X-ray Production, Spectrum and Radiation Protection

X-ray Production, Spectrum and Radiation Protection

RADIATION SCIENCE

CHAPTER 4

• X ray production
• X-ray spectrum
• Radiation quantity, quality and intensity
• Control of scatter
• Radiation protection and personnel monitoring

✓ X-Ray Production

• X-rays are produced in an X-ray tube when high-speed
• electrons (kinetic energy) interact with a metal target (usually
• tungsten). ➢ Electrons traveling from cathode to anode constitute the
• x-ray tube current and are sometimes called projectile
• electrons.
• When these projectile electrons hit the heavy metal atoms
• of the x-ray tube target, they transfer their kinetic energy
• to the target atoms.
• The projectile electron interacts with the orbital electrons
• to produce characteristic x-rays or the nuclear field to
• produce Bremsstrahlung x-rays of target atoms.
• These interactions result in the conversion of electron

kinetic energy into thermal energy (heat) and x-rays.

Anode Heat

• Most of the kinetic energy of projectile electrons is
• converted into heat.
• Approximately 99% of the kinetic energy of projectile
• electrons is converted to heat.
• Only approximately 1% of projectile electron kinetic
• energy is used for the production of x-radiation.Two major mechanisms create X-rays:
• Bremsstrahlung Radiation (Braking Radiation)
• Bremsstrahlung x-rays are produced when a projectile
• electron is slowed by the nuclear field of a target atom

nucleus.

• Bremsstrahlung is a German word that means “sloweddown radiation.” ➢ Bremsstrahlung x-rays can be considered radiation that
• results from the braking of projectile electrons by the
• nucleus.
• Produces a continuous spectrum of photon energies.
• Is the major source of diagnostic X-rays.
• Characteristic Radiation
• Characteristic x-rays are emitted when an outer-shell
• electron fills an inner-shell void.
• An outer electron fills the vacancy and releases energy
• as an X-ray photon.
• Produces discrete (monochromatic) peaks at specific
• energies characteristic to tungsten (e.g., 59 and 67 keV).✓ X-Ray Spectrum
• The word spectrum refers to the range of values of any
• quantity such as x-rays.
• The X-ray spectrum displays the distribution of photon
• energies produced by the tube.Components
• a)Continuous spectrum
• A continuous spectrum contains all possible values.
• Bremsstrahlung radiation; ranges from 0 keV to a
• maximum equal to the kVp.b)Characteristic/discrete spectrum
• A discrete spectrum contains only specific values.
• Sharp spikes at the energies unique to tungsten.
• Factors influencing the spectrum
• 1.kVp (peak kilovoltage)
• Increases maximum photon energy.
• Shifts the entire spectrum to the right (higher
• energies).
• Increases beam quality and quantity.2.mA or mAs (tube current )
• Linearly increases the number (quantity) of photons.
• Does not change maximum energy or beam quality.
• 3.Filtration
• Removes low-energy photons.
• Decreases quantity but increases average energy.
• 4.Target material
• Higher atomic number → higher energy photons and
• more efficient production.
• 5.Generator type
• (single-phase, three-phase, high-frequency)
• More consistent voltage increases beam quantity and

average energy.

✓ Radiation Quantity

• Also known as beam output or radiation intensity.
• Refers to number of photons produced.
• Depends primarily on mAs.
• Higher mAs = more electrons = more X-rays produced.
• Quantity is directly proportional to mAs.✓ Radiation Quality
• Quality describes the penetrating ability of the X-ray
• beam.
• It is determined mainly by kVp and filtration.
• Higher kVp → higher energy photons → more penetrating
• beam.
• More filtration increases average beam energy (hardens
• the beam).
• Quality is often measured using half-value layer (HVL) —
• the thickness of a material needed to reduce intensity by
• half.✓ Radiation Intensity
• Intensity refers to the rate of energy fluence at a given
• distance.
• Depends on mAs, kVp², filtration, target material,
• distance.
• Follows the inverse square law:
• “Radiation intensity decreases proportionally to
• the square of the distance from its point source.”✓ Control of Scatter Radiation
• Scatter radiation mainly results from Compton
• interactions in the patient.Methods to reduce or control scatter
• Collimation
• Reduces field size → less tissue irradiated → less scatter.
• Most effective method.
• Grids
• Absorb scatter before reaching the detector.
• Used for body parts > 10 cm thickness.
• Improve image contrast but increase patient dose.
• Air Gap Technique
• Increasing distance between patient and detector
• reduces scatter reaching the detector.
• Beam Filtration
• Removes low-energy photons, slightly reducing scatter
• production.
• Optimal kVp Selection
• Lower kVp produces less Compton scatter, but must
• balance with adequate penetration.
• Compression
• Reduces tissue thickness → less scatter.Radiation Protection and Personnel Monitoring
• These are key components of radiation safety, especially
• in medical, industrial, and research environments where

ionizing radiation is used.

A. Radiation Protection

• Radiation protection aims to protect people and the
• environment from the harmful effects of ionizing radiation
• while allowing its beneficial uses.
• Objectives
• Prevent deterministic effects (e.g., skin burns, radiation
• sickness)
• Reduce the probability of stochastic effects (e.g., cancer,
• genetic effects)
• Fundamental Principles (ICRP)
• 1.Justification – Any activity involving radiation must
• provide more benefit than harm.
• 2.Optimization (ALARA) – Radiation exposure should be
• kept As Low As Reasonably Achievable.
• 3.Dose Limitation – Individual doses must not exceed
• recommended limits.
• NB; ICRP ~ International Commission on Radiological
• Protection
• Methods of Radiation Protection
• a)Time: Minimize time spent near radiation sources.
• b)Distance: Increase distance from the source (inverse
• square law).
• c)Shielding: Use appropriate materials (lead, concrete,
• water).
• d)Containment: Sealed sources and controlled areas.
• e)Administrative controls: Work procedures, training,
• signage.
• Personal protective equipment (PPE): Lead aprons,
• gloves, thyroid shields.
• Dose Limits (Typical ICRP Recommendations)
• Occupational workers:
• o 20 mSv/year (averaged over 5 years)
• o Maximum 50 mSv in any single year
• Public: 1 mSv/year
• Lens of the eye: 20 mSv/year (occupational)
• Skin & extremities: 500 mSv/year

✓ Personnel Monitoring

• Personnel monitoring is the measurement and
• assessment of radiation doses received by workers.
• Purpose
• Ensure compliance with dose limits
• Detect abnormal or accidental exposures
• Maintain dose records
• Improve radiation protection practicesPersonnel Monitoring Devices

Personal Dosimeters

• Personal dosimeters are devices worn by radiation
• workers to measure and record the dose of ionizing
• radiation received over a specific period.
• Purpose of Personal Dosimeters
• i ) Measure individual radiation exposure
• ii ) Ensure compliance with dose limits
• iii ) Detect abnormal or accidental exposures
• iv ) Maintain legal dose records
• v ) Improve radiation protection practices
• Types of Personal Dosimeters
• Film Badge Dosimeter
• Principle: Radiation darkens photographic film.
• Features
• Measures gamma, X-ray, and beta radiation
• Different filters help identify radiation type and energy
• Advantages
• Simple and inexpensive
• Permanent dose record
• Limitations
• Sensitive to heat and humidity
• Cannot be reused
• Less accurate at low doses
• Thermoluminescent Dosimeter (TLD)
• Principle: Certain crystals (LiF, CaSO₄) store energy from
• radiation and emit light when heated.Features
• Light output ∝ radiation dose
• Advantages
• High accuracy and sensitivity
• Reusable
• Wide dose range
• Limitations
• No immediate dose readout
• Requires special reader
• Optically Stimulated Luminescence (OSL)
• Principle: Stored energy is released as light when stimulated
• by a laser.
• Advantages
• More sensitive than TLD
• Can be reread multiple times
• Stable dose recordLimitations
• Requires specialized equipment
• Electronic Personal Dosimeter (EPD)
• Principle: Uses semiconductor detectors to measure dose
• electronically.
• Features
• Real-time dose and dose-rate display
• Audible and visual alarms
• Advantages
• Immediate feedback
• Useful in high-risk areasLimitations
• Expensive
• Requires battery and calibration
• Pocket Dosimeter
• Principle: Ionization of air in a small chamber.
• Advantages
• Instant dose reading
• Useful for short-term monitoringLimitations
• Fragile
• Limited accuracy
• Needs frequent recalibration

Special Dosimeters

• Ring dosimeters – monitor hand and finger exposure
• Neutron dosimeters – for neutron radiation fields
• Wearing and Handling Guidelines
• Wear at chest or waist level
• Outside lead apron (one under apron if double-badge
• method)
• Do not share dosimeters
• Store away from radiation when not in use
• Return for reading at scheduled intervalsArea Monitoring Devices
• Area monitoring devices are instruments used to
• measure radiation levels in workplaces.
• Purpose of Area Monitoring
• Detect presence and type of radiation
• Measure dose rate and contamination levels
• Identify radiation hazards and leakage
• Verify shielding effectiveness
• Ensure compliance with safety limits
• Types of Area Monitoring Devices
• Geiger–Müller (GM) Counter
• Principle: Gas ionization produces electrical pulses when
• radiation enters the tube.
• Detects: Alpha, beta, gamma.Advantages
• Highly sensitive
• Quick response
• Portable and easy to use
• Limitations
• Cannot accurately measure dose rate
• Saturates at high radiation levels
• Poor energy discrimination
• Uses
• Radiation surveys
• Contamination detection
• Ionization Chamber Survey Meter
• Principle: Radiation ionizes gas; collected charge is
• proportional to dose.
• Detects: X-rays, gamma raysAdvantages
• Accurate dose-rate measurement
• Wide energy response
• Suitable for high radiation levels
• Limitations
• Less sensitive at low doses
• Larger and more expensive
• Uses
• Area dose-rate monitoring
• Calibration and shielding verification
• Proportional Counter
• Principle: Gas amplification proportional to radiation energy.
• Detects: Alpha, beta, low-energy X-rays
• Advantages
• Can distinguish radiation types
• Good sensitivity
• Limitations
• Complex electronics
• Less portable
• Uses
• Surface contamination monitoring4. Scintillation Detector
• Principle: Radiation produces light flashes in a scintillator,
• converted to electrical signals.
• Detects: Alpha, beta, gamma (depending on scintillator)
• Advantages
• Very sensitive
• Fast response
• Good energy discrimination
• Limitations
• Expensive
• Requires calibration
• Uses
• Environmental and area monitoring
• Low-level radiation detection
• Area Radiation Monitors (Fixed Monitors)
• Description: Permanently installed detectors with alarms.Features
• Continuous monitoring
• Visual and audible alarms
• Data logging
• Uses
• Nuclear medicine labs
• Radiotherapy rooms
• Reactor facilities
• Placement of Area Monitors
• Near radiation sources
• At room entrances
• Controlled and supervised areas
• Waste storage areas
• Records and Responsibilities
• Maintain individual dose records
• Regular review by Radiation Safety Officer (RSO)
• Worker training and health surveillance
• Immediate investigation of overexposures