PRESENTATION. Make up a presentation “RADIOACTIVITY”

Make up a presentation “RADIOACTIVITY”

(See appendix 4)

SECTION 7

NEUTRON INTERACTIONS

LEAD-IN

Comment the statement below.

Neutrons can cause many different types of interactions. The neutron may simply scatter off the nucleus in two different ways, or it may actually be absorbed into the nucleus. If a neutron is absorbed into the nucleus, it may result in the emission of a gamma ray or a subatomic particle, or it may cause the nucleus to fission.

READING

TEXT 1

Before reading the text, decide in small groups (2-3 students) whether these statements are true or false using your knowledge of the subject. Then read the text and check your guesses.

1. Light scattering explains colour of some objects, usually shades of red.

2. The main factor influencing the process of scattering is the ratio of the particle diameter to the wavelength of the radiation.

3. The problem of electromagnetic scattering for large diameters is still being solved and attracts much attention.

4. When the ratio of particle diameter to wavelength is more than about 10, the term scattering is not usually applied.

5. A laser beam is a model for studying coherent backscattering.

1.3. The following sentences have been removed from the text. Choose from the sentences A-J the one which fits each gap (1 – 9). There is one extra sentence which you don’t need to use.

A In the Mie regime, the shape of the scattering center becomes much more significant and the theory only applies well to spheres and, with some modification, spheroids and ellipsoids.

B The first is fairly obvious, that it is difficult to measure the direct backscatter without blocking the beam, but there are methods for overcoming this problem.

C In this size regime, the exact shape of the scattering center is usually not very significant and can often be treated as a sphere of equivalent volume.

D Major forms of elastic light scattering (involving negligible energy transfer) are Rayleigh scattering and Mie scattering.

E When one looks at the sky during the day, rather than seeing the black of space, one sees light from Rayleigh scattering off the air.

F For relatively large and complex structures, these models usually require substantial execution times on a computer.

G The absence of surface scattering leads to a shiny or glossy appearance.

H Weak localization of light can be detected since it is manifested as an enhancement of light intensity in the backscattering direction.

I This phenomenon, is the result of many sinusoidal two-wave interference patterns which add up.

J This shift involves a slight change in energy.

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