Nuclear Transformations 25.2 Nuclear Transformations Radon-222 is a radioactive isotope that is present naturally in the soil in some areas. It has a constant rate of decay. You will learn about decay rates of radioactive substances.

Nuclear Stability and Decay 25.2 Nuclear Stability and Decay Nuclear Stability and Decay What determines the type of decay a radioisotope undergoes?

Nuclear Stability and Decay 25.2 Nuclear Stability and Decay More than 1,500 different nuclei are known. Of those, only 264 are stable and do not decay or change with time. These non-radioactive nuclei are in a region called the band of stability.

The neutron-to-proton ratio determines the type of decay that occurs The main types of nuclear decay include Alpha (loss of 2 protons and 2 neutrons) and Beta (neutron changing into a proton with the loss of an electron)

The main types of nuclear decay include Alpha (loss of 2 protons and 2 neutrons) and Beta (neutron changing into a proton with the loss of an electron)

25.2 Electrons can be involved in nuclear decay: Electron capture involves catching an e- and changing a proton to a neutron. A proton is also changed to a neutron with positron emission. Positrons are particle with the mass of an electron but a positive charge.

25.2 Half-Life A half-life (t1/2) is the time required for one-half of the nuclei of a radioactive sample to decay to products. After each half-life, half of the existing radio- active atoms have decayed into atoms of a new element. Half-lives range from seconds to billions of years, depending on which atom is decaying

The half life for carbon-14 is 5730 years. 25.2 Half-Life As each half life passes, the amount of undecayed nuclide remaining decreases by one half. The half life for carbon-14 is 5730 years. This decay curve shows that during each half-life, half of the radioactive atoms decay exponentially into atoms of another element. INTERPRETING GRAPHS a. Identify What percent of the atoms remains after 1 half-life? b. Describe What percent of the atoms remains after two half-lives? c. Apply Concepts Approximately how many half-lives does it take for 12.5% of the radioisotope to remain?

25.2 Half-Life

25.2 Half-Life The ratio of Carbon-14 to stable carbon in the remains of an organism changes in a predictable way that enables the archaeologist to obtain an estimate of its age. This archaeologist is digging for artifacts. The age of an artifact can often be determined from its measured carbon-14 content.

Nuclear Half Life: Intro and Explanation (5:30) https://www. youtube Nuclear Half Life: Intro and Explanation (5:30) https://www.youtube.com/watch?v=opjJ- 3Tkfyg Nuclear Half Life: Calculations 2 (8:00) https://www.youtube.com/watch?v=WAsmY4 ocWSA

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Where n = the number of half lives 25.1 Or you could multiply the mass by 1 2n Where n = the number of half lives

To determine how much of a nuclide remains undecayed after a certain number (n) of half-lives has passed: Fraction remaining = ( ½ )n = 1/2n Grams left = (original grams)(1/2n)

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Knowns: Want to know: 1 half-life of Mn-56 = 2.6 h mass of 1.0 g after 10.4 h? Starting sample = 1.0 g number of half-lives in 10.4 h? original sample =1.0 g 10.4 h x 1 half-life = 4 half-lives after 1st half life = 0.5 g 2.6 h 2nd half life = 0.25 g 3rd half life = 0.125 g after 4 half-lives there will be = 0.0625 g

Example: Fluorine-21 has a half life of approximately 5 seconds Example: Fluorine-21 has a half life of approximately 5 seconds. What fraction of the original nuclei would remain after 20 seconds? If you began with 40 grams, how many grams would remain? How old is a tree (half life of 5730 years) with a sample that started at 50 grams and ended with 12.5 grams?

Transmutation Reactions 25.2 Transmutation Reactions Transmutation Reactions What are two ways that transmutation can occur?

Transmutation Reactions 25.2 Transmutation Reactions The conversion of an atom of one element to an atom of another element is called transmutation. Transmutation can occur by radioactive decay. Transmutation can also occur when particles bombard the nucleus of an atom.

Transmutation Reactions 25.2 Transmutation Reactions The first artificial transmutation reaction involved bombarding nitrogen gas with alpha particles. The first artificial transmutation reaction involved bombarding nitrogen gas with alpha particles, as illustrated here. Interpreting Diagrams What particles were formed?

Transmutation Reactions 25.2 Transmutation Reactions The elements in the periodic table with atomic numbers above 92, the atomic number of uranium, are called the transuranium elements. All transuranium elements undergo transmutation. None of the transuranium elements occur in nature, and all of them are radioactive.

Transmutation Reactions 25.2 Transmutation Reactions Transuranium elements are synthesized in nuclear reactors and nuclear accelerators. Fermilab is a major accelerator center located in Batavia, Illinois. The main accelerator is a ring that has a radius of 1.0 km.

25.2 Section Quiz. 25.2.

25.2 Section Quiz. 2. When potassium-40 (atomic number 19) decays into calcium-40 (atomic number 20), the process can be described as positron emission. alpha emission. beta emission. electron capture.

25.2 Section Quiz. 3. If there were 128 grams of radioactive material initially, what mass remains after four half-lives? 4 grams 32 grams 16 grams 8 grams

25.2 Section Quiz. 4. When transmutation occurs, the ________ always changes. number of electrons mass number atomic number number of neutrons

25.2 Section Quiz 5. Transmutation occurs by radioactive decay and also by extreme heating. chemical reaction. high intensity electrical discharge. particle bombardment of the nucleus.

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