Researchers from the University of Turku, Finland, have long studied the color-changing properties of the natural mineral hackmanite when exposed to UV radiation or X-rays. Now the research group is studying the reactions of synthetic hackmanite to nuclear radiation. The researchers discovered a unique and new intelligent quality, gamma exposure memory, that enables the use of hackmanite as a radiation detector, for example.
The research group has spent years researching the unique natural mineral hackmanite and its properties. They have developed a method to synthesize hackmanite and have created numerous applications that take advantage of the material’s color-changing and luminescent properties. For example, the group is currently developing a hackmanite-based non-electronic UV radiation dosimeter, which will be tested in the International Space Station. Radiation exposure in space can be measured by observing the change of color of hackmanite from white to pink caused by UV radiation.
The researchers have now also investigated how the synthetic hackmanite reacts when exposed to alpha particles, beta particles (positrons) or gamma radiation. They found that hackmanite also changes color with exposure to these types of radiation, meaning it is also a radiochromic material. This was previously unknown.
The impact of the radiation has been studied in the laboratory of Swedish partners in Umeå, the laboratory of the Finnish Authority for Radiation and Nuclear Safety and the radiochemistry laboratory of the University of Turku by placing hackmanite plates at different distances from radiation sources during different periods of time, exposing them to different doses of radiation.
“Then the samples were photographed and their reflectance spectra were measured to obtain information about their color depth and whether the color was comparable to samples exposed to, for example, UV light and X-rays. The color change when exposed to nuclear radiation was comparable to UV radiation and X-rays, but slower, because most of this radiation passes through the material without affecting it,” said doctoral researcher Sami Vuori.
The color change in hackmanite is similar across all radiation exposures, but there was a slight difference in the spectra of the samples exposed to nuclear radiation. According to the researchers, this was the key to discovering a new function.
Gamma exposure memory enables hackmanite-based non-toxic radiation detectors
The researchers noted that hackmanite stained with nuclear radiation can be returned to its original color, much like exposure to UV radiation and X-rays, namely by heating the material or exposing it to white light.
“However, we have found that hackmanite retains a memory trail from exposure to high-energy radiation such as alpha particles or gamma rays. The memory trail is preserved even when the color is reverted to the original. It becomes visible when the sample is re-stained with a UV lamp. To the naked eye, the color is similar to the material exposed to UV radiation or X-rays, but spectrometry reveals a small but clear change in the shape of the signal,” said the research group’s leader, Professor Mika Lastusaari.
With computational results, the researchers were able to verify that nuclear radiation causes a new type of structural defect in hackmanite. This defect acts as a certain type of memory unit in the material. The radiation does not destroy the hackmanite, but provides a new type of intelligent function, gamma exposure memory, which the researchers say has not been detected in any other material. Despite the gamma exposure memory and structural defect, one of hackmanite’s basic intelligent properties, its ability to repeatedly change color, remains the same.
“The color change in nuclear radiation means that hackmanite can be used to make radiochromic films that are regularly used in various applications of medical physics to measure radiation doses and map the dose distribution. Today’s radiochromic films are mostly made of polydiacetylenes or leucomalachite green.” and are either non-reusable or toxic. Hackmanites offer a non-toxic option that can be used repeatedly. In addition, hackmanite has a memory property that other materials do not have. Hackmanite is also an ecological and inexpensive material that is easy to synthesize,” said Lastusaari .
The study was conducted by the Intelligent Materials Research Group, the Radiochemistry Research Group and the Physics Department of the University of Turku, and the calculations were done at the University Claude Bernard Lyon 1, France. The international research consortium also included the Mineralogical Society of Antwerp, Belgium, the Universities of Tampere and Jyväskylä, Finland, and the Swedish Defense Research Agency.
The study was published in September in the journal Materials Horizons.
Natural mineral hackmanite enables new method of X-ray imaging
Sami Vuori et al, Reusable radiochromic hackmanite with memory for gamma exposure, Materials Horizons (2022). DOI: 10.1039/D2MH00593J
Quote: Hackmanite also changes color when exposed to nuclear radiation: Memory trace enables new uses (2022, September 29) retrieved September 29, 2022 from https://phys.org/news/2022-09-hackmanite-exposure-nuclear-memory -enables .html
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