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4.3 NOTES Nuclear Radiation. IV. Unstable nuclei and radioactive decay. A. Radioactivity The spontaneous emission of radiation which results in a change in an element’s identity . Discovery led to transuranium elements;. B. Types of radiation
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IV. Unstable nuclei and radioactive decay • A. Radioactivity • The spontaneous emission of radiation which results in a change in an element’s identity. Discovery led to transuranium elements;
B. Types of radiation • 1. Alpha radiation: α; actually He atoms and represented 4He2; 2 protons and 2 neutrons; 2p+ are attracted to negatively charged plate;
Sample Problems: Ra-226 decays by alpha emission • 226 = mass number for this particular isotope and 88 is the atomic number of radium; write it as a nuclear symbol; • Decay, emission, produces – all imply particles are on the right side of the arrow so the alpha particle (4He2) is placed to the right of the • –set up as an algebra equation with the arrow being the equal sign. • Top numbers = top numbers, bottom numbers = bottom numbers. • 226Ra884He2 + ??Xx??ans: 222Rn86 • top: 226 = 4 + x • bottom: 88 = 2 + x
2. Beta radiation: β; emission of high speed e-with a -1 charge; 0e-1; • deflected toward the positively charged plate; formed when a neutron decomposed into a proton (which stays in the nucleus) and an e- which is emitted from the nucleus
Example: C-14 decays be beta emission • 14C60e-1 + 14N7
3. Gamma radiation: high energy radiation w/ no electrical charge and no mass; not deflected by electric or magnetic fields; account for most of the energy lost in a nuclear reaction; • Example: U-238 decays by emitting an alpha particle and 2 gamma rays • 238U924He2 + ɣ + 234Th90
4. Other particles: neutrons can also be emitted; 1n0 • 5. Nuclear stability – atomic stability is determined by the proton to neutron ratio; • atoms with too many or too few neutrons are unstable; unstable nuclei will lose energy (in the form of radiation) to become more stable
Sample Problem: U-235 is bombarded with a neutron. A proton is produced as well as another element. What is the other element?Bombarded, collided, struck – all imply particles are on the left side of the arrow. • 235 U92 + 1n01p1 + ans: 235Pa91