33. Example: A radiographer is found to receive an exposure of 1 mSv after he stands for 2 minutes at a certain distance from the source. What is the total radiation exposure received if he stands for a period of 5 minutes at the same distance?
34. Thus, if he spends for 5 minutes, the total exposure will be:
35.
36.
37.
38.
39.
40.
41. What is the concrete thickness required to reduce a radiation dose rate of 80 Sv/hr from a Co-60 source to 2.5Sv/hr? (Given - for concrete is 0.105 cm -1 ). From formula, Therefore; the thickness of concrete required is 80 Sv/hr reduce to 40 Sv/hr need 1HVL 40 Sv/hr reduce to 20 Sv/hr need 2HVL 20 Sv/hr reduce to 10 Sv/hr need 3HVL 10 Sv/hr reduce to 5 Sv/hr need 4HVL 5 Sv/hr reduce to 2.5 Sv/hr need 5HVL
42.
43.
44.
45.
46.
47. Methods of shielding when pipes ducts, conduits or cables must pass through walls of exposure room 4.2 Design of Exposure Room.
57. WARNING NOTICES CAUTIOUS RADIATION MONITORING DEVICES IS NEEDED BEYOND THIS LIMIT Name of RPO: Address: Tel. No: RADIOACTIVE MATERIAL DANGER NO ENTRY Name of RPO: Address: Tel. No:
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
68. Fully Open Sites (Field sites) 5.4 Establishment of Radiographic Boundary
69.
70.
71.
72. Typical Storage Pit Exposure device Storage pit Fence The radioisotope storage pit (bomb-pit) 1.0 meter < 0.25mR/hr or 2.5microSv/hr < 0.75mR/hr or 7.5microSv/hr
73. The bomb-pit or radioisotope storage pit shall be approved by LPTA/AELB before it can be used. 5.5 Storage of Radioactive Source and Radiation Apparatus
Explain the ability of ionizing radiation especially X and gamma radiation to penetrate the object; density is a factor determining how deep the penetration of the radiation into the object; apart from the energy of the radiation; the higher the energy of ionizing radiation the deeper the penetration. Other properties of ionizing radiation: Refracted when passing through media of different density. Some of the radiation be reflected when meeting smooth surface of an object and some penetrated into the object. The energey expressed in eV, keV and MeV Should also explain other properties of ionizing radiation
Discussion Where do you think you should put the film to have optimum image of the internal structure of the specimen???
Directional x-ray tubes are fitted with suitable collimators called cones and diaphragms to reduce the useful beam to a minimum size necessary for the work and to minimise the scattered radiation from the irradiated object.
When the filament in the cathode is heated, free electrons escape from the surface of the material. The potential difference (kV) applied between the cathode and anode will cause acceleration of the electron toward the anode. Sudden stop of the high speed electrons cause transformation of almost 97% of kinetic energy to heat and only small portion of the energy turn into emission of x-ray from the anode. The energy of the x-ray range from 0 to the maximum, which is determined by the kinetic energy of the electrons or kV and also on how rapidly the electrons are decelarated.
High intensity sources such as several curies of 192 Ir and 60 Co are best handled with specific equipment that permit the radiographer to remain several meters from the projector when the source is exposed.
Ensure that the survey meter is used for tasks: To initially check that the safety barriers are positioned where the dose rate is not greater than 7.5 uSv/h. To monitor on a routine basis the dose rate at the safety barriers, particularly when the radiographic techniques varies. To make sure that a source is fully shielded after use or that a source is fully retracted. To help task of locating a lost source (if any).
Where I 1 is the intensity of radiation in unit activity either Ci or Bq, or in unit dose received such as Sv and fraction of the unit(uSv, mSv etc.) at distance d 1 in unit distance such as cm or m Whilst I 2 is the radiation intensity in the respective unit at distance d 2 in unit distance such as cm or m.
Atomic number . Shielding property proportional to atomic number of shielding material. Example lead with atomic number 82 is more effective shielding material than Ni with atomic number 28.
Notes Narrow beam radiation when the radioactive material is a point source The e - x is also known as transmission factor symbolized as , where the above equation may simply rewritten as I x =I 0
If I x =I 0 /2, therefore 2 = e x , where x=x/2 or HVL, thus HVL or x =ln2/ = 0.693/ . I 0 /I n = 2 n Say for (1) half thickness I 0 /I 1 =2 1 , two (2) half thickness I 0 /I 2 =2 2 , and if n half thickness I 0 /I n =2 n Say for a thickness that reduce the intensity to 10 of the original radiation intensity. I0/I10 = 10 = e x where x = TVL, therefore ln10= x, or TVL=2.303/ . How to derive I 0 /I n = 10 n . I 0 /I 1 = 10 1 , I 0 /I 2 = 10 2 , ……. I 0 /I n =10 n
The U having the lowest TVL signifying of its effectiveness in attenuating the ionizing radiation due to highest atomic number (92) compare to lead with atomic number 82. It is noted that density also determined the TVL or /and HVL for example lead with specific density of 11.28 having HVL/TVL higher than tungsten with specific density 19.35.
The working area classified as clean, supervised and controlled area when meeting the following. Source – sealed source. Clean area in the radiation exposure less than 1/10 x annual total dose equivalent (5 mSv/yr) Supervised area if the radiation exposure more than 1/10 of annual dose equaivalent but less than 3/10 of annual dose equaivalent ( more that 5 mSv peryear but less that 15 mSv/year) Controlled area – if the annual dose equaivalent more than 3/5 of annual dose equivalent perannum( more than 15 mSv/yr.)
Movement at site location from a place to another within reasonable site area is considered as movement within site.
![Contents ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)