Rutherford's team discovers the nucleus

In 1906 Ernest Rutherford published "Radiation of the α Particle from Radium in passing through Matter". Geiger expanded on this work in a communication to the Royal Society with experiments he and Rutherford had done passing α particles through air, aluminum foil and gold leaf. More work was published in 1909 by Geiger and Marsden and further greatly expanded work was published in 1910 by Geiger. In 1911-2 Rutherford went before the Royal Society to explain the experiments and propound the new theory of the atomic nucleus as we now understand it.

The key experiment behind this announcement happened in 1909 as Ernest Rutherford's team performed a remarkable experiment in which Hans Geiger and Ernest Marsden under his supervision fired alpha particles (helium nuclei) at a thin film of gold foil. The plum pudding model predicted that the alpha particles should come out of the foil with their trajectories being at most slightly bent. Rutherford had the idea to instruct his team to look for something that shocked him to actually observe: a few particles were scattered through large angles, even completely backwards, in some cases. The discovery, beginning with Rutherford's analysis of the data in 1911, eventually led to the Rutherford model of the atom, in which the atom has a very small, very dense nucleus containing most of its mass, and consisting of heavy positively charged particles with embedded electrons in order to balance out the charge (since the neutron was unknown). As an example, in this model (which is not the modern one) nitrogen-14 consisted of a nucleus with 14 protons and 7 electrons (21 total particles), and the nucleus was surrounded by 7 more orbiting electrons.

The Rutherford model worked quite well until studies of nuclear spin were carried out by Franco Rasetti at the California Institute of Technology in 1929. By 1925 it was known that protons and electrons had a spin of 1/2, and in the Rutherford model of nitrogen-14, 20 of the 21 particles should have paired up to cancel each other's spin, and the final odd particle should have left the nucleus with a spin of 1/2. Rasetti discovered, however, that nitrogen-14 has a spin of 1.

I. Reading exercises:

Exercise1. Read and memorize using the dictionary:

confuse, evolve, embed, decay, discrete, predate, nucleons, profound, foil, at the turn of the 20^th century, plum pudding model, be expanded, announcement, fire, scatter, nuclear spin, eject, pair-up, add particle

Exercise 2. Answer the questions:

1. What does nuclear physics study?

2. What does atomic physics study?

3. When had physicists discovered three types of radiation?

4. Who formulated the idea of mass-energy equivalence?

5. What did Ernest Rutherford publish in 1906?

6. What are the most commonly known applications of nuclear physics?

Exercise 3. Match the left part with the right:

1. Nuclear physics is the field of physics	a. that the atom had internal structure.
2. Particle physics is a field	b. that the beta decay spectrum was continuous rather than discrete.
3. The discovery of the electron by J.J. Thomson was the first indication	c. that has evolved out of nuclear physics.
4. Experiments in 1911 by Lise Meitner and Otto Hahn, and by James Chadwick in 1914 discovered	d. that studies the building blocks and interactions of atomic nuclei.

Exercise 4. Open brackets using the right words:

That is electrons were (ejected/emitted) from the atom with a range of energies, rather than the discrete amounts of energies that were (observed/designated) in gamma and alpha decays.

The Speaking Module

II. Speaking exercises:

Exercise 1. Describe nucleus; electron; neutron; radiation; energy using the suggested words and expressions as in the example:

nucleus the central; positively charged; dense portion of an atom example: Nucleus – the central positively charged, dense portion of an atom.

electron elementary particle; a stable; constituent of ordinary matter; which is the negatively charged; 9.11*10-28 gram; having a mass of about

neutron which has approximately; an elementary particle; the same mass; but lacks electric charge; as the proton; and is a constituent; of all nuclei; greater than 1; having mass number

radiation of waves transmitting energy; the emission and propagation; through space; or through some medium

energy work; the capacity; for doing

Exercise 2. Ask questions to the given answers:

1. Question: ____________________________________ ?

Answer: Ernest Rutherford’s team performed a remarkable experiment.

2. Question: ____________________________________ ?

Answer: A few particles were scattered through large angles.

3. Question: ____________________________________ ?

Answer: The atom has a very small, very dense nucleus containing most of its mass

The Writing Module

III. Writing exercises:

Exercise 1. Complete the sentences with the suggested words: out; at; in; spin; known; well:

The Rutherford model worked quite ______ until studies of nuclear _____ were carried ______ by Franco Rasetti ______ the California Institute of Technology in 1929. By 1925 it was ______ that protons and electrons had a spin of 1/2, and in the Rutherford model of nitrogen-14, 20 of the 21 particles should have paired up to cancel each other's spin, and the final odd particle should have left the nucleus with a spin of 1/2.

Exercise 2. Fill in the table with words from the text and define to what part of speech these words belong to: physics; atomic; nuclei; confuse; arrangement; synonymously; evolve; include; term; nuclear; power; range; common; internal; positively; negatively; physicist; discover; radiation; discrete; eject; observe; decay; indicate; predate; constituents; publish; particle; profound; remarkable; thin; slightly; scatter; eventually; dense; odd.

nouns	adjectives	adverbs	verbs

Exercise 3. Compose a story on one of the topics (up to 100 words):

“Nuclear physics”

“Rutherford’s team discovers the nuclei”

“The Rutherford’s model of the atom”

Lesson 2

The Reading Module