# Lab N3 - McGee 1 Lab N3 Allison McGee Mr Fedorchak Thursday...

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McGee 1 Lab N3 Allison McGee Mr. Fedorchak Thursday 2:00- 4:50pm Partners: Stevie Whitehead Alyssa Woods

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McGee 2 Purpose: The purpose of this experiment is to determine the decay constant and resulting half-life of the radioactive element 137m 56 Ba. Introduction : In the last decade of the 19 th century, it was discovered that certain materials spontaneously gave off penetrating rays of energy. This process was named radioactivity by Marie Curie and subsequent investigations proved the rays were actually of three types. Called Alpha (α) which consisted of a helium nucleus (two protons and two neutrons), Beta (β) which consisted of an emitted electron and Gamma (γ) for convenience, it was found the first two were composed of electrically charged particles and could be stopped by the thinnest sheets of paper. The last type, Gamma, was a highly penetrating form of electromagnetic radiation. The atom from which the radiation is emitted is in an unstable state, and by the emission, tries to lower its energy to a ground state. Since the parent atom is transformed into a new element, the number of original atoms No, is seen to drop according to the formula: N=N o e -λt Equation (1) where N is the population of atoms at a particular time t, and lambda, λ, is the decay constant of the parent atom with the units of time -1 . To find the decay constant, the natural log of both sides of Equation 1 is taken and the terms rearranged as shown below in Equation (2). - ln N/N o =λt Equation (2) A plot of this equation will yield a straight line. The slope of the line is the decay constant, λ.
McGee 3 A quantity related to the decay constant is the half-life with the symbol. This is the time required for one-half of the original element to under go radioactive decay. The half-life for a radioactive material is found from its decay constant by the following formula. t ½ = 0.693/λ Equation (3) Using the Spectech Counter with the Geiger-Muller Probe, we will be able to count the number of radioactive decays within a preset time window over a period of time. For today’s lab, we will be determining the decay constant for an isotope of Barium, 137m 56 Ba. 137m 56

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