Ch. 39 The Atomic Nucleus and Radioactivity
Notes
39.1 The Atomic Nucleusp 610
Nucleon - the principal building block of the nucleus; a proton or a neutron
Strong force - the force that attracts nucleons to one another within the nucleus; a force that is very strong at close distances, but decreases rapidly as the distance increases
The nucleus is held together by the strong, short-range nuclear force. Neutrons must be present in order for the force to overcome the electrostatic repulsion which would be present when two like charges are close together.
Quantum mechanics tells us that particles that are closely bound will have a large kinetic energy. This means when the atoms are smashed together in a collider they will split apart releasing the large amount of energy.
☐ Describe the atomic nuclei
39.2 Radioactive Decayp 611 Figs 39.4-7
Radioactive - term applied to an atoms with a nucleus that is unstable and that can spontaneously emit a particle and become the nucleus of another element
The rules of decay are governed by mass-energy equivalence, meaning the particles only decay when the products of decay have less mass than before.
A neutron is actually unstable, and will decay into a proton and an electron!
Any element heavier than Bismuth can decay, making them radioactive.
Types of particles:
? electrically positive, composed of two protons and two neutrons
? electrically negative, electrons
? electrically neutral, photons with high energy/frequency
Rays of particles can be separated with a magnet.
Roentgen’s accidental experiment produces first x-ray image:
39.4 Radioactive Isotopesp 316 Fig 39.10
Isotopes - a form of an element having a particular number of neutrons in the nuclei of its atoms. Different isotopes of a particular element have the same atomic number but different atomic mass numbers.
Atomic number - number of protons in the nucleus of an atom
Atomic mass number - total number of nucleons (neutrons and protons) in the nucleus of an atom
An ion has a different number of electrons than protons, making it electrically charged. Not all isotopes are radioactive.
☐ Interpret the symbols used to label isotopes of an element
39.5 Radioactive Half-Lifep 615 Fig 39.13
Half-life- the time required for half the atoms of a radioactive isotope of an element to decay. Also used for decay processes in general
We can measure the rate of decay and each element has it’s own unique rate.
From our demo:
Isotope Source / Rays Produced / Half - LifePo - 210 / ? / 138 days
Sr - 90 / ? / 28.6 yrs
Co - 60 / ? / 5.3 yrs
If each sample contains 5 g of radioactive material, and the sample is 30 years old, how much radioactive material remains?