4.1 Natural Radioactivity Based on the number of protons and neutrons, an atom can be stable or unstable. Generally, small atoms require an equal number of p & n for stability, larger atoms require more neutrons. To obtain a more stable state, unstable nuclei disproportionate and emit high energy particles and/or electromagnetic radiation (photons) spontaneously. Alpha Beta Gamma radioactive Stable The name for this process is radioactivity and the substances undergoing such, are said to be radioactive.

:. Called ionizing radiation Radiation strikes molecules in its path e-s may be knocked away, forming unstable particles (ions, radicals) :. Called ionizing radiation These can cause undesirable chem. reactions which may lead to malignant tumors, leukemia, anemia, or genetic mutations.

Biological effect of radiation Figure 04-00-06UN Title: Radiation Penetration Caption: When radiation strikes molecules in its path, electrons may be knocked away, forming unstable ions. For example, when radiation passes through the human body, it may interact with water molecules, removing electrons, and producing H2O+, which can cause undesirable chemical reactions. 3

C  e + N 14 14 6 -1 7 Nuclear Reactions Mass number 14 14 6 6 All nuclear equations show a balance on mass number & atomic number between the reactants and products: Mass number 14 14 14 14 C  e + N 6 -1 7 6 6 Atomic number Top: 209=4+X X = 205 209 4 ? Po  He + ? symbol: 82 = Pb 84 2 ? bottom: 84=2+X X = 82 205 Pb 209 4 Po  He + 82 84 2

Alpha Emission (∝) ► 4He, helium nucleus, contains 2 protons and 2 neutrons ► most ionizing, but least penetrating 5 5

Gamma Emission (γ) The daughter nuclides produced by  ∝ -decay are often obtained in an excited state. The excess energy associated with this excited state is released when the nucleus emits a photon in the  𝛾-ray portion of the electromagnetic spectrum. Most of the time, the  𝛾 -ray is emitted within 10-12 seconds after the  ∝-particle. In some cases, gamma decay is delayed, and a short-lived, or metastable, nuclide is formed, which is identified by a small letter m written after the mass number.  60mCo, for example, is produced by the electron emission of 60Fe. The metastable 60mCo nuclide has a half-life of 10.5 minutes. Since electromagnetic radiation carries neither charge nor mass, the product of  𝛾 -ray emission by 60mCo is 60Co. 6

Technetium (Tc-99m) is a gamma emitter. The most widely used radioisotope for medical diagnostics. It can be injected intravenously as a solution of sodium pertechnatate, NaTcO4. Gamma rays emitted by the technetium are detected to produce a scintigram. whole-body bone scintigrams obtained in an adult demonstrate normal anatomy. Extensive osseous metastases from lung carcinoma.

Beta Emission (𝛽) Turns a neutron into a proton: n  p + e- β particle is a high energy electron 9 9 9

How Long Does the Radioiodine Stay in the Body? Radioactive Iodine ( I-131) therapy is a treatment for an overactive thyroid, a condition called hyperthyroidism. Radioiodine is collected by the thyroid gland. The radiation given off by this form of iodine decreases the function of the thyroid cells and inhibits their ability to grow. This is the desired medical effect of this treatment. Some of the other tissues in your body will receive some incidental radiation. This small amount of radiation has NOT been shown to produce any adverse effect. b emissions g emissions 89.9% 7.3% 131 53 I 54 Xe Xe* I 131 53 Xe 54 -1 + g e 90 % 10 % The radioactive iodine that is not taken up by your thyroid is rapidly eliminated through body fluids such as urine, feces, saliva, and perspiration. How Long Does the Radioiodine Stay in the Body?

Positron Emission 11 11 11 ► Turns a proton into a neutron: p  n + e+ positron has a charge of +1 and negligible mass ► Antimatter, anti-electron 11 11 11

Positron emission tomography (PET) The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer), which is introduced into the body on a biologically active molecule. Fludeoxyglucose is a radiopharmaceutical used in the medical imaging a glucose analog, with the positron-emitting radioactive isotope fluorine-18 substituted for the normal hydroxyl group at the 2' position in the glucose molecule.

PET scan Positron emission tomography http://youtu.be/qgvrF-DHfJs

p + e- → n Electron Capture occurs when an inner orbital electron is pulled into the nucleus no particle emission, but atom changes proton combines with the electron to make a neutron p + e- → n 14 14

Practice An alpha particle is the same as: a. helium-5 nucleus b. helium-4 nucleus c. helium-3 nucleus d. proton 2. Which of the following is the most penetrating? a. alpha particles b. beta particles c. Positrons d. gamma rays 3. What type of shielding is required for gamma radiation? a. Gloves b. paper and clothing c. lead or concrete d. Lab coat and shoes 2 4. The damaging effects of radiation are due to? a. Production of poison b. Generation of isotopes c. Generation of radicals d. Production of new isotopes 15 15

5. The nuclear reaction, 8B  8Be + 0e is an example of: 5 4 +1 Practice 5. The nuclear reaction, 8B  8Be + 0e is an example of: 5 4 +1 a. gamma radiation b. positron emission beta decay alpha decay 6. Write the Nuclear Equation for the Positron Emission From K-40 7. Write the nuclear equation for the beta decay of cobalt-60. 2 8. Write a nuclear equation for the electron capture by Be-7 16

4.4 Half-life of a radioisotope The half-life of a radioisotope is the time for the radiation level to decrease to one-half of the original value. Figure 04-03-03UN Title: Half-life Caption: The half-life of a radioisotope is the amount of time it takes for one-half of a sample to decay. Radioisotopes that are naturally occurring tend to have long half-lives used in nuclear medicine have short half-lives 17

To solve a problem using t1/2 1. Use the half-life as a conversion factor: 1 half-life 8.0 days Example: Use the half-life given above to calculate how many half-lives in 40 days? 40 days x 1 half-life = 5 half-lives 2. Reduce the amount of sample by ½ for every half-life. Example: How many grams left over, after 5 half-lives, if started with 100 g? 100 x ½ x ½ x ½ x ½ x ½ = 3.125 g 100 x (½)5 100 x 1/32 If it helps any, consider: Amount remaining = starting amount x (½)n n = number of half-lives

Practice 9. ) F-18, which has a half-life of 110 min, is used in PET scans. If 100 mg of F-18 is shipped at 8:00 am, how many mgs of the radioisotope are still active if the sample arrives at the radiology laboratory at 1:30 pm? a) 50 mg b) 25 mg c) 12.5 mg 10. Phosphorus-32, a radioisotope used in the treatment of leukemia, has a half-life of 14 days. If a sample contains 8.0 g of phosphorus-32, how many grams of phosphorus-32 remain after 42 days? 19 19