Sara Reausaw Department of Chemistry and Chemical Engineering

1. Sara Reausaw Department of Chemistry and Chemical Engineering South Dakota School of Mines and Technology Rapid City, SD 57701 Rutherford: The Friendly Physicist who Advanced in Chemistry Biography on the life of Ernest Rutherford: Rutherford's Gold Foil Experiment: Rutherford and Geiger together at Manchester developed a device that was able to count alpha particles when it detected them. The new detector consisted of a screen coated with zinc sulfide. Alpha particles would hit the screen and emit a tiny flash of light. Geiger had to peer at the screen through a microscope in order to see the emission that was termed scintillation. Geiger felt that the time had come to perform an experiment. Rutherford noticed alpha particles were colliding with the atoms in the foil. The particles were bouncing off at small angles and this type of interaction is said to be scattered. By counting the scattered particles, Rutherford and Geiger hoped to learn something about atoms. Geiger put a thin foil in front of the narrow beam of particles. The alpha particles went through the foil and exited the other side in a scattered manner. It was calculated that throughout the entire foil, the average angle of deflection of an alpha particle was less than one degree from the center path. Before Ernest Rutherford was born in 1871 his family immigrated to New Zealand from England. Ernest was born on a farm near Nelson that his family ran successfully. He was the fourth of 12 children and enjoyed the hard work associated with the life of being on a farm. He was a good student in school and won a university scholarship to Canterbury College. Here he no doubt was exposed to liberal education. For this was a Christchurch, and in 1892 graduated. Here at Canterbury he had majored in mathematics and physics. He decided to stay at Canterbury College for a further year to continue studying and and to teach. It was during this year that he studied the properties of iron in high-frequency alternating magnetic fields. Cambridge University in England awarded him yet another scholarship to further his education. At twenty-four years old left his fiancee, Mary Newton, in September 1895, to work in the Cavendish Laboratory at the university. This proved to be a turning point in his life. He had brought an electromagnetic wave detector with him, and discovered a way to detect radio signals using magnetized steel needles. In Cambridge he sent a message three quarters of a mile away. A man by the name of J.J. Thompson was impressed with the talents that Rutherford possessed and invited him to collaborate with him. This was the start of a promising career in atomic physics. Early on he found that all known radioactive elements emit two kinds of radiation: positively and negatively charged. Rutherford was responsible for the naming of these terms as alpha and beta. He discovered the half-life by showing that every radioactive element decreases in radioactivity over a unique and regular time, ultimately becoming stable. Frederick Soddy worked with him in 1901 and 1902, and they proved that by expelling a piece of the atom at high velocity, atoms of one radioactive element would spontaneously turn into another. The idea was frowned upon as it was thought to be alchemy. Their beliefs that the atom is indivisible and unchangeable gained recognition by 1904, along with Rutherford’s achievements and publications. His achievements and publications intertwined as he published eighty papers in the span of seven years. In 1898 McGill University, Montreal called the twenty-seven year old Rutherford to head up the Physics Department. McGill University’s topic of interest fell in the work of subatomic physics. This new science was at the hands of Rutherford and his team. They researched the phenomenon of natural radiation. Rutherford, at McGill University, put much investigation in answering the question about what these rays that were capable of passing in various degrees through many substances impervious to light were. It was at this time that he had planned to finally marry his fiancée Mary Newton, yet it was another year and a half before the two became husband and wife. In 1907 he went to accept a chair at the University of Manchester and came in contact with a man by the name of Geiger. Together they set up a center to study radiation. In 1909 Rutherford began performing experiments that would all together change the views upon physics. He discovered the atomic nucleus and developed a model of the atom that resembled the solar system. The nucleus resembled the sun and the electrons resembled the planets in orbit around the sun. Niels Bohr modified the theory by using quantum theory, and this increased the acceptance of the theory all together. During World War I, he left his research to help the British Admiralty with the practical problem of submarine detection. By underwater acoustics he managed to dislodge a single particle that possessed a positive charge. This meant that it must have come from nucleus; Rutherford named this new particle a proton. This was the first “nuclear reaction”, and he was the man responsible for it. It was of some interest to see if any of the alpha particles were in fact deflected more than ninety degrees; this would in turn indicate that some of the alpha particles were returning towards the source. To both Grieger and Rutherford’s surprise, measurements indicated that about one in eight thousand was deflected by a large angle. Rutherford came up with the explanation that the alpha particles must be colliding with something inside the atom that was small and heavy. This center of the atom that is small and heavy is called the nucleus. Nobel Prize Award: Rutherford received the 1908 Nobel Prize in chemistry for his work in dealing with radiation and the atomic nucleus. It was somewhat surprising that a physicist would be awarded the prize in chemistry. During the time in which Rutherford lived, nuclear physics and nuclear were one of the same. Since Rutherford was a Physicist he was slightly put out by the award in chemistry. References: • http://www.xmission.com/~dparker/nucleus.html • http://www.watertown.k12.wi.us/hs/teachers/buescher/atomtime.asp • http://windows.arc.nasa.gov/cgi-bin/tour.cgi?link=/people/modern_era/rutherford.html • http://www.chemistry.co.nz/ernest_rutherford.htm • http://www.pbs.org/wgbh/aso/databank/entries/bpruth.html • http://www.blupete.com/Literature/Biographies/Science/Rutherford.htm • http://www.cbc4kids.ca/general/the-lab/big-bang/99-09-10/default.html • http://dbhs.wvusd.k12.ca.us/Gallery/Gallery11.html • http://www.accessexcellence.org/AE/AEC/CC/historical_background.html Chem 292, Chemistry Outreach Spring 2001 Dr. David A. Boyles and Dr. M. Steven McDowell