Microcalorimeters measure the energy of particles or photons by converting it into heat, which is then measured. They are used in astrophysics and biochemistry. The device consists of an absorber, heat sink, and thermistor. Isothermal microcalorimeters measure chemical interactions and have applications in physical chemistry, biochemistry, and the pharmaceutical industry. They must operate at low temperatures to record minute changes in heat.
A microcalorimeter is a thermally sensitive device used to measure the energy of individual particles or photons, elementary particles of light. It is a type of calorimeter, an instrument that measures the heat released by physical or chemical reactions in a sample. Microcalorimeters are used in astrophysics to measure the energy of X-ray photons from space. A related device, the isothermal microcalorimeter, is used in biochemistry and related fields to detect small changes in energy at low temperatures.
The law of conservation of energy, a fundamental law of physics, states that energy cannot be created or destroyed, it can only be converted into other forms. Microcalorimeters work on this principle. The energy of a physical interaction or a chemical reaction is transformed into heat within the system, and by measuring the resulting change in heat, the energy of the interaction can be deduced.
The type of microcalorimeter used in astrophysics consists of three main components: an absorber, a heat sink, and a thermistor. When an X-ray photon strikes the absorber, energy is transferred to an electron in an atom of the absorber material. This energy excites the electron: it jumps further from the atomic nucleus and breaks free from orbit. Other electrons in the absorber may be excited to a lesser extent by this loose electron, ascending to higher energy orbits around their respective atoms.
Excited electrons release energy as they return to their ground state, or lowest energy state, a stable orbit around atoms. The energy released in this process is stored and converted into heat, resulting in minimal temperature rise in the absorber. A thermometer device in the absorber known as a thermistor detects this temperature change. The heat then flows into the heat sink, returning the absorber to its original temperature. By measuring the temperature change caused by the impact of X-rays, the original energy of the X-rays can be calculated.
The isothermal microcalorimeter works in much the same way, although it is used to measure chemical interactions rather than photon energy. This device consists of a heat sink and a closed reaction vessel in which the chemical reaction takes place. The heat sink ensures that the reaction vessel is kept at a constant temperature, allowing for exact measurements. When the chemical reaction takes place, a certain amount of energy is released in the form of heat or absorbed, causing a temperature change which is recorded by the microcalorimeter. Isothermal microcalorimeters have applications in physical chemistry, biochemistry, and the pharmaceutical industry because they provide a highly sensitive way to analyze the heat flux in a reaction.
Microcalorimeters must operate at low temperatures so that the minute changes in heat they measure can be recorded. For example, devices used in astrophysics are kept close to absolute zero. At this temperature, even the small change in thermal energy caused by the impact of a single photon can be detected. Isothermal microcalorimeters are not as extreme, but are still kept at much lower temperatures than macroscale calorimeters.
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