 [M]- MACROCYCLES An organic molecule with a large ring structure,usually containing over fifteen atoms. M.
- MACROPOROUS ION EXCHANGER An ion exchanger with pores that are largecompared to atomic dimensions. C.
- MAGIC NUMBERS In the shell model of nuclear structure, nucleiwith certain neutron numbers and certain proton numbers are observedto be particularly stable. The values of these so-called "magic" numbers are 2, 8,20, 28, 50, and 82. A higher shell at neutron number 126 exists and thereare theoretical predictions about additional shells for protons and neutrons.
- MANIPULATOR A hand-operated or -controlled device for remotely handling radioactive materials.
- MAN-MADE ELEMENT See artificial element.
- MASKING AGENT A substance preventing the interfering reaction of one ormore foreign substances in a determination by conversion into solublecomplexes, different oxidation states, or other unreactive forms. D.
- MASS DEFECT The difference between the sum of the rest masses ofprotons and neutrons which form a nucleus and the measured mass of the samenucleus.
- MASS-ENERGY EQUIVALENCE The equivalence of mass m and energy E as expressed in Einstein's equation E = mc2.
- MASS EXCESS The excess of the measured mass of an atom over its mass number.
- MASS NUMBER The total number of neutrons and protons in anucleus. Synonymous with nucleon number.
 MASS SPECTROMETRY The use of instruments that analyze ions bymass-to-charge ratio to measure abundances of isotopes.- MATRIX (IN ANALYSIS) In analysis: refers to the analytical sample,considered as an assemblage of constituents, with all their individualproperties. The combined effect that the various constituents of the matrixmay exert on the measure of the analysis of the element is referredto as the matrix effect. C.
- MAXIMUM PERMISSIBLE CONCENTRATION An expected upper limit forthe concentration of a specified radionuclide in a material taken into thebody below which continuous exposure (or in the case of occupational maximumpermissible concentration, exposure for 40h/wk) to the material is notconsidered biologically harmful. NM.
- MCA Multichannel analyzer. See pulse height analyzer, multichannel.
- MEAN FREE PATH The average distance traveled by a particle between collisions.
- MEAN LIFE, RADIOACTIVE The average lifetime of a radioactive nuclide.
- MEAN LIFETIME See average life.
- MEAN LINEAR RANGE See range, mean linear.
- MEAN MASS RANGE See range, mean mass.
- MEASURED SPECTRUM See spectrogram.
- MECHANISM A detailed description of the pathway leading from thereactants to the products, including as complete a characterization aspossible of the composition, structure and other properties of reactionintermediates and transition states. C.
- METASTABLE STATE An isomeric state in an energy state higher than the ground state. meV millielectron volt = 1/0 electron volt.
- MeV Million electron volts or megaelectronvolt.
- MIBK Methylisobutylketone, a common solvent used in extractionseparations.
- MICROAUTORADIOGRAPHY Autoradiography for viewing with a microscope.J.
- MICROSCOPY, NUCLEAR Use of nuclear microprobes to investigatethe elemental structure of biological objects.
- MICRO-PIXE Particle-induced x-ray emission spectroscopy inwhich the particle beam is highly collimated and focused allowing positionsensitive analysis. KE.
- MICROTRON A cyclotron for accelerating electrons.
- MILKING The process of separating a radioactive tracer from a parent radionuclide bound in a radioisotope generator.
- MINERALIZATION 1. Formation of mineral in vivo, e.g., in bone,tooth, etc. 2. Use of reagents and various procedures tocompletely solubilize a solid sample mixture for analysis. (Not recommended.)
- MIRROR NUCLEI A pair of isobars in which the atomic and neutron number of one equals the neutron and atomic number of the other, respectively.
- MIXED LABELED A specifically labeled compound is referred to asmixed labeled when the isotopically substituted compound has more thanone kind of modified atom. C.
- MNAA Molecular neutron activation analysis.
- MODERATION Reduction of the neutron energy by scattering withoutappreciable capture.
- MODERATOR A material used to reduce neutron energy by moderation).
- MODIFICATION, ISOTOPIC A process in which a compound has beengiven an abnormal isotopic ratio in one or more elements present. KE.
- MOLECULAR ACTIVATION ANALYSIS See molecular neutron activation analysis.
- MOLECULAR NEUTRON ACTIVATION ANALYSIS A variation of radiochemical neutron activation analysis in which chemical speciation (often by bioanalytical techniques) is involved in pre-irradiation separation.Synonymous with chemical neutron activation analysis , which is preferred.
- MOLECULAR WEIGHT Also known as the relative molecular mass of asubstance, the molecular weight is the ratio of the average mass per formula unit of a substance to 1/12 of the mass of an atomof nuclide 12C. C.
- MONITOR, BEAM See beam, monitoring.
- MONITOR, FLUX See flux monitor.
- MONOENERGETIC RADIATION Radiation consisting of particles of a single kinetic energy or photons of a single energy or wavelength.
- MSSBAUER EFFECT Resonance absorption of gamma radiation by nuclei arranged in a crystal lattice in such a way that the recoil momentum is shared by many atoms.
- MSSBAUER SPECTROMETRY The spectroscopic technique based on the Mssbauer effect.
- M÷SSBAUER NUCLIDE Any radioactive nuclide that may serve as a radiation source in Mssbauer effect experiments.
- MOTHER In radiochemistry, synonymous with parent. See parent.
- MOTHER LIQUOR The liquid that has passed through a chemical process.
- MPC Maximum permissible concentration.
- Mu The symbol for muonium used to emphasize the analogy of muonium to atomic hydrogen.
- MULTICHANNEL (PULSE HEIGHT) ANALYZER See pulse height analyzer, multichannel.
- MULTIPLE SCATTERING Successive rescattering of radiation within the scattering medium. C.
- MULTIPLICATION NEUTRON The process in which a neutron produces on the average more than one neutron in a medium containing fissile material.
- MULTISCALING A mode of operation of a multichannel pulse height analyzer for studying the time dependence of radiation. The analyzer, when operated in the multiscaling mode, stores all pulses in a fixed channel until a preset time, the "dwell time", elapses, after which the pulses are stored in the next channel, and so on. Dwell times are typically microseconds or larger.
- MU-MESIC ATOM or MOLECULE An atom or molecule which has captured a negatively charged muon into a stable atomic or molecular orbital.
- MUON Mu-meson; a fundamental particle related to the electron.
- MUONIUM An atomic system consisting of a muon and an oppositely charged electron.
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