The becquerel is the SI derived unit of radioactivity. One becquerel is defined as the activity of a quantity of radioactive material in which one nucleus decays per second; the becquerel is therefore equivalent to an inverse second, s−1. The becquerel is named after Henri Becquerel, who shared a Nobel Prize in Physics with Pierre and Marie Curie in 1903 for their work in discovering radioactivity; as with every International System of Units unit named for a person, the first letter of its symbol is uppercase. However, when an SI unit is spelled out in English, it should always begin with a lowercase letter —except in a situation where any word in that position would be capitalized, such as at the beginning of a sentence or in material using title case. 1 Bq = 1 s−1A special name was introduced for the reciprocal second to represent radioactivity to avoid dangerous mistakes with prefixes. For example, 1 µs−1 could be taken to mean 106 disintegrations per second: 1·−1 = 106 s−1. Other names considered were hertz, a special name in use for the reciprocal second, fourier.
The hertz is now only used for periodic phenomena. Whereas 1 Hz is 1 cycle per second, 1 Bq is 1 aperiodic radioactivity event per second; the gray and the becquerel were introduced in 1975. Between 1953 and 1975, absorbed dose was measured in rads. Decay activity was measured in curies before 1946 and in rutherfords between 1946 and 1975. Like any SI unit, Bq can be prefixed. For practical applications, 1 Bq is a small unit. For example, the 0.0169 g of potassium-40 present in a typical human body produces 4,400 disintegrations per second or 4.4 kBq of activity. The global inventory of carbon-14 is estimated to be 8.5×1018 Bq. The nuclear explosion in Hiroshima is estimated to have produced 8×1024 Bq; the becquerel succeeded the curie, an older, non-SI unit of radioactivity based on the activity of 1 gram of radium-226. The curie is defined as 3.7 · 1010 s 37 GBq. Conversion factors: 1 Ci = 3.7×1010 Bq = 37 GBq 1 μCi = 37,000 Bq = 37 kBq 1 Bq = 2.7×10−11 Ci = 2.7×10−5 μCi 1 MBq = 0.027 mCi For a given mass m of an isotope with atomic mass m a and a half-life of t 1 / 2, the radioactivity can be calculated using: A B q = m m a N A ln t 1 / 2 With N A = 6.02214179×1023 mol−1, the Avogadro constant.
Since m / m a is the number of moles, the amount of radioactivity A can be calculated by: A B q = n N A ln t 1 / 2 For instance, on average each gram of potassium contains 0.000117 gram of 40K that has a t 1 / 2 of 1.277×109 years = 4.030×1016 s, has an atomic mass of 39.964 g/mol, so the amount of radioactivity associated with a gram of potassium is 30 Bq. The following table shows radiation quantities in non-SI units. Background radiation Banana equivalent dose Counts per minute Ionizing radiation Orders of magnitude Radiation poisoning Relative Biological Effectiveness Rem Rutherford Sievert Derived units on the International Bureau of Weights and Measures web site
Caesium or cesium is a chemical element with symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of 28.5 °C, which makes it one of only five elemental metals that are liquid at or near room temperature. Caesium has chemical properties similar to those of rubidium and potassium; the most reactive of all metals, it is pyrophoric and reacts with water at −116 °C. It is the least electronegative element, with a value of 0.79 on the Pauling scale. It has only one stable isotope, caesium-133. Caesium is mined from pollucite, while the radioisotopes caesium-137, a fission product, are extracted from waste produced by nuclear reactors; the German chemist Robert Bunsen and physicist Gustav Kirchhoff discovered caesium in 1860 by the newly developed method of flame spectroscopy. The first small-scale applications for caesium were as a "getter" in vacuum tubes and in photoelectric cells. In 1967, acting on Einstein's proof that the speed of light is the most constant dimension in the universe, the International System of Units used two specific wave counts from an emission spectrum of caesium-133 to co-define the second and the metre.
Since caesium has been used in accurate atomic clocks. Since the 1990s, the largest application of the element has been as caesium formate for drilling fluids, but it has a range of applications in the production of electricity, in electronics, in chemistry; the radioactive isotope caesium-137 has a half-life of about 30 years and is used in medical applications, industrial gauges, hydrology. Nonradioactive caesium compounds are only mildly toxic, but the pure metal's tendency to react explosively with water means that caesium is considered a hazardous material, the radioisotopes present a significant health and ecological hazard in the environment. Caesium is the softest element, it is a ductile, pale metal, which darkens in the presence of trace amounts of oxygen. When in the presence of mineral oil, it loses its metallic lustre and takes on a duller, grey appearance, it has a melting point of 28.5 °C, making it one of the few elemental metals that are liquid near room temperature. Mercury is the only elemental metal with a known melting point lower than caesium.
In addition, the metal has a rather low boiling point, 641 °C, the lowest of all metals other than mercury. Its compounds burn with a blue or violet colour. Caesium forms alloys with the other alkali metals and mercury. At temperatures below 650 °C, it does not alloy with cobalt, molybdenum, platinum, tantalum, or tungsten, it forms well-defined intermetallic compounds with antimony, gallium and thorium, which are photosensitive. It mixes with all the other alkali metals. A few amalgams have been studied: CsHg2 is black with a purple metallic lustre, while CsHg is golden-coloured with a metallic lustre; the golden colour of caesium comes from the decreasing frequency of light required to excite electrons of the alkali metals as the group is descended. For lithium through rubidium this frequency is in the ultraviolet, but for caesium it enters the blue–violet end of the spectrum, thus caesium transmits and absorbs violet light preferentially while other colours are reflected. Caesium metal is reactive and pyrophoric.
It ignites spontaneously in air, reacts explosively with water at low temperatures, more so than the other alkali metals. It reacts with solid water at temperatures as low as −116 °C; because of this high reactivity, caesium metal is classified as a hazardous material. It is shipped in dry, saturated hydrocarbons such as mineral oil, it can be handled only under inert gas, such as argon. However, a caesium-water explosion is less powerful than a sodium-water explosion with a similar amount of sodium; this is because caesium explodes upon contact with water, leaving little time for hydrogen to accumulate. Caesium can be stored in vacuum-sealed borosilicate glass ampoules. In quantities of more than about 100 grams, caesium is shipped in hermetically sealed, stainless steel containers; the chemistry of caesium is similar to that of other alkali metals, in particular rubidium, the element above caesium in the periodic table. As expected for an alkali metal, the only common oxidation state is +1; some small differences arise from the fact that it has a higher atomic mass and is more electropositive than other alkali metals.
Caesium is the most electropositive chemical element. The caesium ion is larger and less "hard" than those of the lighter alkali metals. Most caesium compounds contain the element as the cation Cs+, which binds ionically to a wide variety of anions. One noteworthy exception is the caeside anion, others are the several suboxides. Salts of Cs+ are colourless unless the anion itself is coloured. Many of the simple salts are hygroscopic, but less so than the corresponding salts of lighter alkali metals; the phosphate, carbonate, oxide and sulfate salts are water-soluble. Double salts are less soluble, the low solubility of caesium aluminium sulfate is exploited in refining Cs from ores; the double salt with antimony (such as
The cardiac cycle is the performance of the human heart from the beginning of one heartbeat to the beginning of the next. It consists of two periods: one during which the heart muscle relaxes and refills with blood, called diastole, followed by a period of robust contraction and pumping of blood, dubbed systole. After emptying, the heart relaxes and expands to receive another influx of blood returning from the lungs and other systems of the body, before again contracting to pump blood to the lungs and those systems. A performing heart must be expanded before it can efficiently pump again. Assuming a healthy heart and a typical rate of 70 to 75 beats per minute, each cardiac cycle, or heartbeat, takes about 0.8 seconds to complete the cycle. There are two atrial and two ventricle chambers of the heart. At the "Start" of the cycle, during ventricular diastole–early, the heart relaxes and expands while receiving blood into both ventricles through both atria. During ventricular systole the ventricles are contracting and vigorously pulsing two separated blood supplies from the heart—one to the lungs and one to all other body organs and systems—while the two atria are relaxed.
This precise coordination ensures that blood is efficiently collected and circulated throughout the body. The mitral and tricuspid valves known as the atrioventricular, or AV valves, open during ventricular diastole to permit filling. Late in the filling period the atria begin to contract forcing a final crop of blood into the ventricles under pressure—see cycle diagram. Prompted by electrical signals from the sinoatrial node, the ventricles start contracting, as back-pressure against them increases the AV valves are forced to close, which stops the blood volumes in the ventricles from flowing in or out. Due to the contractions of the systole, pressures in the ventricles rise exceeding the pressures in the trunks of the aorta and the pulmonary arteries and causing the requisite valves to open—which results in separated blood volumes being ejected from the two ventricles; this is the ejection stage of the cardiac cycle. After ventricular pressures fall below their peak and below those in the trunks of the aorta and pulmonary arteries, the aortic and pulmonary valves close again—see, at right margin, Wiggers diagram, blue-line tracing.
Now follows the isovolumic relaxation, during which pressure within the ventricles begin to fall and thereafter the atria begin refilling as blood returns to flow into the right atrium and into the left atrium. As the ventricles begin to relax, the mitral and tricuspid valves open again, the completed cycle returns to ventricular diastole and a new "Start" of the cardiac cycle. Throughout the cardiac cycle, blood pressure decreases; the movements of cardiac muscle are coordinated by a series of electrical impulses produced by specialised pacemaker cells found within the sinoatrial node and the atrioventricular node. Cardiac muscle is composed of myocytes which initiate their internal contractions without applying to external nerves—with the exception of changes in the heart rate due to metabolic demand. In an electrocardiogram, electrical systole initiates the atrial systole at the P wave deflection of a steady signal; the cardiac cycle involves four major stages of activity: 1) "Isovolumic relaxation", 2) Inflow, 3) "Isovolumic contraction", 4) "Ejection".
Moving from the left along the Wiggers diagram shows the activities within four stages during a single cardiac cycle.. Stages 1 and 2 together—"Isovolumic relaxation" plus Inflow —comprise the ventricular "Diastole" period, including atrial systole, during which blood returning to the heart flows through the atria into the relaxed ventricles. Stages 3 and 4 together—"Isovolumic contraction" plus "Ejection"—are the ventricular "Systole" period, the simultaneous pumping of separate blood supplies from the two ventricles, one to the pulmonary artery and one to the aorta. Notably, near the end of the "Diastole", the atria begin contracting pumping blood into the ventricles; the time-wise increases and decreases of the heart's blood volume, are instructive to follow. The red-line tracing of "Ventricular volume" provides an excellent track of the two periods and four stages of one cardiac cycle. Starting with the Diastole period: the low-volume plateau of "Isovolumic relaxation" stage, followed by a rapid rise and two slower rises, all components of the "Inflow stage"—increasing to the high-volume plateau of t
International Electrotechnical Commission
The International Electrotechnical Commission is an international standards organization that prepares and publishes International Standards for all electrical and related technologies – collectively known as "electrotechnology". IEC standards cover a vast range of technologies from power generation and distribution to home appliances and office equipment, fibre optics, solar energy and marine energy as well as many others; the IEC manages three global conformity assessment systems that certify whether equipment, system or components conform to its International Standards. The IEC charter embraces all electrotechnologies including energy production and distribution, electronics and electromagnetics, multimedia, telecommunication and medical technology, as well as associated general disciplines such as terminology and symbols, electromagnetic compatibility and performance, dependability and development, safety and the environment; the first International Electrical Congress took place in 1881 at the International Exposition of Electricity, held in Paris.
At that time the International System of Electrical and Magnetic Units was agreed to. The International Electrotechnical Commission held its inaugural meeting on 26 June 1906, following discussions among the British Institution of Electrical Engineers, the American Institute of Electrical Engineers, others, which began at the 1900 Paris International Electrical Congress, continued with Colonel R. E. B. Crompton playing a key role. In 1906, Lord Kelvin was elected as the first President of the International Electrotechnical Commission; the IEC was instrumental in developing and distributing standards for units of measurement the gauss and weber. It first proposed a system of standards, the Giorgi System, which became the SI, or Système International d’unités. In 1938, it published a multilingual international vocabulary to unify terminology relating to electrical and related technologies; this effort continues, the International Electrotechnical Vocabulary remains an important work in the electrical and electronic industries.
The CISPR – in English, the International Special Committee on Radio Interference – is one of the groups founded by the IEC. 82 countries are members while another 82 participate in the Affiliate Country Programme, not a form of membership but is designed to help industrializing countries get involved with the IEC. Located in London, the commission moved to its current headquarters in Geneva in 1948, it has regional centres in Latin America and North America. Today, the IEC is the world's leading international organization in its field, its standards are adopted as national standards by its members; the work is done by some 10,000 electrical and electronics experts from industry, academia, test labs and others with an interest in the subject. IEC standards have numbers in the range 60000–79999 and their titles take a form such as IEC 60417: Graphical symbols for use on equipment. Following the Dresden Agreement with CENELEC the numbers of older IEC standards were converted in 1997 by adding 60000, for example IEC 27 became IEC 60027.
Standards of the 60000 series are found preceded by EN to indicate that the IEC standard is adopted by CENELEC as a European standard. The IEC cooperates with the International Organization for Standardization and the International Telecommunication Union. In addition, it works with several major standards development organizations, including the IEEE with which it signed a cooperation agreement in 2002, amended in 2008 to include joint development work. Standards developed jointly with ISO such as ISO/IEC 26300, ISO/IEC 27001, CASCO ISO/IEC 17000 series, carry the acronym of both organizations; the use of the ISO/IEC prefix covers publications from ISO/IEC Joint Technical Committee 1 - Information Technology, as well as conformity assessment standards developed by ISO CASCO and IEC CAB. Other standards developed in cooperation between IEC and ISO are assigned numbers in the 80000 series, such as IEC 82045-1. IEC standards are being adopted by other certifying bodies such as BSI, CSA, UL & ANSI/INCITS, SABS, SAI, SPC/GB and DIN.
IEC standards adopted by other certifying bodies may have some noted differences from the original IEC standard. The IEC is made up of members, called national committees, each NC represents its nation's electrotechnical interests in the IEC; this includes manufacturers, providers and vendors, consumers and users, all levels of governmental agencies, professional societies and trade associations as well as standards developers from national standards bodies. National committees are constituted in different ways; some NCs are public sector only, some are a combination of public and private sector, some are private sector only. About 90% of those who prepare IEC standards work in industry. IEC Member countries include: Source: In 2001 and in response to calls from t
Cycle per second
The cycle per second was a once-common English name for the unit of frequency now known as the hertz. The plural form was used written cycles per second, cycles/second, c.p.s. c/s, ~, or, just cycles. The term comes from the fact that sound waves have a frequency measurable in their number of oscillations, or cycles, per second. With the organization of the International System of Units in 1960, the cycle per second was replaced by the hertz, or reciprocal second, "s−1" or "1/s". Symbolically, "cycle per second" units are "cycle/second", while hertz is "Hz" or "s−1". For higher frequencies, kilocycles, as an abbreviation of kilocycles per second were used on components or devices. Other higher units like megacycle and less kilomegacycle were used before 1960 and in some documents; these have modern equivalents such as kilohertz and gigahertz. The rate at which aperiodic or stochastic events occur may be expressed in becquerels, not hertz, since although the two are mathematically similar, by convention hertz implies regularity where becquerels implies the requirement of a time averaging operation.
Thus, one becquerel is one event per second on average, whereas one hertz is one event per second on a regular cycle. Cycle can be a unit for measuring usage of reciprocating machines presses, in which cases cycle refers to one complete revolution of the mechanism being measured. Derived units include cycles per day and cycles per year. Revolutions per minute Cycles per instruction Heinrich Hertz Instructions per cycle Instructions per second MKS system of units a predecessor of the SI set of units Normalized frequency Radian per second
Heinrich Rudolf Hertz was a German physicist who first conclusively proved the existence of the electromagnetic waves theorized by James Clerk Maxwell's electromagnetic theory of light. The unit of frequency, cycle per second, was named the "Hertz" in his honor. Heinrich Rudolf Hertz was born in 1857 in Hamburg a sovereign state of the German Confederation, into a prosperous and cultured Hanseatic family, his father was Gustav Ferdinand Hertz. His mother was Anna Elisabeth Pfefferkorn. While studying at the Gelehrtenschule des Johanneums in Hamburg, Hertz showed an aptitude for sciences as well as languages, learning Arabic and Sanskrit, he studied sciences and engineering in the German cities of Dresden and Berlin, where he studied under Gustav R. Kirchhoff and Hermann von Helmholtz. In 1880, Hertz obtained his PhD from the University of Berlin, for the next three years remained for post-doctoral study under Helmholtz, serving as his assistant. In 1883, Hertz took a post as a lecturer in theoretical physics at the University of Kiel.
In 1885, Hertz became a full professor at the University of Karlsruhe. In 1886, Hertz married Elisabeth Doll, the daughter of Dr. Max Doll, a lecturer in geometry at Karlsruhe, they had two daughters: Johanna, born on 20 October 1887 and Mathilde, born on 14 January 1891, who went on to become a notable biologist. During this time Hertz conducted his landmark research into electromagnetic waves. Hertz took a position of Professor of Physics and Director of the Physics Institute in Bonn on 3 April 1889, a position he held until his death. During this time he worked on theoretical mechanics with his work published in the book Die Prinzipien der Mechanik in neuem Zusammenhange dargestellt, published posthumously in 1894. In 1892, Hertz underwent operations to treat the illness, he died of granulomatosis with polyangiitis at the age of 36 in Bonn, Germany in 1894, was buried in the Ohlsdorf Cemetery in Hamburg. Hertz's wife, Elisabeth Hertz née Doll, did not remarry. Hertz left two daughters and Mathilde.
Hertz's daughters never married and he has no descendants. In 1864 Scottish mathematical physicist James Clerk Maxwell, proposed a comprehensive theory of electromagnetism, now called Maxwell's equations. Maxwell's theory predicted that coupled electric and magnetic fields could travel through space as an "electromagnetic wave". Maxwell proposed that light consisted of electromagnetic waves of short wavelength, but no one had been able to prove this, or generate or detect electromagnetic waves of other wavelengths. During Hertz's studies in 1879 Helmholtz suggested that Hertz's doctoral dissertation be on testing Maxwell's theory. Helmholtz had proposed the "Berlin Prize" problem that year at the Prussian Academy of Sciences for anyone who could experimentally prove an electromagnetic effect in the polarization and depolarization of insulators, something predicted by Maxwell's theory. Helmholtz was sure Hertz was the most candidate to win it. Not seeing any way to build an apparatus to experimentally test this, Hertz thought it was too difficult, worked on electromagnetic induction instead.
Hertz did produce an analysis of Maxwell's equations during his time at Kiel, showing they did have more validity than the prevalent "action at a distance" theories. After Hertz received his professorship at Karlsruhe he was experimenting with a pair of Riess spirals in the autumn of 1886 when he noticed that discharging a Leyden jar into one of these coils would produce a spark in the other coil. With an idea on how to build an apparatus, Hertz now had a way to proceed with the "Berlin Prize" problem of 1879 on proving Maxwell's theory, he used a Ruhmkorff coil-driven spark gap and one-meter wire pair as a radiator. Capacity spheres were present at the ends for circuit resonance adjustments, his receiver was a simple half-wave dipole antenna with a micrometer spark gap between the elements. This experiment produced and received what are now called radio waves in the high frequency range. Between 1886 and 1889 Hertz would conduct a series of experiments that would prove the effects he was observing were results of Maxwell's predicted electromagnetic waves.
Starting in November 1887 with his paper "On Electromagnetic Effects Produced by Electrical Disturbances in Insulators", Hertz would send a series of papers to Helmholtz at the Berlin Academy, including papers in 1888 that showed transverse free space electromagnetic waves traveling at a finite speed over a distance. In the apparatus Hertz used, the electric and magnetic fields would radiate away from the wires as transverse waves. Hertz had positioned the oscillator about 12 meters from a zinc reflecting plate to produce standing waves; each wave was about 4 meters long. Using the ring detector, he recorded how the wave's component direction varied. Hertz measured Maxwell's waves and demonstrated that the velocity of these waves was equal to the velocity of light; the electric field intensity and reflection of the waves were measured by Hertz. These experiments established that light and these waves were both a form of electromagnetic radiation obeying the Maxwell equations. Hertz did not realize the practical importance of his radio wave experiments.
He stated that, "It's of no use whatsoever this is just an experiment that proves Maestro Maxwell was right—we just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there."Asked about the applications of his discoveries, Hertz replied, "Nothing, I g
In physics, electromagnetic radiation refers to the waves of the electromagnetic field, propagating through space, carrying electromagnetic radiant energy. It includes radio waves, infrared, ultraviolet, X-rays, gamma rays. Classically, electromagnetic radiation consists of electromagnetic waves, which are synchronized oscillations of electric and magnetic fields that propagate at the speed of light, which, in a vacuum, is denoted c. In homogeneous, isotropic media, the oscillations of the two fields are perpendicular to each other and perpendicular to the direction of energy and wave propagation, forming a transverse wave; the wavefront of electromagnetic waves emitted from a point source is a sphere. The position of an electromagnetic wave within the electromagnetic spectrum can be characterized by either its frequency of oscillation or its wavelength. Electromagnetic waves of different frequency are called by different names since they have different sources and effects on matter. In order of increasing frequency and decreasing wavelength these are: radio waves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.
Electromagnetic waves are emitted by electrically charged particles undergoing acceleration, these waves can subsequently interact with other charged particles, exerting force on them. EM waves carry energy and angular momentum away from their source particle and can impart those quantities to matter with which they interact. Electromagnetic radiation is associated with those EM waves that are free to propagate themselves without the continuing influence of the moving charges that produced them, because they have achieved sufficient distance from those charges. Thus, EMR is sometimes referred to as the far field. In this language, the near field refers to EM fields near the charges and current that directly produced them electromagnetic induction and electrostatic induction phenomena. In quantum mechanics, an alternate way of viewing EMR is that it consists of photons, uncharged elementary particles with zero rest mass which are the quanta of the electromagnetic force, responsible for all electromagnetic interactions.
Quantum electrodynamics is the theory of. Quantum effects provide additional sources of EMR, such as the transition of electrons to lower energy levels in an atom and black-body radiation; the energy of an individual photon is greater for photons of higher frequency. This relationship is given by Planck's equation E = hν, where E is the energy per photon, ν is the frequency of the photon, h is Planck's constant. A single gamma ray photon, for example, might carry ~100,000 times the energy of a single photon of visible light; the effects of EMR upon chemical compounds and biological organisms depend both upon the radiation's power and its frequency. EMR of visible or lower frequencies is called non-ionizing radiation, because its photons do not individually have enough energy to ionize atoms or molecules or break chemical bonds; the effects of these radiations on chemical systems and living tissue are caused by heating effects from the combined energy transfer of many photons. In contrast, high frequency ultraviolet, X-rays and gamma rays are called ionizing radiation, since individual photons of such high frequency have enough energy to ionize molecules or break chemical bonds.
These radiations have the ability to cause chemical reactions and damage living cells beyond that resulting from simple heating, can be a health hazard. James Clerk Maxwell derived a wave form of the electric and magnetic equations, thus uncovering the wave-like nature of electric and magnetic fields and their symmetry; because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. Maxwell's equations were confirmed by Heinrich Hertz through experiments with radio waves. According to Maxwell's equations, a spatially varying electric field is always associated with a magnetic field that changes over time. A spatially varying magnetic field is associated with specific changes over time in the electric field. In an electromagnetic wave, the changes in the electric field are always accompanied by a wave in the magnetic field in one direction, vice versa; this relationship between the two occurs without either type of field causing the other.
In fact, magnetic fields can be viewed as electric fields in another frame of reference, electric fields can be viewed as magnetic fields in another frame of reference, but they have equal significance as physics is the same in all frames of reference, so the close relationship between space and time changes here is more than an analogy. Together, these fields form a propagating electromagnetic wave, which moves out into space and need never again interact with the source; the distant EM field formed in this way by the acceleration of a charge carries energy with it that "radiates" away through space, hence the term. Maxwell's equations established that some charges and currents produce a local type of electromagnetic field near them that does not have the behaviour of EMR. Currents directly produce a magnetic field, but it is of a magnetic dipole type that dies out with distance from the current. In a similar manner, moving charges pushed apart in a conductor by a changing electrical potential produce an electric dipole type electric