Attenuation Coefficient of Reactive Powder Concrete Using Different Energies

Wasan Z. Majeed. Linear and mass attenuation coefficient of reactive powder concrete (RPC) sample ( of compressive strength equal to 70 Mpa) using beta particles and gamma ray with different energies have been calculated as a function of the absorber thickness and energy. The attenuation coefficient were obtained using NaI(Tl) energy selective scintillation counter with Sr/Y beta source having an energy rang from (0.546-2.274) MeV and gamma ray energies (0.569, 0.662, 1.063, 1.17 and 1.33) MeV . The attenuation coefficient usually depends upon the energy of radiations and nature of the material. The result represented in graphical forms. Exponential decay was observed. It is found that the capability of reactive powder concrete to absorber beta particles and gamma ray without any significant reduction in the compressive strength of the sample. That’s mean it is useful to choice this sample for radiation shielding of gamma and beta raywith low thickness.

Linear and mass attenuation coefficient of reactive powder concrete (RPC) sample ( of compressive strength equal to 70 Mpa) using beta particles and gamma ray with different energies have been calculated as a function of the absorber thickness and energy. The attenuation coefficient were obtained using NaI(Tl) energy selective scintillation counter with 90 Sr/ 90 Y beta source having an energy rang from (0.546-2.274) MeV and gamma ray energies (0.569, 0.662, 1.063, 1.17 and 1.33) MeV . The attenuation coefficient usually depends upon the energy of radiations and nature of the material. The result represented in graphical forms. Exponential decay was observed. It is found that the capability of reactive powder concrete to absorber beta particles and gamma ray without any significant reduction in the compressive strength of the sample. That's mean it is useful to choice this sample for radiation shielding of gamma and beta raywith low thickness.

Introduction:-
Beside nuclear facilities (nuclear reactors and particle accelerators), with the increasing use of radiation in medicine, the provision of adequate protection remains an important concern [1][2][3]. The effectiveness of the shielding material is determined by the interactions between the incident radiation and the atoms of the absorbing medium. The interactions which take place depend mainly upon the type of radiation, the energy of the radiation, and the atomic number of the absorbing medium.
Most important characteristic of a material protection is its ability in attenuation of gamma radiation. In general, heavy materials have higher ability in attenuation of gamma-rays.
One of the most widely used materials in reactor shielding is concrete; it is basically, a mixture of cement, sand, coarse aggregates and water. It is cheap, easy to prepare in different compositions, and easy to form and to use in construction works. Radiation shielding concrete can be used to attenuate both neutron and gamma rays. The photon interaction with the matter depends on the incoming photon energy and the density of the shielding material. The concrete shielding properties may vary depending on the material components of the concrete [4].
The attenuation coefficient is an important parameter characterizing the penetration and diffusion of rays in composite materials, and the accurate values linear attenuation coefficient of beta and gamma rays for various media especially composite materials are useful for dosimeter, radiation shielding to choice the suitable type of material to adequately stop various forms of radiations, as well as for many nuclear physics experiments [5]. The attenuation coefficient usually depends upon the energy of radiations and nature of the material [6]. The attenuation coefficient of beta by composite were investigated by Pujol et al. [7]. Also, measurements on attenuation coefficients and range energy relation of beta particles for various absorber at different energies have been reported by various workers as Rocca et al. [8] and Mahajan [9]. The effects of different parameters and energies on the attenuation coefficient for cement and concrete samples were discussed in several studies as in refs. [10][11][12][13][14][15].
This work aims to evaluate the performance of reactive powder concrete composite in attenuating gamma ray and beta particles. In this work the absorption of gamma ray and beta particles in different thickness of reactive powder concrete are studied and measured the linear and mass attenuation coefficient as a function of the energy and absorber thickness. Beta-particles and gamma ray intensities behind the samples with different thickness have been measured. Measurements have been carried out using a collimated beam of pure beta source 90 Sr/ 90 Y with energy (0.546-2.274) MeV and Cs-137, Co-60 and Bi-207 gamma sources with energies (0.569, 0.662, 1.063, 1.17 and 1.33) MeV. The leakage beta-particles and gamma ray intensities behind the samples have been carried out by using sodium iodide crystal NaI(TI) scintillation detector of dimension 2"×2". The incident and transmitted intensities were determined for fixed preset time at 1000 sec in each measurement. The attenuation of radiation expressed as: I=I 0 exp (-μx) ………(1) where I 0 is the number of particles of radiation counted during a certain time duration without any absorber, I is the number counted during the same time with a thickness x of absorber between the source of radiation and the detector and μ is the linear absorption coefficient. This equation may be cast into linear form, The unit of μis cm -1 The mass absorption coefficient, μ m defined as, μ m = μ/ρ μ m is measured in cm 2 /gm and ρ is particle density of absorber in gm/cm 3 .

Material and Methods:-Absorber materials:-
The materials used to prepare the reactive powder concrete samples as absorber with different thicknesses of this work are:  Cement:-An Ordinary Portland Cement (Type-I), Tassluga, was used for all specimens. The results of chemical analysis and physical test are shown in Table 1 and Table 2, respectively. The results of both chemical and physical test were compared with Iraqi Specification No. 5 / 1993 [16].
 Fine Aggregate:-Al-Ukhaider sand of (0.6 mm) maximum size was used as fine aggregate in concrete mixes for all specimens. Sieve analysis of the used sand is shown in Table 3 both with the limit of Iraq Specification No. 45/1993 [16], while the physical properties are shown in Table 4. According to the limit of Iraq Specification the used sand can be classified as Zone 4.
 Water:-Tap water was used for both mixing and curing process. Table 5 shows the chemical analysis of the used water both with the limit of ASTM C 1602/C 1602M-04 [17]specification.
 Silica Fume:-Silica fume conformed to EN 13263, product of Sika, was used as an additives (pozzolanic material) to produce the HPC for all specimens. The chemical composition and ASTM C1240-03 [18] requirements of silica fume are listed in Table 6 and Table7.

 Superplasticizer
A new generation of modified polycarboxylic ether that complies with ASTM C494-05 [19] types A and F (GLENIUM51) was the superplasticizer that used as a superplasticizer to modify the workability of high strength concrete . Table 8 gives the technical description of GLENIUM51.    Absorption 0.6 ---*All the test were conducted by the National Center of Laboratories and Researches (Baghdad).

Casting and Curing of Reactive Powder Concrete Samples
Eight standard cubes of (50x50x50) mm side length were casted using the adopted mix of reactive powder concrete. The process of mixing was similar to the one recommended by ACI Committee Report 544. All the dried materials were mixed well to get homogeneous composition after that (75 % of water amount + 50 % of superplasticiser) were added to the dry composition with additional mixing foe approximately five mints. The residual liquid quantity (25 % of total water + 50 % of superplasticiser) were added with further mixing until the mixture is met.
Water curing was used for 28 days after which three cubes were tested (dry surface) to evaluate the compressive strength 76

Experimental setup:-
The experimental arrangement with the electronic configuration is schematically shown in Fig.1. The assembly was placed in lead castle. Energy calibration was performed using a set of standard gamma sources.

Determination of beta-particles range
The range of beta-particles, for energy range 0.01≤ E ≤ 2.5 MeV can be approximated by Baker and Katz [10 ] : R(kg.m -2 )= 4.12 E n (MeV) …………. (4) where n=1.265-0.0954 lnE max E max is the maximum beta-particles energy in MeV and R is the range of beta-particles in kg.m -2.
Therefore, when the thickness of the attenuator is above the rang of beta-particles the transmitted particles would be nearly stopped, for concrete, sheet of thickness0.5 cm, which is sufficient to stop all beta particles from 90 Sr/ 90 Y.   , respectively. These values give the conclusion that the μ m values decreases as energy increased. Another useful concept is the half-value thickness, X ½ , which is the value of the absorber thickness that will reduce the intensity by a factor of 2. It has been found ranging from 4.5 cm to 6 cm depending on the values of the energies above. Also, beta particles are attenuated in an absorption medium by the various interaction processes, primarily through ionization and radiative energy losses.

Results and Discussion:-
The absorption spectra for beta particles without and in different thickness of absorber from 5 to 25 cm was shown in Fig.8. It is clear that the intensity of beta decrease with increase the thickness of the absorber.  (9) and (10) as a function of energy and thickness, respectively. It is shown that linear attenuation increase with increase energy and decrease with increase the thickness of absorber. Also, these values with mass attenuation coefficients of beta particle are given in Table ( 9).It is shown that the mass attenuation decrease with increase the thickness of absorber and increase with increase energy.

Conclusion:-
The aim of this work was to investigate the performance of low weight materials for shielding gamma ray and beta particles. The attenuation of radiation can be achieved using a wide range of materials and understanding the basic principles involved in the physical interaction of radiation with matter that can help in the choice of shielding for a given application.
The resultsof this research indicated that the thickness affected on the absorption of the energy. The thickness of the sample does really influence the energy that penetrating the sample.  It is clear that the intensity decrease with increase the thickness of the reactive powder concrete samples. For gamma ray, it is found that the linear and mass attenuation coefficient decrease with increase energy. For beta particles, the linear attenuation increase with increase energy and decrease with increase the thickness of absorber. These results improved the capability of reactive powder concrete to absorber gamma ray and beta particles. That's mean it is useful to choice this sample for radiation shielding of gamma and beta raywith low thickness with no significant reduction in the compressive strength.