60 Radioactive Materials Safety Manual Environmental Health and Safety Dosimeter – a portable instrument for measuring and registering the total accumulated exposure to ionizing radiation. (see dosimetry) Dosimetry – the theory and application of the principles and techniques involved in the measurement and recording of radiation doses. Its practical aspect is concerned with the use of various types of radiation instruments with which measurements are made. (see fi lm badge; thermoluminescent dosimeter; GeigerMueller counter) Effective Dose Equivalent – the sum of the products of the dose equivalent to the organ or tissue and the weighting factors applicable to each of the body organs or tissues that are irradiated. Efficiency – (radiation detection instrument) a measure of the probability that a count will be recorded when radiation is incident on a detector. Usage varies considerably so be aware of which factors (window, transmission, sensitive volume, energy dependence, etc.) are included in a given case. Efficiency refers to the percent of total activity present for a given nuclide detected by the radiation detection instrument being used. Electron – negatively charged elementary particle which is a constituent of every neutral atom. Its unit of negative electricity equals 4.8 x 10-19 coulombs. Its mass is 0.00549 atomic mass units. Electron Volt – a unit of energy equivalent to the amount of energy gained by an electron in passing through a potential difference of 1 volt. Abbreviated eV. Radioisotopic energy is typically measured in MeV (million electron volts). Erg – the unit of energy or work in the centimeter-gram-second system; the work performed by a force acting over a distance of one centimeter so as to result in a one gram mass being accelerated at a rate of one centimeter per second each second. Exposure – (1) being exposed to ionizing radiation or radioactive material, (2) a measure of the ionization produced in air by x-ray or gamma radiation. It is the sum of the electrical charges on all ions of one sign produced in air when all electrons liberated by photons in a volume element of air are completely stopped in air, divided by the mass of air in the volume element. The special unit of exposure is the Roentgen. Extremity – hand, elbow, arm below the elbow, foot, knee, or leg below the knee. Eye Dose Equivalent – applies to the external exposure of the lens of the eye and is taken as the dose equivalent at a tissue depth of 0.3 centimeter (300 mg/cm² ). Film Badge – a packet of photographic film used for the approximate measurement of radiation exposure for personnel monitoring purposes. The badge may contain two or more films of differing sensitivity, and it may contain filters which shield parts of the film from certain types of radiation. Fission - the splitting of a nucleus into at least two other nuclei and the release of a relatively large amount of energy. Two or three neutrons are usually released during this type of transformation. Gamma Ray – very penetrating electromagnetic radiation of nuclear origin. Except for origin, identical to X-ray. Geiger-Mueller (G-M) - Counter a radiation detection and measuring instrument. It consists of a gasfilled tube containing electrodes, between which there is an electrical voltage but no current flowing. When ionizing radiation passes through the tube, a short, intense pulse of current passes from the negative electrode to the positive electrode and is measured or counted. The number of pulses per second measures the intensity of radiation. Gray (Gy) – the SI unit of absorbed dose. One Gray is equal to one joule per kilogram (100 rad). Half-Life, Biological – time required for the body to eliminate 50% of a dose of any substance by the regular processes of elimination. This time is approximately the same for both stable radionuclides and radionuclides of a particular element.