Research Article Volume 6 Issue No. 6

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1 DOI 1.41/ ISSN IJESC ` Research Article Volume 6 Issue No. 6 An investigation of the Attenuation of β-particle and to compare the Linear Attenuation Coefficients of Various Materials using G.M. Counter Ritu Jain 1, Priya Shekhawat 2 The IIS University Gurukul Marg, Mansarovar, Jaipur, Rajasthan, India Abstract: These days, people are very much concerned about their safety and health related issues like cancer, tumor etc., as the radioactivity cannot be noticed by our five senses. To know how much radioactivity is there at a place, we need a specific device, which is economical, easy to use, and accurate for work place and monitors the radioactivity level in the area. This paper represents result of the GM tube (Geiger Muller tube), which senses the radioactivity; sense the different types of radiation. Geiger Muller Tube is a portable radiation detector and a measuring instrument used to detect presence of radiation in the surroundings. It also gives us the measure of intensity of radiation. To reduce the radiation to a level safe for humans different shielding materials are used. Keeping this in mind, a study has been done to measure the linear attenuation coefficients of five different materials viz. Lead, Copper, OHP sheet, Tin and Iron. The linear attenuation coefficient of Lead was found to be the highest among all samples and OHP sheet has lowest linear attenuation coefficient. Keywords: radioactivity, Geiger Muller Tube, shielding material, linear attenuation coefficients INTRODUCTION Radioactivity refers to the particles which are emitted from nuclei as a result of nuclear instability. The most common forms of radiation emitted have been classified as alpha (α), beta (β), gamma (γ) radiation. The amount of radioactivity is measured in units of curie (Ci); 1 curie= 3.7 x 1 1 radioactive decay per second, Becquerel (Bq) is also a unit of radioactivity. 1 Bq= 27pCi. Alpha radiation occurs when an atom undergoes radioactive decay, giving off a particle (α-particle) consisting of two protons and two neutrons. Due to their charge and mass, alpha particles interact strongly with matter and travel only a few centimeters in air. Beta radiation takes the form of either an electron or a positron being emitted from an atom. Due to their smaller mass, it is able to travel further in air and can be stopped by a thick piece of plastic. Gamma radiation does not consist of a photon. Having no mass or charge, gamma radiations can travel much farther through air than alpha or beta. Gamma waves can only be stopped by a dense enough layer of some material. Radiation can be a great source of threat to our health, life and the environment if not properly monitored and controlled. All methods for detection of radioactivity are based on interactions of the charged particles. As a result of interaction, ions are produced and reduction in energy is observed. In the case of neutrons and gamma rays, the ionizations produced are caused by secondary charged particles. A detector is defined as a device which converts the energy of nuclear particle or radiation into a useable electric signal. An ideal detector is able to differentiate between various types of radiation and particles and give a signal which is proportional to their energy. Most of the detectors are classified into one of three groups: (1) Gaseous detectors (2) Semiconductor detectors (3) Scintillation detectors. These are also called counters, if the output is measured in terms of the number of counts. Detectors are also classified as electric (Ionization chamber, Proportional counter, G. M. counter, Semiconductor counter), and optical (Scintillation counter, Cerenkov counter, Photographic emulsion, Cloud chamber, Bubble chamber, Spark chamber). Ionization chamber is widely used for the detection and measurement of certain types of ionizing radiation; X-rays, gamma rays and beta particles. Geiger-Muller counter is used for the detection of gamma radiation, X-rays and alpha and beta particles. It can also be adapted to detect neutrons. Proportional counter is widely used where energy levels of incident radiation must be known, such as in the discrimination between alpha and beta particles or accurate measurement of X-ray radiation dose. Semiconductor detectors have found broad application in particular for gamma and X-ray spectrometry and as particle detectors. Bubble chamber is used to detect electrically charged particles moving through it. In the present work dealing with Geiger- Muller counter specifically. Geiger Muller counters have been a fundamental device in radiation detection for decades due to their simplicity and low cost. In 198, Hans Geiger developed a machine that was capable of detecting alpha particles. Geiger s student, Walther Muller, went on to improve the counter in 1928 a way that would allow the counter to detect any kind of ionizing radiation. And thus, the modern Geiger-Muller counter was born and the techniques in radiation detection were forever changed. The Geiger-Muller tube, or GM tube, is an extremely useful and inexpensive way to detect radiation. All nuclear radiations, whether they are charged particles or gamma rays, it will ionize atoms while passing through a gaseous medium. This ionizing property of a nuclear radiation is utilized for its detection. Geiger-Muller counter, commonly called as GM counter or simply as Geiger tube is one of the oldest and widely used radiation detectors. The GM Counter is a versatile device which may be used for counting alpha particles, beta particles, and gamma rays with varying degrees of efficiency. International Journal of Engineering Science and Computing, June

2 Kirandeep et.al. determined the Attenuation Coefficient and Water Content of Broccoli Leaves using Beta Particles.The results show that the water content in the leaves of Broccoli was used to determine their attenuating characteristics to beta particles of 24 Tl. The mass attenuation coefficient was obtained. As the water content in the leaves varies, these parameters also vary. The transmission intensity decreases with increase of water amount in plant leaves. Beta attenuation is a fast, reliable and non-destructive method that provides continuous monitoring of plant water status. The mass attenuation coefficients of some elements H, C, O, Al, Cl, Cu and Ag from compounds and salts were measured by C.S. Mahajan. Sen et al. determined the half-value thickness of aluminum foils for different beta sources by using fractional calculus which showed that reduction of beta-ray intensity with respect to thickness of absorber material exhibits a non-exponential behavior due to the different types of the energy loss processes and many different fractal-like paths followed by beta particles in material. Thontadarya, S. R. studied the effect of geometry on mass attenuation coefficient of β-particles in He investigated the mass attenuation coefficient of β-particles in aluminum for five different β-emitters covering the end-point energy range from.4 to 2.3 MeV adopting two extreme geometries MATERIALS AND METHOD Geiger Counting system type GC62A, which is used in this study, is an Advanced Technology based versatile integral counting system designed around eight bit microcontroller chips. This counting system is useful for carrying out a number of Nuclear Physics experiments. GM 12 is a Halogen Quenched End Window GM Detector; this detector is supplied in a cylindrical PVC enclosure with MHV socket arrangement for applying HV bias voltage. It is suitable for Beta & Gamma Counting. Its operating voltage range is from 45V to 6V.The Gas filled in GM tube are Neon gases and Halogen. The stand for G.M. tube type SG 2 was used to hold PVC enclosed End Window G.M. tube. It has both sample and absorber trays. Source kit of type SK21 was used in the experiment which is a beta source disc evaporated & sealed in a 25mm X 1mm thick plastic disc. 24 Tl was taken as beta source. It has.764mev end point energy. It was discovered by William Crookes. Thallium is found in several ores. 24 Tl is the most stable radioisotope with a half-life of 3.78 years. Beta sources can be used in radiation therapy to kill cancer cells. In the present paper, samples used for finding the linear attenuation coefficient are: Lead, Copper, OHP sheet, Tin and Iron. The atomic number of copper is 29 and its density is 8.9g.cm -3. It is a reddish metal with a face-centered cubic crystalline structure. Copper metallo-organic complexes have radiation protection and radiation recovery activities. They are capable of causing rapid recovery of immune competence and recovery from radiation induced tissue changes. Copper complexes are used in the treatment of cancer and in particular, treating patients undergoing ionizing radiation therapy for their cancer, accidental exposure to radiation, and astronauts undertaking space travel. Atomic number of lead is 82 and its density is 11.34g.cm -3. It is a bluish-white lustrous metal. It is very soft, highly malleable, ductile, and a relatively poor conductor of electricity. However, most lead concentrations that are found in the environment are a result of human activities. Some folk medicines contain lead. Iron has atomic number 26 and density 7.8g.cm -3. It is a lustrous, ductile, malleable, silver-gray metal. Iron does test only very weakly positive for the Ames test for cancer, however, since it is such a strong catalyst and essential for the production of ATP and consequently DNA production. Atomic number of tin 5 and its density is 7.3g.cm -3. It is a soft, pliable, silvery-white metal. The niobium-tin alloy is used for superconducting magnets, tin oxide is used for ceramics and in gas sensors. Tin oxide is insoluble and the ore strongly resists weathering, so the amount of tin in soils and natural waters is low. Density of OHP sheet is 2.641g.cm -3. OHP stands for Overhead projector. OHP sheet is also called as transparent sheet. This is made of a material which is light weight transparent plastic film with superior quality of poly vinyl chloride. These sheets are extensively used and demanded in the market all over the country. The variations of count rate with applied voltage is studied first to calculate the operating voltage of G.M.tube by plotting a graph between applied voltage and number of counts. For the determination of linear attenuation coefficient of different materials a graph is drawn between the thickness of the material and the corresponding number of counts from the G.M. counter. The following formula gives a relation between the intensity and the thickness of the sample: I=I e -µx1/2 where, I=transmitted intensity through absorber of thickness x I = incident intensity of beam µ = linear attenuation coefficient x 1/2 = thickness of the sample log (I/I ) = -µx 1/2 log (.5) = -µx 1/2.693 = -µx 1/2 µ =.693/ x 1/2 For determination of mass attenuation coefficient: µ m =µ/ρ where, ρ=density of the sample RESULTS AND DISCUSSIONS The variations of count rate with applied voltage are studied and thereby the plateau, the operating voltage and the slope of the plateau are determined using the following table. International Journal of Engineering Science and Computing, June

3 counts/6sec. counts/6sec. Counts/6sec. Table 1: Showing the variation of count rate with applied voltage S.No. Voltage (volts) Counts(N) Background counts(n b ) Corrected counts(n- N b ) Determination of Operating Voltage Absorber-Cu Voltage (v) Graph1: Plot of applied voltage v/s Counts/6sec. V 1 (Starting voltage of Plateau)= 39V V 2 (Upper threshold of the plateau)= 54V Plateau length VPL = V 2 - V 1 = (54-39) = 15V V (Operating Voltage) = (V 2 + V 1 )/2 = 54+39/2 = 465V Beta source taken is 24 Tl Operating voltage e = 465V For the calculation of linear attenuation coefficients of different samples graphs are plotted between the thickness of samples and the corresponding no. of counts. Table 2: Showing the variation of number of counts with the thickness of Copper S.No. Thickness(mm.) Counts in 6 seconds Graph2: Plot of Thickness of Cu sheet v/s Counts/6sec Table 3: Showing the variation of number of counts with the thickness of Lead S.No. Thickness(mm.) Counts in 6 seconds Absorber-Pb Graph3: Plot of Thickness of Pb sheet v/s Counts/6sec International Journal of Engineering Science and Computing, June

4 Counts/6sec. Counts / 6 sec. Counts/6sec. Table 4: Showing the variation of number of counts with the thickness of OHP sheet S.No. Thickness(mm.) Counts in 6 seconds Table 6: Showing the variation of number of counts with the thickness of Tin sheet S.No. Thickness(mm.) Counts in 6 Seconds Absorber - OHP sheet Absorber-Sn Thickness (mm) Graph 4: Plot of Thickness of OHP sheet v/s Counts/6sec Graph 6: Plot of Thickness of Tin sheet v/s Counts/6sec Table 5: Showing the variation of number of counts with the thickness of Iron S.No. Thickness(mm.) Counts in 6 Seconds Absorber-Fe Graph 5: Plot of Thickness of Iron sheet v/s Counts/6sec Table 7: Comparative study of Linear/Mass attenuation coefficient for different samples S.No. Sample Linear Attenuation coefficient (cm -1 ) Mass attenuation coefficient (cm 2 /gm) 1. Lead Tin Copper Iron OHP sheet The linear attenuation coefficient of different samples under investigation were found to be in the following order: Pb > Sn > Cu > Fe > OHP sheet. The mass attenuation coefficient were found to be in the following order: Sn>Pb>Cu>Fe>OHP sheet Lead is the most effective shielding material, both for high Z and for density. It may be due to as increasing atomic number of absorber, Bremsstrahlung production increases. Bremsstrahlung consists of X-ray that is produced when high-velocity charged particles are very rapidly accelerated. When a Beta particle passes close to a nucleus, the strong attractive Coulomb force causes the Beta particle to deviate sharply from its original path. It may be due to the stopping power values for beta particles decreases as the atomic number Z of the International Journal of Engineering Science and Computing, June

5 absorber element increases. This occurs because substances of high Z have fewer electrons per gram and these are more tightly bound. Consequently, the range tends to increase as the incident energy is increasing. In other words, as Z increases, the multiple scattering of the electrons increases. The effect of multiple scattering is to increase the actual path of the electron in a substance. This tends to decrease the range, which is the linear distance through the medium. These two effects act to balance each other, so that the density of a substance gives one a good idea of its relative ability to stop electrons. It may be due to the fact that the ability to absorb energy from Beta particle depends on the number of absorbing electrons in path of the Beta i.e. on the areal density of electron (e - /cm 2 ) in absorber, and to a much lesser degree, on the atomic number of the absorber. Areal density is proportional to the product of the absorbing material and linear thickness of the absorber.(t d =ρ*t l ) A small linear attenuation coefficient indicates that the material is relatively transparent, while larger values indicate greater degrees of opacity.for higher atomic number the density of a substance give good idea of stop electrons. As thickness of absorber increases the transmission intensity decreases. REFERENCES [1] Sen, Mursel, Abdullah Engin Calik and Huseyin Ertik (214) "Determination of half-value thickness of aluminum foils for different beta sources by using fractional calculus." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms Vol. 335 pp [2] Thontadarya, S. R. (1984) "Effect of geometry on mass attenuation coefficient of β-particles." The International Journal of Applied Radiation and Isotopes Vol.35 no.1: pp [3] Sabah M. Amanallah (214) Evaluation Of Some Atomic Coefficients For Elements Carbon-Copper- Silver By Using Beta Particles IRAQI Journal Of Applied Physics Vol.1, No.1 and Tl Sources Research Journal Of Physical Science Vol. 1(2). [6] Mahajan, C. S. (212): "Mass attenuation coefficients of beta particles in elements."science Research Reporter 2.2 pp [7] KomalKirandeep, ParveenBala, AmandeepSharma (215) Determination of Attenuation Coefficient and Water Content of Broccoli Leaves using Beta Particles International Conference on Advancements in Engineering and Technology (ICAET 215) [8] Singh, Bhupender, and R. K. Batra (1987). "A method for calculating mass-attenuation coefficients of beta particles." International Journal of Radiation Applications and Instrumentation. Part A. Applied Radiation and Isotopes Vol pp [9] Ahmed, Syed Naeem. (27) Physics and engineering of radiation detection Academic Press. [1] Theodorsson, Pall (1996) Measurement of weak radioactivity. World scientific [11] CY Yi, HS Han, JS Jun, HS Chai, (1998). Calculation of Mass Attenuation Coefficients of Beta Particles Radiation Protection Dosimetry Vol.78(3) pp [12] CY Yi, HS Han, JS Jun, HS Chai, (1999). Mass attenuation coefficients of β+-particles Appl. Radiat. Isot. Vol 51 pp [13] S. Yalcyn, and O. Gürler,(25) Effect of different arrangements of point source, aluminum absorber and detector on mass absorption coefficient of beta-particles Journal of Radio analytical and Nuclear Chemistry Vol. 26, No. 3,p.p [14] Rittersdorf, Ian. (27) "Lab 4 Geiger-Mueller Counting.". [15] Uosif, M. A. M. (214) "Properties of a Some (Ag- Cu-Sn) Alloys for Shielding Against Gamma Rays." International Journal of Advanced Science and Technology Vol. 63 pp [4] Ram, Nathu, IS Sundara Rao, and M. K. Mehta (1982). "Mass absorption coefficients and range of beta particles in Be, Al, Cu, Ag and Pb." Pramana Vol.18.2 pp [5] Chaudhari Laxman M.(213) Study of Attenuation Coefficients of Leaves of Asoka Plant by Using Cs International Journal of Engineering Science and Computing, June