Rhude Jr. Phillip Broughton. Health Physicist, University of California, Berkeley. Richard McCardell. Nuclear Engineer, Idaho Falls. Thomas Cormier. It is made up of high energy photons, and can only be stopped by 6 mm of lead. Atom The basic building block of all matter, made up of a nucleus containing one or more protons positively charged particles and neutrons uncharged particles , and surrounded by an orbiting cloud of electrons negatively charged particles.
When he fired alpha particles at a fine sheet of gold foil, he found that some particles passed through the foil, but some changed direction or bounced back. He concluded that the atoms of the gold foil must be mostly empty space around a dense nucleus, and came up with his atomic model. Some elements such as uranium and radium have so many protons and neutrons in their nuclei that they are too heavy to be stable.
Instead the nucleus of one of these atoms will try to shoot off some of its particles usually in packages of 2 protons and 2 neutrons, known as alpha particles in the attempt to become more stable. Electro-magnetic waves These make up the electro-magnetic spectrum which contains all the frequencies at which electromagnetic waves can occur, from low frequencies radio through light, to high frequencies X rays.
An electro-magnetic wave consists of an electric and a magnetic field travelling together through space. Radioactive dating A method for working out the age of material such as rocks by measuring the amount of radioactive decay that has taken place, that is, the amount of radioactive material usually carbon 14 in the sample being tested. Radioactivity When an unstable atom spits out or emits from its nucleus a subatomic particle and turns into an atom of a different element.
This is also called radioactive decay. Subatomic particles are the particles which make up an atom, including protons, neutrons and electrons. Split the atom Also known as nuclear fission. By bombarding radioactive uranium with neutrons it is possible to split the uranium nucleus in half and release huge amounts of energy. As the nucleus is halved, it emits extra neutrons which spin off and split more uranium nuclei, creating still more energy and setting off a chain reaction.
This chain reaction can be slow and controlled, as in a nuclear plant producing nuclear energy, or become fast and uncontrolled as in the explosion of an atomic bomb. More information Search for resources about Ernest Rutherford or atoms in our catalogue. Footer Menu. I want to Contact Us Christchurch City Libraries. We think of matter as occupying space. But there is a lot of empty space in matter. In fact, most of the matter is empty space.
In , Rutherford and coworkers Hans Geiger and Ernest Marsden initiated a series of groundbreaking experiments that would completely change the accepted model of the atom.
They bombarded very thin sheets of gold foil with fast moving alpha particles. Alpha particles, a type of natural radioactive particle, are positively charged particles with a mass about four times that of a hydrogen atom.
Figure 1. B According to the plum pudding model top all of the alpha particles should have passed through the gold foil with little or no deflection. Rutherford found that a small percentage of alpha particles were deflected at large angles, which could be explained by an atom with a very small, dense, positively-charged nucleus at its center bottom.
Surprisingly, while most of the alpha particles were indeed undeflected, a very small percentage about 1 in particles bounced off the gold foil at very large angles. He could hardly believe what he saw. Rutherford too was astonished. About one in every few thousand of the alpha particles fired at the gold target had scattered at an angle greater than 90 degrees.
In this model electrons were believed to be stuck throughout a blob of positively charged matter, like raisins in a pudding. But this sort of arrangement would only cause small angle scattering, nothing like what Marsden had observed. After thinking about the problem for over a year, Rutherford came up with an answer. The only explanation, Rutherford suggested in , was that the alpha particles were being scattered by a large amount of positive charge concentrated in a very small space at the center of the gold atom.
The electrons in the atom must be orbiting around this central core, like planets around the sun, Rutherford proposed. The atom was mostly empty space.
In March , Rutherford announced his surprising finding at a meeting of the Manchester Literary and Philosophical Society, and in May , he published a paper on the results in the Philosophical Magazine. Later Rutherford and Marsden tried the experiment with other elements as the target, and measured their nuclei as well. The solar system model was not immediately accepted.
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