Nuclear Chemistry. Brief history of nuclear related discoveries Electron, proton, neutron Nuclear transformations Natural radioactivity Half Life, carbon dating Nuclear chemistry equations Chain reaction, atom bomb Applications Nuclear reactors Radioisotopes Personl Exposure
Nuclear reaction: A reaction that changes an atomic nucleus, usually causing the change of one element into another. A chemical reaction never changes the nucleus.
Different isotopes of an element have essentially the same behavior in chemical reactions but often have completely different behavior in nuclear reactions.
The rate of a nuclear reaction is unaffected by a change in temperature or pressure (within the range found on earth) or by the addition of a catalyst.
The nuclear reaction of an atom is essentially the same whether it is in a chemical compound or in an uncombined, elemental form.
The energy change accompanying a nuclear reaction can be up to several million times greater than that accompanying a chemical reaction.Nuclear Changes
Cathode Rays (electrons)first demonstrated by Crookes in1895Early investigator of radiation inside electrical discharge tubes, eventually leading to CRT (Television) tubes. He was one of the first to experiment with radioactivity and its ability to make certain minerals glow. He also invented the ”radiometer” still in use as an educational toy.
ELECTRON - J.J. Thompson 1897found a new particle “boiling off” a heated filament which had <1/1000 mass of hydrogen. It had a negative charge by its magnetic and/or electrostatic deflection. Using similar apparatus he discovered isotopes of the same element with different mass, which led to science of mass spectrometry
PROTON, Goldstein in1888Used high voltage to ionize gases, accelerating particles through holes in cathode, causing “canal rays” (trails looked like canals). Particles were positive. Hydrogen particles later identified as protons by Rutherford in 1919
NEUTRINOPredicted by Wolfgang Pauli in 1930, based on conservation discrepancies. the “little neutron” Indirectly observed in 1942 and1946 via interactions with other particles, directly observed in 1972 “bubble chamber”
Baquerel – observed radioactivity 1896Photographic plate accidentally exposed by Uranium Baquerel is SI unit of radiation, Bq = disintegrations/sec1 Curie = radiation from 1 gram of Radium = 3.7*10^10 Bq
Emissions from Pitchblende (uranium ore)
Found to expose photographic film
We will measure pitchblende today
3 common types of nuclear radiation
Alpha (α), helium nuclei particle, 2He4 = 2p+2n
Very strong but not very penetrating
Beta (β), an electron particle, -1e0
Mildly penetrating, stopped by thick paper
Gamma (γ), radiation similar to X-Ray
Very penetrating, used for imaging
Marie & Pierre Curie, 1905Separated tons of mineral pitchblende to discover and isolate Radium, and polonium (named for Poland). The standard measure for radioactivity is the Curie = Ci
When passed between two charged plates: sheets of paper or by the top layer of skin.
All nuclear decays follow the same curve, 50% of the sample remains after one half-life, 25% after two half-lives, 12.5% after three half-lives, and so on.
Decay of Carbon-14 remains after one half-life, 25% after two half-lives, 12.5% after three half-lives, and so on.Neutron turns into proton + electron (beta particle)Mass remains at 14, but carbon becomes nitrogenintensity of electron emission indicates object’s age
14 remains after one half-life, 25% after two half-lives, 12.5% after three half-lives, and so on.C is continually produced in the atmosphere and incorporated into life cycles, so 14C amount in living things is constant. Upon death, no more 14C is absorbed, so concentration decreases. Measuring the remaining radioactivity provides an age estimate. The half life of 14C is 5730 years. The method is good for estimating age of objects 500 to 50,000 years old.
Radioisotopes used internally for medical applications will have short half-lives so that they decay rapidly and do not remain in the body for prolonged periods (Tc-99, ½=6hrs)
Health professionals who work with X rays or other kinds of ionizing radiation protect themselves by surrounding the source with a thick layer of lead or other dense material.
Protection is also afforded by controlling the distance between the worker and the radiation source because radiation intensity (I) decreases with the square of the distance from the source. We will demonstrate inverse square law this week in lab.
The intensities (I) of radiation at two different distances (d) are given by the equation:
I1d12 = I2d22Radiation Intensity
Enormous ratio between mass & Energy
c = 3*10^8 meters/sec
c2 = 9*10^16 meters2/sec2
How much energy is that ?
1 gram U235 converts to 3.4*10^8 kcal
Hiroshima bomb converted only a few grams
E=mc ionizing radiation protect themselves by surrounding the source with a thick layer of lead or other dense material. 2, so light has mass E=mc2, E= hc/λ, so m=h/(c*λ)= 3.4E-36 kg/photonThis is about 1 millionth the mass of an electron(Although very tiny, mass of light has important consequences
A chain reaction requires a minimum amount of material for to be self sustaining
Plutonium-239 the size of a softball is enough to make a nuclear weapon.Critical Mass
Nuclear Fusion to be self sustainingPrinciple source of energy in stars from fusing hydrogenatom of helium weighs slightly less than 4 hydrogen, balance is energy
Polonium Poisonings to be self sustainingAlexander Litvenenko ex-KGB agent and critic of Russian politics. At lunch in London with ”friends” he ingested 10 micrograms Po-210, 200x a lethal dose of extremely radioactive alpha-emitter, and died 3 weeks later. There is some suspicion Yasser Arafat may have been similarly poisoned
The simplest device for detecting exposure to radiation is the photographic film badge.
The film is protected from exposure to light, but any other radiation striking the badge causes the film to fog.
The Geiger counter is an argon-filled tube. The inner walls are given a negative charge, and a wire in the center is given a positive charge.
Radiation ionizes the argon atoms, which briefly conduct a current between the walls and the center electrode.
The current is detected, amplified, and used to produce a clicking sound or to register on a meter.
Scintillation, emission of light plastics, a small flash of light results, which can be measuredObserved by Crooks in 1895, using luminescence of ZnS, whichbecame basis of “picture tubes” in television. Radiation generating a single photon of light can be amplified108 by “photomultiplier” tube.
The most versatile method for measuring radiation in the laboratory is the scintillation counter.
In this device, a substance called a phosphoremits a flash of light when struck by radiation.
The number of flashes are counted electronically and converted into an electrical signal.
Marie & Pierre Curie, 1905http://discoveringsomethingneweveryday.blogspot.com/2013/08/why-is-radon-hazard.htmlSeparated tons of mineral pitchblende to discover and isolate Radium, and polonium (named for Poland). The standard measure for radioactivity is the Curie = Ci
14http://discoveringsomethingneweveryday.blogspot.com/2013/08/why-is-radon-hazard.htmlC is continually produced in the atmosphere and incorporated into life cycles, so 14C amount in living things is constant. Upon death, no more 14C is absorbed, so concentration decreases. Measuring the remaining radioactivity provides an age estimate. The half life of 14C is 5730 years. The method is good for estimating age of objects 500 to 50,000 years old.
14http://discoveringsomethingneweveryday.blogspot.com/2013/08/why-is-radon-hazard.htmlC is continually produced in the atmosphere and incorporated into life cycles, so 14C amount in living things is constant. Upon death, no more 14C is absorbed, so concentration decreases. Measuring the remaining radioactivity provides an age estimate. The half life of 14C is 5730 years. The method is good for estimating age ofobjects 500 to 50,000 years old.
Beta Particlehttp://discoveringsomethingneweveryday.blogspot.com/2013/08/why-is-radon-hazard.htmlUnstable isotope emits electron having negative charge, nucleus of parent changes charge in the other direction, creating a new element. Example is Carbon-14 used for dating historical objects. Note another particle with zero mass and charge, the “Neutrino” … more about that later
Positron Emissionhttp://discoveringsomethingneweveryday.blogspot.com/2013/08/why-is-radon-hazard.htmlUnstable nuclei can also emit a positive electron, a form of “anti-matter” which turns into energy upon meeting it’s opposite. Mass and charge must balance
Emission of http://discoveringsomethingneweveryday.blogspot.com/2013/08/why-is-radon-hazard.htmlg rays causes no change in mass or atomic number.
g emission usually accompanies emission of other rays but it is often omitted from nuclear equations.
Their penetrating power makes them both dangerous to humans and useful in medical applications.
Atomic Bomb Explosionhttp://discoveringsomethingneweveryday.blogspot.com/2013/08/why-is-radon-hazard.htmlAutomatic Camera situated 7 miles from blast with 10 foot lens. Shutter speed 1/100,000,000 second. Joshua tree’s near base vaporized in microseconds.