I worked on a research project at Lawrence Berkeley National Lab to develop ceramic scintillators for medical and security applications. I synthesized barium-based ceramic samples doped with elements like europium, measured their performance through techniques like X-ray diffraction and luminescence, and analyzed the results. The most promising sample was lanthanum barium chloride doped with 5% europium, which showed high transparency and light output. Further experiments aim to optimize europium concentration to improve scintillator characteristics.

1. Dear Professor/Dean Majda,
I am pleased to share with you my results from this semester as I enrolled in Chem196 this Fall
2014. My semester’s research at Lawrence Berkeley National Lab has been a continuation of my
research from when I started in April. I joined the Scintillator Development Group with the goal
of discovering how ceramic scintillators detect radiation for medical device applications and also
homeland security purposes. I had the honor and privilege of working with my supervisor, Dr.
Gascon, as we experimented with a variety of ceramic samples, which are more durable and
much cheaper to process than single crystals. My responsibilities for the barium-based
scintillators as transparent ceramics project entailed synthesis, characterization, and analysis

2. Synthesis
I was in charge of measuring accurate amounts of pure compounds, such as BaCl2,
BaBr2, EuCl2, etc., inside an Argon filled glove box and inputting data into an Elog network
system. After filling a set of three carbon crucibles containing barium chloride beads combined
with other pure dopant powders, they were ready for sintering. I then loaded this set of
hygroscopic raw materials from a sealed tube in order to minimize exposure to air, preventing
oxygen contamination, into a furnace. About five to six days later, the solid state physics of
ceramic processing is complete as the materials were melted to temperatures above 900 degrees
Centigrade (depending on the compounds melting temperature) and slowly cooled down to room
temperature with annealing steps in between. After removing the samples from the furnace, I
recorded the weights and appearance by taking pictures as you can see in Figure 1 (Appendix A).
Now my ceramic samples are ready to be characterized and analyzed..
Characterization/Analysis
There are many ways to measure the performance of a scintillator, but the most
fundamental of characterizing any material is X-ray Diffraction (XRD). So next, I prepared XRD
slides as well as cuvette holders inside a glove-box. Results show that the structure of BaCl2 is
orthorhombic, whereas BaLaCl2 and BaCeCl2 are cubic. So I deduced from figure 2 that a cubic
structure can be achieved at room temperature by using elements such as Cerium and Lanthanum
to stabilize the cubic phase of BaCl2, as you can visualize in the hypothetical representation in
figure 3 (Appendix A). Hypothetical, meaning ceramics are not perfectly symmetric as in the
schematic, since there are many defects and grain boundaries within itself. It is not uncommon
for cubic structures to be more transparent than non-cubic. So there are a variety of ways to
measure transparency, however the instrument that was available for use at LBNL, called
Filmetrics, measured both reflection and transparency simultaneously.
But first, the samples must undergo polishing and lapping up until 0.9 µm powders are
used to decrease the thickness to about 1 mm. This process normally takes up to several hours
per sample and with experience I developed methods to shorten my time polishing in a fume
hood; nonetheless polishing and lapping are very important steps, since the performance of a
scintillator improves with higher transparencies. From figure 4, a comparison of the different
grits and lapping powders shows that the finer powders result in higher transparency of the
sample (Appendix A). And from figure 5, the more cubic structures show higher transparency
(Appendix A). Also note that the temperature profile from sintering has an effect on how
transparent the sample becomes. From figure 5, the samples with annealing steps, where holding
the temperature for a fixed amount of time (approximately three to six hours) as it cools slowly
down to room temperature, increases its transparency. So a scintillator’s overall performance
improves with higher transparency, because it is more efficient at converting gamma rays into
visible photons.
To measure the light output of a ceramic, I used a photomulitiplier tube (PMT) very
similar to the schematic in figure 6 (Appendix A). I place my samples onto the photocathode
window using optical grease and covered it with white teflon tape. The type of radiation source
used for this project is Cs-137. The gamma rays energize the crystal and the pulsed height
measurement (PHM) in figure 7 shows the amount of light output when converting the channel
number to ph/MeV. Another quality that can be extracted from PHM is energy resolution (ER) or
the peak height vs width ratio. So the shallower and wider the peak, the poorer the ER is. A
ceramic that emits the same light intensity consistently will have a sharp peak and higher ER,

3. which is a very high performing and desirable ceramic, such as LaBaCl2 (5%) shown in figure 7.
We have to be cautious when measuring PHM since there may or may not be quantum
efficiencies effecting the measurement of the light output. For instance, the light’s properties
being emitted from a scintillator could be in a much higher or lower frequency (shorter or longer
wavelength) regime than what the PMT can actually measure. More specifically LBNL’s PHT
had the ability to measure light in the 300-700 nm range or visible light spectrum, hence
avoiding quantum inefficiencies whenever my scintillator sample emits light within the PMT
operating range.
So lastly, to make sure that I am indeed operating within the visible light spectrum, I
measured the nature of the light emitted using X-ray excited optical luminescence. As seen in the
top-left of Fig 8 there are two main emission bands for BaCl2, one band around 300 nm and the
other around 400 nm (Appendix A). The 400 nm is related to extrinsic impurities. In the top right
portion of fig 8, relative intensities vary significantly for my samples and these variations are tied
to differences in the temperature profile, crucible size, Argon flow through the furnace, etc
(Appendix A). The emission also depends on the compound, as shown in the bottom-left of fig 8.
BaBrCl and LaBaCl2 show the emission of the 5d-4f transition of Europium centered at 430 nm
while the CeBaCl2 seems shifted to lower wavelengths due to the presence of activated Cerium.
When co-doped to improve the strength of my ceramics I also observed a shift to longer
wavelengths for Rb co-doping and a decrease in the band at 560 nm directly related to Oxygen
contamination.
Conclusion:
The objective of my research is to develop ceramic scintillators that detect radiation
mainly for medical device applications and also for homeland security purposes. Ba-based
ceramics have a number of advantages over more traditional scintillators: they have a lower cost
of fabrication, are less hygroscopic than the commonly used LaBr3:Ce or SrI2:Eu single crystals,
and are easier to handle. Moreover, Barium has the highest detection efficiency of all known
scintillators and is an abundant, inexpensive element, which makes it a suitable candidate for
large scale production of scintillator materials. The most challenging part in this entire project is
that halide ceramics are difficult to produce. With only a select few pieces of literature involving
halide ceramics, my research is cutting edge science.
To summarize the results, if the sample is not transparent, then light is scattered within
the sample when energized by gamma radiation consequently the collected data is distorted
where no conclusion can be drawn. So I strive to make ceramics transparent as a top priority.
Cubic structured materials are generally more transparent than non-cubic structures. The
temperature profile of the annealed samples show higher strength and higher transparency.
Activated Europium 2+ doping serves a trap for electron-hole pairs. The light emitted have
different light output intensities depending on the concentration of the activator within the
ceramic. Throughout all of my experiments, LaBaCl2 doped with Eu has proven to show the best
overall characteristics. So after producing 58 samples at LBNL, Dr. Gascon and I are
experimenting with different Eu concentrations trying to optimize light output combined with
strength properties.

4. Appendix A
Figure 1: Picture of the holder including a set of samples inside the crucibles
(Carbon crucibles in middle and left. Glass crucible on right)
Figure 2: Left: X-ray diffraction patterns for BaCl2 and on the Right: BaLaCl2 (5% Eu). The
first pattern shows an orthorhombic structure and the second shows the stabilized cubic structure
using Lanthanum.
Figure 3: Main crystal structures of the samples tested in this project. Cubic structure of Barium
Chloride is on the left and orthorhombic structure on the right.

5. Figure 4: Transmission spectra obtained for BaCl2 as function of grit size for polishing and
powder size used for lapping.
Figure 5: Left: Transmission spectra obtained for LaBaCl2 (5%) as function of structure.
Right: Transmission spectra obtained for BaBrCl as function of annealing steps

6. Figure 6: A schematic of the basic components of a photomultiplier tube (PMT)
Figure 7: Pulsed Height Measurement (PHM) for LaBaCl2 (5% Eu). I measured an ER of about
9% and a channel number of 1474 that is equivalent to about 10,800-10,900 ph/MeV

7. Fig 8: X-Ray Luminescence (XRL)
Top Left: X-ray luminescence for several samples of BaCl2 Top-Right: Crucible size vs Argon
flow
Bottom-Left: BaBrCl vs CeBaCl2 vs LaBaCl2 Bottom-Right: BaBrCl co-doped with Eu and K,
Rb, Cs and Na