What Is Neutron Cross Section
Introduction
Neutron cross sections are fundamental parameters in nuclear physics, representing the likelihood of various interactions between neutrons and atomic nuclei. Understanding these cross sections is crucial for applications ranging from nuclear reactor design to medical treatments and astrophysical research.
Neutron cross sections vary depending on the energy of the neutron and the type of interaction it undergoes with a nucleus. These interactions can include scattering, absorption, and fission, each playing a vital role in different applications.
Types of Neutron Interactions
- Elastic Scattering: Neutrons collide with nuclei without any energy loss, changing direction.
- Inelastic Scattering: Neutrons transfer some energy to the nucleus, resulting in excitation.
- Absorption: Neutrons are absorbed by the nucleus, potentially leading to radioactive decay or fission.
Applications of Neutron Cross Sections
Neutron cross sections are pivotal in various applications:
- Nuclear Reactor Design: Accurate cross section data ensure efficient and safe reactor operation.
- Medical Treatments: Neutron therapy relies on precise neutron interactions to target cancerous cells.
- Astrophysics: Understanding stellar nucleosynthesis and neutron star composition.
- Material Science: Investigating material properties through neutron scattering techniques.
Neutron Cross Section Table for Elements
The neutron cross section of an element describes the probability of a neutron interacting with the nuclei of that element. The value is usually given in units of barns (b), where 1 barn = 10−2410^{-24} cm². The cross section is an important property in fields such as nuclear physics, nuclear reactors, and radiation shielding.
Here's a table showing the neutron cross section values for several common elements, focusing on the total, thermal, and fission cross sections 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 |
5335 |
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 |
1000 |
680 |
0.3 |
5800 |
|
Thorium (Th) |
Thorium-232 |
36 |
5.7 |
0.1 |
0 |
|
Plutonium (Pu) |
Plutonium-239 |
748 |
2.6 |
0.17 |
8400 |
|
Neptunium (Np) |
Neptunium-239 |
71 |
16.5 |
0.2 |
1600 |
|
Boron (B) |
Boron-10 |
384 |
3835 |
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 |
|
Aluminum (Al) |
Aluminum-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 has a very high thermal neutron cross section, which is why it is widely used in neutron moderating applications (like water in reactors).
- Uranium-235 and Plutonium-239 are highly fissile materials, making them essential in nuclear reactors and weapons.
- Boron has a very large neutron capture cross section, making it useful in neutron shielding and control rods in nuclear reactors.
- Lead and Iron have low neutron interaction cross sections, which makes them effective as radiation shielding materials.
· For more information, please check Stanford Advanced Materials (SAM).
Frequently Asked Questions
What is a neutron cross section?
A neutron cross section quantifies the probability of a neutron interacting
with a specific nucleus, measured in units called barns.
Why are neutron cross sections important in nuclear reactors?
They determine how neutrons behave within the reactor, affecting the chain
reaction's sustainability and reactor efficiency.
How do neutron cross sections vary with energy?
Different interactions dominate at different neutron energies, leading to
variations in cross section values across energy ranges.
Where can I find detailed neutron cross section data?
Comprehensive data is available in nuclear databases such as the National
Nuclear Data Center (NNDC) and specialized scientific publications.
Can neutron cross sections be used in medical applications?
Yes, they are essential in neutron therapy, which targets cancer cells while
minimizing damage to healthy tissue.
