Ch 19 - Radioactivity and Nuclear Chemistry Flashcards
nuclear processes often result in
one element changing into another frequently emitting a tremendous amount of energy
Radioactivity
the emission of subatomic particles of high energy electromagnetic radiation by the nuclei of certain atoms
Radioactive
atoms which emit subatomic particles of high energy electromagnetic radiation by their nuclei
phosphorescence
long lived emission of light that sometimes follows the absorption of light by certain atoms and molecules
- it’s the glow in glow in the dark toys
Antoine-Henri Becquerel
French scientist in 1896 who hypothesized phosphorescence was related to X-rays.
- used the term uranic(from uranium in the crystal) rays to describe what he thought was an X-ray pattern on a photographic plate from a potassium uranyl sulfate crystal wrapped in black cloth - later recanted his hypothesis when he discovered the pattern was created in sunlight or without it
Marie Sklodowska Curie
one of first women in France to pursue doctoral work
discovered two new elements(polonium and radium) which emitted uranic rays - renamed uranic rays to radioactivity
Becquerel, Curie and he husband were awarded
the Nobel prize in physics in 1903 for discovering radioactivity
Marie Curie won a second Nobel prize in
1911 for discovering the two new elements in her research
Main types of radioactivity
- alpha(a) and beta(B) decay
- gamma(y) ray and positron emission
electron capture
some unstable atomic nuclei can attain greater stability by absorbing an electron from one of the atoms own orbitals
isotope notation review
- A/Z(X)
- A = mass number
- the sum of the number of protons and the number of neutrons in the nucleus
- Z = atomic number
- the number of protons in the nucleus
- X = chemical symbol
- N = A – Z
- the number of neutrons or the difference that must be covered due to a lack of protons
- 21/10(Ne)
- 21 – 10 = 11 neutrons and 10 protons
- 20/10(Ne)
- 20 – 10 = 10 neutrons and 10 protons
Nuclide
a specific isotope(or species) of an element when discussing nuclear properties
the main subatomic particles, protons, neutrons, and electrons use similar notation to elements
- 1/1(p), 1/0(n),0/-1(e)
- the bottom number for protons and neutrons represents the proton total
- electron bottom number is different
Alpha(a) Decay
occurs when an unstable nucleus emits a particle composed of two protons and two neutrons
- identical to a helium-4 nucleus - 4/2(He)
nuclear equation
an equation that represents nuclear processes such as radioactivity
when an element emits an alpha particle, the number of protons
in its nucleus changes transforming the element into a different element
parent nuclide
the original atom
daughter nuclide
the product of the decay
the alpha particle is by far the most massive of all particles emitted by radioactive nuclei
- has the greatest potential to interact and do damage other molecules, including biological
ionizing power
the ability of radiation to ionize other molecules and atoms
alpha has the highest
ionizing power
penetrating power
the ability to penetrate matter
alpha has the LOWEST penetrating power due to largest size
- can be stopped by paper, cloth, air and subsequently a low level alpha emitter that remains outside the body is relatively safe
- if ingested it becomes very dangerous as there is direct contact with organ tissue
Beta(B) Decay
occurs when an unstable nucleus emits an electron
- if a nucleus changes to a proton it spits its electron out
- neutron -> proton + emitted electron
- 1/0n->1/1p + 0/-1e
- the -1 reflects the charge of the electron
- the atomic number will change by 1 because it now has an additional proton
228/88Ra->228/89Ac+0/-1e
- the equation is balanced
Beta(B) Decay ionizing and penetrating power
lower ionizing power but higher penetrating power than alpha particles
- requires something like a sheet of metal or thick piece of wood to stop - possesses a higher risk outside the body than an alpha emitter but lower damage if ingested than an alpha emitter
Gamma(y) Ray Emission
electromagnetic radiation, high-energy(short wavelength) photons
- significantly different than alpha and beta decay - o/oy - no charge or mass
gamma rays do not change the
mass or atomic number of the element
gamma rays are usually
emitted in conjunction with other types of radiation
gamma rays ionizing and penetrating power
- lowest ionizing power but higher penetrating power
- requires several inches of lead shielding or thick slabs of concrete to stop
- most dangerous outside the body and least dangerous if ingested
Positron Emission
occurs when an unstable nucleus emits a positron
- 1/1p -> 1/0n + 0/+1e
- when an atom emits a positron its atomic number decreases by 1
- 30/15P->30/14Si+0/+1e
- similar to beta particles in their ionizing and penetrating power
positron
the antiparticle of the electron with the same mass as an electron but the opposite charge
- if a positron and electron collide they annihilate each other releasing energy in the form of gamma rays - a proton is converted into a neutron and emits a positron - proton-> neutron + positron - 0/+1e
- 1/1p -> 1/0n + 0/+1e
- when an atom emits a positron its atomic number decreases by 1
- 30/15P->30/14Si+0/+1e
- similar to beta particles in their ionizing and penetrating power
Electron Capture
a particle being absorbed by instead of emitted from an unstable nucleus
- occurs when a nucleus assimilates an electron from an inner orbital of its electron cloud - like positron emission, the net effect of electron capture is the conversion of a proton into a neutron - Proton + electron->neutron - 1/1p+0/-1e->1/0n - the atomic number will decrease by 1 as a proton is lost - 92/44Ru+0/-1e->92/43Tc
nucleus is a collection of
protons and neutrons
the strong force
a fundamental physics concept which attracts all nucleons(protons and neutrons) together over a very short distance
nucleon
protons and neutrons
protons and neutrons occupy energy levels inside the nucleus similar to how electrons function around the nucleus
- this is why adding more neutrons does not continue to stabilize a nucleus as the energy payback from the strong force is not enough to compensate the increased energy state
the ratio of neutrons to protons(N/Z) is very important to determining
nuclear stability
valley(island) of stability
the graphical representation of stable nuclei
- 1-20 protons = 1/1 ratio - 21-40 protons = N/Z = 1.25 - 41-80 protons = N/Z = 1.50 - 84+ stable nuclei do not exist - Bismuth(83 protons) is the heaviest element with a stable nuclei
N/Z too high
have too many neutrons and tend to convert neutrons to protons via Beta(B) decay
N/Z too low
- convert protons to neutrons via positron emission or electron capture
- Alpha decay also raises the N/Z ratio for nuclides in which N/Z>1 but a much smaller
magic number
the uniquely stable nucleons with certain numbers
- N or Z = 2,8,20,28,50,82 - N = 126
atoms with a Z(# prtons)>83 are
radioactive and decay
an atom will continue to decay until
a stable nuclide is reached
Film-badge Dosimeters
consist of photographic film held in a small case that is pinned to clothing
- worn by individuals who regularly work around radiation, collected regularly to and processed to monitor a persons exposure - more exposure of the film the more radioactivity the person has been exposed to
Geiger-Muller Counter
instrument(Geiger counter) which passes particles emitted by radioactive nuclei through an argon filled chamber
- creates a trail of ionized argon atoms which electricity is passed through and heard by an audible click noise - more clicks is more radiation
Scintillation Counter
radioactive emissions pass through a material(NaI or CsI) that emits ultraviolet or visible light in response to excitation by energetic particles
- the light is detected and turned into an electrical signal which can be read on a meter
Rate = kN
- N = number of radioactive nuclei
- k = rate constant
half life
the time it takes for one half of the parent nuclides in a radioactive sample to decay to the daughter nuclides
t1/2 =
0.693/k
a short half life means
decays quickly
the integrated rate law
- ln([A]t/[A]0) = -kt
- ln(Nt/N0) = -kt
- ln(rate(t)/rate0)=-kt
radiocarbon dating
technique devised in 1949 by Willard Libby to estimate the ages of fossils and artifacts
nuclear fission
the splitting of uranium atoms(U-235 isotope) releasing a great amount of energy
chain reaction
neutrons produced by the fission of one uranium nucleus would induce fission in other uranium nuclei
- self amplifying chain capable of producing quite a bit of energy
critical mass
there must be a large amount of U-235 to create a self sustaining chain reaction to make a bomb
a nuclear power plant cannot become
a nuclear bomb
nuclear fusion
the combination of two light nuclei to form a heavier one
both fusion and fission emit
large amounts of energy because they both form daughter nuclei with greater binding energy energies per nucleon than the parent nuclei
nuclear fusion is the energy source of
the stars
nuclear fusion is the basis for modern nuclear weapons
- hydrogen bombs
- up to 1000 times the explosive force of the first atomic bomb
fusion reactions require two positively charged nuclei fuse together requires
extremely high temperatures
a fusion bomb has a small fission bomb detonated first to create
the temperatures necessary for fusion
fusion produces about
10 times the energy per gram of fission
in nuclear reactions matter can be
converted to energy
E = mc^2
- E = energy
- m = mass lost
- c is the speed of light
fission produces over a
million times more energy per mole than a chemical process
mass defect
the difference in mass of the reactants to products
- exist in all stable nuclei
nuclear binding energy
the energy corresponding to the mass defect, obtained from E-mc^2
- the mount of energy required to break apart the nucleus into its component nucleons
1amu =
931.5MeV
a higher binding energy yields a more
stable(lower potential energy) nuclide
transmutation
nuclear reactions transform one element into another
linear accelerator
an accelerator in a straight line
cyclotron
an accelerator in two semi circles that spirals a particle out towards a target
3 types of radiation effects
- acute radiation damage
- increased cancer risk
- genetic effects
1 gray(Gy) = 1 J/kg body tissue
1 rad = .01J/kg body tissue
biological effectiveness factor(RBE = relative)
a correction factor
- usually multiplied by the dose in rads to obtain the dose in a unit called rem
rem – roentgen equivalent man
(dose rads)(BEF) = dose in rems
on average we are exposed to 310 mrem of radiation per year from natural sources
- a majority of it from radon
