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10: the Discovery of Hydrogen Isotopes

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10: the Discovery of Hydrogen Isotopes #10: The Discovery of Hydrogen Isotopes Dean Zimmerman -305199754 Introduction Hydrogen was “discovered” many times by early chemists, who reported observing flammable gas while conducting their experiments. For instance, in 1671, Robert Boyle (English chemist- 1627- 1691) described an experiment where adding Iron to hydrochloric acid and sulfuric acid gave off “pale blue flame”. The problem with early chemists’ inability to formally discover hydrogen was that they did not comprehend the nature of gases very well; back then they believed all gasses were air with impurities [1]. It wasn’t until 1766 when the “father of modern chemistry”, Antoine-Laurent Lavoisier formally discovered hydrogen, Greek word for “Water former”. Isotopes are atoms of the same elements which have the same atomic number but different atomic mass. Isotopes generally share similar chemical properties due to having the same number of protons, and interact with other compounds similarly due to having the same number of electrons. It is the variation in neutrons which distinguishes isotopes. Deuterium, one of hydrogen’s isotopes having 1 neutron, was discovered by Harold Urey, Chemistry professor at the University of Colombia, who received a noble prize for his work in 1934. Possible existence of hydrogen isotopes were suspected in 1910 as Fredderick Soddy developed the concept of isotopes. Scientists were then in a race to find Hydrogen’s isotope due to Hydrogen’s simplicity which would contribute to the atomic theory. Professor Urey began his research under the assumption that Hydrogen isotopes existed in very low concentrations naturally due to hydrogen’s atomic mass being slightly above 1.000. Urey then conducted an experiment in which he brought 4L of hydrogen liquid to boil very slowly until only 1mL remained in the flask. His hypothesis was that; of the remaining hydrogen liquid, the heavy hydrogen would be in higher concentrations. Urey then submitted the 1mL to spectroscopy analysis, an analysis in which added energy to the system excites electrons to a higher energy state and when the electrons return to their ground state the energy difference is emitted as photons. By analysing the spectral lines emitted from the sample, Urey identified an atom never been seen before, called Deuterium. Hydrogen has 3 known Isotopes: Protium, Deuterium, and Tritium. Protium, being the ‘ordinary’ hydrogen atom we are familiar with, having no neutrons in the nucleus, having an abundance of 99.985% in nature. Deuterium, also known as “Heavy Hydrogen” is the second isotope of hydrogen having a neutron in the nucleus, doubling the atom’s mass and having an abundance of 0.015%. Lastly, tritium is hydrogen’s third isotope having 2 neutrons in the nucleus. Tritium is a radioactive atom due to its nucleus’ instability. 1 Hydrogen- http://www.chemistryexplained.com/elements/C-K/Hydrogen.html#b Figure 1- Three Known Isotopes of Hydrogen [2] Deuterium and Tritium both have very significant applications in today’s world, which will be discussed later in this paper. Deuterium Deuterium is very similar to 1-Hydrogen (Protium) in that it bonds similarly and is stable. Deuterium, can bond with oxygen to form “heavy water”, which is similar to water only 10% heavier. An Interesting property of heavy water is that heavy ice (heavy water solid) is denser than water, sinking, depicted in Figure 2. Although Deuterium is very similar to Protium, they do have some distinct physical properties which are due to the relative large difference in mass. For instance, deuterium has a boiling point 3 degrees higher than Protium and reacts slower. [3] Figure 2-Glass of water with floating ice and sinking heavy ice (D2O) Extraction Canada is the world’s supplier of heavy water. Heavy water isn’t manufactured but rather extracted from natural quantity found in lakes (0.015% of H). Previous extraction methods suggested performing electrolysis, running an electric current to drive a non-spontaneous reaction. The electrolysis 2 Hydrogen Isotope Picture- http://education.jlab.org/glossary/isotope.html 3 http://www.popsci.com/diy/article/2006-07/ice-capades decomposed the water to Oxygen and Hydrogen gas, and due to deuterium larger mass and higher boiling temperature, the heavy hydrogen is found at the remaining one-millionth volume [4]. This method works, however it isn’t cost efficient and therefore isn’t promising on a large scale extraction. The plant in Canada directly separates heavy water from water by the use of hydrogen sulphide as an agent [5], see Figure 3. Figure 3- Heavy Water Extraction Plant in Canada Application Deuterium has many useful applications and due to its unlimited availability (from lakes and oceans) and cheap extraction methods, looks promising. One application noteworthy is the strengthening of silicon microchips by Deuterium, discovered by Joe Lyding and Karl Hess at the Beckman Institute’s for Advanced Science and Technology, University of Illinois. Prior to their discovery, the silicon microchips were treated with hydrogen gas during the annealing process (a form of heat treatment used on metals in order to soften it, relieving internal stresses thereby making it easier to machine [6]). Researchers at the Beckman Institute discovered a simple yet important discovery, instead of treating the chip with hydrogen, deuterium is used which dramatically increases the strength and prolongs the life of the chip. How is the microchip strengthened by the deuterium replacing the hydrogen? First let’s look at the microchip with hydrogen, so far the use of hydrogen as a protective agent has been standardized in technological silicon microchips. The problem with the hydrogen is that energetic electrons passing through the microchip have enough energy to knock the hydrogen atoms out, thus decreasing the performance and life time, being a concern for future smaller microchips. The researchers discovered that by using heavy hydrogen as the protective agent in the microchip will strengthen it by 10-50 times. The deuterium atoms can withstand the energetic electrons thus improving the microchip’s performance and reliability of the microchips [7]. 4 Deuterium Extraction by Electrolysis- http://www.britannica.com/nobelprize/article-9435309 5 Heavy Water- http://www.sno.phy.queensu.ca/sno/D2O.html 6 Oxford Dictionary of Physics 7 Deuterium in Silicon microchips, clip- http://www.youtube.com/watch?v=w9dHeUzwOfI&feature=related Another important application of deuterium is its use in nuclear power reactors. Heavy water is formed from deuterium, and is used as a moderator and heat transfer agent. Its function as a moderator is crucial in slowing down the emitted neutrons from nuclear reactions which increases the fission reaction rate (nuclear reaction in which a large nucleus splits into smaller nuclei thereby emitting large amounts of energy and neutrons). The use of heavy water in CANDU (Canada’s nuclear power reactors) enables it to use non-enriched natural uranium, being very cost efficient. An additional significant application of heavy hydrogen is nuclear fusion. Nuclear fusion reaction is a reaction in which smaller nucleolus atoms collide and fuse together, overcoming repulsive forces, thereby forming larger atoms and releasing large amounts of energy [8] (Example: Hydrogen bomb). Fusion reaction yield enormous amounts of energy, being able to harness this energy efficiently while controlling the reaction (avoiding a massive explosion) will be the ultimate energy source. Deuterium can be used as the fuel for controlled fusion reaction, this will replace gasoline. One gallon of Gasoline (3.785L) outputs 108 Joules of Energy, enough to boil 300L of water from room temperature, costs $3.4[9] (Price in U.S as of 19/1/2012). Whereas deuterium used as a fuel in fusion reaction, from 1 gallon of water 0.12g can be extracted at a price of $0.04 [10], which would release 1010Joules, enough to boil 30,000L of water at a fraction of the price of gasoline. See Chart 1 for summarized comparison Fuel Method Resources Energy $3.4 buys Efficiency Cost ($/Gal) Output you, energy Factor (J/Gal) (J) Gasoline Combustion 3.4 108 108 1 Deuterium Fusion 0.04 1010 * 85*1010 8500 *1010 Joules/gallon of water (0.12g of D) Aside from direct dollar costs, the gasoline availability is limited whereas deuterium in comparison is unlimited (70% of the earth is water). Furthermore, this energy source will trim down dependence on corrupt middle-eastern countries, saving the world lots of troubles. Using nuclear fusion as an energy source definitely seems promising, however isn’t realistic at the moment as many difficulties must be resolved. Tritium As mentioned, Tritium is an isotope of hydrogen having two neutrons in its nucleus. Tritium is radioactive, having a half life of 12.3 years [11]. Tritium, being radioactive, means the nucleus can break- apart (decay) actively releasing radiation, which can damaged cells, damage DNA and cause Cancer. Due to tritium’s instability its abundance is 10-16% [12] in nature, and therefore has to be artificially produced. 8 Oxford Dictionary of Physics 9 Gasoline Price- http://www.eia.gov/petroleum/gasdiesel/ 10 Physics for Scientists and Engineers- Serway, 6th edition pg. 1488 11 General Chemistry- Principles and Modern Applications, 9th edition- pg 1060 12 Tritium-http://wwsw.ead.anl.gov/pub/doc/tritium.pdf Production Tritium occurs naturally in the environment in extremely low quantities to be practically recovered and so has to be artificially produced. There are several production methods of tritium, the most common and efficient large scale production method is the one used in Savannah River Site (SRS) in South Carolina. At SRS neutrons are fired at a target consisting of lithium, neutrons react with the lithium and produce tritium along with other by-products. Application The main application and purpose of production of tritium is for nuclear weapon, specifically the hydrogen bomb and nuclear bomb.
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