Chapter 29 Flashcards
(17 cards)
What is the nucleus made of?
What does Z stand for?
What does A stand for?
Nucleus is made of protons and neutrons (known as nucleons)
Atomic number, Z, is the number of protons in the nucleus, also the number of electrons
The nucleon number, A, is the total number of neutrons and protons, A=N+Z
Mass of nucleus is proportional to A (mass in u (atomic mass units) is A)
Slide 18-20 March 28
What are isotopes of elements?
Different nuclides of the same element have different numbers of neutrons (different N)
These nuclides are called isotopes of the element
Different isotope have the same chemical properties but different nuclear properties
How is the nucleus held together?
Strong nuclear force- attractive force, very short range, each nucleon is only attracted to its nearest neighbours (exert strong nuclear force only to neighbours)
Coulomb force is long range force
Electric forces between the protons in the nucleus are repulsive
What determines the stability of the nuclei?
Stability of nuclei is determined by the balance between the repulsive electric force between protons and the attractive strong nuclear force between nucleons
As nucleon # increases, neutrons are favoured over protons because the neutrons do not experience the repulsive electric force
Because of Coulombs repulsion, the proton energy levels become progressively higher than the corresponding neutron energy levels as A increases
Slides 24-26 March 28
What is the binding energy of a nucleus?
Eb
Energy that must be supplied to separate a nucleus into individual protons and neutrons
Eb=(total energy of Z protons and N neutrons)-(total energy of nucleus)
Eb=(Δm)c^2
Eb= [(Zmp+Nmn)-mnucleus] x c^2
(c is different value for nucleus)
Slides 27-30 March 28
What is radioactivity?
Radioactive nuclei are unstable (they decay, undergo spontaneous nuclear reactions, by emitting radiation to become more stable)
Slides 4-8 April 2
What a r the 3 distinct types of natural radioactivity?
- Alpha- positively charged and least penetrating, identified by Rutherford
Helium-4 nuclei (2 protons and 2 neutrons)
Can barely penetrate a piece of paper - Beta- negatively-charged and medium penetration power, identified by Rutherford
Electrons or positrons (positive electrons)
Can penetrate few mm of aluminum - Gamma- uncharged and most penetrating, identified by Villard
Are photons
Can penetrate several cm of lead
Slides 9-10 April 2
What is radioactive decay (3 types)?
Radioactive decay is a quantum-mechanical process (described in terms of probability)
Can specify which nucleus will decay in a sample
Alpha decay- many involve a change in both atomic number and nucleon number
Beta decay- change in atomic number
Gamma decay- emission of a photon
What is alpha decay?
The original (parent) nucleus is converted to a product (daughter) nucleus by the emission of an alpha particle
The alpha particle is a helium-4 nucleus (2P+2N)
Slides 26-27 April 2
What is beta decay?
Refers to 3 different radioactive processes
Beta-minus decay- electron and antineutrino are released
Neutron in nucleus is converted to a proton
Beta-plus decay- a positron and neutrino are released
Proton in nucleus is converted to a neutron
Electron capture- an orbital electron is captured by the nucleus
Results in a proton in the nucleus converting to a neutron, releases a neutrino
Slides 28-34 April 2
What is gamma decay?
Does not charge nucleus into a different nuclide
Gamma ray photon is emitted when a nucleus in an excited state makes a transition to a lower-energy state
Gamma decay oils often a result of a daughter nucleus being in an excited state following a previous alpha or beta decay
Slide 2 April 4
What the equation altering the N=Noe^-λt equation using activity (R) for radioactive dating?
R=Roe^-ln(2)t/T1/2
Slide 3-4 April 4
What is carbon dating?
Radioactive carbon-14 is produced from nitrogen in the atmosphere by neutrons released from nuclei by collisions with cosmic rays
When an organism is alive, the conc of carbon-14 in its tissue is the same as in atmosphere, but when it dies the amount of carbon-14 in the tissue decreases because it is no longer being replenished
Can be used for specimens up to 25000 years old
What are nuclear reactions?
An induced (doesn’t occur spontaneously) nuclear reaction can be caused by a collision between a nucleus and another particle
The kinetic energies of the reactants provide the energy required for the reaction to occur
Induced nuclear reactions follow the same conservation laws as radioactive decay
Rutherford was the first to observe
Slides 12-13 April 4
What are Q values?
What are the two energy meanings of the Q value?
The Q value is the energy equivalent of the mass difference between the reactants and the products in a nuclear reaction
Q=[Mreactants - Mproducts] x c^2
If Q is positive, energy is released (exothermic)
If Q is negative, energy is required (endothermic)
What is the biologically equivalent dose (BED)?
The absorbed does of x-ray or gamma radiation that causes the same biological damage as 1 gray of the radiation being used
What is background radiation?
Average annual dose of about 3mSv due too natural sources
Radon gas and its daughters account for 67% of natural radiation (dangerous because it is an alpha emitters which can be inhaled and daughters embed in lungs)
Potassium-40 and Carbon-14 enter our bodies via food and water
Cosmic rays account for 10%
