2 Contents 1. Introduction 2. Objectives of Radiation Protection 3. Radiation Protection Systems4. Intervention5. Protection Against Radiation Hazards6. References
3 IntroductionRadiation protection principles are related to the source and individual.There are two systems of radiation protection;Proposed and continuing practice that cause exposure,Intervention that reduces exposure.Both systems are used in three types of exposures, i.e. workers, medical and public.
4 Objectives of Radiation Protection Prevent the occurrence of deterministic effect by restricting doses to individuals below the relevant thresholds.2.Reduce induction of stochastic effect.Deterministic effect is the effect where the intensity of effect increases with dose. There are thresholds for deterministic effects.Stochastic effect is the probability of occurrence is proportional to the dose. No threshold can be invoked for them.
5 Radiation Protection Systems 3 Principles used in Radiation Protection Systems:Justification of PracticeOptimization of Protection and SafetyDose Limit
6 Radiation Protection Systems Justification of PracticeIn proposed and continuing practices, the justification of practice must be such that the work uses radiation because it gives benefit (or gain) to the exposed individuals or to society that exceeds radiological risk.Justification in intervention provides more benefit in comparison to if there were no intervention.
7 Radiation Protection Systems Optimization of Protection and SafetyBased on the principles of ALARA (As Low As Reasonably Achievable).For any given radiation source within a practice, the magnitude of individual doses, the number of people exposed, and the likelihood of incurring exposures should be kept to as low as reasonably achievable, taking economic and social factors into considerations.
8 Radiation Protection Systems Dose LimitDose limit is used to apply controls on each individual’s accumulation of dose.Dose limits are not :a line of demarcation between “safe” and “dangerous”,the sole measure of the stringency of a system of protection.Dose limits do not include medical exposures and natural background radiation.
9 Radiation Protection Systems Annual Dose Limits (ADL)There are different categories of dose limits for :radiation workers;members of the public;trainees of radiation;planned special exposures; andfemale pregnant workers.
10 Radiation Protection Systems 1. ADL for Occupational ExposureApplicationADL (mSv)Annual dose limit for the whole body exposure of worker20Female pregnant worker: dose to the foetus accumulated over the period of time between confirmation of pregnancy and the date of birth< 1Partial body exposure of a worker :i. Limit for the effective dose-equivalentii. Limit on average dose in each organ or tissueiii.Limit for lens of the eyesiv.Limit on equivalent dose for the hands and feet50500150
11 Radiation Protection Systems 2. ADL For Exposure of Members of PublicApplicationADL (mSv)Dose limit for the whole body exposure1Average dose for lens of the eyes15Average dose for the skin50Effective dose limit for a person who knowingly assits in the support of a patient during the period of diagnostic examination or treatment of the patient< 5Effective dose limit for a person below the age of 16 years visiting patient undergoing treatment or diagnostic examination< 1
12 Radiation Protection Systems In a calendar year (mSv) 3. Dose Limit for Apperentice and StudentsApprentices and students in radiation work (in a supervised or controlled areas) must not be less than 16 years old.ApplicationIn a calendar year (mSv)Dose limit for the whole body exposure6Average dose for lens of the eyes50Equivalent dose to the extremities150Equivalent dose to the skin
13 Radiation Protection Systems Dose Limit in Special CircumstancesRefers to voluntary exposure during normal operation whereby one or more of the annual dose limits for a worker are likely to be exceeded.Conditionsi. Allowed only in situations when alternative techniques, which do not involve such exposure, cannot be used.ii. Shall be carried out when approved by the appropriate authorities (i.e. AELB or the Ministry of Health of Malaysia).iii. Temporary and is subjected to review by the appropriate authorities
14 Radiation Protection Systems 4. InterventionIntervention is carried out when:an emergency situation occurred;a directive issued by appropriate authority in any other temporary exposure situation to reduce or avert temporary exposures;the appropriate authority directs the remedial action to reduce or avert chronic exposure as specified by them.The form, extent and duration of intervention shall be optimized to produce the maximum net benefit in the social and economic circumstances.
15 Radiation Protection Systems 5. Protection Against Radiation HazardsMade based on engineering as well as administrative controls.One method of control against radiation hazard employing both engineering and administrative controls is through the classification of areas.Working areas may be classified according to :clean area,supervised area &controlled areas.Classification of areas take into account the likelihood and magnitude of potential exposures (risk) and the nature and extent of the required protection and safety procedure.
16 Radiation Protection Systems 5. Protection Against Radiation Hazards... continueClean AreaWork area where the annual dose received by a worker is not likely to exceed the dose limit for a member of the public.
17 Radiation Protection Systems 5. Protection Against Radiation Hazards... continueSupervised AreaWork area for which the occupational exposure conditions are kept under review even though specific protective measures and safety provisions are not normally needed.Area is clearly demarcated with radiation warning signs and legible notices clearly posted.
18 Radiation Protection Systems 5. Protection Against Radiation Hazards… continueControlled AreaWork area where specific protection measures and safety provisions could be required for controlling normal exposures or preventing the spread of contamination during normal working condition and preventing or limiting the extent of potential exposures.Annual dose received by a worker in this area is likely to exceed 3/10 Annual Dose Limit.Area is clearly demarcated with radiation warning signs and legible notices clearly posted.
19 Radiation Protection Systems 5. Protection Against Radiation HazardsControl Against External ExposureThree methods of radiation protections that can be used - shielding, time and distance
20 Radiation Protection Systems 5. Protection Against Radiation HazardsShieldingMaterial may be used to attenuate radiation and thus provide shielding against external exposure.Shielding takes into considerationthe density and thickness of shielding materials,the quality of radiation.Quality of radiation refers to type of radiation, its energy, the flux and dimension of source.
21 Radiation Protection Systems 5. Protection Against Radiation HazardsContinue ...Selection of shield depends on the types of radiation.Alpha particles lose energy rapidly in passage through matter and hence do not penetrate far. No shielding is required against alpha particles.Beta particles do not lose energy so rapidly compared to alpha particles, and are therefore more penetrating. Materials composed of elements of low atomic number such as Perspex and aluminum and thick rubber are most appropriate for the absorbance of beta particles.
22 Radiation Protection Systems 5. Protection Against Radiation HazardsContinue ...Neutrons are uncharged particles and can penetrate matter considerably. Shields use on neutron is directed towards reducing the energy of the neutrons to levels that can easily be absorbed Neutron (< 1 MeV)A reduction of the energy of neutron is best accomplished by collisions with atoms of light elements, e.g. hydrogen. Neutrons (> 1 MeV)Energy of fast neutrons is best reduced using water and paraffin wax. 20 cm of paraffin wax will attenuates 1 MeV fast neutrons by a factor of 10
23 Radiation Protection Systems 5. Protection Against Radiation HazardsContinue ...Attenuation of x-and gamma-rays require the use of high atomic number materials. The most suitable material is lead and iron.In the medium energy range (0.50 – 0.75 MeV) the density of the material is more important than the atomic number. At higher and lower energy ranges, materials of higher atomic number are more effective.
24 Radiation Protection Systems 5. Protection Against Radiation HazardsComparison- types of radiation and shielding required
25 Radiation Protection Systems 5. Protection Against Radiation HazardsTimeDose = Dose rate x timeThe longer the exposure time the higher is the dose received and vice versa.
26 Radiation Protection Systems 5. Protection Against Radiation HazardsDistanceReduction of radiation dose inversely proportional the square of the distance or it follows the inverse square law equation.I1I2=d1d22where I1 and I2 are radiation intensities at distances d1 and d2 respectively.
27 Radiation Protection Systems 5. Protection Against Radiation HazardsControl of Internal ExposureInternal exposure is attributed to radiation exposures from radionuclides inside the body.There are three modes of entry by radionuclides into the body; i.e. inhalation, ingestion and penetration through the skin.Protection against such radiation hazards may be overcome through:the use of personal protective equipment,having proper facilities to handle unsealed sourceshaving procedures to safely handle them.
28 Radiation Protection Systems 5. Protection Against Radiation HazardsRadiation Personal Protective Equipment (PPE)Worn by radiation workers to reduce the risk of radiation exposure from internal radiation exposure and radioactive contamination.The last line of defense in controlling risk from ionizing radiation.Since the radiation hazards still exist, PPE should only be used to complement other means of radiation hazard control already in place.
29 Radiation Protection Systems 5. Protection Against Radiation Hazards... continueExamples of personal radiation protection equipments/ clothing include:Laboratory coatOverall or boiler suitRubber glovesOvershoesRubber bootsBreathing apparatus(example - Pressurized clothing, SCABA + whole body suit (Self Contained Breathing Apparatus))
30 Radiation Protection Systems 5. Protection Against Radiation HazardsSafety Equipment And Facilities At The Place Of WorkThese equipments are not worn by workers but are used by them to reduce exposure and contamination.Safety facilities include building design incorporating safety features to handle radiation and radioactivity. Examples of such equipment and facilities are:Remote-handling tongsLead brickLiquid transfer systemRadioactive containersVentilated facility
31 Radiation Protection Systems 5. Protection Against Radiation HazardsSafety Procedures and SurveillanceHandling of unsealed sources increases the risk of internal radiation exposure and contamination.Safety procedures employed in work related to handling unsealed sources must stress the importance of preventing inhalation, ingestion and penetration of radionuclides through the skin, and contamination of personnel and working areas in normal routine procedure and emergency situations.
32 Radiation Protection Systems 5. Protection Against Radiation Hazards... continueHaving a safe working procedure does not guarantee its compliance. Surveillance of compliance and monitoring of radiation levels must be carried out periodically. Both visual surveillance and those using radiation monitoring and detectors must be used.