
POPOP shifts the light that is emitted by PPO,
the primary fluorophore. With POPOP added in
small amounts, the signal dramatically shifts to
a broader spectrum with a higher channel Compton
edge.
Micelles are dynamic molecular assemblies that we
use to solubilize organic scintillator within an
aqueous environment. The surfactant molecules
that make micelles have polar heads that interact
favorably with water. Surfactant molecules have
nonpolar tails that form the middle of a micelle.
The micelle interior is where organic
scintillator is driven and made soluble.

Emily and Stephen at work, taking measurements
with the BETTY Daq.
An early experiment tested the effect of PPO on
the signal. PPO is the primary fluorophore in
our liquid scintillation experiments. With PPO,
there is sn increase in signal and the Compton
edge is shifted to the right.
We have established the primary components that
must be included in the scintillating mixture.
Qualitative results have convinced us that PPO,
POPOP, and a suitable scintillator are needed.
POPOP is difficult to dissolve and a derivative
may be substituted. Surfactants have been used
to solubilize the organic scintillator molecules
in a water-based gel. Future work will focus on
development of a high performing aqueous liquid
or gel that will scintillate and remain stable
for weeks at a time.
a
A transparent gel made of 50 water, 25
surfactant, and 25 scintillator, by volume, was
studied. The gel gives a weak signal, compared
to both toluene and the solid standard. However,
we are in the early phases of making an aqueous
scintillator. Better performance is a goal of
the future.