Scrabble?! MILLIROENTGEN

Definitions of MILLIROENTGEN in various dictionaries:

The roentgen or röntgen () (symbol R) is a legacy unit of measurement for the exposure of X-rays and gamma rays. It is defined as the electric charge freed by such radiation in a specified volume of air divided by the mass of that air. In 1928 it was the first international measurement quantity for ionising radiation to be defined for radiation protection, and was an easily replicated method of measuring air ionization directly by using an ion chamber. It is named after the German physicist Wilhelm Röntgen, who discovered X-rays. Although relatively easy to measure, it had the disadvantage that it was only a measure of air ionisation and not a direct measure of radiation absorption in other materials. As the science of radiation dosimetry developed, it was realised that the ionising effect, and hence damage, was linked to energy absorbed by irradiated materials, and new radiometric units for radiation protection were defined from 1953 onwards which took this into account. A new quantity Kerma was defined which can measure air ionisation, and is the modern metrological successor to the roengten, and from this the absorbed dose can be calculated using known coefficients for specific target materials. In radiation protection the absorbed dose is the energy absorption which is an indication of likely acute tissue effects occurring at high dose rates, and from low levels of absorbed dose the equivalent dose, representing the stochastic health risk, can be calculated; for which the current SI units used are the gray (Gy) and the sievert (Sv) respectively. The roengten has been redefined over the years. It was last defined by the US National Institute of Standards and Technology (NIST) in 1998 as 2.58×10−4 C/kg, with a recommendation that the definition be given in every document where the roentgen is used. One roentgen deposits 0.00877 grays (0.877 rads) of absorbed dose in dry air, or 0.0096 Gy (0.96 rad) in soft tissue. One roentgen of X-rays may deposit anywhere from 0.01 to 0.04 Gy (1.0 to 4.0 rad) in bone depending on the beam energy. This tissue-dependent conversion from kerma to absorbed dose is called the F-factor in radiotherapy contexts. The conversion depends on the ionizing energy of a reference medium, which is ambiguous in the latest NIST definition.