nuclear chemistry principles and applications. isotopes recall that most elements consist of a...

Download Nuclear Chemistry Principles and Applications. Isotopes Recall that most elements consist of a distribution of various isotopes. Isotopes of the same

Post on 28-Dec-2015

218 views

Category:

Documents

0 download

Embed Size (px)

TRANSCRIPT

  • Nuclear ChemistryPrinciples and Applications

  • IsotopesRecall that most elements consist of a distribution of various isotopes.Isotopes of the same element have the same atomic number but different atomic masses.The atomic mass in the periodic table is a statistical average over all of the isotopes for the element.Some isotopes are stable, and some decompose through radioactivity.

  • Radioactive isotopesChange through 3 different processesAlpha (a) decay nucleus emits an a particle (a helium nucleus). Nucleus becomes element with an atomic number two less than original and isotopic mass 4 less than original.Beta (b) decay nucleus emits a b particle (an electron). Nucleus becomes element with atomic number one more than original and same isotopic mass as original. Gamma (g) decay nuclear atomic number and isotopic mass unchanged. High energy photon emitted.

  • b emission -- + or - ?Normal b emission is an electron negatively charged. Usually happens when there are excess neutrons. A neutron decomposes to give a proton and an electron (and a neutrino)Variant on b emission is a positron, positively charged anti-matter to an electron. Happens when there is an excess of protons in the nucleus. Proton gives a neutron and a positron (and a neutrino).

  • Sources of radioactive isotopesNaturally occurring, four series found:Thorium (4n series)Neptunium (4n+1 series)Uranium radium (4n+2 series)Uranium actinium (4n+3 series)Plus isotopes can be manufactured in nuclear reactors and in various kinds of accelerators.More manufactured isotopes than those found in nature.

  • Radioactive shieldinga particles easily shielded if source is external. Normal skin protects body.b particles electrons are emitted. Clothing, gloves will protect body.g rays high energy, requires extensive shielding. (e.g., lead box)Damage to body is caused by creation of unstable chemical species in the body.Limit time exposure, use shielding, protective clothing

  • Balancing nuclear equationsA nuclear equation is balanced when the sum of the mass numbers and the sum of atomic numbers of the particles and isotopes are the same on both sides of the equation.Example a decay of neptunium to proactinium

  • Balancing nuclear equationsExample bismuth going to polonium

    Example manufacture of curium from plutonium

  • Examples to work outAlpha decay of

    Beta decay of

  • Examples of reactionsBeta decay (with positron emission) of

    Bombardment reaction

  • Measuring radiation -- disintegrationsCurie (Ci) number of disintegrations per per second. Based on 3.7 x 1010 atoms of radium (1 gram of radium) disintegrating per second. 1 Ci = 3.7 x 1010 disintegrations per second.Bequerel (Bq) 1 disintegration per second.1 Ci = 3.7 x 1010 Bq

  • Measuring radiation -- absorptionRad amount of radiation absorbed per gramSI counterpart gray (Gy)1 Gy = 100 radsRem (radiation equivalent in humans) Rem = rad x factorThe factor is an adjustment for the damage potential of the radiation.SI counterpart sievert (Sv)1 Sv = 100 rems

  • ExampleThe recommended dosage of iodine-131 is 4.20 microCi/kg of body weight. How many microcuries of iodine-131 are needed for a 70.0 kg patient with hyperthyroidism?

  • Half-life of isotopesThe half-life of a radioisotope is the amount of time it takes for one-half of a sample to decay.Many uses in archaeology, paleontology, and geochemistry for assigning ages to artifacts, fossils, and mineral deposits.

  • Example on half-lifeTechnetium-99m is an ideal radioisotope for scanning organs because it has a half-life of 6.0 hours and is a pure gamma emitter. Suppose that 80.0 mg were prepared in the technetium generator this morning. How many milligrams would remain after the following intervals?One half-lifeTwo half-lives18 hours24 hours