Background

The efficient shielding of ionizing X-ray and gamma radiation is required in medical, nuclear and aerospace industries. High Z elements such as lead, tungsten, bismuth and uranium are often used to attenuate X-ray radiation, where the shielding ability is dependent on the density and mass of the material, leading to heavy shielding materials. Further, most shielding materials are rigid solids and lack flexibility for conformal protection. To form conformal protection, a promising way is to shrink the size of effective metals and add them into a polymer matrix. Even though polymer matrices are inferior to metals for radiation shielding, they offer advantages such as flexibility, workability, chemical stability, and low cost. Lead powders are added into fabrics to form shielding aprons and coverings, but the formation of pin holes in polymer-metal composites allow incident photons to penetrate polymer regions, leading to the issue of low shielding ability.

The challenge of forming conformal light-weight polymer composites is twofold. It is hard to find a process that can incorporate metal powders in polymer sheets with sufficient metal content for effective radiation attenuation and robust enough to avoid structural deterioration such as tearing and cracking of polymer.

Nanoparticles of high-Z elements have been added in polymers to block X-ray radiation, but so far it has been observed that these nanoparticles tend to form aggregates in the polymer composite, or leach out and cause toxic effects to humans. From materials aspect, lead which is widely used in powder-loaded shielding sheets; is very toxic, and may leak due to aging, damage, embrittlement, and cracking of polymer. It is therefore imperative to use other non-toxic metals to minimize these negative impacts.

Technology Overview

Northeastern researchers have developed a nanoparticle-polymer composite for enhanced shielding of X-ray radiation, in which bismuth nanoparticles made with cellulose nanofibers form a composite with PDMS. The X-ray radiation shielding abilities of the nanoparticle-polymer composite was assessed in transmission mode and compared to those of microparticle composites. It was found that the nanoparticles effectively shield X-ray radiation at much lower mass ratio without scarifying mechanical strength of polymer. A four times reduction in the total mass of the bismuth material is identified when 5 nm nanoparticles are used in the composite to shield a given flux and energy of radiation, compared to existing microparticles.

The enhanced radiation shielding is attributed to close packing of nanoparticles normal to incoming X-ray direction, which is enabled by strong affinity of nanoparticles to interstitial space of cellulous nanofibers and an even distribution of the nanoparticles in the polymer matrix.

Benefits

A tougher nanoparticle polymer composite that will last longer than existing microparticle polymer composites
Dense packing of ultra-small bismuth nanoparticles to minimize void space
Light weight, low cost, structural conformability

Applications

Light‑weight and low-cost radiation and electromagnetic wave attenuated apron for protection of pregnant women
Protection shield for medical associates during diagnosis or X-ray exams
Radiation protection for workers in the heavy metal manufacturing locations
Use in shield clothing and masks for communities working on ground nuclear weapons testing sites
Cosmic ray protection for pilots in aerospace research

Opportunity

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Enhanced Radiation Shielding with Conformal Light-weight Nanoparticle-polymer Composite

IP Status

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