Radiation Safety for Industrial Radiography PDF

RADIATION SAFETY FOR INDUSTRIAL RADIOGRAPHY  Basics of Atomic Structure and Radioactivity 1- Radiation: energy in transit, either as particles or electromagnetic waves. 2- Radioactivity :  characteristic of various materials to emit ionizing radiation as it move to groun...

RADIATION SAFETY FOR INDUSTRIAL RADIOGRAPHY  Basics of Atomic Structure and Radioactivity 1- Radiation: energy in transit, either as particles or electromagnetic waves. 2- Radioactivity :  characteristic of various materials to emit ionizing radiation as it move to ground state(from un stable to stable atom)  Spontaneous transformation of an unstable atom and often results in the emission of Radiation.  Process referred to as transformation decay or a disintegration of an atom.  Exposure to a radiography source can’t make some materials radioactive. 3- Ionization : the removal of electrons from an atom (occur when high energy radiation interacting with matter)  Ionization Splitting an atom into positive and negative component  Ion: Atom lost electron(s) 4- Atom is the smallest part of each element Consists of  Proton – contained in the nucleus of the atom. Has a positive electrical charge  Neutron-- contained in the nucleus of the atom. Has no electrical charge  Electron– Circle about the atom in well-defined orbits. Has a negative electrical charge 5- Isotopes : atoms of an element have same number of protons and electrons , but different number of neutrons 1 of 22  Characteristics and interaction of radiation with Matter 1- Electromagnetic waves ( X- ray and Gamma Rays) Characteristics of X and Gamma Rays  Electromagnetic Radiation with energy inversely proportional to their wavelength.  no electrical charge and no rest mass  Not effected by magnetic or electric field  Travel in straight lines at the same speed as light  Penetrate matter  absorbed by matter  scattered by matter  expose film by ionization  cause certain materials to fluoresce  Invisible and cannot be detected by any of the senses.  main different between X-ray & gamma ray is the origin 2- particles waves Alpha Particles  Positively charged particles.  Helium nuclei consisting of two protons and two neutrons with a double positive charge.  Easily stopped by paper or skin  Only hazardous if alpha- emitting materials are swallowed or breathed into the body.  Deposits a large amount of energy in a short distance of travel Beta particles  Negatively charged electrons  Greater penetrating power than alpha particles  Stopped by thin layers of water, glass or metal.  Beta emitting material can be hazardous if taken into the body 2 of 22  3- number of photons transmitted through a material(photon penetration) depends on:  Photon energy  Atomic number of the shielding material  Shielding material thickness. 4- Intensity of Radiation: measure of the number of photons (rays) available per time Intensity depend on  activity of radiation source  type of radiation source  distance between radiation source & object  Radiation Units (Ci ,Sv, Gy, Rad, rem, rontgen) and their relations 1- Activity ( source strength):  measured in curie(Ci) or Becquerel (Bq)  Bq(SI unit) : amount of material which will produce 1 nuclear decay per second or disintegration per second(dps)  1Ci = 3.7*1010 Bq , 1Ci= 37GBq , 1Ci= 37000MBq  G=109 , M=106 , K=103  n= 10-9 , µ = 10-6 , m = 10-3 Example1: 50Ci = 50*3.7*1010Bq = 1.85*1012 Example 2: 185MBq = 185*106/3.7*1010= 50*10-4Ci = 5mCi 2- half live time(t1/2) : The time required for half the number of nuclease (source activity) in a sample to change into the more stable material 3 of 22   t1/2(Ir192)=74day , t1/2(Co60)=5.3years  A=A0/2n (A0:initial activity, n:numbers of half lives , A:activity after(n) half lives ) Example1: what will be the new strength of 100Ci, Ir192 isotope after 3 half lives? Answer: 12.5Ci Example 2: What will be the new strength of 100Ci Ir192 isotope after 296 day? Answer: 6.25Ci Example3: How many half lives (days) need to reduce the Ir192 activity from 40Ci to 2.5 Ci Answer: 4half lives (296 days). 3- Exposure: Expresses the amount of ionization (electrical charge) produced x – or gamma in a defined mass of air.  The Roentgen(R) is the unit used to measure exposure.  R=2.58*10-4 coulom per Kg of dry air. 4- Absorbed dose: amount of energy imparted to matter by ionizing radiation.  Measured by Rad , Gray  Rad (Radiation Absorbed Dose): dose of 100 ergs of energy per gram of matter.  Gray (SI unit): 1 joule of deposited energy per kilogram of tissue.  1Gray = 100 Rad = 100 Roentgen. 5- Equivalent dose: amount of the radiation absorbed by biological tissue  Biological effect of radiation depend on  Absorbed dose  Type of radiation (alpha particles 20 time damaged than beta particles)  Equivalent does unit: Rem( Roentgen Equivalent in Man) & Sievert (Sv)  1Sv( SI unit ) = 100 Rem  Example: 50mSv= 50000µSv= 5Rem=5000mRem. 6- Three ways to reduce dose :  Limiting time in the radiation field.  Stay away from the source as much as possible (distance).  Place something to absorb the radiation between you and the source (Shielding). 4 of 22 7- Dose = Dose Rate * Time (D=DR*T)  Example1: The dose rate is 0.2 Rem/hr. How long will it take to receive a dose of 100mRem? Answer 0.5hrs(30minute).  Example2: a survey meter reading168 µSv/hrs, what will be the dose on mRem after 5 hours23minutes? Answer: 90.4mRem. 8- Inverse Square Law  Example1: A person moved from 10m to 20m from a radioactive source. The dose rate at new location will be? Answer: ¼.  Example2: The intensity of radiation is 530 R/h at 5 feet away from a source. What is the intensity of the radiation at 10 feet? Answer: Rework the equation to solve for the intensity at distance 2 I2 = I1 x D12 / D22 Plug in the known values I2 = 530R/h x (5ft)2 / (10ft)2 I2 = 132.5 R/h In this instance the distance has been doubled and the intensity at that point has decreased by a factor of four.  Example3: A source is producing an intensity of 456 R/h at one foot from the source. What would be the distance in feet to the 100, 5, and 2 mR/h boundaries? Answer : Convert R/hour to mR/hour 456R/h x 1000 = 456,000 mR/h Rework the equation to solve for D2 5 of 22  Plug in the known values and solve D2= 67.5 feet  Example4: Ir-192 source has an activity of 30 Ci, what is the dose rate at 20 meters? Answer: I(Rem/hr)= RHM* A(Ci)/ d2 I= 0.55*30/400 = 0.04125Rem/hr = 41.25mRem/hr  Example5: An Ir-192 source of 1702 GBq was used, at what distance you will put the warning signs and the rope? Answer: d=√ RHM*A(Ci)/I(Rem/hr) A(Ci) = 1702GBq/37 = 46Ci Put the warning Signs at 0.75mRem/hr I= 0.00075 Rem/hr D= √ 0.55 * 46/0.00075 = 183.67 m 9- Half value layer (HVL): the amount of a material required to reduce the radiation to ½ its original intensity. Approximate HVL for Various Materials when Radiation is from a Gamma Source (provide on Exam) Half-Value Layer, mm (inch) Source Concrete Steel Lead Tungsten Uranium Iridium-192 44.5 (1.75) 12.7 (0.5) 4.8 (0.19) 3.3 (0.13) 2.8 (0.11) Cobalt-60 60.5 (2.38) 21.6 (0.85) 12.5 (0.49) 7.9 (0.31) 6.9 (0.27)  HVL = 0.693/ µ (µ: attenuation coefficient).  I=I0/2n 6 of 22  Example1: If the half value layer for concrete is 1.6 inches for Ir-192, how many inches of concrete are needed to reduce a radiation level of 64mRem/h to 2mRem/h? Answer: I=I0/2n 2= 64/2n 2n = 32 n= 5 Thk.= n* HVL = 5* 1.6 = 8 inches Example2: If you use Co-60 source in the field and you are using 2.5 inches lead sheet as a shielding. And the incident intensity is 22microSv/h before the sheet, what will be the intensity after the sheet (HVL for lead for Co-60 0.5 inch.)? Answer: I=I0/2n I0= 22 µSv/hrs , n=Thk./HVL = 2.5/0.5 = 5 I= 22/25 = 22/32 = 0.6875µSv/hrs  Biological Effects of Radiation on the Human Body Biological effect: ionizing radiation cause damage change the cell function to that cell is called a mutated cell. Some mutations can lead to cancer  Acute Dose: Large radiation dose in a short period of time.  Somatic Effects: This is the biological effects that occur on the exposed individuals, they may develop years after the exposure to radiation (Cancer, Cataracts, and Life shortening).  Genetic Effects: Effects that may be transmitted to future generation.  All of organs may be damaged by overexposure to radiation  Organs most Radiosensitivity: blood tissue, lymphoid organs, bone marrow, testes, ovaries, intestines.  Contamination: The deposition of unwanted radioactive material on the surfaces of structures, areas, objects, or people. It may also be airborne, external, or internal (inside components or people). 7 of 22   Radiographic projectors and Equipment  Approved Sealed Radioactive Sources: Sealed Radioactive sources used for Industrial Radiography in Saudi Arabia Ir-192, Se-75, and Co-60 Element Characteristics Cobalt Iridium Isotope 60 192 Half Life 5.3 yrs 74.3 Days Gamma Ray (MeV)1 1.33-1.77 0.31-0.47-0.60 R/hr/Ci(RHM) at 1 meter (1Foot) 1.35 (14.5) 0.55 (5.9) Safe distance & shielding required More than Ir192 Less than Co60 4 technicians 2 technicians Crew (2vehicle )2 (1 vehicle ) 1. Mev(million electron volt) 2. At least one member of the radiographic crew using Co-60 shall have authorization for Co-60 on the Radiographer's permit  Radiography source are always special form  Exposure devices are divided in to Three classes I. Portable (class P) II. Mobile(class M) III. Fixed ( class F) Allowed Dose Class 50mm from At Surface 1 m from surface surface P 200mRem/hr 50 mRem/hr 2 mRem/hr M 200mRem/hr 100 mRem/hr 5 mRem/hr F 200mRem/hr 100 mRem/hr 10 mRem/hr 8 of 22 9 of 22  Projectors (radiographic exposure devices), controls, and guide/extension tubes shall be inspected and maintained by third party (manufactures or his representative / suppler).  When a radioactive source is in its shielded position inside the radiographic projector, the maximum at any exterior surface, shall not exceed 2 mSv (200 mR) per hour, or shall not exceed 0.1 mSv (10 mR) per hour at 1 meter from any exterior surface.  In an exposure devise, the outlet nipple end of the device traditionally has a highest reading  Sealed source are required to be leak tested at intervals not exceed 6months by use wet cotton.  Complete Service in accordance with the manufactures recommendations "Radiographic Exposure Device Maintenance" shall be performed at intervals not exceeding 12 months or 1 Year.  Each radiographer is responsible for checking his own radiographic equipment (projectors, control (crank) unit, guide tube, and extensions) prior to each day's assignment.  Any equipment that fails a daily inspection should be removed from service  Guide tube: inspect guide tube that will be used for cuts, inward dents by hand  Crank unit (control unit) : check the freedom of movement of the control cable  In addition to daily inspection, inspection & maintenance of radiographic equipment (Crank Unit, Guide Tube, extension) is required at intervals not exceed three months.  Collimator: A radiation shield made of lead or other heavy metal which is used to limit size, shape and direction of the primary radiation beam(For application of Ir-192 gamma-ray radiography, only Tungsten Collimators shall be used). 10 of 22  Radiation Detectors 1. Thermoluminescence Dosimeter (TLD)  TLDs are used to accumulate an individual’s permanent dose record , and are also used as back-up for dosimeter should it go off scale for any reason  The TLD shall be worn at chest level and care shall be taken that it is correctly positioned so that the front of the TLD is facing out.  Possession of a TLD shall not be considered as authorization to use radioactive materials.  Light, heat &mechanical pressure as well as radiation can effect TLD.  When not in use, TLD badges shall be stored in a radiation free location.  Anytime there is reason to believe that the TLD has been exposed to radiation other than normal usage (e.g., accidentally dropped in an exposure area), all work will cease immediately, equipment secured and returned to storage and concerned personal of high exposure are ceased from work, The individual will not resume duties associated with radioactive material until cleared to do so by RPU/EPD.  TLD must be proceed at intervals not exceed one month 2. Electronic Pocket Dosimeters (EPD)/ Personal Radiation Alarm.  Dosimeter accumulative doses or quantities of gamma &X-ray radiation over some short period of time (usually hours).  Electronic Pocket Dosimeters shall be calibrated at intervals of not greater than one year.  Dosimeter reading are required at end of each shift (frequently Check)  Pocket dosimeters must be zeroed at the beginning of each day. 11 of 22   Read Pocket dosimeters having a range of 0 to 2 mSv, 0 to 2000 µSv (0 - 200 mRem).  Acceptable dosimeters must read within ± 20% of calibration levels. If an individual’s Electronic Pocket Dosimeter displays a dose greater than the investigation level dose or dosimeter is off scale  work will cease immediately.  An immediate radiation survey of the area and equipment shall be performed If the source is in the shielded position If the radiation source cannot be shielded &confirm by radiation survey that there is no release of radiation  insure access into the area is restricted to  secure equipment prevent a radiation hazard.  notify the Area RPO  notify the RPO.  Work is not to resume until the malfunctioning  Exposed TLD badge(s) will be processed as soon dosimeter has been replaced and the Area as possible. Coordinator or RPO has approved  All personnel associated with the radiation incident shall not be allowed to return to work until the results of the TLD badge evaluation are received 12 of 22  3. Radiation Survey Meters (Rate Alarm Meters):  Survey meter is a device that indicates the immediate dose rate& the of the strength radiation intensity (radiation level).  Radiation survey Meters shall be Geiger Mueller type with a measurement range from 2 µSv/hr (0.2 mRem/hr) to at least 10 mSv/hr (1000 mRem/hr).  Usage - Each radiographic technician shall have in use a radiation survey Meter during all aspects of use, handling or storing radioactive material.  At least two radiation survey meters shall be in use during the transportation of radioactive material.  An operational test of the survey meter shall be performed each day prior to the commencement of work. This operational test shall include a "battery check"& Physical damages& if it properly to detect radiation.  All Radiation survey meters issued for use shall have been calibrated within the past six (6) months.  If for any reason, one survey meter is inoperable or considered to be malfunctioning, radiographic operations shall cease immediately and shall not be resumed until the survey meter is replaced.  In the case where all survey meters are inoperable or considered to be malfunctioning, the area shall be considered as a radiation incident, and the Controlled Area maintained until a working survey meter can be obtained and used to verify the radiation condition.  Dose Limits:  Annual dose limit Annual Dose limit Application Occupational Public Effective dose(whole 20mSv(2Rem) 1mSv(0.1Rem) body ) Not exceed 100msv per 5 years Not exceed 5msv per 5 years Lens of the eye 150mSv(15Rem) 15mSv(1.5Rem) The Skin 500msv (50Rem) 50mSv(5Rem) The Head-Feet 500msv (50Rem) 50mSv(5Rem) 13 of 22   Investigation Level Dose:  Daily dose in excess of 500 μSv (50 mR)(0.5mSv)  Monthly dose in excess of 1000 μSv (100 mR)(1mSv)  Restricted Areas: 1. Controlled Area  Radiation levels at the Controlled Area boundary shall not exceed a measured 7.5 μSv/hr (0.75 mRem/hr).  A radiation survey shall be conducted as soon as the source is exposed to confirm correct barrier radiation limits.  The radiographer must complete a radiation survey at each radiographic work location.  Access to the controlled area is restricted to authorized radiation workers only.  Anytime control of this area cannot be maintained, all work is to cease immediately and shall not be resumed until control is regained.  If any unauthorized person enters the radiation area the source will be retracted and no exposures made until the area is cleared. 2. Supervised (Observed) Area:  The Supervised Area is based on an estimated distance where the dose level averaged over one hour will not exceed 2.5 μSv/hr (0.25 mRem/hr). Though it is not required to establish a barrier at this limit. 14 of 22 3. Controlled Area Warning Signs and Barrier Tape or Rope:  Minimum of four (4) free-standing radiation warning signs shall be posted at the Controlled Area boundary so that warning is provided for all approachable directions.  When the radiographic exposure device is elevated such as on a platform, in a confined space, or in a ditch, an additional sign shall be placed at the point of entry.  Signs shall have a minimum height of 1 meter. Radiation warning shall be in both Arabic and English languages and have the international radiation trefoil symbol.  In remote areas where there is a limited or no presence of personnel other than the radiographic crew, such as pipeline work, barrier tape or rope is not required unless even with limited other personnel, such personnel could interfere with the radiographic operations.  Where radiography is being conducted in "multi-story" applications and access to the level (and above or below) where the work is conducted, additional barricades shall be established at each accessible level.  Barrier tape, if used, shall include wording in Arabic and English languages and the trefoil radiation symbol continually printed long the length of the tape. Tape shall have a yellow background with wording and symbols including stripes, if present, with black print. 15 of 22   Barrier Rope, if used, shall be bright orange in color and shall have approved radiation warning pennants spaced every 3 meters or less.  Work Permit:  At least one member of a Radiographic crew should be in possession of a valid Work Permit Receiver's card.  Only Hot Work permits shall be used unless all equipment including the Survey Meter is certified intrinsically safe.  Work Permit is a permission issued by the Inspection Department to a contractor on a project basis.  Radioactive Source Storage:  The design of all radioactive storage facilities (permanent and temporary) must be approved by RPU/EPD as SAEP1141.  Radiation Warning signs (in Arabic and English) should be displayed on all doors, cover of the pit and fences of all types of the storage facilities.  The Contractor shall maintain a utilization log, The log shall be kept at the storage pit and shall show as a minimum provided date, time, and who a source was issued to, where it is located at all times, and when returned and by who.  Permits for temporary storage facilities are issued for a period not to exceed 6 months.  The maximum allowable sources in the pit is 3 sources by 200Ci strength.  Radioactive materials use for industrial radiography offshore shall be limited to Ir-192, strength not exceeds 30 Ci. 16 of 22  Transportation : Label Surface Radiation level Radiation level at 1meter White I label 0 ≤0.5mRem/hr (0.005mSv/hr) Yellow II label >0 >0.5mRem/hr(0.005mSv/hr but but ≤ 1mRem/hr ≤ 50mRem/hr(0.5mSv/hr) Yellow III label >50mRem/hr(0.5mSv/hr) But ≤200mRem(2.0mSv/hr) > 1mRem/hr  Transport Index: is a number representing the maximum radiation dose in mrem unit (or μSv/10) at a distance of 1 m from the surface of the package.  Vehicles used for the transport of radioactive material used for industrial radiography shall be equipped with a storage compartment designed for that purpose. The storage compartment SHALL be securely affixed to the vehicle.  The maximum Transport Index does not exceed the requirements of Yellow Label II which is 0.5 mSv/hr (50 mRem/hr) at the surface and 0.01 mSv/hr (1 17 of 22  mRem/hr) at one meter. Further, the dose level at any occupant position or exterior surface of the vehicle shall not exceed 7.5 μSv/hr (0.75 mRem/hr).  "Danger Radiation" signs on the front and rear of the vehicle shall be fixed During the radioactive material transport.  An Emergency Contact information card shall be prominently displayed within the passenger compartment of the vehicle clearly identifying that in the event of an emergency.  The emergency procedure to be followed should be available in the passenger compartment.  All personnel must have in use required personal dosimetry and survey instrumentation at all times when radioactive materials are stored or transported in the vehicle.  The maximum permissible speed for vehicular transport of radiographic projectors is 90 km/hr.  For air transportation of radioactive isotopes, the shipper must follow the requirements of (IATA).  Radioactive sources transported by boat (Water Transportation) must be secured in a Type B transport container having a maximum "Yellow Label-II" transport classification.  Package include radioactive material must be have warning labels place on four sides and show content, weight, activity &transport index  Handling Sealed Sources:  The primary responsibility of radiographer is to protect themselves & other from radiation exposure.  RT Level II technician must have a minimum of 3 years field experience to be assigned to work with Trainees and RT Level I technicians. 1. Dosimetry:  Verifies correct dosimetry is in use and if start of day, zeros pocket dosimeter,  Verifies survey meters (minimum one per radiographer) are on, calibrated and functioning properly. 2. Receives radiographic exposure device (projector):  Together with the designated Issuer/Receiver, collects the projector from the storage cell/pit.  Verifies Source Serial Number. 18 of 22  Verifies that the vehicle has the required associated equipment, radiographic accessories, and safety equipment.  With the Issuer/Receiver conducts a "Daily Inspection" of the projector and conducts radiation survey.  Assures that the Issuer/Receiver has logged out the projector with the correct data and destination. 3. Prepares/confirms transport vehicle requirements:  Attaches the required radiation warning signs to the transport vehicle (front & rear sides) prior to loading of the projector.  Assures that current revision of the Radiation Protection procedure is in the vehicle and readily accessible for reference.  Assures that emergency contact information is readily available and visible not only to himself but in the event of an emergency, to response personnel. 4. Loads Projector:  Secures the projector as required by the Protection procedure and any current Radiation Protection (Safety) Advisories in the transport vehicle.  Performs a survey of the exterior of the transport box, exterior of the vehicle and the passenger compartment.  Transports the projector to the designated work assignment site without detour or route deviation not exceeding 90Km/hr. 5. Site Setup and Exposure:  Establishes barrier to projected distances. Assures that the minimum numbers of warning signs (4) are sufficient to cover all possible areas on ingress.  Performs set-up of the projector and associated equipment in accordance with the radiation Protection procedure and current Radiation Protection Advisories.  Upon connection of the controls, performs a check of the projector selector ring and controls. Any indication of malfunction or sluggish operation shall give cause for immediate stop of work and return of the projector to the point of issue.  Performs radiographic assignment.  Conducts a verification exposure to evaluate dose levels at the established barrier limits and adjust distances where required. 19 of 22   Frequently monitors pocket dosimeter throughout the performance of radiography.  When performing radiographic operations a radiation survey shall be made after each exposure to determine that the radiation source has been properly returned to its shielded position. The survey shall continue as the radiographer approaches the projector with readings taken at all sides of the projector to assure proper retraction. A survey of the projector starts from the back(connector end ) &he will continue moving the survey meter around the projector completing a 360 degree survey of the projector 6. Completion of Assignment:  Secures all equipment and loads transport vehicle.  Performs a survey of the exterior of the transport box, exterior of the vehicle and the passenger compartment.  Verifies that required vehicle warning signs are in place.  Transports the projector to the next assigned work site or point of issue without detour or route deviation not exceeding 90Km/hr. 7. Return of Projector to the storage site:  Returns the projector to the designated Issuer/Receiver.  Together with the Issuer/Receiver, performs a survey of the projector as well as a visual inspection.  Assures that the source is logged in by the Issuer/Receiver with the correct data.  With the Issuer/Receiver, stores the projector in the appropriate cell/pit.  Records dosimetry data. 8. Source surveys should always be made before, during and after each exposure and when loading and/or unloading a radiographic projector.  Emergency cases: I. Fire involving Radioactive Source: immediately call firefighting department &inform them the radioactive source involved in the fire. II.Radioactive source could not be fully retracted into projector (source stuck):  Try to re-track the source back to the safe container  If source did not back to safe position conduct area survey & reset the controlled area if needed.  Secure &monitoring the area, evacuate any near area effected by radiation. 20 of 22  III. Road accident while carrying radioactive source: conduct area survey &put barricades to prevent people from coming near the source.  Radiation Safety Regulations in Industrial Radiography 1- Radiation safety Officer (RSO): An individual technically competent in radiation protection matters relevant to a specific radiation practice. This individual is designated by the user organization, licensed by the government regulatory authority (KACARE) of radiation protection and approved by Radiation Protection Unit (RPU) of Environmental Protection Department (EPD). 2- RPP: Radiation Protection Permit (permission for individuals to conduct radiography) issued by Radiation Protection Unit of Environmental Protection Department for industrial radiographers working on Saudi Aramco properties. The RPP is obtained after passing an exam by RPU/EPD and it is valid for three years. 3- Radiation workers must be Received training in radiation protection each 12 months. 4- RPU: Saudi Aramco Radiation Protection Unit of Environmental Protection Department/EPD. 5- EPD: Saudi Aramco Environmental Protection Department. 6- High Radiation Area: Any area, with levels of radiation in which a major portion of the human body could receive a dose in excess of 1 mSv/hr (100 milli-Rem / hour). 7- King Abdullah City for Atomic and Renewable Energy K.A.CARE( previously KACST) : National authority responsible for radiation protection in Kingdom of Saudi Arabia (KSA). 8- Safety procedure that should be followed for radiation protection inside ARAMCO projects is SAEP 1141 and GI 150.003. 9- ALARA (As Low As Reasonably Achievable). 21 of 22