Nuclear Transformation 28.2

Stability Stability comes from the neutron to proton ratio Below the atomic number 20 the ratio is 1 (equal) Above 20, more neutrons than protons, ratio is 1.5 85 % of all nuclei are unstable

Decay Some nuclei have to many neutrons They decay by turning neutron to a proton and emit a beta particle Beta decay

Decay Other nuclei are unstable because they have to few neutrons Become stable by converting a proton to a neutron This creates a positron

Decay All nuclei with atomic number greater than 83 are radioactive They have too many neutrons and too many protons Most emit alpha particles.

Decay Mass is not conserved Lost mass is converted to energy (radiation)

Half Life Time that is required to decay half of radioisotope nuclei to product After 1 half life, half of radioactive atoms have decayed to a new element

Half Life # of ½ lives= Total Time half life length Scientists use half life to determine age of ancient artifacts Carbon dating- known time to convert isotope of C-14 to N-14 # of ½ lives= Total Time half life length Sample(final)= Sample(initial) x (1/2)number of half lifes

Half Life Read pg. 814-815 How many half-lives of carbon 14 is 75,000 years? What percentage of the carbon 14 remains after this number of half lives?

Transmutation Conversion of one element to another Radioactive decay is one way transmutation occurs Also occurs when nucleus is bombarded by high energy particles protons, neutrons or alpha particles

Transmutation Ernest Rutherford 1919 performed earliest artificial transmutation What element is named after him? Explain his experiment.

Transmutation Rutherford lead to finding proton Chadwick’s transmutation in 1932 lead to finding neutron Read pg. 844 Link to Physics

Transuranium elements Atomic number 92 and above All go thru transmutation None occur in nature All are radioactive

Transuranium elements First artificial elements made in 1940 18 more have been made, atomic numbers 95 through 112 and more to come

Discussion Alchemists tried for years to turn common metals in to precious metals No chemical reaction can achieve their goal Thru transmutation you can