X-ray transmission through nanostructured and microstructured
CuO materials
M.Z. Botelho
a, R. K ¨unzel
b,, E. Okuno
b, R.S. Levenhagen
c, T. Basegio
d, C.P. Bergmann
d aA´rea de Ciˆencias Tecnolo´gicas, Centro Universita´rio Franciscano, Rua dos Andradas, 1614, CEP 97010-032 Santa Maria, RS, BrazilbUniversidade de Sao Paulo, Instituto de Fı´sica, Departamento de Fı´sica Nuclear, Cidade Universita~ ´ria, CEP 05508-090 Sao Paulo, SP, Brazil~
cUniversidade Federal de Sao Paulo, Departamento de Ciencias Exatas e da Terra, Rua Arthur Ridel, 275, Jardim Eldorado, CEP 09941-510 Diadema, SP, Brazil~ dUniversidade Federal do Rio Grande do Sul, Escola de Engenharia, Departamento de Materiais, Avenida Osvaldo Aranha, 99, CEP 90035-190 Porto Alegre, RS, Brazil
a r t i c l e
i n f o
Article history:
Received 31 May 2010 Received in revised form 31 October 2010
Accepted 4 November 2010
Keywords:
CuO nanoparticles CuO microparticles X-ray attenuation
a b s t r a c t
This study presents a comparison of the X-ray transmission through microsized and nanosized materials. For this purpose CuO nanoparticles, with 13.4 nm average grain size, and CuO microparticles, with a mean particle size of 56mm, were incorporated separately to beeswax in a concentration of 5%. Results show that the transmission through the above material plates with microsized and nanosized CuO was almost the same for X-ray beams generated at 60 and 102 kV tube voltages. However, for the radiation beams generated at 26 and 30 kV tube voltages the X-rays are more attenuated by the nanostructured CuO plates by a factor of at least 14%. Results suggest that the difference in the low energy range may be due to the higher number ofparticles/gramin the plates designed with CuO nanoparticles and due to the grain size effect on the X-ray transmission.
&2010 Elsevier Ltd.
1. Introduction
Nanostructured materials are defined as those materials whose structural elements have dimensions in the 1–100 nm range (Moriarty, 2001). These materials can be composed of nano size grains, which consist of many atoms (Lines, 2008). Grains of conventional materials have sizes that are in the range of tens of microns to one or more millimetres (Lines, 2008). Due to their very small size, these materials can present novel chemical and physical properties relative to the same chemical compound with dimen-sions in the microscopic or macroscopic range (Poole and Owens, 2004). Nanomaterials can also exhibit enhanced mechanical per-formance and offer interesting possibilities for structural applica-tions (Poole and Owens, 2004; Lines, 2008).
Recent publications in the literature propose the use of nano-particles and nanostructures embedded in a polymeric matrix for
X-ray and
g
ray shielding purposes (Friedman and Singh, 2003;Taylor, 2007; Haber and Froyer, 2008). In fact, some properties of nanostructured materials are attractive for radiological protection applications, especially in the design of lighter and lead-free aprons for individual protection (Scuderi et al., 2006). However, the application of nanostructures for radiological protection purposes still requires to evaluate if these materials attenuate the X-ray beams in the same form as the conventional materials.
In this work we have measured the X-ray transmission through microsized and nanosized materials. For this purpose, copper oxide (CuO) microparticles have been used as the starting material in the production of the CuO nanoparticles. These microparticles and nanoparticles were incorporated to beeswax and rectangular plates were produced for each material. The X-ray transmission measure-ments through these materials were carried out for X-ray beams generated with the voltage ranging from 26 to 102 kV.
2. Materials and methods
2.1. Samples production
CuO nanoparticles have been of great interest due to their potential applications in many important fields of science and technology such as gas sensors, magnetic phase transitions, catalysts and superconductors (Zhu et al., 2004). Besides, copper (Cu) filters are used in conventional radiology clinical procedures in order to improve image quality and reduce the radiation dose delivered to the patient.
In this work, CuO nanoparticles with a mean grain size of 13.4 nm and CuO microparticles with 56
m
m average particle size were used in order to investigate the X-ray transmission through these materials. The CuO microparticles (Vetec Quı´mica Fina, Brazil), with 97% purity, were used as starting material in the nanoparticle production. Nanoparticles were produced by the usual combustion method (Toniolo et al., 2010). The grain sizeContents lists available atScienceDirect
journal homepage:www.elsevier.com/locate/apradiso
Applied Radiation and Isotopes
0969-8043&2010 Elsevier Ltd. doi:10.1016/j.apradiso.2010.11.002
Corresponding author.
E-mail address:[email protected] (R. K ¨unzel).
Applied Radiation and Isotopes 69 (2011) 527–530
Open access under the Elsevier OA license.
was determined by means of X-ray diffraction using Cu K
a
radiation on a Phillips X-ray diffractometer (model X’Pert MPD) (Toniolo et al., 2010).Plates composed of CuO and beeswax were produced by incorporating CuO particles to beeswax in a concentration of 5%. One group of plates was produced by incorporating CuO nanopar-ticles to beeswax. The second group of plates was produced by mixing microsized CuO particles to beeswax. A third group of plates of pure beeswax was also produced. The dimension of each plate
was about 10 cm10 cm and thickness 2 mm. A total number of
six plates of each type were prepared. The chemical analysis of the beeswax plates were performed with the aid of a Perkin-Elmer CNH 2400 equipment. The measured chemical content is hydrogen
83.1770.03%, carbon 14.0670.01% and nitrogen 0.9070.01%.
2.2. X-ray transmission measurements
The X-ray attenuation measurements were carried out by positioning each material samples, separately, at 30 cm from the focal spot and the ionization chamber at 30 cm from the samples (Fig. 1). X-ray attenuation measurements were performed for tube voltages between 26 and 102 kV. X-ray beams with 60 and 102 kV
tube voltages were generated by a Philips Duodiagnostic digital equipment with a tungsten anode tube connected to a three-phase generator. X-ray beams with voltages between 26 and 30 kV were produced by a GE clinical mammography unit, model Senografe MMR, with a molybdenum (Mo) anode tube and Mo filter also connected to a three-phase generator. The ionization chamber used in the exposure measurements in conventional radiology was a
105–6 and in mammography a 105–6 M, both coupled to a
radiation monitor model 9015, and manufactured by Radcal (Radcal Co, USA).
The X-ray beams emitted by both equipments were character-ized through the measurement of the half value layer (HVL) and the voltage applied to the X-ray tube. The experimental kV values were obtained at both systems with a non-invasive kVp meter RTI, model PMX III (RTI Electronics AB). For each X-ray equipment the HVL values were evaluated by using aluminum foils, with thicknesses between 0.05 and 1 mm, purity 99%.
The X-ray attenuation by thebeeswax+CuOsamples containing nanoparticles or microparticles and pure beeswax has been evaluated for a large range of mass per unit area and X-ray beam energies. In all cases the irradiated area by the X-ray beam, at a distance of 30 cm from the focal spot, has been fixed as 5 cm5 cm. For each plate set the measurements were performed three times.
2.3. X-ray spectroscopy
Spectrum measurements were carried out with the aid of a Philips equipment MG 450 model, designed for industrial applica-tions, connected to a constant potential generator. The detector system used in the X-ray spectra measurements was a
XR-100T-CdTe/PX4 (Amptek, Inc., Bedford, MA) with 3 mm3 mm nominal
active area and nominal depletion layer thickness of 1 mm. This system is cooled by Peltier cells to around 243 K and has a 100
m
mBe window. An Amptek tungsten collimator with 1000
m
maper-ture and 2 mm in thickness was used in front of the detector. The energy calibration of the spectrometer was performed by using the measured spectra of
g
rays and X-rays emitted by241Am,133Baand152Eu radioactive sources.Fig. 2presents a schematic setup of
the experimental arrangement used in the measurement of the transmitted radiation through the samples. Transmitted spectra measurement have been performed in the industrial system with the detector positioned in the center of the radiation field at 480 cm from the focal spot. A lead collimator with aperture of 1.6 cm has been positioned after the sample (Fig. 2). Alignment between the focal spot and CdTe detector was performed by using a laser device. X-ray spectra were generated at a nominal tube voltage of 26 kV and 126 mAs. Experimental spectra measured with CdTe detector were corrected for all possible partial interactions of incident photons with the detector (K ¨unzel et al., 2006).
3. Results and discussion
Fig. 3 presents the results related to the X-ray transmission through pure beeswax, microsized CuO incorporated to beeswax and nanosized CuO incorporated to beeswax. The data have been Fig. 1.Illustration of the experimental setup used in the measurements of the
transmitted radiation through the materials in a clinical mammography system and in a conventional radiology equipment. The collimator corresponds to those internal to the clinical equipment provided by the fabricant.
Fig. 2.Illustration of the experimental setup used in the spectra measurements of the transmitted radiation through the materials.
M.Z. Botelho et al. / Applied Radiation and Isotopes 69 (2011) 527–530
gathered for beams generated with a maximum energy of 102, 60, 30 and 26 keV and in the range of mass per unit area between 0.17 and 1.05 g/cm2.
According to the results illustrated inFig. 3 it is possible to observe that the transmission through the microsized CuO and nanosized CuO, both incorporated to beeswax, does not provide differences for X-ray beams generated for 60 and 102 kV tube voltages. On the other hand, the transmitted air kerma through these samples, measured for X-ray beams generated at 26 and 30 kV tube voltages, is more attenuated, by a factor of at least 14%, by the nanosized CuO incorporated to beeswax with respect to the microsized CuO ones over the entire range of mass per unit area studied in this work.
The difference in the X-ray attenuation by CuO microsized and nanosized materials for low energy beams probably cannot be assigned to the particles distribution in the beeswax once this effect is not observed in the transmission of high energy X-ray beams. The X-ray beams generated by the Mo/Mo anode/filter mammography equipment, with a maximum energy of 26 and 30 keV, are composed mainly by photons with energy lower than 20 keV, specifically at 17.44 and 19.6 keV, that corresponds to the energy of the characteristic X-rays emitted by molybdenum.
In the diagnostic energy range, the total attenuation by a material is determined by both photoelectric and Compton inter-actions. Basically, in the low energy range, the photons interact with the materials mainly by means of photoelectric effect, while at the high energy range the Compton scattering dominates. Attenua-tion decreases with increasing photon energy because of the energy dependence of the photoelectric effect. The total X-ray attenuation
cross-section for the mixtureCuO + beeswax presents a K-edge
located at 8.98 keV, which is due to the Cu present in the material. At the K-edge the attenuation is increased. As the photons energy increases the total attenuation by the mixture decreases. Besides,
due to the particle size, the number of Cuparticles/gramin the nanostructured plates is higher than that for the microsized material. Therefore the probability of a low energy X-ray photon to interact and to be absorbed may be higher for nanostructured mixture than for the microstructured material.
The influence of the sample grain size on the intensity of transmitted radiation has been addressed by several authors in the literature (Berry, 1970; Holynska, 1972). These studies present results relative to grains with size in the range between 30 and 300
m
m. According to the results presented byHolynska (1972)the grain size effect decreases significantly with increasing absorbed radiation energy. On the other hand, according to this author the grain size effect increases with the increase of the mass per unit area of the sample.In Fig. 4the ratio between the air kerma values transmitted through the microsized material and through the nanosized ones is displayed as a function of the mass per unit area and X-ray beam energy. In this figure KM stands for the transmitted air kerma through the microsized material whereas Kn stands for the nanosized ones. The data show that for the X-ray beam generated with a maximum energy of 60 keV, this ratio remains about 1.0 over all the mass per unit area range, that is, the X-ray transmission through both materials is about the same over all the mass per unit area studied in this work. The results for the 102 kV beams are similar to those calculated for the 60 kV beams. On the other hand, for the X-ray beams generated with a maximum energy of 26 and 30 keV, the effect of the grain size on the X-ray transmission increases with increasing of mass per unit area of the sample. The results gathered in this work are in agreement with the results published in the literature for grains with dimensions in the range between 30 and 300
m
m.Fig. 5presents the measured X-ray spectra transmitted through 0.1770.02 g/cm2of the microsized and nanosized materials. The
Fig. 3.Transmission of X-ray beams through microsized and nanosized CuO incorporated to beeswax and pure beeswax as a function of the mass per unit area.
spectra have been measured by using a nominal tube voltage of 26 kV and the data were registered with the aid of a CdTe detector. The data displayed inFig. 4show that in the low energy range, the nanostructured material is more effective to absorb the radiation, mainly the photons with energy lower than 20 keV where the photoelectric effect dominates.
4. Conclusion
This work compares the X-ray beams attenuation by nanostruc-tured and microstrucnanostruc-tured materials. For this purpose air kerma
values related to X-ray beams emitted with maximum energy of 26, 30, 60 and 102 keV have been measured. Results show that the transmitted air kerma values, for X-ray beams produced at 60 and 102 kV, are about the same for the samples with nanosized CuO and samples with microsized CuO. On the other hand, for beams generated at 26 and 30 kV, the air kerma values are lower for the samples produced with nanosized CuO. Therefore, the samples with nanostructured CuO are more effective for low energy X-ray photons attenuation compared to the samples produced with microstructured CuO. These results suggest that the nanostructured materials can be effectively used for radiological protection purposes because the X-ray attenuation by these materials is about the same or higher than those observed for microstructured materials. However, the compar-ison of the X-ray absorption by other nanostructured materials is necessary in order to evaluate if they also present a similar attenua-tion pattern as CuO nanoparticles.
Acknowledgments
The authors thank Clinica Radiolo´gica Caridade, Santa Maria/RS for providing their X-ray equipments for this research. This work was partially supported by Brazilian Agency Fapesp (Fundac-ao de~
Amparoa Pesquisa do Estado de S ao Paulo) through Process 2010/~ 06814-4 and CNPq through grant 307095/2008-8.
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Fig. 4.Experimental dependence of grain size effect with the radiation energy and mass per unit area for the samples produced with CuO microparticles, 56mm, and CuO nanoparticles, 13.4 nm, both incorporated to beeswax.
0.0E+00 2.0E+03 4.0E+03 6.0E+03 8.0E+03 1.0E+04 1.2E+04
0 5 10 15 20 25 30
Counts
Energy (keV)
microsized CuO nanosized CuO
Fig. 5.Transmitted energy spectra through the microsized and nanosized materials measured for 26 kV tube voltage.
M.Z. Botelho et al. / Applied Radiation and Isotopes 69 (2011) 527–530
