National Metrology Laboratory Research Articles

Comparison of the results of absolute measurements of absorbed dose in a beam of gamma radiation with two calorimeters of different design

In the period from 1958-1959 there was a widespread demand for accelerators generating high-energy radiat'ions; intense l-radiation isotopic sources were manufactured and reactors were built. These installations are not only sources of et, B, and y radiation but also sources of neutron and proton radiation. The application of the various types of radiation in technological processes has led to the necessity for a quantitative estimate of the absorbed energy in appropriate units, as the unit of exposed dose - theroentgen-is applicable only for X and ~ radiation. The International Commission on Radiological Units and Measurements flCRUM) recommended in 1953 a new quantity - the absorbed dose. The unit of absorbed dose was 1 radl equal to 100 erg/g. In the SI system, this unit is the joule per kilogram of substance and is equal to 100 tad. The new concept is applicable for a quantitative estimate of the absorbed energy of all forms of radiation, including proton and neutron radiation. A somewhat greater time, however, was required in order to develop methods for the absolute determination of the absorbed dose. In the early years the absorbed dose was determined either by a numerical method using ionization measurements or by means of chemical dosimeters (for example, the ferrosulfate dosimeter). The ionization method requires a precise determination of W, the average energy of ion formation; the use of chemical dosimeters requires a precise determination of G, the average radiation-chemic al yield. Determination of G was effected by means of calorimeters. The calorimetric method is the most direct, as the calorimeter measures directly the energy absorbed by the substance. Calorimetric measurements, because of their complexity have been used by metrology laboratories only for the calibration of other dosimetric systems. Starting in 1927 a number of projects were undertaken to construct calorimeters for measuring the absorbed dose of ionizing radiations [1-6]. Even the national metrology laboratories, carrying directly the responsibility for unity and accuracy of the absorbed dose measurements and therefore, using as standards the most proven methods, are currently designing calorimeters for the measurement of absorbed dose. One of the first metrology organizations in the USSR to use calorimeters for absorbed dose measurements was the All-Union Scientific Research Institute for Physieoteehnical and Radiotechnical Measurements (VNIIFTRI). The operating principle and the layout of the calorimeter is described in [7, 8].

Verifying Position Errors In CNC Gear Measuring InstrumentsUsing A Laser Interferometer With Dynamic Data Capture Software

CNC gear measuring instruments measure gears by scanning across the tooth surface. A Renishaw laser interferometer system with position based dynamic data capture hardware and software was used to verify position errors on slides at the normal scanning speed used when measuring gears. The results from a Hofler EMZ 632 CNC gear tester in the UK national Gear Metrology Laboratory are presented and show that the techmque generates realistic data for calibration purposes under closely controlled laboratory conditions. A comparison between data gathered under dynamic conditions and static conditions is made. Some important considerations applying the technique are discussed.