7. Measurement of mass attenuation coefficients by Si(Li), NaI(Tl) and Cd(Tl) detectors

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1 Transworld Research Network 37/661 (2), Fort P.O. Trivandrum Kerala, India Nuclear Science and Technology, 2012: ISBN: Editor: Turgay Korkut 7. Measurement of mass attenuation coefficients by Si(Li), NaI(Tl) and Cd(Tl) detectors Mustafa Recep Kaçal 1, İbrahim Han 2 and Ferdi Akman 3 1 Giresun University, Faculty of Arts and Sciences, Department of Physics, Giresun, Turkey 2 Ağrι İbrahim Çeçen University, Faculty of Sciences and Arts, Department of Physics, Ağrι Turkey; 3 Bingöl University, Faculty of Arts and Sciences, Department of Physics, Bingöl, Turkey Abstract. Mass attenuation coefficients of the some elements were determined for two photon energies using different three detectors. The samples were irradiated using 10 mci Cd-109 and 100 mci Am-241 radioactive point sources. The photons were separately counted by Si(Li), NaI(Tl) and Cd(Tl) detectors. It was observed that the mass attenuation coefficient decreases with increasing energy and increases with increasing atomic number. The measured values are compared with the theoretical ones calculated using WinXcom program. Introduction This chapter concerns determination of photon attenuation or absorption properties of a material using the application of Lambert Beer s law with standard transmission method by adopting narrow beam geometry. The photon attenuation properties of a material can be evaluated by means of the linear attenuation coefficients (μ), mass attenuation coefficients (μ/ρ) and related Correspondence/Reprint request: Dr. Mustafa Recep Kaçal, Giresun University, Faculty of Arts and Sciences Department of Physics, Giresun, Turkey. mustafakacal@hotmail.com

2 60 Mustafa Recep Kaçal et al. parameters such as mean free path (mfp) and half value layer (x 1/2 ) etc. In this method, these parameters are determined using from the spectrum obtained by sample and without sample each measurement. Photon spectra are recorded in the following order: firstly, source spectrum recorded with source but without sample and the incident spectrum (without attenuation) is obtained. The transmitted spectrum recorded with source and sample and the transmitted spectrum I (after attenuation) are obtained. In both the spectra the photo-peak had Gaussian distribution. Finally, by integrating the incident spectrum and the transmitted spectrum over selected width of the photo-peak, incident intensity I 0 and transmitted intensity I are obtained. Generally, Si(Li), NaI(Tl) or Cd(Tl) detectors are used for count of photons. In this study for corporation all of these are used. When an x-ray beam passes through any matter, its intensity progressively reduces as a consequence of a complex series of interactions between x-ray photons and atoms of the attenuating medium. The linear attenuation coefficient (μ, cm -1 ) is defined as the probability of a radiation interacting with a material per unit path length [1]. It is related mass attenuation coefficient (μ/ρ gcm -2 ). The μ/ρ is a measure of the average number of interactions that occur between photons and matter mass per unit area. The accurate attenuation coefficient values of materials are a very essential parameter in nuclear and radiation physics, radiation dosimetry, radiography, spectrometry, crystallography, biological, medical, agricultural, environmental and industrial. Historical background and current status of topic Since the mass attenuation coefficients are important in fundamental physics and many applied fields, the accurate values of mass attenuation coefficients for X- and γ- rays in several materials are essential for some fields such as, nuclear, radiation physics, radiation dosimetry, biological, medical, agricultural and industrial. Recently, there are a great number of experimental and theoretical investigations of mass attenuation coefficient. The mass attenuation coefficients for C 2 H 4, CO 2, N 2, O 2, CF 4, Ne, H 2 S, HCl, Ar, Air, Mg, Al, SiO 2, (C 2 H 5 ) 3 PO 4 materials have been determined by [2]. Hubbell presented tables of mass attenuation coefficients for 40 elements and 45 mixtures and compounds over the energy range from 1 kev to 20 MeV [3]. These tables were be reiterated with tabulation for all elements in the atomic range 1 Z 92 and 48 additional substances of dosimetric interest by the Hubbell and Seltzer [4] and Berger and Hubbell [5]. The photon attenuation coefficients in certain tissue equivalent compounds, perspex,

3 Mass attenuation coefficients 61 polyethylene, polycarbonate and teflon have been measured at energies 13.37, 17.44, 22.10, and kev [6]. Wang et al. measured systematically the mass attenuation coefficients in the range of X-ray energies between 1.486keV and kev for SiH 4 and; between kev and kev for Si [7]. Khanna et al. have measured γ-ray attenuation coefficients in some heavy metal oxide borate glasses at 662 kev [8]. Mass attenuation coefficients of kev photons were measured in elements with atomic number ranging from low to high, and including lanthanides whose K-shell binding energies were close to those of incident photons [9]. Sing et al. determined attenuation coefficients for some dilute solutions (Li 2 SO 4 H 2 O, CuSO 4. 5H 2 O, NiSO 4.6H 2 O, MgSO 4. 7H 2 O, NH 4 Cl) at 662 kev [10]. Orlic et al. published total photon mass attenuation coefficients for photon energies between 100 ev and 1000 MeV [11]. Measurements have been made to determine γ-rays attenuation coefficients very accurately by using an extremely narrow-collimated-beam transmission method and the effect of the sample thickness on the measured values of the mass attenuation coefficients (μ/ρ) cm 2 /g of perspex, bakelite, paraffin, Al, Cu, Pb and Hg have been investigated at three different γ-ray energies (59.54, and kev) [12]. The transmissions of γ- rays at the energies, 81, 356, 511, 662, 835, 1274 and 1332 kev have been studied on the alloys brass, bronze, steel, aluminum-silicon and lead-antimony [13]. The mass attenuation coefficients for 22 high purity elemental materials (C, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Rh, Pd, Ag, Cd, In, Ta, Pt, Au and Pb) were measured in the X-ray energy obtained by a variable-energy X-ray source range from 13 kev to 50 kev using a high purity germanium detector with thin (50 mm) Be window [14]. Angelonea et al. were measured the total absorption coefficients for some selected organic compounds relevant to health physics, Triaflol BN (C 3 H 4 O 2 ) n, Triaflol TN (C 12 H 18 O 7 ) n, Kapton (C 44 H 20 O 10 ) n, and Melinex (C 10 H 8 N 4 O 4 ) n in the X-ray energy range from 13 kev up to about 40 kev using a collimator, high purity germanium detector with thin Be window and variable energy X-ray source [15]. Söğüt et al. measured the total mass attenuation coefficients of Fe and Cu in various compounds using a Si(Li) detector with a resolution of 155 ev at 5,9 kev [16]. Turgut et al. were measured the total mass attenuation coefficients for the elements Co, Mn and Co 2 O 3, compounds CoCl 2.6H 2 O, CoSO 4, CoSO 4.7H 2 O, MnCO 3, KMnO 4, MnCl 2.2H 2 O and MnCl 2.4H 2 O at different energies between and kev using a secondary excitation method [17]. The μ m values around the K-shell absorption edge of Nb, Zr and Mo as a parametric X-ray radiation (PXR) application of monochromatic hard X-ray radiation sources have been

4 62 Mustafa Recep Kaçal et al. measured [18]. The gamma-ray attenuation coefficients for bismuth borate glasses were measured [19]. İçelli et al. were measured the mass attenuation coefficients for V 2 O 3, VO 2, VF 3, NH 4 VO 3, VF 4, NiF 2, NiCl 2, NiCl 2 H 2 O, NiF 2 4H 2 O, NiCl 2 6H 2 O and Ni (ClO 4 ) 2 6H 2 O in the X-ray energy range from to kev using a Si (Li) detector [20]. İçelli et al. were measured to determine variation of the mass attenuation coefficients of H 3 BO 3 according to percentage increasing concentration of H 3 BO 3 by using an extremely narrow-collimated-beam transmission method in the energy range kev with an X-ray transmission method [21]. The μm values of Ag in the kev energy range with a level of uncertainty between 0.27% and 0.4% away from the K-edge were evaluated [22]. The X-ray linear attenuation coefficients was measured using characteristic X-rays with energies kev produced by X-ray fluorescence using a secondary target system, and 140 kev γ-rays obtained from an unsealed Tc source for materials containing elements from hydrogen to calcium [23]. Measurements have been made to determine the mass attenuation coefficients of undoped n- type InSe, and Gd, Ho, Er doped n-inse single crystals using a Si(Li) detector in the energy region kev X-ray energies with energy dispersive X-ray fluorescence systems [24]. Chitralekha et al. have been measured mass attenuation coefficients for mono- and disaccharides at photon energies 5.947, and kev [25]. The μ m values for YBaCuO and BiPbSrCaCuO superconductors at 511keV, 661keV and 1274 kev energies and for MgB 2 superconductor at some energy between 14.1keV and 29.7keV have been measured [26, 27]. The μ m values for BiPbSrCaCuO superconductor have been measured at different energies [28]. The X-rays attenuation coefficients for Cu, In and Se in elemental state and the semiconductor CuInSe 2 were measured at 15 different energies from 11.9 to 37.3 kev by using the secondary excitation method [29]. Rettschlag et al. determined plutonium photon mass attenuation coefficients by using a collimated-beam transmission method in the energy range from 60 kev to 2615 kev [30]. The mass attenuation coefficients for cornea taken from keratitis patient and soft contact lens (-1.75, -3.75, -4 diopties), leiomyomata uteri and uterus were measured in the X-ray energy (5.9 kev) using a Si(Li) detector and Fe-55 annular source [31]. The mass attenuation coefficients were measured for various binary and ternary 3d transition metal alloys at different energies [32, 33, 34]. The total mass attenuation coefficients (for GaAs, GaAs (semi-insulating; S-I) GaAs:Si (N+), GaAs:Zn, InP:Fe, InP:Fe As, InP:S and InP:Zn crystals were measured at various photon energies [35]. The mass attenuation coefficients (μ m ) for SiO2 {Quartz (1101), Quartz

5 Mass attenuation coefficients 63 (110 0) and Quartz (0 0 01)}, KAlSi 3 O 8 {Orthoclase (010), Orthoclase (10 0)}, CaSO 4. 2H 2 O (gypsum), FeS 2 (pyrite) and Mg 2 Si 2 O 6 (pyroxene) natural minerals at 22.1, 25.0, 59.5 and 88.0 kev photon energies [36]. The total mass attenuation coefficients (μ/ρ) for pure Au and Au 99 Be 1, Au 88 Ge 12, Au 95 Zn 5 alloys were measured at 59.5 and 88.0 kev photon energies [37]. Özdemir and Kurudirek determined total mass attenuation coefficients for 21 different compounds at kev using a narrow beam good geometry setup [38]. The mass attenuation coefficients of the kev radiation of Am- 241 point source in boron ores such as tincal, ulexite and colemanite were determined experimentally by a scintillation detector and theoretically [39]. Sharanabasappa et al. were measured mass attenuation coefficients for chromium and manganese compounds around absorption edge and for magnesium, nickel, copper, molybdenum and tantalum and three biological equivalent materials are compared with standard theoretical values [40, 41]. The mass attenuation coefficients, partial interactions and the effective atomic numbers (Z eff ) of Bi 2 O 3, PbO and BaO in xr m O n : (100-x) P 2 O 5 (where x=30 x 70 (%by weight)) glass system have been investigated on the basis of the mixture rule at 662 kev [42]. Un et al. were determined the total mass attenuation coefficients, μ m, for PbO, barite, colemanite, tincal and ulexite at 80.1, 302.9, 356.0, and kev photon energies by using NaI(Tl) scintillation detector [43]. The photon attenuation coefficients of concrete includes barite in different rate were measured [44]. Kirdsiri et al. were measured photon attenuation coefficients of silicate glasses containing Bi 2 O 3, PbO and BaO for comparison of radiation shielding and optical properties [45]. Gamma-ray attenuation coefficients of some building materials available in Egypt and photon attenuation parameters in different solid state track detectors in the energy range 1 kev 100 GeV were determined [46, 47]. In the present study, mass attenuation coefficients of V, Fe, Ni, Zn, Mo, Ag, Sb, Nd, Gd, Dy, Pt, Hg, Tl, Pb, Bi and U at 59.5 kev and 88 kev photon energies were measured by Si(Li), NaI(Tl) and Cd(Tl) detectors. The measured mass attenuation coefficients are compared with the theoretical values. Detectors Semiconductor detector is fabricated from either elemental or compound single crystal materials, having a band gap of approximately 1 to 5 ev. The group IV elements silicon and germanium are by far the most widely-used semiconductors, although some semiconductors materials are finding use special applications as development work on them continues. Semiconductor

6 64 Mustafa Recep Kaçal et al. detectors have a p-i-n diode structure, in which the intrinsic region is created by depletion of charge carriers when a reverse bias is applied across the diode. When photons interact within the depletion region, charge carriers (holes and electrons) are freed and are swept to their respective collecting electrode by the electric field. The resultant charge is integrated by a charge sensitive preamplifier and converted to a voltage pulse with amplitude proportional to the original photon energy. The advantage of semiconductor detectors is their excellent energy resolution; a disadvantage is that semiconductors usually have complex energy spectra showing the effect of charge carrier trapping and prominent K X-ray escape peaks. Trapping of either holes or electrons at sites of crystal defects and impurities, results in reduced efficiency of charge collection [48]. Sodium Iodide is an instrument for detecting X-rays and gamma rays. NaI is a kind of scintillation crystal with favorite properties, crystalline sodium iodide (NaI) converts an X-ray or gamma-ray photon into a pulse of visible light, the high Z of iodine in NaI gives good efficiency for gamma ray detection, and a small amount of Tl is added in order to activate the crystal, so the designation is usually NaI (Tl) for the crystal. The thallium activated sodium iodide scintillation detector produces energetic recoil electrons from photon interactions inside the crystal, which undergo inelastic collisions within the lattice to excite secondary electrons to the conduction band. Some of these electrons subsequently de-excite via the emission of photons in the visible region. This scintillation light is measured by a photomultiplier tube, where the photoelectrons are accelerated and multiplied through secondary emissions from a number of dynodes. The current pulse from the photomultiplier tube is passed through a charge sensitive preamplifier and fed to a shaping amplifier which is connected to a multi-channel pulse height analyzer (MCA) [49]. Cadmium Telluride (CdTe) detector has a combined high atomic numbers, with a good band gap energy for room temperature operation (1.5eV), and the probability of photoelectric effect in CdTe is 4-5 times higher than in Ge for typical gamma ray and X-ray irradiation on the cathode side, although CdTe detectors are efficient for low energy gamma rays. X-rays and gamma rays interact with CdTe atoms to create an average of one electron/hole pair for every 4.43 ev of energy lost in the CdTe. Depending on the energy of the incoming radiation, this energy loss is dominated by either the photoelectric effect or Compton scattering. The probability or efficiency of the detector to stop the incoming radiation and create electron/hole pairs increases with the thickness of CdTe [49]. The charge generates in CdTe, as an incident γ-ray or X-ray interacts with the semiconductor device and generates a number of

7 Mass attenuation coefficients 65 electron-hole pairs. These electron-hole pairs drift under the influence of an applied electric field and induce a charge Q on the electrodes, the induced charge Q is converted into a voltage pulse using a charge or current sensitive preamplifier, where ideally the output voltage is proportional to the initial deposited energy. Experimental The experimental arrangement used in the present work is shown in Fig kev and 88 kev γ-rays of Cd-109 (10mCi) and Am-241 (100mCi) radioactive point sources were used to excite the targets, respectively. The intensities of fluorescent X-rays were measured using a high-resolution Si(Li), Cd(Tl) and NaI(Tl) detectors. The Si(Li), Cd(Tl) and NaI(Tl) detectors have a resolution of 160 ev at 5.90 kev, 1,5 kev at 122 kev and 8.5 kev at 662 kev, respectively. Spectroscopically pure foil samples of mass thickness ranging from to g/cm 2 were used. The samples were placed in between the γ-ray source and the detector. The detector absorbs a narrow beam of gamma rays passed through the sample. To minimize the effect of small angle scattering in the target transmitted gamma rays were further collimated. The spectra were obtained for a period 600s for each one of energy and elements. The measurements were repeated 5 times and took average of these measurements in order to minimize statistical error. A typical spectrum is given in Fig. 2. Figure 1. Experimental setup.

8 66 Mustafa Recep Kaçal et al. 4.0x x x10 5 without absorber with absorber 2.5x10 5 Counts 2.0x x x x Energy Figure 2. The spectra of Am-241 radioactive point source without absorber and with absorber (Ti). Mass attenuation coefficients for the elements at incident energies are determined by the transmission for collimated mono-energetic beam. If a material of thickness x (cm) is placed in the path of a beam of gamma or X-ray radiations, the intensity of the beam will be attenuated according to Beer Lambert s law: where I 0 and I are the unattenuated and attenuated photon intensity, respectively, μ m (cm 2 /g) is the mass attenuation coefficient of the material and t(g/cm 2 ) is sample mass thickness. Mathematical rearrangement of Eq. (1) yields the following equation for the mass attenuation coefficient: (1) The mass attenuation coefficients (μ m ) values for present elements obtained experimentally in the present investigation and a comparison with the theoretical values obtained by WinXcom program [14]. This program depends on applying the mixture rule to calculate the partial and total mass attenuation coefficients for all elements, compounds and mixtures at standard as well as selected energies. (2)

9 Mass attenuation coefficients 67 Table 1. The experimental and theoretical values of mass attenuation coefficients μ m (cm 2 /g). Discussion The experimental and theoretical results for the mass attenuation coefficients (μ m ) are presented in Table 1. It is clearly seen from Table 1 that the mass attenuation coefficients depends on the photon energy. The mass attenuation coefficients of materials are decrease with increasing photon energy. As shown in Table 1, the experimental mass attenuation coefficients for almost all samples are agreement theoretical values of ones. The theoretical mass attenuation coefficients were calculated using XCOM program. The total experimental uncertainty of the measured mass attenuation coefficients depends on the uncertainties of the evaluation of peak area of I 0 intensity without attenuation and I intensity after attenuation, mass thickness measurements and counting statistics. I 0 intensity without attenuation and I intensity after attenuation for kev and 88 kev

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