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Converters & Calculators
What Is Neutron Cross Section
Introduction
Neutron cross‐sections are fundamental parameters in nuclear physics that quantify the probability of various interactions between neutrons and atomic nuclei. The understanding of these cross‐sections is essential for applications that range from the design of nuclear reactors, to medical treatments, and astrophysical research.
The neutron cross‐sections vary according to the neutron’s energy and the type of interaction it undergoes with an atomic nucleus. These interactions include scattering, absorption and fission, each playing an important role in specific applications.
Types of Neutron Interactions
- Elastic Scattering: Neutrons collide with nuclei without losing energy, thereby altering their direction.
- Inelastic Scattering: Neutrons transfer a portion of their energy to the nucleus, which results in its excitation.
- Absorption: Neutrons are absorbed by the nucleus, which may lead to radioactive decay or fission.
Applications of Neutron Cross‐Sections
Neutron cross‐sections are essential for various applications:
- Design of Nuclear Reactors: Accurate cross‐section data ensures efficient and safe reactor operation.
- Medical Treatments: Neutron therapy relies on precise neutron interactions to target cancerous cells while minimising damage to healthy tissue.
- Astrophysics: Understanding stellar nucleosynthesis and the composition of neutron stars is supported by neutron cross‐section data.
- Materials Science: Material properties are investigated using neutron scattering techniques.
Neutron Cross‐Section Table for Elements
The neutron cross‐section of an element describes the probability that a neutron will interact with its nuclei. The value is typically given in units of Barns (b), where 1 Barn = 10⁻²⁴ cm². This property is vital in fields such as nuclear physics, reactor design and radiation shielding.
The following table presents the neutron cross‐section values for several common elements, focusing on the total cross‐section, the thermal neutron cross‐section and the fission cross‐section, where available.
|
Element |
Isotope |
Total Cross‐Section (b) |
Thermal Neutron Cross‐Section (b) |
Capture Cross‐Section (b) |
Fission Cross‐Section (b) |
|
Hydrogen (H) |
Hydrogen‑1 |
20.5 |
5 335 |
0.33 |
0 |
|
Carbon (C) |
Carbon‑12 |
1.7 |
2.2 |
0.0035 |
0 |
|
Oxygen (O) |
Oxygen‑16 |
0.02 |
0.0002 |
0.0001 |
0 |
|
Uranium (U) |
Uranium‑238 |
280 |
2.7 |
0.1 |
50 |
|
Uranium (U) |
Uranium‑235 |
1 000 |
680 |
0.3 |
5 800 |
|
Thorium (Th) |
Thorium‑232 |
36 |
5.7 |
0.1 |
0 |
|
Plutonium (Pu) |
Plutonium‑239 |
748 |
2.6 |
0.17 |
8 400 |
|
Neptunium (Np) |
Neptunium‑239 |
71 |
16.5 |
0.2 |
1 600 |
|
Boron (B) |
Boron‑10 |
384 |
3 835 |
0.005 |
0 |
|
Boron (B) |
Boron‑11 |
5.5 |
3.0 |
0.01 |
0 |
|
Iron (Fe) |
Iron‑56 |
2.6 |
2.2 |
0.02 |
0 |
|
Cobalt (Co) |
Cobalt‑59 |
35 |
0.2 |
0.02 |
0 |
|
Copper (Cu) |
Copper‑63 |
5.1 |
0.4 |
0.01 |
0 |
|
Zinc (Zn) |
Zinc‑64 |
3.0 |
0.1 |
0.01 |
0 |
|
Lead (Pb) |
Lead‑208 |
0.22 |
0.0004 |
0.01 |
0 |
|
Nickel (Ni) |
Nickel‑58 |
3.0 |
0.03 |
0.01 |
0 |
|
Silicon (Si) |
Silicon‑28 |
1.0 |
0.2 |
0.001 |
0 |
|
Aluminium (Al) |
Aluminium‑27 |
1.6 |
0.3 |
0.002 |
0 |
|
Magnesium (Mg) |
Magnesium‑24 |
3.2 |
1.0 |
0.02 |
0 |
|
Calcium (Ca) |
Calcium‑40 |
1.1 |
0.04 |
0.0008 |
0 |
|
Argon (Ar) |
Argon‑40 |
0.04 |
0.006 |
0.0006 |
0 |
- Hydrogen exhibits a very high thermal neutron cross‐section; consequently, it is frequently used for neutron moderation (for example, water in reactors).
- Uranium‑235 and Plutonium‑239 are highly fissile materials that are essential in nuclear reactors and in weapons systems.
- Boron possesses a large neutron capture cross‐section, which renders it suitable for neutron shielding and control rods in nuclear reactors.
- Lead and Iron exhibit low neutron interaction cross‐sections, thereby making them effective materials for radiation shielding.
Further information is available at Stanford Advanced Materials (SAM).
Frequently Asked Questions
What is a neutron cross‐section?
A neutron cross‐section quantifies the probability that a neutron will interact with a specific nucleus, expressed in units known as Barns.
Why are neutron cross‐sections important in nuclear reactors?
They determine how neutrons behave within a reactor, thereby affecting the sustainability of the chain reaction and reactor efficiency.
How do neutron cross‐sections depend on energy?
At different neutron energy levels, specific interactions dominate, resulting in varying cross‐section values across energy ranges.
Where can I find detailed data on neutron cross‐sections?
Detailed data are available in nuclear databases such as the National Nuclear Data Center (NNDC) and in scientific publications.
Can neutron cross‐sections be used in medical applications?
Yes, they are fundamental for neutron therapy, which aims to target cancerous cells while minimising damage to healthy tissue.
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