Nuclear Radiation 1 I. Radioactive Isotopes A radioactive isotope has an unstable nucleus and emits radiation to become more stable. Isotopes of elements may be stable or unstable. 2
II. Nuclear Radiation Is the radiation emitted by an unstable atom. Takes the form of alpha particles, neutrons, beta particles, positrons, or gamma rays. There are more types! 3 III. Alpha Decay When a radioactive nucleus emits an
alpha particle, a new nucleus has: A mass number that is 4 less than that of the initial nucleus. An atomic number that is decreased by 2. 4 IV. Balancing Nuclear Equations In a balanced nuclear equation, the sum of the mass numbers and the sum of the atomic numbers for the nuclei of the reactants and the products must be equal. MASS NUMBERS 251 =
251 247Cm + 4He Total = 251Cf 98 96 2 Total = 98 = 98
ATOMIC NUMBERS 5 V. Equation for Alpha Decay Write an equation for the alpha decay of STEP 1 Write the incomplete equation 222 Rn ? 86 Rn.
222 + 4He 2 STEP 2 Determine the mass number of the new nucleus. Mass number: 222 4 = 218 STEP 3 Determine the atomic number of the new nucleus. Atomic number: 86 2 = 84 6
V. Equation for Alpha Decay STEP 4 Determine the symbol of the new nucleus. Symbol of element 84 = Po STEP 5 Complete the equation 222Rn 218Po + 4He 86 84
2 7 VI. Beta Decay A beta particle, Is an electron emitted from the nucleus. Forms when a neutron in the nucleus breaks down. 1 n
0 0 -1 e + 1H 1 8 Writing An Equation for a Beta Emitter 42 Potassium is a beta emitter. 42K new nucleus + 0e
19 -1 The atomic number of the new nucleus increases by 1. Mass number : (same) = 42 Atomic number: 19 + 1 = 20 Symbol of element 20 = Ca The nuclear equation is: 42K 42Ca + 0e
19 20 -1 9 VII. Positron Emission In positron emission, A proton is converted to a neutron and a positron. 1p 1n + 0e 1
0 +1 The mass number of the new nucleus is the same, but the atomic number decreases by 1. 49Mn 49Cr + 0e 25 24 +1 10
VIII. Gamma Radiation In gamma radiation, Energy is emitted from an unstable nucleus and indicated by m(=metastable). The mass number and the atomic number of the new nucleus are the same. 99mTc 99Tc + gamma 43 43 11 Summary of Types of Radiation
12 Summary of Changes in Mass and Atomic Numbers 13 IX.Half-Life The half-life of a radioisotope is the time for the radiation level to decrease (decay) to one-half of the original value. 14
X. Radiation Exposure What determines how much radiation a person is exposed to: amount of radioactive source type of radioactive source (alpha, beta, gamma?) half-life of radioactive substance distance from radioactive source shielding between person and radioactive source duration (time) of exposure 15
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