IOSR Journal of Applied Physics (IOSR-JAP)

May - Jun 2014Volume 6 - Issue 3

Version 1 Version 2 Version 3 Version 4

Paper Type : Research Paper
Title : Determination of electron and hole effective masses in thermal oxide utilizing an n-channel silicon MOSFET
Country : India
Authors : Ravi Kumar Chanana
: 10.9790/4861-06310107  logo
ABSTRACT: The gate tunnelling electron current and the substrate hole current obtained from carrier separation in an n-channel Si MOSFET are used to determine the parabolic electron and hole effective masses in the thermal oxide. The oxide voltages for electron and hole conduction in the n-MOSFET in inversion are formulated, and the carrier effective masses of 0.42m for electron and 0.58m for hole for a free Fermi gas model of carriers at the emitting electrode are determined using the Fowler-Nordheim tunnelling characteristics. These carrier masses are related to the band offsets in SiO2/Si<100> MOS devices accurately through the MOSFET model for the first time.

[1]. H.S.Chang, H.D.Yang, H.Hwang, H.M.Cho, H.J.Lee andD.W.Moon, "Measurement of the physical and electrical thickness of ultrathin gate oxides", J.Vac.Sci.Technol., vol. 20,pp. 1836-1842, Sep. 2002.
[2]. R.K. Chanana, "Determination of hole effective mass in SiO2 and SiC conduction band offset using Fowler-Nordheim tunneling characteristics across metal-oxide-semiconductor structures after applying oxide field corrections", J. of Applied Physics, vol. 109, pp. 104508-1 to -6, May 2011.
[3]. M. Lenzlinger and E.H. Snow, "Fowler-Nordheim tunneling into thermally grown SiO2", J. of Applied Physics, vol. 40, pp. 278-283, Jan. 1969.
[4]. R.B. Laughlin, "Optical absorption edge of SiO2", Physical Review B, vol. 22, pp. 3021-3029, Sep. 1980.
[5]. V.V. Afanasev, "Valence band offset and hole injection at the 4H-, 6H-SiC/SiO2 interfaces", Applied Physics Letters, vol. 77, pp. 2024-2026, Sep. 2000.


Paper Type : Research Paper
Title : Aberrated Edge imaging with annular apertures
Country : India
Authors : A. Narsaiah, M.Venkanna, D. Karuna Sagar
: 10.9790/4861-06310812  logo

ABSTRACT: In this paper, we have studied the aberrated images of coherently illuminated straight edge objects with annular aperture in the presence of apodisation. The analytical studies were made for annular apertures apodised with Shaded aperture under the influence of defocus and primary spherical aberrations. The effect of aperture obscuration and apodisation on the edge ringing and peak intensity has been considered.

Key words: Aberrations, Annular aperture, Coherence, Edge objects, imaging systems.

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Paper Type : Research Paper
Title : Effect of Different Current Densities in the studies of1/f noise on the thin films of Silver
Country : India
Authors : S.Victor Vedanayakam, D. Punyaseshudu
: 10.9790/4861-06311319  logo

ABSTRACT: Silver (Ag) thin films are having remarkable characteristics. They have found extensive applications in electronic and optical devices. Silver thin films have potential applications in ultra-high density optical non-volatile memories, transparent electrodes and in fluorescence imaging. Measurements of nonlinear properties are very interesting from the point of the view of optoelectronic and all optical switches. Hence these films are studied in the present work. 1/f noise and nonlinear effects in Silver thin films for different current densities on varying the thickness of the films, at room temperature are studied. The specific dependence of 1/f noise on the thickness of the film, the effect of current densities on 1/f noise for the films of various thicknesses (430Ao to 1180Ao) has been investigated. It is noticed that, for a constant current, the thickness of the film leads to an increase of 1/f noise.1/f noise plays an important role in choosing frequency band in which a device can be effectively used. Silver thin films are regarded as a material with many attracting properties such as good conduction, high transmission coefficient etc. It is specially used in optoelectronic devices.

Key Words: 1/f noise, , Ag film, FFT, Current densities, frequency band, γ value, etc.

[1]. A. Van der Ziel, In: Proc. of the Symposium on 1/f Fluctuations, I. Int. Conf. on 1/f Noise, ed. by T. Musha (Tokyo Institute of Technology Press, Tokyo, Japan, 1977), p 1.
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Paper Type : Research Paper
Title : Determining The Diameter Of Erythrocyte By Means Of Manual Laser
Country : India
Authors : Petar V. Vuca, Kikinda
: 10.9790/4861-06312021  logo

ABSTRACT: The article gives instructions on carrying out the school experiment with laser light. Numerical value of the diameter of erythrocyte has been determined.

[1]. R. Krsnik. Suvremene ideje u metodici nastave fizike. Školska knjiga. Zagreb,2008 (R. Krsnik, Modern Ideas in Methodics of Teaching Physics, Školska knjiga, Zagreb,2008)
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Paper Type : Research Paper
Title : Electrical and photovoltaic properties of CuTPP/p-Si organic-inorganic hybrid hetrojunction
Country : Egypt
Authors : M.M.El-Nahass, Mossad EL- Metwally, A.A.M.Farag, Shokry Menshawy, F.S.H. Abu-Samaha, Eman Elesh
: 10.9790/4861-06312229  logo

ABSTRACT: Thin films of 5,10,15,20-Tetraphenyl-21H,23H-porphine copper(II), CuTPP were prepared by conventional thermal evaporation technique on p-Si substrates to form CuTPP/p-Si organic-inorganic hybrid hetrojunction. The temperature-dependence of the electrical characteristics of the CuTPP/p-Si heterojunction in the temperature range of 298–353 K was studied. The barrier height and ideality factor of the heterojunction were determined as a function of temperature.

[1]. J. J. M. Halls, C. A.Walsh, N. C. Greenham, E. A. Marseglia, R. H. Friend, S. C. Moratti, , and A. B.Holmes, Nature 376(1995)
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Band Gap".

Paper Type : Research Paper
Title : Effects of CdCl2 concentration and gamma irradiation on the structural, thermal and electrical conductivity properties of HPMC polymer electrolyte films.
Country : India
Authors : N Sandhya Rani, J Sannappa, T Demappa, Mahadevaiah
: 10.9790/4861-06313041  logo

ABSTRACT: Solid polymer electrolyte films based on hydroxypropyl methylcellulose (HPMC) with different concentrations of cadmium chloride (CdCl2) were prepared by solution cast method. Different techniques has been employed to investigate the effects of structural, thermal and ionic conductivity behavior of these polymer electrolyte films upon gamma irradiation with different doses of 20, 60 and 100 kGy.

1]. Reichmanis, E., O'Donnell, J. H. "The Effects of Radiation on High-Technology Polymers", ACS Symposium Series 381, eds., ACS, Washington, D. C., 1989, pp 224-254.
[2]. Hoyle, C. E., Kinstle, J. F., "Radiation Curing of Polymeric Materials", ACS Symposium Series 417, eds., ACS, Washington, D.C., 1990, p 106
[3]. Clough, R., Shalaby, S. W.,"Radiation Effects on Polymers" ACS Symposium Series 475, eds., ACS Washington, D.C., 1991, p 326.
[4]. E. A. B. Moura, A. V. Ortiz, H. Wiebeck, A. B. A. Paula, A. L. A. Silva, and L.G.A.Silva, "Effects of gamma radiation on commercial food packaging films - study of changes in UV/VIS spectra," Radiation Physics and Chemistry, 2004, vol. 71, pp. 199–202.
[5]. Sadler, G. Chappas, W. Pierce, D.E., " Evaluation of e-beam, gamma and x-ray treatment on the chemistry and safety ofpolymers used with pre-packaged irradiated foods", A review. J. Food Add. and Contam., 2001, 18 (6) : 475 - 501.

Paper Type : Research Paper
Title : Cosmic Ray and Geomagnetic Response to High Speed Solar Wind Streams
Country : India
Authors : N.K.Sharma . Tufail Ahmad
: 10.9790/4861-06314249  logo

ABSTRACT: The study of cosmic ray intensity and geomagnetic response have been carried out with the data registered by ground based and satellite data on 24-hour scale during 1996, 2000 and 2008 which corresponds to solar minimum of solar activity cycle 23 during 1996 and 2008 followed by a solar maximum in the year of 2000. The minimum of solar activity cycles are characterized by different polarity of the north pole of the sun's magnetic field as the polarity reversal occurs during 2000. The results presented in this paper indicate that cosmic ray intensity and geomagnetic field is highly disturbed during the passage of these streams at Earth. The average time-profile of the decrease in cosmic ray intensity produced by streams associated with coronal holes and solar flares during the maximum epoch of solar activity cycle 23 is explained in terms of existing models of solar modulation of cosmic rays. The comparison of modulation features during the different magnetic conditions i.e. during 1996 & 2008 shows that drift effects are less dominant in the short-term modulation of cosmic rays. These results indicate that the solar wind streams are playing an important role in the transient modulation of cosmic ray intensity.
Key Words: Sun: Solar activity, Polarity Reversal, Galactic Cosmic rays (GCR) and Forbush decreases (Fds)

[1]. Crooker, N.U and Siscoe, G I: Physics of the Sun, 3P.A. Sturrock (ed.), D.Reidel Publication. Co. Dordrecht, 193-249 (1986).
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[3]. Iucci N M, Parrisi M, storini M and Villoresi G: Nuovo Cimento, 2C, 421 (1979).
[4]. Lockwood, J.A., Webber,W R and Jokippii,J.R : J.Geophys.Res. 91, 2851 (1986).
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Paper Type : Research Paper
Title : Softening transitions in ferroelectric Pb (Zr, Ti) o3 ceramics doped with neodymium oxide and lanthanum oxide
Country : India
Authors : T. Kamakshi, Dr. P. S. V. SubbaRao
: 10.9790/4861-06315055  logo

ABSTRACT: The effect of La3+ and Nd3+ on dielectric and ferroelectric properties of Pb(Zr0.52Ti0.48)O3 was studied. The powders were prepared by "mixed oxide" route followed by calcinations at 8000c for 4 h. XRD analysis of the calcined powders confirms the tetragonal phase in the undoped PZT, PLZT and PNZT ceramics were identified. SEM study of sintered pellets reveals the decrease in grain size with the change in dopant as 1at% Nd3+ and 1at% La3+ respectively. The dielectric properties were maximum for 1at% Nd3+ and 1at% La3+ respectively. Based on the above study, it is concluded that PZT doped with La3+ and Nd3+ produce softening transitions in PZT.
Keywords: lead zirconate titanate; mixed oxide; dielectric; softening transitions

[1] Uchino K. Ceramic actuators—Principles and applications. Mater Res Bull 1993, 18: 42–48
[2] Newnham RE, Ruschau GR. Smart electroceramics.
[3] Panda PK, Sahoo B, Raja S, et al. Electromechanical and dynamic characterization of in-house-fabricated amplified piezo actuator. Smart Mater Res 2012, 2012: 203625.
[4] Haertling GH. Ferroelectric ceramics: History and technology. J Am Ceram Soc 1999, 82: 797–818.
[5] Sahoo B, Panda PK. Fabrication of simple and ring-type piezo actuators and their characterization. Smart Mater Res 2012, 2012: 821847.

Paper Type : Research Paper
Title : Growth and characterization of a novel crystal-barium malate trihydrate
Country : India
Authors : A Lincy, V Mahalakshmi, J Thomas , KV Saban
: 10.9790/4861-06315661  logo

ABSTRACT: Barium malate trihydrate crystals are grown by limited diffusion technique in hydro-silica gel. Relevant functional groups are identified from the FT-IR spectrum. Single crystal XRD shows that the crystal system is monoclinic with space group P21/n. The optical band gap of the material, estimated using DRS, is 1.028 eV. The material exhibits a three stage thermal decomposition pattern.
Keywords: Crystal growth, Crystal structure, Diffuse reflectance spectroscopy (DRS), Infrared spectroscopy, Thermogravimetric analysis (TGA)

[1] T. Pal, T. Kar, T. G. Boceli and L. Rigi, Morphology, crystal structure and thermal and spectral studies of semiorganic nonlinear optical crystal LAHClBr, Cryst. Growth Des. 4, 2004, 743-747.
[2] J. Sun, J. Zheng, Y. Che and B. Xi, Growth and properties of organic nonlinear optical crystals: L-tartaric acid–nicotinamide and D-tartaric acid–nicotinamide, J. Cryst. Growth, 257, 2003, 136-140.
[3] P. V. Dhanaraj, N. P. Rajesh, G. Vinitha and G. Bhagavannarayana, Crystal structure and characterization of a novel organic optical crystal: 2-Aminopyridinium trichloroacetate, Mater. Res. Bull., 46, 2011, 726-731.
[4] Y. R. Martin, M. H. Molina, J. Sanchiz, C. R. Perez, F. Lloret and M. Julve, Crystal structures and magnetic properties of two- and three-dimensional malonato-bridged manganese(II) complexes, Dalton Trans., 11, 2003, 2359-2365.
[5] C. Desplanches, E. Ruiz, A. Rodriguez-Fortea and S. Alvarez, Exchange coupling of transition-metal ions through hydrogen bonding: A theoretical investigation, J. Am. Chem. Soc., 124, 2002, 5197-5205.

Paper Type : Research Paper
Title : On the use of the Hill's model as local isotherm in the interpretation of the behaviour of the adsorption energy distributions
Country : Tunisia
Authors : Yosra Ben Torkia, Mohamed Khalfaoui, A. Ben Lamine
: 10.9790/4861-06316273  logo

ABSTRACT: Activated carbons are reported to show promise for separation processes and natural gas storage, since they have a strongly heterogeneous surface. In that context, a thorough investigation of the energetic heterogeneity of activated carbon surfaces is essential for the development and improvement of materials designed for specific applications. We have carried out this study, to determine the Adsorption Energy Distribution (AED) corresponding to the adsorption of methane, ethane, and nitrogen on activated carbon at different temperatures by using the Hill model as local isotherm. At first, the integral equation itself is deduced by a reasoning based on the local adsorption isotherm. Then, to solve the integral equation a numerical method is proposed. The Hill isotherm was established by applying the grand canonical ensemble in a statistical physics treatment. This treatment allowed us to define the parameter n, which represents the number of molecules adsorbed per site. We have supposed as a first approach that the energy distribution function has the shape of the normal Gaussian distribution. The influence of the adsorbate type and the values of parameter n at different temperatures on the behaviour of the AED, have been studied.
Keywords: Adsorption energy distribution; Activated carbon; Statistical physics; Integral equation; Hill isotherm.

[1] Shaheen A. Al-Muhtaseb, J. Chem. Eng. Data 55 (2010) 313–319.
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[4] J. D. Morrison and S. Ross. Surface Sci. 62 (1977) 331.
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Paper Type : Research Paper
Title : Detection of Seismo-ionospheric Anomalies using Wavelet based
techniques
Country : India
Authors : Anjana Sonakia, D.K. Sondhiya, S.K. Kasde, Harsha Jalori , A.K. Gwal
: 10.9790/4861-06317491  logo

ABSTRACT: A number of papers have reported on anomalous variation in ionospheric foF2 parameter and/orionospheric total electron content (ITEC) in the vicinity of earthquake's epicenter few days prior to theearthquake. In this work empirical dependency for the seismo-ionospheric disturbances relating the earthquake< magnitude and the epicenter distance are obtained. They have been shown to be similar to those obtained earlier earthquakes. The dependences indicate the process of spreading the disturbance from the epicenter towards periphery during the earthquake preparation process. Large lead times for the precursor occurrence (up to 34 days for M=5.8–5.9) tells about a prolong preparation period. It is shown that different analyses of observed foF2 values lead to different conclusions regarding possible ionospheric precursors. Here we analyze the foF2 and ITEC observations over Greece prior to the three very large earthquakes of January 08, 2006,February 14, 2008 and June 08, 2008, using the wavelet based techniques.
Keywords:Wavelet Transform, ionospheric anomalies and foF2 parameter

[1] S.A. Pulinets, and K.A. Boyarchuk, Ionospheric Precursors of Earthquakes (Springer, Berlin, Germany, 2004).
[2] S.A. Pulinets, A.D. Legen_ka, T.I. Zelenova, Local-time dependence of seismo-ionospheric variations at the F-layer maximum. Geomagn.Aeronom, 38, 1998, 400–402.
[3] J.Y. Liu, Y.I. Chen, S.A. Pulinets, Y.B. Tsai, and Y.J. Chuo, Seismoionospheric signatures prior to MP 6.0 Taiwan earthquakes. Geophys, Res. Lett. 27, 2000, 3113–3117.
[4] R.D. Hunsucker, Radio Techniques for Probing the Terrestrial Ionosphere, (Thomson Press India Ltd., 1991).
[5] Y.I. Chen, J.Y. Liu, Y.B. Tsai, C.S. Chen, Statistical tests for preearthquakeionospheric anomaly, Terr., Atm. Ocean Sci. 15, 2004, 936– 943.

Paper Type : Research Paper
Title : Defect Generation in Bipolar Devices by Ionizing Radiation
Country : Malaysia
Authors : Fuei Pien Chee, Haider F. Abdul Amir, Saafie Salleh
: 10.9790/4861-063192101  logo

ABSTRACT: This paper reviews typical effects occurring in bipolar junction transistors (BJTs) due to gamma (γ) rays irradiation. The detrimental consequences of this interaction can be categorized into two: the transfer of energy to electrons due to ionization and electronic excitations; and also the transfer of energy to atomic nuclei. The radiation damage induced by this interaction was studied using in situ method by comparing the current-voltage characteristics of the devices under test (DUTs) at different biased collecting current and operating modes. The high energy from gamma radiation is found to induce both temporarily and permanent damage in the DUTs depending on the current drive and total dose absorbed. The most significant radiation damage in the BJT is the creation of electron-hole pairs which increases the probability of recombination at the base region of BJTs. The DUTs are found to exhibit minor annealing effect at post-irradiation and the results also show that devices operating in higher bias current are more capable of withstanding the effect by gamma radiation.
Keywords: bipolar junction transistor (BJTs), gamma (γ) rays, in situ, recombination, ionizing radiation

[1] P. J. Baines, and A. Côté, Promising Confidence- and Security-Building Measures for Space Security, A Safer Space Environment, 4, 2009, 5-16.
[2] F. P. Chee, H. F. A. Amir, and S. Salleh, Range distribution and electronic stopping power for Cobalt (Co) ions in Gallium Arsenide (GaAs) optoelectronic devices, Modeling, Simulation and Applied Optimization (ICMSAO), 2011 4th International Conference on. IEEE, 2011, 1-5.
[3] R. Krause-Rehberg and H. S. Leipner, Positron annihilation in semiconductors: defect studies, Vol. 127 (Springer, 1999).
[4] J. R. Srour, C. J. Marshall and P. W. Marshall, Review of displacement damage effects in silicon devices, Nuclear Science, IEEE Transactions on, 50(3), 2003, 653-670.
[5] P. J. Sellin and J. Vaitkus, New Materials for Radiation Hard Semiconductor Detectors, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 557(2), 2006, 479-489.

Paper Type : Research Paper
Title : Optical Properties of Copper (I) Oxide Thin Films Synthesized by SILAR Technique
Country : Nigeria
Authors : Oluyamo, S.S, Nyagba, Mbafan .S , Ojo, Ambrose . S.
: 10.9790/4861-0631102105  logo

ABSTRACT: In this research work, Copper(I)oxide (Cu2O) thin films were synthesized using Successive Ionic Layer Adsorption and Reaction (SILAR) technique. Fixed concentrations and temperature of two anionic precursors (1.0M at 70oC for KOH and NaOH) and same cationic precursor (Copper Sulphate complex solution at room temperature) were used to obtain two set of films.Optical properties and applications of the films were examined. X-ray diffraction (XRD) analysis showed that both films are polycrystalline with a simple cubic structure. The absorbance, transmittance and reflectance of the material revealed Cu2O applicability as a Transparent Conducting Oxide (TCO). The energy band gaps obtained were 2.2 and 2.3eV for the different precursors. This indicates that the choice of precursor in this deposition technique has an effect on the energy band gap of the material.
Key words: SILAR, Optical properties, Anionic precursor, TCO, Energy band gap

[1]. Andreas,Stadler (2012). Transparent Conducting Oxides-An Up-to-Date Overview,Materials, 5, 661-683.
[2]. Liqui, Men; Qiying, Chen; Hirokazu, Tada; Hirofumi, Yamada and Kazumi, Matsuushige (1999). Nano Meter Scale Current-Voltage Characteristics of C60 films. Mol. Cryst. and Liq. Cryst., 337, 519-523.
[3]. Pierson, J.F., Thobor-Keck, A., Billard A. (2003). Cuprite, Paramelaconite and Tenorite films Deposited by Reactive Magnetron Sputtering, Applied surface science, 210, 359-367.
[4]. Richardson T.J., Slack J.L., Rubin M.D. (2000). Electrochromism of Copper Oxide thin films, Proceedings of the 4th International meeting on Electrochromism, Uppsala.
[5]. Ramesh, Chandra; Praveen,Taneja and Pushan,Ayyub(1999). Optical properties of Transparent Nanocrystalline Cu2O thin films Synthesized by High Pressure Gas Sputtering,Nano-Structured Materials, 4, 505-512.

Paper Type : Research Paper
Title : Measurement of dc Electrical Conductivity of Chemically Synthesized Pyrrole Aniline Copolymers
Country : India
Authors : H R Wasnik , D S Kelkar, V Y Ganvir
: 10.9790/4861-0631106109  logo

ABSTRACT: Chemical oxidative copolymerization of pyrrole and aniline was performed for three feed ratios at room temperature (30oC) using FeCl3 as an initiator. The synthesis was carried out for two different initiator concentrations. The I – V plots for the respective samples have been plotted which indicate the linear or ohmic behavior of the samples with respect to field variation. The dc electrical conductivity of the copolymers was measured at a field of 27V/cm using two probe method in the temperature range of 313-673K. The log σ versus 1/T graphs for these samples have been plotted in the same temperature range. The results show transitions of the samples from metallic to semiconducting behavior and vice versa depending upon each sample at a particular temperature specific for the sample. The results show reduction in the conductivity of prepared copolymers on comparison with that of the homopolymers..
Keywords: Aniline, copolymer, electrical conductivity, pyrrole.

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[4]. S. Panero, P. Prosperi, F. Bonono, B. Scrosati, A. Corradini, M. Mastragostino, Characteristics of electrochemically synthesized polymer electrodes in lithium cells—III. Polypyrrole , Electrochimica Acta, 32 (7) , 1987, 1007 –1011.
[5]. T. Otero, I. Cantero, B. Azcano, Optimization of poly-3-methylthiophene to be used in advance polymer batteries, International Journal of Hydrogen Energy 25 , 2000, 221 –233,.


Paper Type : Research Paper
Title : Study of Photon Propagation with various Energies through Bone by Monte Carlo Simulation
Country : Iran
Authors : A. Yavara , I. Forouzankia , S. Mohammadi , M. F. Rahimi
: 10.9790/4861-0631110114  logo

ABSTRACT: The aim of radiation therapy is to maximise the dose to the tumour, while minimising the dose to healthy tissue. The Monte Carlo (MC) simulation by advantages of high accuracy, low cost, and describing the coupled transport of electrons and photons in complex geometries is used increasingly in radiation therapy. Since 50-80% of the human body is water, many studies have carried out the photons propagation in tissue, although no serious study has performed in bone. The bone, because of its high density, as well high ability of scattering and absorption of photons is important matter in radiation therapy. The aim of present work was the MC simulation of photons propagation with various energies in bone. The MC simulation was written in Fortran 77 program. Emigration of photons in bone was determined using MCNP-4C code to evaluate the results of MC method. The depth of first interaction of photons 1, 5, and 10 MeV in bone were determined in 2.26, 2.90, and 4.40 cm using the MC method, which were a good consistent with those of MCNP results 2, 3, 4 cm, respectively.
Keywords: Monte Carlo simulation, photon propagation, bone, MCNP code

[1] Crowe, S. B. 2011. The development of Monte Carlo techniques for the verification of radiotherapy treatments. Ph.D. thesis. Queensland University of Technology, Australia.

[2] Moreno, M. Z. 2005. Monte Carlo simulations for dosimetric verification in photon and electron beam radiotherapy. Ph.D. thesis. Universidade Nova De Lisboa, Portugal.

[3] Spiga, J. 2010. Monte Carlo simulation of dose distributions for synchrotron microbeam radiation therapy. Ph.D. thesis. UniversitaDegliStudi Di Cagliari, Italy.
[4] Sidek, M. A. J. 2010. Monte Carlo investigations of radiotherapy beams: studies of conventional, stereotactic and unflattened beams. Ph.D. thesis. The University of Birmingham, United Kingdom.
[5] Verhaegen, F. &Seuntjens, J. 2003. Monte Carlo modeling of external radiotherapy photon beams. Journal of Physics in Medicine and Biology. 48(21): R107.

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