SYSTEMS of UNITS & RADIOLOGIC UNITS

SYSTEM OF UNITS SI MKS CGS BRITISH

BASIC QUANTITIES LENGTH MASS TIME

SYSTEM OF UNITS LENGTH MASS TIME SI MKS CGS BRITISH METER CENTIMETER FOOT MASS KILOGRAM GRAM POUND TIME SECOND

The International System of Units (abbreviated SI from the French phrase, Système International d'Unités) is the most widely used system of units. It is the most common system for everyday commerce in the world, and is almost universally used in the realm of science

Scientists, chiefly in France, had been advocating and discussing a decimal system of measurement based on natural units at least since 1640, but the first official adoption of such a system was after the French revolution of 1789. The metric system tried to choose units which were non-arbitrary and practical, merging well with the revolution's official ideology of "pure reason"; it was proposed as a considerable improvement over the inconsistent customary units which existed before, whose value often depended on the region

According to a survey taken many years ago, the only other countries that have not officially adopted the metric system are Liberia (in western Africa) and Myanmar (also known as Burma, in Southeast Asia). These two countries did not have an official policy of converting to metric, at least at the time of the survey. Despite recent repeated inquiries to the governments of both Liberia and Myanmar, no response from either country has been received as to whether an official policy has been adopted since this survey was conducted. Their Web sites utilize both inch-pound and metric units. Visitors to these countries report some evidence of the use of the metric system. Most other countries have either used the metric system for many years, or have adopted the metric system within the last 30 or 40 years. There is controversy about how to define whether a country is metric. Metrication is a process that does not happen all at once, but is rather a process that happens over time. Although nearly every country has taken steps to replace traditional measurements, the fact remains that among countries with non-metric usage the U.S. is the only significant holdout.

SI UNITS LENGTH----METER (m) MASS-------KILOGRAM (kg) TIME--------SECOND (s)

1 METER The most important unit is that of length: one metre was originally defined to be equal to 1/10 000 000th of the distance from the pole to the equator along the meridian through Paris. (Prior discussions had often suggested the length of a seconds pendulum in some standard gravity, which would have been only slightly shorter, and perhaps easier to determine.) This is approximately 10% longer than one yard. Later on, a platinum rod with a rigid, X-shaped cross section was produced to serve as the easy-to-check standard for one metre's length. Due to the difficulty of actually measuring the length of a meridian quadrant in the 18th century, the first platinum prototype was short by 0.2 millimetres. More recently, the metre was redefined as a certain multiple of a specific radiation wavelength, and currently it is defined as the distance travelled by light in a vacuum in a specific period of time. Attempts to relate an integer multiple of the metre to any meridian have been abandoned

1m=100 cm=1000 mm

1cm=10mm 1m=100 cm 1m=100 x 10= 1000 mm

The original base unit of mass in the metric system was the gram, chosen to match the mass of one cubic centimetre of water. For practical reasons, the reference standard that was deposited at the Archives de la république on June 22, 1799 was a kilogram (a cylinder of platinum). One kilogram is about 2.2 pounds. In 1889, the first General Conference on Weights and Measures (CGPM) sanctioned a replacement prototype, a cylinder of a 90% platinum, 10% iridium alloy; this has served as the standard ever since, and is stored in a Paris vault. The kilogram became the base unit in 1901.

1 kg=1000 g ??? YES !

The metric unit of time became the second, originally defined as 1/86 400th of a mean solar day. The formal definition of the second has been changed several times as more accurate definitions became possible, based first on astronomic observations, then the tuning fork clock, quartz clock, and today the caesium atomic clock

TIME 1 MINUTE =60 SEC. 1 DAY =24 HOURS 1 DAY = _____MINUTES 1DAY = _____SECONDS

MKS SYSTEM Length---METER (m) Mass-----Kilogram (kg) Time-----Second (s)

CGS system Length---centimeter (m) Mass-----gram (g) Time-----Second (s)

Examples of SI derived units Derived quantity Name Symbol area square meter m2 volume cubic meter m3 speed, velocity meter per second m/s acceleration meter per second squared   m/s2 wave number reciprocal meter m-1 mass density kilogram per cubic meter kg/m3 specific volume cubic meter per kilogram m3/kg current density ampere per square meter A/m2 magnetic field strength   ampere per meter A/m amount-of-substance concentration mole per cubic meter mol/m3 luminance candela per square meter cd/m2 mass fraction kilogram per kilogram, which may be represented by the number 1 kg/kg = 1

BRITISH SYSTEM OF UNITS

British system Length---Foot (ft) Mass-----Pound (lb) Time-----Second (s)

METRIC BRITISH CONVERSION yard = 0.9144 metres - same in US 1 pound = 0.453 592 37 kilograms - same in US 1 gallon = 4.546 09 litres - different in US

RADIOLOGIC QUANTITIES SI UNITS EXPOSURE ---AIR KERMA (Gya) ABSORBED DOSE---GRAY (Gyt) EFFECTIVE DOSE---SEIVERT (Sv) RADIOACTIVITY---BECQUEREL (Bq)

RADIOLOGIC QUANTITIES CUSTOMARY UNITS EXPOSURE ---Roentgen (R) ABSORBED DOSE---rad (rad) EFFECTIVE DOSE---rem (rem) RADIOACTIVITY---curie

EXPOSURE ( INTENSITY) The roentgen (R) is a measure of radiation intensity of x rays or gamma rays. It is formally defined as the radiation intensity required to produce and ionization charge of 0.000258 coulombs per kilogram of air. It is one of the standard units for radiation dosimetry, but is not applicable to alpha, beta, or other particle emission and does not accurately predict the tissue effects of gamma rays of extremely high energies. The roentgen has mainly been used for calibration of x-ray machines..                   

1R=2.58 x 10-4 C/kg 1 AIR KERMA=100R

ABSORBED DOSE The rad is a unit of absorbed radiation dose in terms of the energy actually deposited in in any kind of matter, including tissue. The rad is defined as an absorbed dose of 0.01 joules of energy per kilogram of tissue. This applies to any kind of radiation: x-rays, gamma rays, beta rays, etc.

rad= RADIATION ABSORBED DOSE 1 Gray=100 rad

EFFECTIVE DOSE The biologically effective dose in rems is the radiation dose in rads multiplied by a "quality factor" which is an assessment of the effectiveness of that particular type and energy of radiation. For alpha particles the relative biological effectiveness (rbe) may be as high as 20, so that one rad is equivalent to 20 rems. However, for x-rays and gamma rays, the rbe is taken as one so that the rad and rem are equivalent for those radiation sources. 1 Sv = 100 rem

The SI derived unit of activity, usually meaning radioactivity The SI derived unit of activity, usually meaning radioactivity. "Radioactivity" is caused when atoms disintegrate, ejecting energetic particles

RADIOACTIVITY The curie (Ci) is the old standard unit for measuring the activity of a given radioactive sample. It is equivalent to the activity of 1 gram of radium. It is formally defined by: 1 curie = amount of material that will produce 3.7 x 1010 nuclear decays per second. 1 becquerel = amount of material which will produce 1 nuclear decay per second. 1 curie = 3.7 x 1010 becquerels