PCN NDT Radiographic Testing Level 2 Exam flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Inverse square law

Exposure rate from a point source falls with the square of distance: I1/I2 = (d2/d1)². Doubling the distance reduces the dose rate and the film exposure to one quarter.

Half value layer

The thickness of a material that reduces the intensity of a radiation beam to half its original value: HVL = 0.693/μ. It is used in shielding calculations and to describe beam quality.

Photoelectric absorption

A photon transfers all its energy to a bound electron, which is ejected. The probability rises steeply with atomic number and falls with photon energy, giving strong contrast at low kilovoltage.

Geometric unsharpness

Blurring of the image caused by the finite source size. It is calculated as Ug = F·t/d, where F is the source size, t the object-to-detector distance and d the source-to-object distance.

Occupational dose limit

ICRP and IRR17 limit the effective dose to 20 mSv per year averaged over five years, with a maximum of 50 mSv in any single year.

ALARA principle

Radiation doses are kept as low as reasonably achievable, taking economic and social factors into account, while still producing radiographs of the required quality.

Controlled area

A defined area where radiation dose rates or doses require special protection measures and restricted access. Its boundaries are marked and entry is controlled under local rules.

Sealed source leak test

A wipe test of a sealed source, container and guide tube, carried out at intervals not exceeding six months and after any incident, to detect removable radioactive contamination.

Ir-192 half-life

73.8 days. Activity falls by half in that period, so exposure times must be increased regularly and the source replaced when output becomes impractical.

Bremsstrahlung

The continuous X-ray spectrum produced when electrons are decelerated in the anode target. Its total intensity increases with target atomic number, tube current and the square of the accelerating voltage.

Focal spot size

The area of the anode where electrons strike and X-rays are produced. A smaller focal spot sharpens the image but limits the tube current that can be applied.

Co-60 gamma energies

Co-60 emits gamma photons of 1.17 and 1.33 MeV and has a half-life of 5.27 years. Its high penetration suits thick steel sections above about 50 mm.

Characteristic curve

A plot of film density against log relative exposure showing fog, toe, a straight-line region of maximum contrast, shoulder and Dmax. It describes film speed and contrast.

Film density

D = log10(I0/It), where I0 is the incident light intensity and It is the transmitted intensity. A density of 3.0 means only 0.1% of the light is transmitted.

Lead intensifying screen

A thin lead foil placed in contact with the film. It emits electrons that expose the emulsion, reducing exposure time, and it absorbs low-energy scatter.

Safelight

Filtered darkroom illumination that does not significantly fog the film during normal handling. Its suitability is confirmed by a safelight test at the specified distance and time.

Source-to-film distance

The distance from the radiation source to the film. Increasing SFD reduces geometric unsharpness but increases the exposure time according to the inverse square law.

Double wall single image

An exposure technique in which the beam passes through two walls but only the weld nearest the film is imaged. It is used when the pipe bore is inaccessible.

Technique class B

The higher sensitivity class of ISO 17636-1, requiring a smaller source size, larger source-to-film distance, higher film density and better image quality indicator values than class A.

IQI film-side placement

When the source side is inaccessible, the image quality indicator is placed on the film side and marked with a lead letter F; sensitivity is then affected by the full object thickness.

IQI sensitivity

Expressed as a percentage: the diameter of the smallest visible wire divided by the material thickness, multiplied by 100. A lower percentage indicates better sensitivity.

Duplex wire IQI

A pair of wire gauges used to measure image unsharpness. The smallest wire pair that can still be resolved indicates the basic spatial resolution of the image.

Scatter radiation

Photons deflected or re-emitted within the object, cassette or surroundings. Scatter reduces image contrast and is controlled by collimation, filters, lead masking and screens.

Total unsharpness

The combined effect of geometric, film and screen unsharpness, approximated by Ut = (Ug³ + Ui³)^(1/3). The largest individual component dominates the result.

Lack of penetration

A root discontinuity appearing as a straight dark line of near-uniform width where weld metal has not fused into the root; it must be distinguished from root concavity.

Tungsten inclusion

Dense particles trapped in a TIG weld that appear as bright, sharply defined spots, because tungsten attenuates the beam far more strongly than the surrounding steel.

Planar discontinuity

A crack, lack of fusion or lack of penetration lying essentially in one plane. Detection depends strongly on beam angle, and such flaws are often more damaging than rounded porosity.

Acceptance criteria

The limits defined by the applicable code, such as ISO 5817 quality levels B to D or ASME UW-51, that decide whether an indicated discontinuity is acceptable or requires repair.

Technique sheet

A document recording all exposure parameters for a component: material, thickness, source, source-to-film distance, kilovoltage or activity, exposure time, film, screens and IQI.

Traceability

The ability to link a radiograph and its report to the source, film batch, screens, IQI, equipment and calibrated instruments through recorded serial numbers and calibration dates.

PCN Level 2 validity

Certification to ISO 9712 is valid for five years. Revalidation is required at the mid-term point and re-certification by examination before the five-year expiry.

Non-conformance

A failure to meet a specified requirement. It triggers documented corrective action and, where needed, retest or repair, with all records retained alongside the radiographs and report.