Stability of nuclei

1. Stability of nuclei • Most chemicalreactions involve either the exchange or sharing of electronsbetween atoms. Nuclear chemistry involves changes in the nucleus. • Transmutation is when the nucleus of one element is changed into a different element. • The ratio of the neutronsto protons determines the stability of a given nucleus, thus, the ratio in all nuclei with atomicnumbers greater than 83have unstablenuclei and are radioactive.

2. Stability of nuclei • Radioisotopes are elements that are unstable and thus radioactive. • When an unstable nucleus decays, it emits radiation in the form of alpha particles, betaparticles, positronsand / or gammaradiation. • An alphaparticle is a helium nucleus composed of 2protons and 2neutrons; represented by the symbol 2Heor αand is found in Table Oon the Reference Table.

3. Stability of nuclei • A betaparticle is an electron whose source is an atomicnucleus, while a positronis identical to an electron except that it has a positivecharge and they can be found on Table Oon the Reference Table. • Almost all nucleardecay also releases some energy in the form of gammarays. • Radiation can be harmfulwhen it interacts with livingthings.

4. Stability of nuclei • In Alpha decay, a nucleusejects an alpha particle and becomes a smallernucleus with lesspositive charge; it can be summarized as follows: • Atomic # decreases by 2 • # of protons decreases by 2 • # of neutrons decreases by 2 • Mass # decreases by 4

5. Stability of nuclei • Beta decay has the effect of turning a neutronin the nucleus into a protonand an electron; it can be summarized as follows: • Atomic # increases by 1 • # of protons increases by 1 • # of neutrons decreases by 1 • Mass # remains the same

6. Stability of nuclei • Positron emission is interpreted as the production of a positronduring the conversion of a protonto a neutron; it can be summarized as follows: • Atomic # decreases by 1 • # of protons decreases by 1 • # of neutrons increases by 1 • Mass # remains the same

7. Stability of nuclei • As in chemical equations, massand chargemust balance on both sides of the equation • all the top #s on the left must equal the top #s on the right AND • all the bottoms #s on the left must equal all the bottom #s on the right

8. transmutations • Nuclear reactions can either be naturallyoccurring or artificial. • Natural transmutations are: alpha, beta, and positrondecay that occur as a result of unstable neutron-to-protonratios and consist of a single nucleusundergoing decay.

9. transmutations • Artificial transmutation is the bombarding of a nucleus with high-energy particles to bring about a change; scientistsin research and commercial settings perform artificialtransmutations and will have two reactants, a fastparticle and a targetmaterial.

10. transmutations • There are 2different types of artificial transmutations; the first type involves the collision of a chargedparticle with a targetnucleus and the second type involves the collision of a neutronwith a targetnucleus.

11. Fission, fusion & half-life • A fission reaction involves splitting of a heavy nucleus to lighter nucleiand a fusion reaction involves combining light nuclei to a heavier nucleus. • In both types of reactions, the total massof the products is lessthan the total nuclear mass of the reactants.

12. Fission, fusion & half-life • The lossof mass in these nuclear reactions represents a conversion of some matterinto energyexpressed by AlbertEinstein in his famous equation: E = mc2. The massthat has been converted to energyis called the mass defect. • The energy produced by nuclearreactions is far greater than that of chemicalreactions.

13. Fission, fusion & half-life • The chemical reaction, decomposition, is similar to fissionreactions because oneis splitting up into twoplus energy. • The chemical reaction, synthesis, is similar to fussionreactions because twoare combining into oneplus energy.

14. Fission, fusion & half-life • Radioactive substances decay at a constantrate and the number of unstablenuclei that will decay in a given time can be predicted. • Half-life is the time it takes for half the atoms in a sample to decay.

15. Fission, fusion & half-life • Each isotopehas its own half-life. The shorterthe half-life of an isotope, the lessstable it is. Table Nin the Reference Tables give the nuclide, half-life, decay mode, & nuclide name. • The back of the Reference Table gives the half-life formulaswhich are: • Fraction remaining = (½) t/T • Number of half-life periods = t/T • Where t is time elapsedand T is half-life

16. Uses & dangers of radioisotopes • Radioisotopes have many practical applications in industry, medicine, and researchbut also have potential dangersbecause of the harm that can be done by the releaseof radiation. • Carbon- 14is used in datingpreviously living materials.

17. Uses & dangers of radioisotopes • A tracer is any radioisotope used to follow the path of a material. The ability to detectradioactive materials and their decayproducts makes it possible to determine their presenceor absencein a substance. • C-14and P-31are tracers and C-14is used to map the path of carbon in metabolic processes.

18. Uses & dangers of radioisotopes • Radioactiveisotopes and gammarays are absorbed in varyingamounts by different materials and the thickerthe material, the more radiation will be absorbed. Radiation products can be used to measure the thickness of plastic wrapor aluminum foilor to test the strength of a weld.

19. Uses & dangers of radioisotopes • Certain radioactive isotopes are used in the body as tracers because they have shorthalf-lives and are quicklyeliminated from the body. • Thyroid conditions use I-131to detect and treat because the I-131accumulates in the thyroid gland, therefore, when a person has an overactive thyroid I-131can be given in large enough doses to destroy some of the thyroid and reduceits production.

20. Uses & dangers of radioisotopes • Co-60emits large amounts of gamma radiation as it decays and thus can be aimed at canceroustumors, whereby killing the rapidly growing cells of the tumor than normalcells. • In order to kill bacteria in foods, beams of gammaradiation and the two used to destroy anthrax bacilli are C-60and Cs-137.

21. Uses & dangers of radioisotopes • Cancerous tumors can accumulate Tc-99and thus is used for detectionpurposes since it has a shorthalf-life and is quicklyeliminated by the body. • Radiation not only destroys unwanted cancerouscells but it also can destroy normaltissue which can cause serious illness, deathand can be passed on from generationto generation.

22. Uses & dangers of radioisotopes Nuclear power plants are an issue because the waste/decayproducts have longhalf-lives which have the potential of being released into the airor water.