Individual dosimetry in planned, existing and accidental exposure situations

Transcription

1 Individual dosimetry in planned, existing and accidental exposure situations T. Salah El Deen,M. A M Gomaa, T. Morsy and M.H.Shabon Radiation Protection services and consultation group Atomic Energy Authority Cairo Egypt Talaatsalah2002@yahoo.com ABSTRACT Ionizing radiations are in use for peaceful uses in Egypt for more than sixty years. Individuals working in planned exposure situations such as industry, medicine,agriculture and education. workers are regularly monitored for individual dose estimation. Individuals working in existing exposure situations such TE-NORM workers are also monitored. Film badges and TLD dosimeters are in use for estimation of external exposure. Whole body counters and contamination monitors are in use for estimation of internal exposure. For emergency exposure situations, where individuals with no personnel dosimeters, individual doses were reconstructed as in the case of 2000 Meet Halfa accident. 1-INTRODUCTION Following the new 2007 ICRP recommendations ( 1) which is known internationally as ICRP The following Situation terms are defined as follows:- Planned exposure situations which are defined as situations that may occur during the operation of a planned situation, or from a malicious act, or from any other unexpected situation, and require urgent action in order to avoid or reduce undesirable consequences. Existing exposure situations which are defined as situations that already exist when a decision on control has to be taken, including prolonged exposure situations after emergencies. Emergency exposure situations which are defined as Situations that may occur during the operation of a planned situation, or from a malicious act, or from any other unexpected situation, and require urgent action in order to avoid or reduce undesirable consequences. Definitions of Exposed Individuals Exposed individuals are the exposed individuals, namely workers, the public, and patients. They essentially correspond to individuals whose exposures fall into the three categories of exposure. A given individual may be exposed as a worker, and/or as a member of the public, and/or as a patient. A worker is defined by the ICRP Commission as any person, who is employed, whether full time, part time, or temporarily, by an employer and who has recognized rights and duties in relation to occupational radiological protection. A self-employed person is regarded as having the duties of both an employer and a worker. Workers in medical professions involving radiation are occupationally exposed. A member of the public is defined by the ICRP Commission as any individual who receives an exposure that is neither occupational nor medical. A large range of different natural and man-made sources contribute to the exposure members of the public

2 A patient is defined by ICRP as an individual who receives an exposure associated with a diagnostic, interventional, or therapeutic procedure. 2-EXPERIMENTAL 2.0. Sixty years experience for peaceful uses of atomic energy Interest in radiation physics was initiated by Egyptian pioneers such as K A Mahmoud who led radiation physicists and radiation protection experts in Egypt and abroad for years. For more information about history of radiation protection, Please see Gomaa-IRPA-12 ( 2008)(2). Radiation protection activities were grouped in the sixties within the Egyptian Atomic Energy Authority ( EAEA)as, radiation control group, external dosimetry group, Internal dosimetry using whole body counters group and radio assay group, radiation medical monitoring group, waste disposal, decontamination and transport of radioactive sources group, environmental monitoring group and calibration group. With the wide spread of peaceful used of atomic energy activities in Egypt radiation protection activities were carried out in and outside EAEA. In 1990 attention was paid to radiation protection during radiographic processes. Radiation protection in radiation medicine was in action for years but radiation protection in nuclear medicine was introduced in In Egypt and due to the use of radioactive sources in the petroleum industries for several reasons, radiation protection activities was also directed to NORM monitoring and to Petroleum waste containing NORM. For more than 15 years, NORM site monitoring as well as personnel monitoring were carried out in general and in cases of contaminated platform 3.0 Individual dosimetry 3-RESULTS AND DISCUSSION For individual monitoring of exposed workers, Film badges or thermo luminescence dosimeters are in use. In cases where individual may be suspected to be contaminated internally, contamination monitors are used to monitor the site and whole body counters to monitor individuals. In the following section some results to reflect experience gained in individual dosimetry. 3-1Natural sources of ionizing radiations Cosmic ray exposure to member of the public in flights Computer Program CAIR-6 was developed at the Civil Aero medical Research Institute of the US federal Aviation Administration in Oklahoma (Friedberg et al, 2002 ;) ( 5) it used to calculate the effective dose of galactic cosmic radiation received by an adult on a nonstop aircraft flight during any month from January 1958 to the present Ferrari et al (2001) ( 6).It can also calculate effective dose rate from galactic radiation at any specific location in the atmosphere at altitude up to feet

3 Flight data Flight ID of 1 st 20 characters Number of route altitudes Minutes clamping to 1 st route altitude 1 st route altitude of : feet minutes 2 st route altitude of : feet minutes Minutes descending to destination airport effective dose μ Sv Fig (1) Schematic diagram of computer program for calculating flight radiation dose CARI-6 In Table -1 individual doses received by members of the public during their flight from Cairo to major cities. Individual exposures were estimated using Code CARI-6 Flight route Altitude (Ft) X10 3 Duration time (h) Effective dose(µsv) Cairo- Montréal Cairo Cairo Johannesburg-Cairo Cairo-New York-Cairo Cairo-Beijing-Cairo Cairo Korea -Cairo Cairo Tokyo-Cairo Cairo-Dubai-Singapore-Melbourne- Dubai-Cairo

4 Cairo-Osaka-Cairo Table (2) computed effective dose board of air craft by computer System CARI -6 for Middle East country route Flight route Altitude (Ft)X 10 3 Duration time (h) Effective dose (µsv) Cairo- Damascus-Cairo Aswan Jeddah-Cairo Sharm-Riyadh- Cairo Sharm- Khartoum- Cairo Cairo- Kuwait-Cairo Cairo-Alain Cairo Cairo- Sharjah- Cairo Cairo- Doha -Cairo Cairo Muscat Cairo Cairo-Amman -Cairo Sharm-Bahrain- Cairo Cairo- Dubai- Cairo Cairo Abu-Dhabi -Cairo Cairo-Tunis -Cairo Cairo Cairo -Casablanca -Cairo NORM Exposed Individual Individual doses to maintenance temporary workers at a contaminated oil field are reported in Table -1.The personnel dosimeters used were film badges. Table -3 Gamma ray individual doses to NORM temporary workers Individual dose in msv No of individuals The total number of temporary workers were 780 and the individuals received personnel dose up to 3 msv with an average individual dose was less than 0.8 msv during maintenance work. For more information see Gomaa 2010(3). 3-2Artifical sources of ionizing radiations Monitoring of individuals working in nuclear medicine unit Individuals working in nuclear medicine unit handling I-131 are monitored using whole body counter the estimated results of the committed equivalent dose ranged between 1.8 to μsv. Results are shown in Table (4)

5 Table (4) Activities and committed equivalent dose due to I-131 for some individuals Case Counts/ second Activity (Bq) CED (µsv) Meet Halfa Accident Dose reconstruction Radiation Dose Estimates of Exposed Groups. Using the Gamma Factor of 0.13 msv per hour at one meter for one Giga Bq and the activity of the source of 31.5 Ci on May 5, and Ci on June 26; the effective doses were 151 msv per hr at one meter and 93 msv per hr at on meter on the dates indicated respectively. The exposures were protracted and subject to several known variables including frequency, mode, duration and exact dose rate at time of exposure. This particular situation renders precise dose estimates to the exposed groups very difficult to achieve and subject to a wide margin of error. Dose Estimates to Family Members. Dose estimates to this members family would be based on the type and severity of the biological effects incurred to each individual. The biological indicators used for dosimetric purposes would include such criteria as degree and extent of skin burns, changes of peripheral blood cells, severity of bone marrow affection, gastrointestinal disturbances and cytogenetic findings. Taking into account the dose rate on May 5, and on June 26; and considering the acute effects acquired by the members of the family, it would be rational to postulate a cumulative dose of Gy to the father, and a cumulative dose of Gy to the younger son. Both died from bone marrow failure, severe skin burns and gastrointestinal manifestations. Cumulative doses to the wife and sister approximate to about 3.5-4Gy; and to the older son would be about 4.5 Gy localized to the lower right quadrant of the abdomen. The cumulative dose to the elder daughter reached 4 Gy to the whole body affecting bone marrow deposits. The cumulative dose to the younger daughter is of the same magnitude, with characteristic localization to the skin of both hands, Rt. Knee and Rt. thigh. Dose estimates to radiation survey groups. These include a total of individuals. These groups were exposed to low level radiation during the survey operations. Personal dose-meters carried by some individuals during the survey procedures gave readings between 1-15 msv. Dose estimates to family associates. As previously mentioned, the number of family associates was about 50 individuals. The exposure doses to this group would range between 0.5 and 5 msv

6 Tabl-4 Radiation Dose Estimates to Exposed Groups A- Family Members (Protracted Exposure) Members Father Dose (Gy) Total Body Younger Son 5-6 Total Body Elder Son Sister Wife Younger Daughter Elder Daughter Localized Total Body Total Body Localized Total Body B- Radiation Survey Groups C- Family Associates Number Dose (msv) Number Dose ( msv) individuals 1-15 msv 50 individuals 1-5 msv 4-CONCLUSION Experience gained in individual dosimetry to workers, public and patient was reviewed for planned exposure situation, existing exposure situation and in emergency exposure situations. The Examples of planned exposure situations were for cosmic ray exposure to public, existing exposure situation for norm workers and emergency exposure situation for meet halfa accident. 5-REFERENCES [1] International Commission on Radiological Protection Recommendations of ICRP. Annals of the ICRP 37(2-4). ICRP Publication 103, Elsevier Ltd [2[ M A Gomaa, Regional and national radiation protection activities in Egypt, IRPA-12, October 2008, Buenos Aires-Argentina. [3[ M A Gomaa, personnel dosimetry to radiation workers upgrading old petroleum oil field, 6 th NORM International symposium, March 22-26,2010, Marrakesh, Morocco, [4] El-Naggar, A.M., M.H.M. Mohammad and M.A. Gomaa. The radiological accident at Meet Halfa, Qaluobiya, Egypt, p in: The Medical Basis for Radiation-Accident Preparedness: The Clinical Care of Victims (R.C. Ricks, M.E. Berger and F.M.O Hara Jr., eds.). The Parthenon Publishing Group, New York, [5] Friedberg W,Copeland k Duke FE,Nicholas JS, Darden Jr EB,O Brien K Radiation Exposure of Air crew,occupational Medicine: State of the Art Reviews 17(2): , (2002) [6] Ferrari A, Pelliccioni M, Rancati T. Calculation of the Radiation Environment Caused by Galactic Cosmic Rays for Determining Air Crew Exposure Radiat Prot Dosimetry: 93(2): (2001)