Principal Nuclear Reaction – Neutron Sources

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Do curso por National Research Nuclear University MEPhI

Nuclear Reactor Physics Basics

classificações

National Research Nuclear University MEPhI

Nuclear Reactor Physics Basics

classificações

This engineering course is designed to introduce students to a range of concepts, ideas and models used in nuclear reactor physics. This course will focus on the physical theory of reactors and methods of experimental studies of the neutron field. This course is based on the course “Neutron transport theory” which has been taught at the National Research Nuclear University “MEPhI” for the past 20 years. What you'll learn: • Define basic processes that may occur in the reactor core, laws, equations, and the limits of applicability of models describing the neutron field in the reactor; • Demonstrate practical experience of calculating the distribution of neutrons in media; • Demonstrate the ability to analyze the process of slowing down neutrons in various media (typical for nuclear fission reactors) from the standpoint of understanding the physics of the process; • Evaluate important reactor parameters including performance and safety.

Na lição

Introductions to Nuclear Reactor Physics

In this module students will learn about the neutron field and main functions to describe it. Students will study the concepts of neutron flux, net current, one-way currents and vector of net current.

The Properties of Free Neutrons and It’s Classification8:46

Principal Nuclear Reaction – Neutron Sources4:20

Main Properties of Nuclear Fission6:47

Conheça os instrutores

Yury Volkov
Senior lecturer, PhD in Nuclear Engineering
Department of Theoretical and Experimental Physics of Nuclear Reactors

Because the free neutrons are non-stable particles, it requires external,

i.e. it does not depend on the field of neutron sources.

The first reaction is α-n reaction as used by Chadwick when

he first discovered the neutron. For example, in an n-source

such as 241Am/Be, 241Am undergoes α-decay; the α-particle

can be absorbed by a light element such as beryllium, which

then decays by neutron emission.

(α, n) reaction can only take place if the first the kinetic energy of α-particle

is above Coulomb barrier of the target nucleus and second

the excitation energy of a compound nucleus, resulting after the capture

of α-particle, is higher than the binding energy of a neutron in the compound nucleus.

An alternative is a γ-n source. For example: Radioactive

decay sources have the advantage of being small and highly

portable, but they have low intensity and are always “on”.

They can be used for testing (e.g., of the neutron detectors), in medicine

(e.g., for activation analysis, cancer treatment with 252Cf needles),

and for low-resolution/low-flux radiography.

The reaction of (γ, n) reaction may occur if the excitation energy is higher than

the binding energy of a neutron in the nucleus. Usually the binding

energy of a neutron in the nucleus is 6–8 MeV and it is too much

for the reaction but the nucleus of 9 Be and deuterium 2 H have

abnormally low energy of binding it is enough for γ–n reaction.

The next sources, is basis of the (p, n) reactions. Bombarding a target

by protons, it is possible to obtain a monochromatic neutron source.

Because of the need of penetration through the Coulomb barrier,

the appropriate targets are limited to light nuclei.

The next sources based on a fusion reaction. This sources is

higher intensities can be produced by small accelerator-based neutron sources.

Over the years, these have evolved sufficiently, so that compact

portable sources are now commercially available from a range of vendors.

They are normally based on the “D-T” reaction: deuterium and tritium

They are widely used for industrial and security applications based

on the fast neutron radiography and prompt gamma activation analysis.

Last but not least, the neutron reaction in which an incident

neutron is absorbed by a target nucleus, resulting

in a splitting of the target nucleus into two new atoms.

The fission process often produces free neutrons and photons

(in the form of gamma rays), and releases a large amount of energy.

In the process of fission reactions in the first stage a compound

nucleus is formed which is in a highly excited state. To describe

the further behaviour the Fission model of droplet nuclei

is well suited. Fluctuation drops will eventually lead to its rupture.

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