SCI has had a Personal Dosimetry Service since 1993, when it was authorized by the Nuclear Safety Council(CSN). This authorization has been revalidated after successfully passing the periodic inspections carried out by the CSN itself.
In addition, this personal dosimetry service has been part of the intercomparison campaigns organized by the CSN at national level, always with satisfactory results.
What is dosimetry?
Radiation dosimetry is the technique used by scientists to study the relationship between quantitative measurements of radiation and its effects on a system, usually biological.
Dosimetry is essential to quantify the incidence of biological changes as a function of the amount of radiation received, as well as to monitor the radiation exposure of living beings and its effects on the environment.
ASPECTS OF SCI’S PERSONAL DOSIMETRY SERVICE
Types of dosimetry
This, in turn, is divided into several types of dosimetry depending on their location.
Dosimeters placed at chest level are used to carry out the test. The use of the dosimeter is personal and must be used when there is a risk of exposure to ionizing radiation.
These dosimeters are used to estimate the doses received by the whole body of workers exposed to ionizing radiation. They are found in terms of ‘surface dose equivalent‘ (Hs = Hp (0.07)) and ‘deep dose equivalent‘ (Hp = Hp (10)).
According to the current regulation “R.D. 783/2001 (article 27)“, the doses received by exposed workers must be determined with a periodicity of no more than one month, therefore, the period of use of the dosimeters, and therefore, their reading, must be monthly.
Each person (user) of the facility (entity) that is registered in the Dosimetry Service will be assigned 2 dosimeters that will be used alternately (the dosimeter being used should not be sent until the new one is received).
If plumbed garments (apron, vest,…) are being used, the dosimeters will always be below them.
Dosimetry of extremities
Ring dosimeters are used for this type of dosimetry. Before starting this type of dosimetry, the user in question must be registered in the body.
This ring is used when it is estimated that the radiation doses received in the extremities (hands) may be considerably higher than the doses of body dosimetry.
The use of the ring is personal and must be used when there is a risk of exposure to ionizing radiation. If gloves are worn, the ring should be placed under the glove.
The ring is placed on a finger of the hand, with the detector facing the radiation beam, and is used to estimate the doses received in the extremity (hand) of the worker exposed to ionizing radiation, in terms of equivalent dose to the extremity (Hext = Hp(0.07)).
When both hands may be subjected to a significant risk of ionizing radiation, this type of dosimetry is assignedto both hands. For this purpose, a ring is placed on 1 finger of each hand (for example, they are used by Nuclear Medicine, PET, etc. personnel).
For each limb of the user of the facility that is discharged in the Dosimetry Service, the following will be assigned 2 ring dosimeters, to be used alternately by months, taking into account that the dosimeter will not be sent until the change is received, and that the periodicity of use, and therefore the reading, must be monthly.
The same dosimeters are used as those used to evaluate the body but placed at the level of the abdomen. This dosimetry is intended for pregnant workers exposed to ionizing radiation. It is used to estimate the dose received by the fetus. With this dosimetry the ‘abdomen dose’ (Habdomen = Hp (10)) is obtained.
Exposed pregnant workers must wear both the personal dosimeter and the abdominal dosimeter. For monitoring purposes, it should be taken into account that the fetal dose limit (1 mSv from the time of pregnancy) is equivalent to the abdominal dose limit (2 mSv from the time of declaration of pregnancy).
The types of non-personal dosimetry are:
Area dosimetry for personal dose assignment
This type of dosimetry is performed by means of dosimeters equal to the body dosimeters, which are placed in representative points of the location of the exposed workers when they are performing their work.
Doses are obtained in terms of ‘surface equivalent dose‘ (Hs = Hp (0.07)) and ‘deep equivalent dose’ (Hp = Hp (10)). The Dosimetry Service will provide these doses to the facility so that the UTPR or SPR of the facility can perform the dose estimation of the exposed workers, being only possible for those workers classified as category B.
Area dosimetry for zone evaluation
It is performed with dosimeters equal to the body dosimeters that are placed at strategic points (with probability of obtaining higher dose values) around enclosures, to check the adequacy of the shielding, and therefore, of the environmental monitoring.
The Dosimetry Service will provide the facility with doses in terms of surface equivalent dose (Hs = Hp (0.07)) and deep equivalent dose (Hp = Hp (10)).
It is performed by means of dosimeters equal to body dosimeters, which are used by those responsible for radiological protection of the facilities for the evaluation of different situations or for the performance of investigations.
The Dosimetry Service will provide the person in charge of radiation protection at the facility with the doses, in terms of surface equivalent dose (Hs = Hp (0.07)) and deep equivalent dose (Hp = Hp (10)).
Types of dosimeters
There are two types of Dosimeters
Dosimeters used for dosimetry: body / abdomen / personal dose assignment area / zone evaluation / control area
They are thermoluminescence dosimeters. They consist of 4 elements: 2 of them of nLi2nB4O7:Cu and other 2 of CaSO4:Tm, introduced in plastic carriers, which have a thin plastic window.
They are used for the detection of X-rays and Gamma rays as well as Beta corpuscular radiation. When the readings of the 4 elements are obtained, an algorithm is applied to evaluate the type of radiation (photons or Beta particles), its energy and the equivalent surface(Hs=Hp(0.07)) and deep(Hp=Hp(10)) doses.
They are thermoluminescence dosimeters, consisting of a 7Li211B4O7:Cu element, inserted in a ring. They are used to measure X, Gamma and Beta radiation.
After reading the element, the equivalent dose is obtained for the extremity where the ring was worn (right hand or left hand)(Hext. = Hp (0.07)).
Dosimetry service standards and formats
SCI’s Dosimetry Service has established standards for the correct use of dosimeters. Among them is the procedure to be applied in case of loss of dosimetry information(PID) for personal dosimetry, according to CSN indications.
Loss of dosimetric information
Loss of dosimetric information may be due to:
Loss of the dosimeter.
In addition to the material loss of the dosimeter, it is considered as loss of the dosimeter when it is not returned within a period of time exceeding 5 months. It will be treated as a loss of dosimetric information.
Deterioration of the dosimeter.
An anomalous reading.
The loss of dosimetric information leads to the assignment to the user of a dose representative of the fraction of the annual dose limit corresponding to the period of use of the dosimeter.
This dose, taking into account the regulations in force(R.D. 783/01), will be:
For Surface Equivalent Dose (Hp(0.07))= 40 mSv/month.
For Deep Equivalent Dose (Hp(10))= 2 mSv/month.
In the case of loss of dosimetric informationdue to non-return of the dosimeter, the period of use will be considered to be the alternate months of the period in which the dosimeter has not been returned, i.e. 3 months. The following doses will be assigned:
For Surface Equivalent Dose (Hp(0.07))= 120 mSv.
For Deep Equivalent Dose (Hp(10))= 6 mSv.
These assigned doses (administrative doses) may be modified due to loss of dosimetric information. For this to be possible, these 3 circumstances must be met:
The change must be authorized by the owner of the installation.
It must be justified and documented by a person qualified in radiation protection.
It must be given with the agreement of the employee involved.
The proposal must include the 3 signatures and the original document must be sent to the Dosimetry Service.
Dosimetric reports can be divided into two: personal and non-personal.
Personal dosimetry reports
These reports are, in turn, divided into two other reports:
General dosimetry report
It contains the monthly dosimetric data of the users of the facility. Both body dosimetry information and ‘other dose’ information is displayed. Among these ‘other doses’ are: extremities, abdomen, etc…
The body indicates for each user the monthly equivalent doses assigned, both shallow and deep, in addition to those accumulated in an official year, and in the case of the deep dose, the accumulated dose in 5 official years.
In the case of the so-called ‘other doses’, it is indicated for each user the monthly equivalent doses assigned for extremities (right ring dose and/or left ring dose) and/or abdomen, as well as the accumulated doses in the official year for extremities, and in the period of pregnancy for abdomen.
Individual dosimetry report
This report contains the dosimetric information for a period of time for a user of the facility. It displays both body dosimetry information and ‘other dose’ information.
The body indicates for the user the equivalent doses assigned in each month of the period, both superficial and deep, in addition to those accumulated in the official year, and in the case of the deep dose, the accumulated dose in 5 official years.
In the case of the so-called ‘.other doses‘, it indicates for the user the equivalent doses assigned in each month of the period, of extremities (right ring dose and/or left ring dose) and/or abdomen, as well as, the accumulated doses in the official year for extremities, and in the period of pregnancy for abdomen.
NON-PERSONAL DOSIMETRY REPORTS
These non-personal reports are divided into general and by measurement point.
General dosimetry report
It contains the monthly dosimetric information of the measuring points of the installation. For each measurement point, the equivalent doses, surface and deep, assigned in the month will be indicated.
Dosimetric Report by Measuring Point
It contains the dosimetric information of a period of time for a measurement point of the installation. For each point, the equivalent doses, surface and deep, assigned in each month of the period are indicated.
The standards of our Dosimetry Service include clarifications on dosimetry reports.
According to current regulations(R.D 783/2001) the Dose Limits for workers exposed to ionizing radiation are:
Per official year:
Surface: 500 mSv.
Depth: 50 mSv.
Extremities: 500 mSv.
Crystalline: 150 mSv.
For 5 official years (consecutive).
Deep: 100 mSv.
Dose limit during pregnancy (from the time of declaration of pregnancy):
Abdomen: 2 mSv.
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