Material Guides

September 17, 2024

Author: Max Haydon

What is Neutron Shielding and What are the Most Effective Materials for Protection?

In the world of radiation protection, neutron shielding plays a critical role in ensuring the safety of people and the environment. Neutron radiation, a type of ionising radiation, is especially challenging to manage due to its unique properties.

Unlike gamma rays, which are photons, neutrons are uncharged particles. This lack of charge allows neutrons to penetrate materials more deeply and cause significant damage at the atomic level.

For this reason, selecting the right neutron shielding materials is crucial to attenuate and absorb this radiation effectively. In this blog, we’ll explore what neutron shielding is, why it’s necessary, and the most effective materials used in this field.

Where is Neutron Radiation Shielding Necessary?

Neutron radiation is commonly encountered in environments where nuclear reactions occur, such as nuclear power plants, research reactors, and medical facilities that use radiation for diagnostic or therapeutic purposes.

These settings often involve neutron sources from nuclear fuel or other radioactive materials. Effective shielding is necessary in these environments to protect personnel, patients, and sensitive equipment from the harmful effects of neutron and gamma radiation.

Deceleration of Fast Neutrons

One of the first steps in neutron shielding is to slow down fast neutrons. Fast neutrons are high-energy particles that can penetrate deeply into materials, posing a significant risk.

Materials that are rich in hydrogens, such as water, paraffin, or pure polyethylene, are particularly effective at decelerating these neutrons. Hydrogen atoms, having a mass similar to that of neutrons, are effective at reducing the neutron’s energy through repeated collisions, a process known as neutron moderation.

Absorption of Thermal Neutrons

Once fast neutrons are slowed down to become thermal neutrons, the next challenge is to absorb them. Thermal neutrons can be absorbed by certain materials, preventing them from causing further damage or producing additional radiation. Boron is one of the most effective neutron-absorbing materials.

When boron atoms capture neutrons, they undergo a nuclear reaction that results in the production of alpha particles. These alpha particles are relatively harmless in the context of external radiation, as they have very limited penetration power and are easily stopped by surrounding material.

Common Neutron Shielding Materials

Hydrogen: Critical for Shielding

Hydrogen plays a crucial role in neutron shielding due to its ability to attenuate fast neutrons. The light atomic mass of hydrogen allows it to effectively transfer energy during collisions with neutrons, slowing them down to thermal levels where they can be more easily absorbed by other materials, such as boron.

Paraffin

Paraffin is a hydrogen-rich material that is often used in neutron shielding applications. Its ability to slow down fast neutrons makes it an effective moderator. Paraffin is also relatively easy to shape and install, making it a practical choice for custom shielding solutions.

Concrete

Concrete is a versatile and widely used shielding material, particularly in nuclear power plants and research facilities.

It provides both neutron and gamma radiation shielding due to its density and composition, which can include additives like boron for enhanced protection. Concrete’s structural properties also make it ideal for constructing large shielding barriers.

WEP Resin

WEP (Water Extended Polyester) resin is another composite shielding material that combines the benefits of hydrogen-rich compounds with the structural integrity of a polymer.

WEP resin can be moulded into various shapes, making it suitable for complex shielding applications where traditional materials might be difficult to use.

Borated Polyethylene

Borated polyethylene is a composite material that combines the neutron moderation properties of hydrogen with the neutron absorption capabilities of boron.

This dual-action material is highly effective in a variety of shielding applications, from medical facilities to nuclear reactors. Its lightweight and easy-to-process nature make it a preferred choice for custom shielding solutions.

Raybloc often adds sheets of borated polyethylene in conjunction with lead sheets to create ionizing radiation protective doorsets that can also shield against neutron radiation.

Properties of Neutron Radiation Shielding Materials

Various Hydrogen Contents

Different neutron shielding materials contain varying levels of hydrogen, which influences their effectiveness in slowing down fast neutrons. Materials with higher hydrogen content, such as pure polyethylene neutron shielding, are particularly effective at moderating neutrons, making them essential in shielding designs.

Boron Carbide or Lithium Additivation

Adding boron carbide or lithium to shielding materials enhances their neutron absorption capabilities. These elements are known for their high neutron capture cross-section, meaning they can efficiently absorb thermal neutrons and prevent further radiation interactions.

High Resistance Against High-Energy Radiation

Neutron-shielding materials must withstand the intense conditions of high-energy radiation environments.

Composite materials, such as WEP resin or borated polyethylene, are designed to maintain their shielding properties even under prolonged exposure to both neutron and gamma radiation, ensuring long-term protection.

Low Weight

Weight is an important consideration in shielding design, particularly in applications where mobility or structural load is a concern. Materials like borated polyethylene offer excellent neutron shielding while remaining lightweight, making them ideal for portable or temporary shielding solutions.

Easy Processing

Ease of processing is another critical factor, especially for custom shielding applications. Materials that can be easily molded, cut, or shaped, such as WEP resin or polyethylene, allow for more versatile and tailored shielding solutions.

Neutron Shielding Performance and Service Life

The performance and service life of neutron shielding materials depends on several factors:

Operating Temperature: High temperatures can affect the structural integrity and shielding properties of certain materials, so it’s essential to choose materials that can withstand the expected temperature range.
Intensity of the Neutron Radiation: The level of neutron radiation will dictate the thickness and type of shielding required. Higher radiation levels may require composite materials or thicker layers of traditional materials.
Material Thickness: The thickness of the shielding material directly impacts its ability to attenuate and absorb neutrons. Thicker materials generally provide better protection but may also add weight and cost.
Combination with Other Materials: Combining different materials, such as borated polyethylene with lead or concrete, can enhance overall shielding effectiveness by addressing both neutron and gamma radiation.
Ambient Conditions: Environmental factors, such as exposure to moisture, chemicals, or mechanical stress, can impact the durability and effectiveness of shielding materials. It’s important to choose materials that can withstand the specific conditions of the installation site.

Neutron Shielding Materials – Fields of Application

Neutron shielding materials are used in various applications, including:

Research Reactors: Protecting researchers and equipment from neutron radiation.
Power Stations: Ensuring the safe operation of nuclear reactors.
Gloveboxes: Containing and shielding radioactive materials during handling.
Dry Cask Storage Containers: Safely storing spent nuclear fuel.
Detection Units: Shielding sensitive detectors from background neutron radiation.
Body Scanners: Protecting patients and operators from unnecessary radiation exposure.
Truck Scanners: Shielding equipment used in the detection of radioactive materials in cargo.

The Challenge of Neutron Radiation Shielding

Neutron radiation shielding presents unique challenges due to the penetrating nature of neutrons and their ability to activate other materials, potentially creating secondary sources of radiation.

Selecting the right shielding material requires a deep understanding of the radiation environment, the properties of potential shielding materials, and the specific application needs. At Raybloc, we specialise in designing and installing custom neutron shielding solutions that meet the highest safety and compliance standards.

FAQs

Does aluminium foil stop nuclear radiation?

No, aluminium foil is not effective at stopping most types of nuclear radiation. While it may attenuate low-energy radiation and alpha particles, it is not suitable for stopping neutrons or high-energy gamma radiation.

Is water a neutron moderator?

Yes, water is an excellent neutron moderator due to its high hydrogen content, which makes it effective at slowing down fast neutrons.

How much does a nuclear reactor cost?

The cost of a nuclear reactor can vary widely depending on the size, design, and location, but it typically ranges from several hundred million to billions of dollars.

Does nuclear energy produce high hydrogen content?

Nuclear energy itself does not produce hydrogen, but the processes involved in nuclear reactions often involve materials rich in hydrogen, such as water used as a coolant and moderator in reactors.

How do you measure the attenuation of effective shielding?

The attenuation of shielding is measured using detectors that assess the reduction in radiation levels after passing through the shielding material. The effectiveness is typically expressed as a percentage reduction or in terms of the material’s attenuation coefficient.

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Max Haydon

Head of Business Development at Raybloc (X-Ray Protection) Ltd

"I’m Max, one of the Haydon brothers carrying on the family legacy of Raybloc alongside Founder (and Father), Sean Haydon. My late grandfather, Leonard Street - fondly nicknamed “Gangy” by me and my brothers - founded Raybloc alongside my dad, and their dedication to precision, proactivity, and continuous improvement inspires everything I do.

With a Master’s in Physics with Medical Physics from the University of Nottingham, I’m serious about creating valuable content for our customers but always keep things human and approachable. The most rewarding part of my job? Knowing that Raybloc’s radiation shielding systems make healthcare environments safer, improve patient experiences, and support NHS staff in reducing waiting times. It’s a great feeling to know the work we do has such a positive impact.

Outside of work, I’m usually strumming my guitar, singing along to The Beatles, or creating original music inspired by 60s and 70s legends. Looking ahead, I’m passionate about expanding Raybloc into new industries and forging partnerships with people who share our mission to make meaningful change."