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ReectionWavelength, refractive index of particle, and refractive index of medium are constantIntensity of scattered light is dependent on particle diameterParticleRefractionLightAbsorptionDiffractionViable Particle CounterXL-10B (2011)Rion developed the XL-10B viable particle counter by applying technologies acquired in the develop-ment and production of particle counters. Viable particles are irradiated with a violet laser of a spe-cic wavelength to induce autouorescence by a certain substance inside the cell. This uorescence is detected to make real-time measurements of the number and size of the viable particles. The process requires no preprocessing of the samples, such as dyeing or cell culturing.particle diameter of 0.03 μm, a world-lead-ing achievement at the time.“We developed these models by bringing together all of Rion’s technologies. Rion’s strengths lie in precision and durability, qualities that make our instruments reliable and trouble-free. It’s an approach we’ve cultivated throughout our long history.”Continuing to Develop Particle Counters in Response to the Needs of the TimesRion has won trust both in Japan and abroad for its dedication to the devel-opment of precision particle counters. In 2011, it introduced the world’s rst viable particle counter (picoplankton counter TM) to the market. This device is capable of dis-tinguishing viable particles from nonviable particles in water and can make real-time measurements of viable particles like bac-teria and plankton. The mechanism of mea-surement relies on a biological substance present inside viable particles that exhibits autouorescence. Upon irradiation with a violet laser, this induces autouorescence in the particles, and the uorescence emitted is detected using a uorescence meter. The counter can instantaneously determine whether the particles being counted are viable or nonviable.“The most important process at sites where foodstus, drinking water, and water for medical and pharmaceutical uses are han-dled is conrming freedom from contam-ination by foreign materials like bacteria. Despite requirements for thorough sani-tary and contamination control, conven-tional monitoring was mainly implemented by measurements based on the cell culti-vation method. Conrming the presence of bacteria by cell cultivation takes three to ve days, during which the plant has to be shuttered. In contrast, a viable particle counter can instantly determine the pres-ence of bacteria, fungi, and yeasts sim-ply by passing the water to be managed through the instrument. Real-time water quality monitoring signicantly reduces the cost and labor associated with the task. We anticipate growing demand for these instruments.”Since 2020 and the Covid-19 pandemic, demand for detecting viruses, bacteria, and other airborne organisms has increased.“Viruses and bacteria don’t become air-borne on their own—they have to ride on other kinds of particles. We see increasing demand for counting microplastics, some-thing being recognized as a serious issue. We’re currently developing particle count-ers to respond to all these needs.”Even now, the particle counter team is test-ing new approaches as part of vigorous and persistent eorts to develop sensors and detection technologies that will push the limits of minimum measurable particle diameter and respond to the needs of the times.What are particles?Particles (ne particles) are dened as matter of sub-micron size (less than 1 µm or so in diame-ter) that remain suspended in air or liquid with-out settling. Different elds use different methods to measure such particles. To manage building air conditioning systems or when measuring PM2.5, particles are monitored by measuring their weight in a given quantity of air. In environments like semi-conductor cleanrooms, hospital operating rooms, or spaces in which pharmaceuticals are manufac-tured, particles are monitored by size and count. Suspended particles in cleanrooms are counted by the light scattering method; cleanliness is rep-resented by the size of the particles determined from the amount of scattered light (light-scattering equivalent diameter).Interaction between light and particlesOnce particles become smaller than the wavelength of light, the scattering of light energy by the par-ticles becomes dominant over reected or diffract-ed light. The intensity of the scattered light exhibits a specic correlation to the particle size, the re-fractive indices of particles and medium, and the wavelength of light. Thus, the particle size can be determined by measuring the amount of scattered light.Particles in the atmosphere0.00010.0010.010.11.0101001,00010,000Tobacco smokeSome examples of particlesCementPigmentHairSootSporeDust from heavy industrySilica sandPollenVirusMicrobeBacteriumFungusAlgaZnO, MgOChemical substanceGas moleculeUltrane particlesFine particlesParticle diameter[µm]Coarse particles11

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