This invention relates to a reusable personal monitor in form of a handsome card providing a quantitative determination of harmful threatening ionizing irradiation.
Dosimeters suitable to detect and to quantify harmful or threatening ionizing irradiation are known for years. Especially people working with radioactive isotopes as in analytical research laboratories, in nuclear medical research, in nuclear power-stations and in non-destructive testing of materials should be under permanent preventive controll in order to be informed about the dose of ionizing radiation to which they have been exposed within a well-known working time. Well-known types of dosimeters are e.g. based on CsI-crystal scintillators, mostly in form of a pencil, which provide permanent controll. When a quantified critical or treshold value becomes exceeded, a system in form of a sound alarm may warn the controlled person. Nowadays electronic gadgets such as personal identification, personal xe2x80x9cirradiation historyxe2x80x9d, etc., have become available, even in contact with a network, in order to maximize personal security measures.
Another detection system makes use of detectors in form of a badge which, after having been borne during a certain period of time are controlled centrally. Quantifying irradiation can be based on silver halide photography (as e.g. in nuclear power-stations, described as in xe2x80x9cGebrauchsanweisung fxc3xcr das Personendosimeter mit Ganzkxc3x6rperdosimetersonden, Typ GSF-Film-GD 10/20, GSF-Forschungszentrum fxc3xcr Umwelt und Gesundheit GmbHxe2x80x94Institut fxc3xcr Strahlenschutzxe2x80x94Auswertungsstelle fxc3xcr Strahlendosimeterxe2x80x94Stand: 1 Mxc3xa4rz 1994). Another quantifying method can be based on thermoluminescence (e.g. with LiF detectors) or on PSL-dosimetry wherein phosphate glass becomes stimulated with a pulsed ultraviolet laser and wherein erasure is performed thermically. Advantageously both detection systems based on thermoluminescence and PSL-dosimetry can be reused.
Another detector offering the same advantage of reusability is a stimulable phosphor medium as has been disclosed in EP-A 0 844 497 and in EP-A 0 892 283.
In EP-A 0 844 497 a method has been disclosed of checking whether an article has been inspected by penetrating radiation. In particular however it relates to a method making it possible to check whether if a piece of luggage has been inspected by X-rays and to a method for personal monitoring. Therein a label according to the first embodiment of this invention can beneficially be used as means for personal monitoring. When a person working in an environment with penetrating radiation carries such a label, the label can be used to determine the dose of penetrating radiation absorbed by that person. The amount of energy of the penetrating radiation stored in the phosphor is proportional to the absorbed dose and can be read out and the remaining amount of energy stored in the phosphor can be erased by erasing radiation. It was found that the ease of erasure was related to the energy of the penetrating radiation that irradiated the label. E.g. energy stored in the label by irradiation with Co60 (1 MeV) radiation is less easily erased than the energy stored in the label by irradiation with penetrating radiation of 50 keV. Thus the time needed to erase the amount of energy stored in the phosphor to a given level is a function of the energy of the penetrating radiation that left said amount of energy stored in the phosphor and by checking the amount of energy left in the phosphor after a given time the energy of the penetrating radiation can be determined. It is clear that for each type of storage phosphor used in the label a calibration of the readings both to determination of the amount of energy stored and to the determination of the energy of the radiation causing the amount of energy to be stored has to be performed. This can easily be done by irradiating the label with a known dose of penetrating radiation of known energy and reading out the amount of energy stored in the phosphor (this is proportional to the absorbed dose) and erasing the amount of energy stored in the phosphor and controlling at given time intervals the amount of energy left in the phosphor (this is proportional to the energy of the penetrating radiation to which the label with the phosphor has been exposed). The phosphor can be calibrated so that the energy of the penetrating radiation can be assessed by reading the time needed to reach an erasure depth (erasure depth: the degree to which the amount of energy stored has been erased.).
Therefore the invention encompasses a method for personal monitoring comprising the steps of
providing a person entering an area where penetrating radiation is used with a label comprising a storage phosphor wherein an amount of energy of said penetrating radiation, proportional to a dose absorbed by said phosphor is stored,
reading out said amount of energy stored in said phosphor, assessing said absorbed dose, while leaving a fraction of said stored energy in said phosphor,
erasing said fraction of said stored energy from said phosphor by overall exposure to erasing radiation during an erasing time to reach a predetermined erasure depth, and noting said erasure time.
In a label according to the first embodiment of that invention and used for personal monitoring it is possible to incorporate different phosphors for the detection of penetrating radiation of different energy. As suggested it is, e.g. possible to include in the label a first patch of phosphor dedicated to the detection of Co60 radiation, a second patch of phosphor dedicated to the detection of Ir192 radiation, a third patch of phosphor dedicated to the detection of radiation of X-ray between 50 and 400 keV, a fourth patch of phosphor dedicated to the detection of ultraviolet radiation. It is also possible to cover a label, according to the first embodiment of that invention, used for personal monitoring, wherein only one type of phosphor is present with different filters so that , e.g., on one patch of the phosphor a filter letting only Co60 radiation pass is present, on a second patch a filter letting only Ir192 radiation pass, on a third patch a filter letting only pass X-rays with energy between 50 and 400 keV, etc.
In a second embodiment of that invention, means for storing energy of penetrating radiation are means that convert the energy of absorbed penetrating radiation into electrons, these electrons being stored in an electronic memory that can repeatedly be read-out.
In EP-A 0 892 283 a personal monitor has been disclosed comprising a storage medium for absorbing incident radiation energy, wherein said storage medium comprises a storage phosphor panel capable to store radiation energy originating from radiation having a wavelength of 350 nm or less, wherein said panel is covered with an optical filter absorbing radiation having a wavelength of 350 nm or more and wherein said panel is present in a housing, being preferably provided with a shutter element to avoid exposure at those moments when it is undesirable or irrelevant. More particularly said incident radiation is therein substantially composed of UV-B and UV-A rays in the wavelength range from 250 to 350 nm and said storage phosphor panel comprises storage phosphors having a dark decay of 2 hours or more as it was an object of that invention to provide a personal monitor as an indicator making it possible to check in a quantitative way any amount of harmful (sun) rays irradiating the human skin, more in particular to provide a quantitative indicator for measuring irradiation of the human skin by (over)exposure to harmful UV-A and UV-B radiation originating from sun-rays and/or solar panels and to provide a method for quantitatively checking the amount of accumulated radiation and comparing it with radiation doses tolerable within a certain exposure time as a function of age, location on earth, skin type, protection factor of sun cream used, etc. Said personal monitor therefore further comprises a digital memory storing medium, preferably an EPROM, a bubble memory, a non-volatile RAM or a magnetic memory.
In the same Application a method to determine in a quantitative way stored amounts of radiation energy originating from radiation having a wavelength of 350 nm or less, has been described wherein said method comprises the steps of:
i) providing a personal monitor as described hereinbefore;
ii) opening the housing of said monitor thereby irradiating said storage phosphor panel covered with said optical filter by incident radiation in such a way that said panel is exposed proportionally and simultaneously with an object which is sensitive to said radiation;
iii) closing the said housing,
iv) reading out said storage phosphor panel by the steps of entering the personal monitor in a read-out apparatus, removing the optical filter covering the storage phosphor panel, adding stimulating-energy to the said storage phosphor panel, digitally detecting energy released from said storage phosphor panel by a detector; and v) erasing stored rest energy.
In that Application said stimulating energy is originated from visible light, from thermal energy or from electroluminescent energy and detecting said released energy proceeds by an optical system comprising a photomultiplier, a photodiode, a phototransistor or a gas detector. Further said optical system collimates light with optical fibres, leading it to a light detector, wherein, before entering said light detector, an optical filter is present absorbing stimulating radiation and transmitting fluorescent light.
An apparatus for readout of storage means according to the method described above is also claimed wherein said apparatus comprises a DSP(digital signal processing)-chip in order to quantitatively determine energy released by said storage means. If disadvantages of those systems are not related with costs as for systems making use of stimulable phosphors, aspects of customization as opening the housing of the personal monitor before exposure (forgetting it makes that the indicator is not exposed at all), entering the personal monitor (indicator) in a read-out apparatus, removing the optical filter covering the storage phosphor panel, etc., will form a barrier and therefore any practical customer-friendly realization, especially with respect to the housing, of a practical and inexpensive personal monitor is desired.
Therefore it is an object of the present invention to provide a practical, inexpensive and customer-friendly personal and reusable monitor in order to determine in an easy and quantitative way stored amounts of harmfull radiation energy originating from ionizing radiation.
Further objects and advantages of the present invention will become clear from the detailed description hereinafter.
The objects of the present invention are realized by providing a device for recording and storing incident radiation energy and for reading said energy comprising:
a stimulable phosphor absorbing and storing said energy and being stimulable with a wavelength xcexa,
an electroluminescent phosphor emitting, upon application of an electrical field, stimulation light with wavelength xcexa wherein said device is equipped with means in order to apply an electrical field on said electroluminescent phosphor, and wherein said stimulable phosphor and said electroluminescent phosphor are positioned relative to each other so that said light emitted by said electroluminescent phosphor reaches said stimulable phosphor for stimulating said phosphor in order to release stimulated light as a detectable signal.
Said device is thus realized as a reusable personal monitor in form of a handsome, inexpensive card providing, after reading out the captured irradiation energy, a quantitative determination of harmful threatening ionizing irradiation as will become clear from the description and of the drawings hereinafter.