ASNT Level 3 Radiographic Testing Course
ASNT Level 3 Radiographic Testing Course Fees 450 $ | ASNT Level 3 Radiographic Testing Course Exam Fees To be informed | ASNT Level 3 Radiographic Testing Course Duration 20 Days | ASNT Level 3 Radiographic Testing Course Location Muscat
Radiographic testing (RT)
Radiography monitors the varying transmission of ionising radiation through a material with the aid of photographic film or fluorescent screens to detect changes in density and thickness. It will locate internal and surface-breaking defects.
History of radiographic testing
X-rays were discovered in 1895 by Wilhelm Conrad Roentgen (1845-1923) who was a Professor at Wϋrzburg University in Germany. Whilst performing experiments in which he passed an electric current through a Crookes tube (an evacuated glass tube with an anode and a cathode), he found that when a high voltage was applied, the tube produced a fluorescent glow.
Roentgen noticed that some nearby photographic plates became fogged. This caused Roentgen to conclude that a new type of ray was being emitted from the tube. He believed that unknown rays were passing from the tube and through the plates. He found that the new ray could pass through most
substances. Roentgen also discovered that the ray could pass through the tissue of humans, but not bones and metal objects. One of Roentgen's first experiments late in 1895 was a film of the hand of his wife.
In addition to conventional film radiography, digital radiographic systems are now widespread within the
NDT industry. The use of photostimulable phosphor (PSP) bearing imaging plates with photomultipliers to
capture image signals and analogue-to-digital converters (ADC) are used extensively in computed
radiography (CR).
Direct radiography (DR) systems are also used based upon complementary metal oxide sensor (CMOS) technology and TFT (thin film transistors). These systems have the ability to directly convert light into digital format; additionally, they may be coupled with a scintillator which coats CMOS and charged couple device (CCD) sensors. The scintillator converts photon energy to light before the sensor and ADC converts to digital format. Systems which use scintillators in this way are often referred to as indirect systems.
Quality issues of any digital system are based upon the effective pixel size and the signal-to-noise ratio (SNR). The benefits of using digital systems are the speed of inspection and the absence of chemical processing requirements and wet film; however, the initial equipment costs will be high.
Properties of Penetrating Radiation (X- and Gamma)
Radiation has six basic properties:
1 Can penetrate material (therefore penetrating radiation).
2 Can ionize matter (therefore ionizing radiation).
3 Propagates in a straight line (rectilinear propagation)
4 Can cause fluorescence of some materials.
5 Can cause chemical effects.
6 Has physiological effect.
Penetrating radiation can be used in non-destructive examination (NDE) because it travels in a straight line and may be absorbed as it passes through matter. ASNT Level 3 Radiographic Testing Course covers the extent to which it is absorbed depends upon three factors:
1 Thickness of the absorber.
2 Physical characteristics of the absorber (in particular its density and atomic number).
3 Wavelength or photon energy of the radiation itself.
Penetrating radiation can be detected using a photographic emulsion or by other means. The system used to detect the radiation must be capable of differentiating between different intensities of radiation.
Ionising Radiation
The two types of penetrating radiation most used in industrial radiography, X and gamma rays, are often referred to as ionising radiation. This is because the nature of their interaction with matter is to cause ionisation. Ionisation is caused by loss of an orbiting electron which leaves the atom in an electrically positively charged state (+ ion).
ASNT Level 3 Radiographic Testing Course covers Alpha and beta particles, which are products of radioactive fission also cause ionisation and are therefore included within the term ‘ionising radiation’. Neutron radiation is a hazard in the nuclear power industry, it can [indirectly] cause ionisation, and it is therefore often included within this group of types of radiation referred to as ionising. Alpha and beta particle radiation are covered in greater detail in Sections 6 and 7.
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