The Kilogram unit is about to be redefined

The kilogram (kg) has been used as a standard mass measurement since the French revolution, based on the exact mass of a metal block being stored in Paris. However, the kilogram may be about to be created for a new, more precise definition and for the first time there will be no need to reference a particular material.

Kilogram units will be redefined

Scientists who specialize in mass and measuring units have developed a method of describing the kilogram by measuring the exact number of atoms in a piece of silicon. They hope, it will overcome the gradual change in the mass of the International kg Model currently being used as the basic reference for the weight measurement unit around the world.

Kilogram is currently being identified by a cylindrical specimen, about the size of a golf ball, made up of 90% platinum and 10% iridium, which is being stored in France. Over time, cylindrical specimens, which consisted of 90% platinum and 10% iridium, lost small amounts of metal due to erosion as well as packaging and transporting it. The weight of the standard kg sample decreased by 0.0001g, which is equivalent to the weight of a dust particle, in the last century, meaning it will become less accurate. The researchers now discover that they can create a way to determine the kilogram accurately, reliably and without changing through the use of mathematical quantities.

The weight of the specimen is used for the definition of the kilogram in the old way.

At a conference held at the Royal Society of Science in London in January 2011, the researchers discussed alternatives to an aging ring of metal that are taking on the standard kilogram role of the world by A kilogram builds on a basic constant. Its mass is changing, and scientists don't know the reason. Its mass varies up to 50 micrograms compared to the 'national level copies' supplied to measurement laboratories around the world. The change in mass may be due to the gradual loss of hydrogen held in the alloy when tempering the upper cylinder, or perhaps due to the use of abrasive powder and poor quality cleaning fluids to clean it first. Here, according to Terry Quinn, former head of the International Institute of Metrology - BIMP. 'Did the kilogram prototype lose mass? Or are national copies getting worse? The answer is that we don't know - there's nothing more stable to compare. So we need something better , ' said BIMP physicist Michael Stock.

Then, in October 2011, the Paris Conference of Weights and Measures is expected to begin the process of changing the definition of the kilogram with a definition based on fundamental constants such as Avogadro's constant. , the number of atoms in a mole, and the Planck constant, the constant that relates the energy of a photon or a particle to its energy. If people can agree on technologies to do this work, the redefinition process will be completed this year. Other units have been redefined in similar ways. The meter was once defined as the length of the circumference of the Earth, but now it is defined as the distance that light travels for a certain period of time. In addition, the unit of seconds, once defined as a fraction of a day, is now defined as the length of a precise number of transitions in a cesium atom. At that time, the scientists held two different options. An option to define the kilogram is the mass of a certain number of silicon-28 atoms. The second option uses a mass meter called 'Watt balance' to define the kilogram according to voltage and current.

For the plan to use silicon-28 atoms, a research team led by Peter Becker of the Academy of Physics and Engineering Problems in Braunschweig, Germany, revealed a breakthrough in an effort. force to measure the number of atoms in a silicon sphere, thereby allowing them to calculate the Avogrado constant to an unprecedented accuracy. First, they used lasers to scan through a pure silicon sphere, thereby measuring its volume. They then used X-ray diffraction to estimate the volume that each atom occupies. That will result in an accurate count of the number of atoms in the sphere, but it is not possible because the silicon-28 stem crystal has a large number of silicon-29 and silicon-30 isotopes. Using a technique called isotope dilution mass, Becker and colleagues have just created a sphere in which the unwanted Si-29 and Si-30 isotopes are almost completely absent. As a result, they calculated Avogrado constant with a 3.0 x 10 ^ -8 error. Becker told New Scientist magazine that if they could refine their techniques a bit more, and reduce the measurement error to 2.0 x 10 ^ -8, they would dare to bet a good enough method. to define the kilogram is the mass of some silicon-28 atoms.

Meanwhile, the Watt balance method is basically a scale with a prototype kilogram on one side and an electric field from the other. Extremely sensitive electronic devices, such as Josephson contacts, can be used to balance and calculate the exact current and voltage needed to balance the kilogram. The above method will define the kilogram according to Planck's constant. Metrology institutes around the world are trying to improve the Watt balance method, but each experiment has its own error level to be overcome. The Canadian National Research Commission, for example, has just discovered a systematic error in a scale provided by the UK that needs to be overcome.

Compare old and new definitions of some units of measurement.

After more than four years of controversy and research, Dr. Giovanni Mana from the Italian National Metrology Research Institute and colleagues developed a new definition by calculating a mathematical constant, called the Avogadro number. - the number of atoms or molecules in a given physical volume . The number they found " big enough to reach" - 6,02214086 × 10 ^ 23, is much larger than the number of grains of sand on Earth or the number of stars in the universe. It allows the number of silicon atoms in 1kg to be calculated with an accuracy of approximately 20 atoms per billion atoms, through the definition it is related to Avogadro number. This number is then attached to another mathematical constant called Planck's constant, which is used to describe the behavior of quantum particles.

The new definition, if recognized, could allow scientists to change the way they determine 1kg after decades of research. First proposed in 1795, the kilogram was originally determined using the weight of water in a cube of 10 centimeters in volume at the melting point of the water. In 1799, this determination was changed, based on a piece of platinum, but then, the kilogram was defined as the mass of a cylindrical block of 39.7mm composed of 90% platinum and 10% iridium.

All other kilogram calculations are now based on this golf ball-sized metal block, which is being kept at the Office of International Weight and Measurements Units near Paris. According to Dr. Mana, the new definition of the kilogram will eventually free scientists from having to use a certain object under the control of the French authorities. He stressed: "In measurement, it is important to ensure independence and democracy, avoid the dictatorship of a single country or laboratory".

Kilogram is currently the only standard measure based on a physical artifact. Other units, such as meters and seconds, have been defined without reference to a specific object. For example, 1 meter was originally defined in 1793 as 1 / 10,000,000 distance from the equator to the North Pole, but it is now defined as 1/299792458 distance of light moving in a foot environment not in 1 second.The new definition of kilogram still needs to get approval from scientists at the Global Conference on Weight Measurements and International Metrology, which takes place in 2018, and scientists also say If we weigh our weight now, please subtract 60 micrograms per kilogram from your body to keep up with the new definition.