Rad Physics Ch.2
What is centripetal force?
-"center-seeking" force -states that opposite charges attract one another and like chargers repel -balances the force created by electron velocity
Alpha particles:
-2 protons and 2 neutrons -mass of 4amu -compared to an electron, an alpha is large and exerts great electrostatic force -emitted only from nuclei of heavy elements -light elements cannot emit alphas because of less mass -after emission from a radioactive atom, It travels at high velocity through matter -easily transfers kinetic energy to orbital electrons of other atoms -average alpha possesses 4-7 MeV of KE -energy is quickly lost (short range in matter) -nearly harmless because It is deposited in the superficial layers of the skin
What is Niels Bohr remembered for?
-Bohr atom -miniature solar system in which electrons revolved about the nucleus in prescribed orbits or energy levels -represents the best way to picture the atom -number of electrons is equal to the number of positive charges in the nucleus
How many substances or ELEMENTS have been identified today?
118 -92 are naturally occurring -26 are artificially produced in high-energy particle accelerators
If atoms large enough to have electrons in the T shell existed, what would be the maximum number allowed in that shell?
200
How can you calculate the maximum number of electrons per shell?
2n^2, where n is the shell number -K shell would be first shell
Hydrogen, oxygen, carbon and nitrogen compose more than ______ of the human body.
95%
What is the arrangement of the periodic table of the elements?
An arrangement of all known elements into rows and columns. The rows relate to the number of electron shells present; the columns relate to the number of electrons in the outermost shell.
Describe how ion pairs are formed.
An ion pair is formed when an electron is removed from an atom by ionizing radiation
Why doesn't an electron spontaneously fly away from the nucleus of an atom?
Electrostatic force of attraction (centripetal force) and electron binding energy
How are graphs of radioactive half life disintegration shown?
semilog form
What was the first civilization to begin the investigation of the structure of matter?
the Greeks
What is ionization potential?
the amount of energy needed to ionize an atom
The number of protons determines:
the chemical element
The larger and more complex the atom:
the higher is the binding energy for electrons in any given shell
A change in the number of neutrons doesn't ionize an atom because:
the neutron is electrically neutral
Where is most of the mass of an atom contained at?
the nucleus
What was John Dalton known for?
-Dalton atom -experiments showed that the elements could be classified according to integral values of atomic mass -said that an element was composed of identical atoms that reacted the same way chemically -physical combination of one type of atom with another was seen as an "eye and hook" affair -size and number of eyes and hooks was different for each element
What is Ernest Rutherford known for?
-Rutherford atom (nuclear model) -described the atom as containing a small, dense, positively charged center (nucleus) surrounded by a negative cloud of electrons
Elements of group 1:
-alkali metals (except hydrogen) -soft metals that combine readily with oxygen and react violently with water
Electrons:
-carry one unit of negative electric charge -revolves about the nucleus in precisely fixed orbits
Isotopes:
-contain the same number of protons but varying numbers of neutrons -most atoms have more than one stable isotope -describes all atoms of a given element -have different nuclear configurations but react the same way chemically
During the Greek civilization, what 4 substances did scientists believe that all matter was composed of?
-earth, air, water, and fire -all matter could be described as combos of these 4 substances
Beta emission:
-electron created in the nucleus is ejected from the nucleus with sufficient kinetic energy -results in a small quantity of mass and one unit of electric charge -a neutron undergoes conversion to a proton increase in the atomic number by 1, atomic mass stays the same -changes the atom from one type of element to another
The number of electrons in the outermost shell is:
-equal to its group in the periodic table -determines the valence of an atom
What is centrifugal force?
-flying-out-from-the-center force -electrons maintain their distance from the nucleus while traveling in a circular or elliptical path
Elements of group VII:
-halogens -easily vaporized and combine with metals to form water-soluble salts
Isobars:
-have different numbers of protons and different numbers of neutrons but the same total number of nucleons -transitions from parent atom to daughter atom result from a release of a beta particle or a positron -parents and daughter are atoms of different elements
Isomer:
-have the same atomic number and the same atomic mass number -identical atoms except that they exist at different energy states because of differences in nucleon arrangement
What is J.J.Thomson known for?
-investigated the physical properties of cathode rays (electrons) -Thomson atom -concluded that electrons were an integral part of all atoms -described the atom as looking something like plum pudding -plums were negative charges (electrons) and the pudding was a shapeless mass of uniform positive electrification -number of electrons was thought to equal the quantity of positive electrification because atom was known to be electrically neutral
Beta particles:
-light particles with an atomic mass of 0 -carry one unit of negative or positive charge -originate in the nuclei of radioactive atoms -traverse air after emission, ionizing several hundred atoms per centimeter -range is longer than that of alphas
Alpha emission:
-much more violent than beta emission -consists of 2 protons and 2 neutrons bound together with an atomic mass of 4 -nucleus must be extremely unstable to emit an alpha -when It does, It loses 2 units of positive charge and 4 units of mass -atom is now chemically different and lighter by 4amu ***only heavy radioisotopes are capable of alpha emission
Protons and neutrons:
-nearly 2000 times the mass of an electron -neutron is slightly heavier than proton -atomic mass number of each is 1 -proton carries one unit of positive electric charge -neutron carries no charge because It is electrically neutral
Elements of group VIII:
-noble gases -highly resistant to reaction with other elements
How do radioisotopes disintegrate?
-not all at once -disintegrate into stable isotopes of different elements at a decreasing rate so that the quantity of radioactive material never quite reaches zero
2 primary sources of naturally occurring radioisotopes:
-originated at the time of the earth's formation and are still decaying very slowly -continuously produced in the upper atmosphere through the action of comic radiation
What are nucleons?
-protons and neutrons -composed of quarks that are held together by gluons
What are radioisotopes?
-radioactive numbers have same number of protons -changed into a different atomic species by disintegration of nucleus accompanied by the emission of ionization radiation
For what is Dmitri Mendeleev remembered for?
-showed that if the elements were arranged in order of increasing atomic mass, a periodic repetition of similar chemical properties occurred -first periodic table of elements (only 65 at the time) -showed that the elements could be placed in one of eight groups
What is significant about particle accelerators?
-structure of the atomic nucleus is slowly being mapped and identified -more than 100 subatomic particles have been detected and described
How does the removal of an electron from its atom work?
-x-ray transfers energy to an orbital electron and that electron is ejected out of the atom -x-ray ceases to exist, and an ion pair is formed -atom is now a positive ion because It contains one more positive charge than negative charge
What are photons?
-x-rays and gamma rays are called this -no mass and no charge -travel at the speed of light -considered energy disturbances in space
Describe the difference between alpha and beta emission.
Mass and charge on the particle. An alpha particle has four units of mass and two units of positive charge. A beta particle has essentially no mass and one unit of negative charge.
What is a chemical compound?
New substance that is formed when two or more atoms of different elements combine
Who developed the concept of the atom as a miniature solar system?
Niels Bohr
Isotones:
atoms with different atomic numbers and different mass numbers but a constant value for the quantity A-Z -same number of neutrons in the nucleus
What is the relationship between the electrons' binding energy and the atom's nucleus?
The closer the electron is to the nucleus, the greater is its binding energy
What property of an atom does binding energy describe?
The energy required to hold nucleons together as a nucleus (nuclear binding energy). The energy required to maintain electrons in orbit about the nucleus (electron binding energy).
Describe an alpha particle.
The nucleus of the helium atom—two neutrons and two protons.
Why does It take more energy to ionize a large atom than a small atom?
because electrons of atoms with many protons are more tightly bound to the nucleus than those of small atoms
Which particle emission occurs more frequently?
beta emission
What can the atom be viewed as?
a miniature solar system with the sun as the nucleus and the the planets as the electrons -arrangement of electrons around the nucleus determines the manner in which It interacts
2 main types of particulate radiation:
alpha and beta particles
Chemical symbols:
alphabetical abbreviations of elements
What word did the Greeks use to describe the smallest part of the 4 substances of matter?
atom, meaning "indivisible"
When precision is not need, atomic mass is measured in:
atomic mass numbers -atomic mass number of an electron is zero
Because an atomic particle is extremely small, its mass is expressed in ____ for convenience.
atomic mass units (amu) -one atomic mass unit is equal to 1/12 the mass of a carbon-12 atom -electron mass is 0.000549amu
What is the number of protons in an atom called?
atomic number, represented by Z
What is a molecule?
atoms of various elements that combine together
What are isotopes?
atoms that have the same number of protons but differ in the number of neutrons -behave in the same way during chemical reactions
What are the 2 main ways radioisotopes can decay?
beta emission and alpha emission
What are ionic bonds?
bonding that occurs because of an electrostatic force between ions *when an atom gives up its electron to another atom, It becomes ionized because It has lost an electron and now has an imbalance of electric charges. The atom it lost it to also is ionized because It gained an electron. *the two atoms become attracted to each other because they have opposite electrostatic charges
What is elemental mass?
characteristic mass of an element that is determined by the relative abundance of isotopes and their respective atomic masses -calculate the average of all isotopes
What are covalent bonds?
chemical union between atoms formed by sharing one or more pairs of electrons
What do the different electron shells represent?
different electron binding energy -given the names K, L, M, N and so forth
The outer shell is always limited to:
eight electrons
List the fundamental particles within an atom.
electron, proton, and the neutron
How does carbon-14 dating determine the age of petrified wood?
fixed 14C in petrified wood decays, while 14C in living wood is replenished
Except the lightest atoms, the number of neutrons is always ______ than the number of protons.
greater -the larger the atom, the greater number of neutrons over protons
What is the alpha particle equivalent to?
helium nucleus
When is an atom considered to be ionized?
if an atom has an extra electron or has had an electron removed -an ionized atom carries a charge equal to the difference between the numbers of electrons and protons
The max number of electrons that exists in each shell ____ with the distance of the shell from the nucleus.
increases
What is the K shell?
innermost electron shell
Why does the progression of atom growth stop at the 4th period?
instead of simply adding electrons to the next outer shells, electrons are added to an inner shell -atoms associated with this are called transitional elements -outer shell still will never have more than 8 electrons -chemical properties depend on the number of electrons in the 2 outermost shells
The number of electron shells is equal to:
its period in the periodic table
What is radioactive decay/radioactive disintegration?
naturally occurring process where an unstable atomic nucleus relieves its instability and transforms itself into another atom through the emission of one or more energetic particles *atoms involved are called radionuclides *any nuclear arrangement is called a nuclide
What is quantum chromodynamics (QCD)?
newer model that accurately describes the details of atomic structure
Can atoms be ionized by changing the number of positive charges?
no, they are bound together very strongly within the nucleus. ionization occurs with the addition or removal of electrons
Are all K-shell electrons bound with the same binding energy?
no; the greater the total number of electrons in an atom, the more tightly each is bound
What determines the chemical properties of an element?
number and arrangement of electrons in outer shell
How do you find the atomic mass number?
number of protons plus the number of neutrons -always a whole number
What is the only difference between electrons and negative beta particles?
origin -betas originate in the nuclei of radioactive atoms -electrons exist in shells outside the nucleus of atoms
Ionizing radiation can be classified into 2 categories:
particulate radiation and electromagnetic radiation
Elemental groupings are determined by:
placement of electrons in each atom
What is a positron?
positive beta particles -same mass as electrons and considered to be antimatter
What is a positron?
positive beta particles that have the same mass as electrons and considered as antimatter
What do physicists call the shell number n?
principal quantum number -every electron in every atom can be precisely identified by 4 quantum numbers, most important of which is the principal quantum number -other 3 quantum numbers represent existence of sub shells, but not important to radiologic sciences
What is the most important factor that affects nuclear stability?
the number of neutrons -when a nucleus has too many or too few neutrons, the atom can disintegrate radioactively, bringing the number of neutrons and protons into a proper and stable ratio
The total number of electrons in the orbital shells is exactly equal to:
the number of protons in the nucleus
What is an atom?
the smallest particle of matter that has the properties of an element -subatomic particles are much smaller than the atom
What is electron binding energy?
the strength of attachment of an electron to the nucleus
What is radioactive half life?
the time required for a quantity of radioactivity to be reduced to one half its original value
What is the radioactive half-life?
the time required for a quantity of radioactivity to be reduced to one-half its original value
Why can an atom not be ionized by the addition or removal of a protons?
they are bound very strong together, and that action would change the type of atom
"W" is the chemical symbol for what element?
tungsten
Around 80% of the human body is made up of:
water molecules
What 4 basic essences modified the substances determined by the Greeks?
wet, dry, hot and cold
What is a photon?
x-rays and gamma rays that have no mass or charge, travel at the speed of light, and are considered energy disturbances in space
Can protons and electrons be classified as particulate ionizing radiation?
yes, if they are in motion and possess sufficient kinetic energy (cannot cause ionization at rest)
How much energy is needed to ionize tissue atoms?
~34 eV **binding energy of outer shell electrons of tissue is ~10 eV **the difference (24eV) causes multiple electron excitations, which causes heat
