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G. Berkin. Lead free X-ray s hielding glass. International Journal of Academic Res earch Part A; 2013; 5(5), 29-34.
DOI: 10.7813/2075-4124.2013/5-5/A.4
LEAD FREE X-RAY SHIELDING GLASS
Genco Berkin
Assist. Prof. Halic University, Faculty of Architecture, Istanbul (TURKEY)
gencoberkin@halic.edu.tr
DOI: 10.7813/2075-4124.2013/5-5/A.4
ABSTRACT
In hospitals’ monitoring rooms for X-ray radiography, there are special windows for doctors to monitor the
patient. These special lead glasses are X-ray repelling. Lead is used in the glass batch for X-ray repelling as its
atomic radius is high. Recent studies on lead showed that this material is hazardous to both human beings and
the environment. In this study, as an innovation trial in the glass production, strontium is used instead of lead in
the glass batch. Several glass composition alternatives have been carried out to replace the lead with strontium in
the glass batch. The glass samples have been analyzed for X-ray repelling function.
Key words: Strontium; Lead; Glass
1. INTRODUCTION
In recent years, there has been considerable interest in disposal of lead in the built environment. Through
Life Cycle Analysis (LCA) of products, materials and processes studies, we see that lead has a potential impact
on living organisms. High concentrations of lead in soils near highways and in aerosols in metropolitan areas
suggest that lead alkyl additives in gasoline are the major contributor of lead to the present environment. Locally,
however, other sources of lead may be important. Earlier researches have revealed that high lead concentrations
disposed from smelters cause brown fields. O’Connel et al. (2008) pointed out that heavy metals’ waste streams
from a variety of industrial sources pose a significant threat to receiving waters. Their research work has focused
on the use of adsorbents and adsorption in the treatment and recovery of these metals from waste streams. In
addition to these, the lead content in building materials is also a threat for the human beings and the environment.
Lead is added to the construction metals; low-melting alloys and many bearing metals as alloys of lead. Lead
oxide from metals is considered to be a health and environmental concern. It is especially so in the glass-
manufacturing environment where particles of lead oxide may be airborne. When the lead glass is recycled by
grinding operations, lead oxide could be inhaled. Material toxicity is of increasing concern with the growing
number of building products. Therefore, as the architect is responsible for the choice of building materials, he/she
has to consider the impact assessment of the building materials. The ultimate aim of the impact assessment is
selection of materials with the least environmental decay. Recently there is a tendency to use elements with low
impact: In some cases, instead of lead, barium is added to the concrete to shield the radiation (Kilincarslan et al.,
2007). Through research conducted by Lakhkar NJ et. al, we are aware of the effect on structure, degradation and
cytocompatibility of strontium oxide doped quaternary glasses. A research which commits the X-ray shielding of
monitoring rooms which does not contain lead in it is lacking in the literature survey. In this study strontium and
barium has been put in the glass batch to be replaced by lead for X-ray repelling function.
2. RADIATION SHIELDING GLASS
In the radiation industry, especially the atomic and nuclear technology plants have “hot cell” units. “Hot
cells” are used to inspect spent nuclear fuel rods and to work with other items which are high-energy gamma ray
emitters. In order to view what is in the hot cell, lead glass is used. These special glasses are also used as
particle detectors, dosimeters, x-ray imaging screens, and radiation-absorbing windows that shield against
nuclear and x-radiation. “There are several densities for lead glass, but the most common is 5.2 g/cc. Large
concentrations of lead have been used to make radiation shielding glass for use in nuclear “hot cells” primarily as
viewing windows behind which mechanical and chemical operations are conducted with radioactive components”
(Harper, 2001, p.638).
Hospitals’ monitoring rooms (for x-ray radiography) are also shielded with lead sheets and there is one
window (a glass made out of 90% lead) to monitor the patient while resting on the bed. They are labeled as RD 50
glasses. Use of lead as building material is very old but recently scientists has put forward that lead is not healthy
for humans and is not an environmental friendly material. In this respect, we shall use an alternative material
instead of lead as a building material wherever possible. In literature survey, we trace that some hospitals try to
avoid lead sheets. Instead of lead, they use concrete blocks reinforced with barium oxide. This heavy concrete
aggregates are barite (BaSO4), limonite (2Fe2o3H2O) and magnetite (Fe3O4) (Harper, 2001; Shelby, 1997).
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Fig. 1. Radiation Shielding Lead Glass (RD 50) in a Monitoring Room in Turkey
Fig. 2. Radiation Shielding Lead Glass used as a Partition in a Monitoring Room.
We also see lead use in everyday objects for radiation shielding. “In color television picture tubes,
electrons hitting the aperture mask or screen have about 25 kV kinetic energy. Some of this energy is converted
to x-rays, 0,5 Å (angstrom) or greater wavelength, as the electrons are scattered or absorbed. The x-rays can be
effectively absorbed by the neck, funnel, and panel glasses of the picture tube by incorporating heavy metal (high
atomic number) elements such as strontium, barium, zirconium and lead into the compositions. Color television
neck and funnel glasses often contain between 20 or 30 wt% PbO. Barium oxide (BaO), strontium oxide (SrO),
and zirconium oxide (ZrO2) are also added to the composition and they provide the required magnitude of x-ray
absorption” (Harper, 2001, p. 637). These glasses contain no more than 10 wt% BaO, SrO and ZrO2 in the
composition. Méar et al., (2006), have categorized cathode-ray tube glasses disposed from T.V.’s and thought
ways of recycling the waste. Their research has been carried out to examine potential re-use applications for CRT
glass (Méar, 2006).
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The use of filter glasses in general demonstrates the difference in attitude to transmission control when
real and essential results are required. This is most typically relevant in radiation protection glasses. “Nuclear
technology has demanded the development of glasses in which the absorption of dangerous radiation by lead has
given us high lead content glasses” (Wiggington, 1996, p.289). This phenomenon has reduced the expansion of
environmental friendly glasses.
3. LEAD AND THE BUILT ENVIRONMENT
Lead enters the biosphere from lead-bearing minerals in the lithosphere through both natural and human-
mediated processes. The manufacture of consumer products such as lead glass, storage batteries, and lead
additives for gasoline also contributes significantly to stationary source lead emissions. “Since 1970, the quantity
of lead emitted from the metallurgical industry has decreased somewhat because of the application of control
equipment and the closing of several plants, particularly in the zinc and pyrometallurgical industries” (EPA, 1977).
Lead is hazardous as stated by Annink et al. (1996). Production, outdoor use of lead sheet and lead paint all
cause pollution through release of lead particles. “Up to now the environmental profiles of individual products and
processes have mainly been identified by means of Life Cycle Analysis (LCA) studies, which map out the
environmental effects of a particular material, from extraction through to production, use, demolition and
recycling.” (Anink et al., 1996, p.8). Balanli and Ozturk (2006 ) stated that lead affects virtually all the systems in
our body. When in our bodies, lead can cause damage to our internal organs, brain, nervous system and
reproductive system. When accumulated in high amounts, lead can be fatal. High blood lead levels of lead can
cause birth defects in unborn children, shorten attention spans and create behavior problems in children (p.48).
Routes of exposure to lead include contaminated air, water, soil, food, and consumer products. According to the
National Institute of Environmental Health Services (NIEHS), long-term effects to young children from even small
exposures to lead can lead to nervous system disorders, lowered IQ’s, impaired memory and reaction times. Lead
was gradually banned in construction materials since 1977. As stated earlier, lead is hazardous in living
environments when used as a building material. However, we still find a few lead use in the several building
materials where there is no alternative product to fulfill the needs. “As lead obstructs the exposure of radiation,
sheet lead is used for roofing; and it is used primarily for its corrosion resistance in flashing, spandrels, gutters,
and downspouts” (Akers, 2000). Lead-based coatings are common in older buildings and can include varnishes.
Other lead-containing building materials include window glazing putty; batteries for lighting, exit signs, and
security systems; solders and pipes; mortar, acoustic materials, flashing, plastic coloring (wiring and blinds); and
ceramic glazes. Roaf et al.(2001) claimed that lead is a poison that affects multiple systems of the body including
the nervous system and brain, blood forming system, digestive system, kidneys, and reproductive system (p.135).
Lead contamination pervades the modern environment. According to Venolia (1999), lead sources are found
inside the buildings. Lead glass is used in the hospitals’ monitoring rooms as stated earlier. Hain (1995) puts
forward that lead is used as a protective material in the radiation shielding as its density is very high: 11340 kg/m3
(p.123). We should ban the lead use in the glass production and search green ingredients for building materials.
4. THE CHARACTERISTICS OF STRONTIUM AND ITS USE IN THE INDUSTRY
Strontium is an alkaline earth metal commonly found in nature especially in igneous rocks and used in
sugar industry. Certain deep-sea creatures incorporate strontium into their shells as strontium sulfate, and stony
corals require it, which is why it needs to be added to the water in aquarium. It is not regarded as toxic. D’Arcy
Thompson, (1995), stated that “in the majority of cases, the skeleton of the Radiolaria is composed, like that of so
many sponges, of silica; in one large family, the Acantharia, and perhaps in some others; it is made of a very
unusual constituent, namely strontium sulphate” “In 1787, a dealer in mineral specimens in Edinburgh, Scotland,
was offered a newly discovered specimen that had been found in a mine at Strontian, on the West coast. In 1799,
another strontium mineral was discovered in Sodbury, England, where locals were using it as gravel for paths in
ornamental gardens. This was strontium sulfate and the mineral was named celestite. Strontium metal itself was
isolated in 1808 by Humphry Davy in London by the same process by which he had recently isolated barium and
calcium: the electrolysis of a mixture of the chloride and mercury oxide. The chief ores are celestite (also known
as celestine, SrSO4) and strontianite (strontium carbonate, SrCO3). The main mining areas are UK, Mexico,
Turkey and Spain. World production of strontium ores is about 140000 tones per year from an unassessed total of
reserves. Most strontium is used as the carbonate in special glass for television screens and visual display units.
Generally, strontium becomes immobilized in the environment by precipitation as strontium carbonate or
incorporated into invertebrate shell material” (Emsley, 2001, p.405).
5. THE CHARACTERISTICS OF BARIUM AND ITS USE IN THE INDUSTRY
Barium sulfate is used for its high density, insolubility and x-ray opacity. Its name originates from a Greek
word meaning ‘heavy’. “Barium sulfate occurs naturally as the mineral barite and was first investigated by
Vincenzo Casciarolo, in Bologna, Italy, in the early 1600s. In circa 1770, Dr. William Withering had found another
curiously heavy mineral in Cumberland, England. He called it whitherite and it was later shown to be barium
carbonate. In 1808, Sir Humphry Davy was able to produce it by the electrolysis of molten barium hydroxide, at
the Royal Institution in London. The chief mined ores are barite (barium sulfate), which is also the most common,
and whitherite (barium carbonate). The main mining areas are the UK, Italy, Czech Republic, USA and Germany,
with about 6 million tones being produced each year. Reserves are reported to exceed 400 million tones. Barium
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metal is made from barium oxide (BaO) by heating with aluminum. Barium is abundant in the Earth’s crust. Barium
is also used in medical treatment. Barium absorbs X-rays and thus shows up clearly X-ray pictures” (Emsley,
2001, p.49). Barium is used in heavyweight concrete as aggregates. Studies on barite show that using barite
instead of normal aggregate increased linear absorption coefficients (Kilincarslan et al., 2007).
6. MATERIALS AND METHODS
Producing glass as a building material requires considering all its physical properties, its ability to transmit
radiation in general, and visible light in particular, which gives glass its unique significance. As Wiggington has
reported, in the light transmission, the particles discharge their energy in the form of photons that escape from the
atoms at the speed of light and interact with whatever they hit, passing easily through space and bouncing off or
being absorbed by various gasses and non-transparent solids (Wiggington, 1996, p. 247). As we are aware from
the earlier studies, the density of elements that form the glass batch plays a major role in controlling the refractive
index (Shelby, 1997, p. 197). This case has been especially the same in lead glass production. The lead has
placed in the glass batch for its high density and big atomic diameter specifications. Through this knowledge the
research has been carried out with the intention to compose a glass batch in search of combined atoms that are
high in atomic weight and big in diameter for shielding x-rays. We have designated strontium and barium
elements as the alternative of lead since their densities are big and they are not hazardous.
Fig. 3. Radiation Shielding Strontium-Barium Glass Sample.
Looking at the x-ray absorption versus wavelength tables and to enable the material to shield radiation we
must take into consideration in seeking to unite the most effective wavelength locations of the different elements’
absorption edges; as state of the art we could use barium and strontium together in a glass batch.
Table 1. The glass composition used in the radiation test (%)
SiO2 BaO SrO CeO Soda Al2O3 Potassium Nitrate Sulfate
60.05 14.68 14.54 0.2 7.60 1.95 0.58 0.40
We have foreseen that as barium’s atomic diameter is quite big, it would not permit x-rays to some
extremity. Likewise strontium also has a big diameter. The absorbed rays would possibly turn into heat energy.
The tendency of these glasses to discolor by the radiation rays has been prevented by the introduction of 0.2%
cerium oxide as a stabilizer. In this study we wished to see, with a trial-error method, using strontium and barium
in the glass batch to stop x-rays.
7. RESULTS
Obtained results through laboratory tests show that strontium-barium glass composition shields x-rays up
to 90 kV kinetic energy in 50 mAs. This result is sufficient for Rontgen monitoring rooms.
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Fig. 4. A Comparison of Different Thickness Glasses Tested for X-Ray Shielding.
8. DISCUSSION AND CONCLUSION
Looking at these results we could reasonably infer that strontium-barium glass is not hazardous and could
be replaced with lead glass (RD 50). Our study has corroborated that strontium-barium glass could be used for
shielding x-rays in hospitals’ monitoring rooms. Researchers could look to find ways for creating better building
materials to shield the gamma rays out of this ecologic compound.
As we know from former studies lead is hazardous to the environment and human beings. We should ban
the use of lead in all the building materials. This work provides relevant results as expounded in the Materials and
Methods section that strontium-barium glass could be used as an alternative architectural product that shields x-
rays in the hospitals’ monitoring rooms. Adding strontium and barium into glass batch instead of lead on one hand
may solve environmental and health hazard problems, on the other hand, the end product may be used as an
alternative for its lower cost in the hospital’s monitoring rooms so as to create a sustainable development. Further
research on shielding gamma rays glass could be useful to yield eliminating the lead in the glass batch that is
used by mammography monitoring medical staff.
The author would like to express appreciation to radiologist Dr. H.Cetin Oner and Dr. Erdem Ozgulen for
providing technical instructions and unlimited access to available laboratory, and to chemist Hande Sengel from
Sisecam Istanbul glass factory for useful advice on optimizing the glass composition and for the laboratory
facilities.
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