WO1999014573A1

WO1999014573A1 - A dosimeter for sun radiation

Info

Publication number: WO1999014573A1
Application number: PCT/IL1998/000434
Authority: WO
Inventors: Ori Faran; Ezra Natan; Dmitry Lastochkin
Original assignee: Skyrad Ltd.
Priority date: 1997-09-16
Filing date: 1998-09-08
Publication date: 1999-03-25
Also published as: AU9093298A; EP1019697A1; EP1019697A4

Abstract

A dosimeter for sun radiation capable to change its original color due to a chemical reaction induced by exposure to UV radiation. The dosimeter comprises a matrix with a chemical compound distributed therein and capable to undergo the chemical reaction upon absorbing the UV radiation with an efficacy equivalent to at least 1 MED accumulated during at least 15 min of exposure.

Description

A dosimeter for sun radiation

Field of the invention

The present invention refers to an ultraviolet radiation dosimeter The ultraviolet region (UV region) is a region of the electromagnetic spectrum adjacent to the low end of the visible spectrum The UV region extends between 400-100 nm, and is divided into 3 sub regions the UVA region (400-320 nm), the UVB region (320-280 nm), and the UVC region (280-100 nm)

Of the three regions, the exposing to radiation in the UVB region is considered to be the most dangerous to human beings, since it causes several types of the must common cancer in human beings, i e skin cancer One of the types of this cancer, namely melanoma, is lethal In addition to the above, exposure to radiation in the UVB region can cause skin aging and is also harmful to eyes

Radiation in the UVA region mainly causes damage, such as photo-aging, to the skin. Radiation in the UVC region does not penetrate the ozone layer, which fortunately also blocks most of the radiation in the UVB and the UVA region In the last two decades the levels of UV radiation that reach the earth, have increased substantially due to the depletion of the ozone layer, caused by the release of various chemicals in the form of aerosols into the atmosphere

In some parts of the world the level of UV radiation has increased by 30-50%. The consequence of this process is a substantial increase in the danger of exposure to the sun's radiation It is believed, for example, that every 1% increase in the level of UV radiation, corresponds to a 4% increase in the number of skin cancer cases Indeed, according to medical statistics the number of skin cancer cases has increased by hundreds of percents in the last 20 years UV radiation induces biological effects depending on the particular wavelength of the radiation It is known to evaluate total biological or hazard weighted irradiation by multiplying the spectral irradiation at each wavelength by the biological or hazard weighted factor and then summation results of the multiplying over all the wavelengths

Biological or hazard factors are obtained from the so-called action spectrum according to Environmental health criteria 60 "Ultraviolet radiation" issued by the World Health Organization, Geneva, 1994. An action spectrum is a graph of the reciprocal of the radiant exposure required to produce the given harmful effect at each wavelength, AΑ the data in such graphs are normalized to the datum at the must efficacious wavelength. By summation of the biologically effective irradiation over the exposure period, the biologically effective radiant exposure ( efficacy in J/m²) can be calculated. The action spectrum graph for UV induced erythema was adopted worldwide by many organizations such as:

1. ACGIH (American Conference of Governmental Industrial Hygienists)

2. WHO (World Health Organization)

3. UNEP (United Nations Environment Program) 4. INIRC (International Non Ionizing Radiation Committee)

The action spectrum graph is a complex curve, obtained by statistical analysis of many research results establishing the minimum radiant exposure to the UN radiation at different wave lengths sufficient for causing erythema. The most commonly used quantity of radiation associated with the erythemal potential due to exposure to UV radiation is the number of so-called minimum erythemal doses (MED) caused by the exposure. An MED is defined as the radiant exposure of the UV radiation that produces a just noticeable erythema on previously unexposed skin. The radiant exposure to monochromatic radiation at around 300 nm with the maximum spectral efficacy, which is required for erythema corresponds to approximately 200 to 2000 J/m² efficacy, depending on the skin type.

The skin reacts to radiation by changes in the melanin content. Subsequent to the change in the melanin content reddening occurs, and then soreness and signs of sun burning appear. There exist 5 types of skin types which differ according to the color of human hair, eyes, and skin, and by their reaction to overexposure to UV radiation. The permissible time for exposure to UV radiation on a mid summer day changes from 15 minutes for skin type no.l, to about 2 hours for skin type no.5 (without using sun screen). Most people are not aware of the danger that can arise even after limited exposure to UV radiation, because the dose is accumulated during the exposing for varying periods of time in a daily life routine. The first visible sign is usually sunburn, which might only become visible after a few hours. This means that the individual becomes aware of the danger only after the damage has already been done. It should be emphasized that skin cancer might even appear years later.

Unfortunately, most people routinely do not use sun screens unless they are on the beach or a trip. Even then people usually do not use means of protection before they become exposed to the sun's radiation, and do not repeat applying sunscreen during exposure to the sun.

UV radiation level changes continuously, because of latitude, air pollution, season of year, clouds, and other factors. Therefore, it is very difficult to give accurate, reliable and timely warnings to the public about the UV radiation levels for specific location and day time. The only practical means that the public can use to defend itself is a personal dosimeter.

There is a known-in-the-art disposable dosimeter for sun radiation as per Shiseido Co.'s US patent No.4829187. This dosimeter employs a photo sensitive composition consisting of a discoloring agent, a photo activator and a UV-ray absorber. The photo activator forms free radicals by the irradiation of UV rays and the discoloring agent exhibits a color change in the visible region of a spectrum through the action of free radicals and a UV-ray absorber. The disadvantage of this dosimeter is associated with the fact that its principle of operation, and therefore the compound employed therein, is neither suitable to measure the radiation dose which is equivalent to an MED, nor is it selective to different types of the user's skin. The known dosimeter is designed in such a manner, that the amount of UV-radiation necessary for inducing the color change can be either 1-100 J/cm² or 10^"5 J/ cm². These values are far away from the magnitude of UV-radiation corresponding to an MED, which is about 20 mj/cm² for skin type no.2. Also known is a method and device for monitoring UV radiation as disclosed in Cybrandian Ltd.'s US patent No. 5117116. In the specification of this patent it is mentioned that to facilitate quantifying the minimum dose of UV radiation an individual can tolerate, the dose of UV radiation which induces reddening in the skin is referred to as the Minimum Erythemal Dose. This dosimeter employs a chemical compound capable of changing its color on being subjected to UV radiation reflected from the skin of the user. The principal disadvantage of this provision is associated with the fact that various types of skin in various conditions reflect differently and therefore cause enormous uncertainty in the determining of the actual dose of UV radiation to which the skin of an individual has been subjected irrespective of whether this dose is attributed as an MED or not. Furthermore, there is no mention in the specification of the above patent how the outside temperature might influence the performance of the chemical compound. Since for monitoring reflected radiation the dosimeter should be provided with a dedicated support means capable of directing the reflected radiation upon the chemical compound the dosimeter's construction is complicated and inconvenient to use.

There is known a sunburn dosimeter as disclosed in American Cyanamid Co.'s US patent No.3903243. The principle of operation of this dosimeter is based on comparing the color change of a test area bearing chemical compounds capable of changing their color depending on the cumulative exposure to UV radiation with a standard area. The standard area bears a chemical compound which changed its color after exposure to different predetermined quantities of sunburn radiation. Unfortunately, the chemical compounds employed in this dosimeter are not chosen depending on their sensibility to a radiation, the amount of which is equal to an MED. These compounds are chosen depending on their capability for coloration after exposure to radiation referred to arbitrary time units and assuming that there exists a linear relationship between the ultimate time of exposure and the skin type. This assumption is not correct from the medical point of view. It should also be mentioned that comparison of a test area with a standard area is inevitably subjective and therefore renders the dosimeter less accurate.

Furthermore, there is known an ultraviolet radiation dosimeter as per Trumble's US patent No.3787687. The principle of operation of this dosimeter is similar to the previously mentioned dosimeter and is based on the comparison of a standard color chart with the color of a chemical compound exposed to UV radiation. The chemical compounds employed in this dosimeter are not chosen deliberately depending on their sensitivity to an MED of radiation or to skin type. Furthermore, none of those dosimeters has the ability to keep its color unchanged after exposure to the sun radiation at temperature up to 50°C, and to revert its color only after it was kept for several hours in darkness.

Thus, one can see that despite the existence of various UV radiation dosimeters there is still a need for a new, convenient, accurate and safe dosimeter which is both capable of giving timely and unequivocal warning to the user about the amount of sun radiation to which he has been exposed and which can be used by individuals with different skin types.

In medical literature it is known that the so called "repair time" of the human skin is in the order of one day. Therefore the most essential feature of a reversible dosimeter should be its ability to revert to its original color only after it was kept in the darkness for several hours and no more then one night. None of the mentioned above prior art dosimeters have that ability.

Summary of the invention The main aim of the present invention is to provide for a new and improved dosimeter, which is simple, cheap, convenient and is suitable for daily use by individuals.

The further object of the present invention is to provide a dosimeter employing active photochromic compound which changes its color after exposure to the sun's radiation with the efficacy of at least 1 MED. The present reversible dosimeter advises the user to terminate exposure to the sun's radiation after the whole dosimeter's surface has changed its initial color to the color that appears at the border of the surface. This coloration signifies that the user has already been exposed to 1 MED radiation.

Another object of the present invention is to provide a dosimeter which is equally suitable for use by individuals with different types of skin. Still a further object of the invention is to provide a dosimeter which can be conveniently worn by the user or attached to various equipment.

Yet another object of the invention is to provide a dosimeter which in contrast to the known in the art dosimeters does not require the procedure of comparing with a reference chart. Brief description of the drawings WO^j 99^y/u14^57^/ύ3 PCT/IL98/00434

Fig. 1 shows example of an action spectra graph.

Fig. 2 shows the relative intensity of UV solar radiation versus wavelength.

Fig. 3 is a graphic illustration of solar radiation efficacy as a function of time. The graph refers to skin type No.2 and corresponds to 1 MED monochromatic radiation with wavelength 297 nm.

Figs. 4a,b,c,d,e,f show applications of the new dosimeter which can be either worn by a user or attached to various equipment.

Figs. 5a-5e show various cross-sections of the dosimeter in accordance with various embodiments thereof. Figs. 6a-6c schematically show the dynamic output (change of color)^' of the dosimeter as function of the increasing radiation dose received by the dosimeter.

Fig. 7 shows the reaction of photochemical dissociation of the carbonyl.

Fig. 8 shows the chemical formula of viologens

Fig. 9 shows the chemical reaction responsible for change of color which is governed by the electron transfer.

Fig.10 shows the chemical formula of spiropyrans and spirooxazines suitable for use in the present invention.

Fig.11 shows the chemical reaction governed by the ion mechanism responsible for change of color in spiropyrans and spirooxazines. Fig.12 shows the chemical formula of bisimidazole derivatives suitable for use in the present invention.

Fig.13 shows the chemical reaction governed by the mechanism of radical dissociation.

Detailed description of the preferred embodiments Since the device in accordance with the present invention functions as a dosimeter and not as a detector, it is very important that it be attached to the user's clothing or equipment in such a manner that it absorbs the same amount of sun radiation as that to which the user is exposed. The specific photochromic substances employed in the dosimeter of the present invention are selected in such a manner that they are sensitive to exposure to solar radiation in the UV region, but not necessarily at the wavelengths which corresponds to the peak of action spectrum as shown in fig. 1, because this wavelength band (around 300 nm) is beyond the visible spectrum in which it is desirable that the color change takes place.

On the other hand the desirable wavelength band in which the photochromic compound changes its color should not be too far from the wavelength corresponding to the action spectrum peak. This is required in order to ekminate possible mistakes associated with the extrapolation from the wavelength at which a particular photochromic compound changes its color to the wavelength corresponding to the action spectrum peak. The amount of UV radiation that can present a danger to an individual exposed to the sun's radiation is determined on the basis of existing action spectra and available data for each skin type. An average integral of the intensity of radiation vs. time is calculated from the MED efficacy-time dependence available for monochromatic radiation of 297 nm. An example of this dependency referring to skin type No. 2 is shown in fig. 3. The effective intensity of irradiation at a particular wavelength or band, to which the employed photochromic compound is sensitive is determined from the dependence of UV radiation intensity vs. wavelength. The example of this function is shown in fig. 2. This intensity is then extrapolated to the intensity of an irradiation taking place at 297 nm and at the conditions to which the user will be exposed. In laboratory conditions the color change of the dosimeter can be induced by exposing the dosimeter to a radiation dose produced by a sun simulator (type 16S, manufactured by Solar Light co.), capable of emitting up to 20 times the sun radiation intensity in the UV region. The simulator is provided with a radiation dose control means that allows to set the radiation in J/m² to the desired dose in MED. For this purpose individual samples of photochromic compounds are distributed on the surface of 1 square cm and subjected to high intensity radiation so as to induce change of color. Afterwards the samples are subjected to the sun's radiation. The reversibility of color and the influence of ambient temperature are tested both in the UV region and in full spectrum of the sun's radiation. With reference to figs 4a,b,c,d,e,f it is shown how the new reversible dosimeter, can be worn by a user as a sole independent item, i e bracelet, watch strap or medallion, or applied to a clothing, hat, footwear, equipment etc. as a garment, symbol or the like In accordance with the present invention the dosimeter comprises an active chemical compound capable to undergo photo-chemical reaction accompanied by changing of its color and an absorber. Both the chemical compound and the absorber are distributed within a polymeric matrix. The particular combination of an active chemical compound and an absorber and material of the matrix for use in the dosimeter is chosen in such a manner that the dosimeter changes color during exposure to solar radiation, the efficacy of which exceeded the individual's permissible MED corresponding to his personal skin type Provided in accordance with the invention are up to 5 types of dosimeters which can be combined, each of them capable of responding to solar radiation dose, which is corresponding to 1 MED required for a particular skin type By virtue of this provision the user can avoid damage to his sldn and/or his eyes Since the new dosimeter operates continuously irrespective of whether it is exposed either to direct or reflected sun radiation it can be appreciated that the dosimeter does not affect the user's daily activities. By virtue of this provision the public's attitude to use such a dosimeter will be more positive and thus there will also be increased awareness of the danger of exposure to UV radiation. The user can also use the dosimeter simultaneously with a sun screen by applying it to the dosimeter surface, and thus increase the permissible time of exposure to the sun's radiation.

With reference to figs. 5a-e the construction of the dosimeter will now be explained The dosimeter comprises a polymeric matrix 2. The aim of the matrix is to carry an active chemical compound therein, to reliably protect it from corrosion due to ambient humidity and to impart thereto machinability. The matrix material should be thermally stable, i.e., should not alter its opaqueness after heating up to 50 degrees C so as to retain its transparency sufficient for visualizing the variation of color of an active compound incorporated in the matrix. As an example of a suitable matrix material one can use various optically transparent materials, for example polycarbonates, polystyrenes, polyolifines, polyacrylates such as polymethylmethacrylates, polyvinyl derivatives, polyesther derivatives, polyvinyl chloride; cellulose derivatives such as cellulose acetate, polyurethanes, polyethylene terephthalate, silicone resins such as LSR (liquid silicone rubber), triethylene glycole dimethacrylate (TEGDM, commercially known as CR-39), epoxys etc. Transparent copolymers and blends of dissimilar transparent polymers are also suitable as a matrix material. Fig.5a shows the matrix within an active photochromic compound 4 distributed therein. It might be recommended to attach to the matrix a thin filter film F so as to prevent undesirable color changes induced by irradiation with wavelengths corresponding to another part of electromagnetic spectrum and thus to control the dynamics of color change. Instead of attaching the filter film the matrix may contain an UV absorbing material 6 distributed therein. The principle of choosing of the active compound in accordance with the present invention will be explained further. The UV absorber consists of a material that is capable of partially absorbing the UV radiation. By virtue of this provision it becomes possible to control the amount of accumulated radiation to which the active compound is exposed. Examples of materials suitable for use as absorbers include: 2,4-bis(2,4-dimethylphenyl)-6-(2-hydroxy-4-n-octyl-oxyphenyl)-l,3,5-triazine.

2-hydroxy-4-(N-octoxy)benzophenone. 2-(2-hydroxy-5-methyl-phenyl)-2H-benzotriazole. 2-(2H-benzotriazol-2-YL)-4,6-ditertpentylphenol. 2,2'-dihydroxy-4,4'-methoxybenzophenone. 2,2',4,4'-tetrahydroxybenzophenone.

2,2'-dihydroxy-4,4'-dimethoxybenzophenone. In practice the total thickness of the matrix layer lies between 0.25-2.5 mm. The active compound and absorbing material can be incorporated within the matrix by means of any known-in-the-art suitable method, for example by compounding or casting. The dosimeters can be manufactured by any known-in-the-art suitable method, for example by injection molding or extrusion. In practice the amount of an active compound or absorbing material within the matrix varies between 0.1 to 10 weight percent depending on the matrix material, type of an active compound and particular type of the user's skin. Fig.5b shows an embodiment of the present invention in which the active compound and absorbing material are substantially homogeneously distributed within the matrix. Fig.5c shows an alternative embodiment of the dosimeter in which the active compound is distributed in one part of the matrix, while the absorbing material is distributed in the other part thereof and there is provided a border line 8 separating there between. The direction and slope of this border line is deliberately chosen so as to create a gradient of thickness of the layer containing the absorber, i.e. a minimum thickness thereof at one lateral side 10 of the dosimeter, which gradually increases to a maximum thickness thereof at the opposite lateral side 12 of the dosimeter. It can be appreciated that the effective concentration of the active compound also varies along the same border line from being correspondingly at its maximum at the side 10 and at its minimum at the opposite side 12. By virtue of this provision it is possible to control the amount of radiation accumulated by the active compound residing in different locations within the matrix and thus to achieve dynamic response of the active compound to the radiation dose the user has been exposed to. Referring now to figs. 6a-c it can be seen that by virtue of the gradient of absorber concentration, the coloration of the active compounds takes place not simultaneously over the whole surface of the dosimeter, but initiates at the side 10 and then gradually expands towards the opposite side 12 as shown in fig. 6b until the entire surface of the dosimeter changes its color as shown in fig. 6c. It can be advantageous to add to the polymeric matrix a dye or an organic pigment in order to impart suitable initial color to the dosimeter surface which could strengthen the contrast with the color of the active material after it has been exposed to the UV radiation. The classes of the organic pigments suitable for this purpose comprise Phtalocyanine, Quinacridone, Isoindolinone, Perylene, Anthraquinone, etc.

It can readily be appreciated that by the variation of thickness of the layer containing the UV absorbing material it is possible to render the dosimeter employing the same active compound suitable for users having different skin types. Figs.5d-e show two additional embodiments of the dosimeter in which the thickness of the absorber containing layer varies.

In fig.5d the active compound is distributed in the lower portion 16 of the matrix and its concentration is homogeneous. Within the upper portion 14 of the matrix is distributed the absorbing material and there is deliberately created a gradient of thickness of this portion and thus of the effective concentration of the absorber along a border line 18. One can see that at the left side of dosimeter the active compound is separated from the upper surface exposed to UV radiation only by the transparent matrix, while at the opposite side it is separated from this surface by the matrix with the absorber distributed therein. The lower and upper layers of the matrix can be made of similar or dissimilar material and thus, one can provide even better control of the dynamic response of the active compound to the UV radiation. Fig. 5e shows the embodiment similar to that shown in fig. 5c while the gradient of thickness of the absorber containing matrix is arranged in such a manner that at the left side of the dosimeter the active compound is separated from the upper surface by the matrix with absorber and at the opposite side the active compound is separated from the upper surface solely by the matrix.

Having explained the construction of the new dosimeter it will now be explained in more detail how the chemical compounds employed therein are chosen. It has been empirically established that those photochromic compounds which satisfy the following criteria can be advantageously employed in the dosimeter according to the present invention:

1. The active compound should be capable of undergoing photochemical reactions accompanied by coloration in response to cumulative UV radiation of which the efficacy corresponds to at least 1 MED. The photochemical reaction should be accompanied by relatively slow change of the compound's color during at least 15 min (for skin type No. 1) and no longer than during several hours (for skin type No.5).

2. The compound should not change or reverse its color after it has been exposed to the sun radiation for at least 8 hours at a temperature up to 50 C.

3. The reverse reaction should take place after the dosimeter has been kept for several hours in darkness (and no more then one night). The number coloration/discoloration cycles without significant fatigue should be between 10 to 300 depending on the particular application of the dosimeter. 4. The mechanism of photochemical reaction responsible for coloration of the active compound should be at least one mechanism chosen from the group including photochemical dissociation of carbonyl group, electron transfer, formation of ions, and radical dissociation. Some non exhaustive representative examples of active photochromic compounds which satisfy the above criteria are listed below: a) Chromium hexacarbonyl for example as described in Massey, A. G.; Orgel, L. E. Nature, 4796, 1387 (1961). Presented with reference to fig. 7, the reaction of photochemical dissociation of the carbonyl, responsable of the change of color. b) Viologens derivatives, as described for example in Kamogawa, H.; Mizuno, H. J. Polym. Sci., 17, 3149 (1979). This class of compound is represented by the general formula shown in fig 8. in which Rl and R2 represent an alkyl group, an aromatic group or a carboalkoxy group and X a Halogen. The chemical reaction governed by the electron transfert is presented with reference to fig. 9. c) Spiropyrans (X = C) and Spirooxazines (X = N) derivatives are represented by the general formula shown in fig 10. In the above formula Ri , R₂, R₃ , R4, R5, 5 , 7 represent independently an alkyl group, an aromatic group, an alkoxy group, a nitro group or a halogen, Xi can represent the group CH or the heteroatom N . For example as described in Berman, E.; Fox, R. J. Am. Chem. Soc, 81, 5605 (1959). The chemical reaction governed by the formation of ions is presented with reference to fig. 11. d) Bisimidazoles derivatives for example as described in White, D. M.; Sonnenberg, j J. Org. Chem., 29, 1926 (1964). This group of compounds is represented by the general formula shown in fig 12. In the above formula R represents a phenyl group, a methylphenyl group, a methoxy phenyl group or Halogen phenyl group. Presented with reference to fig. 13, the mechanism of radical dissociation.

The present invention will now be disclosed with reference to non limiting examples 1-3 below. Example No. 1

The dosimeter is designed for skin type No. 2 and has total thickness of 1 mm. The matrix is manufactured in the form of a film by casting from the polymer solution. The lower layer of the matrix is made of PMMA and has thickness 0.5 mm. Distributed within the layer is 4 weight percent of an active photochromic material, which is Chromium-hexacarbonyl. The upper layer has thickness 0.5 mm, made of PMMA. Distributed within this upper layer is 1 weight percent of a UV absorber, which is 2-(2-hydroxy-5-methyl-phenyl)-2H-benzotriazole, The dosimeter in this example refers to an embodiment shown in fig.5c with an upper layer having gradient of thickness. The upper layer is cast separately and then attached to the matrix. The dosimeter changes its color from transparent to yellow after irradiation of 1 MED ( skin type 2). The dosimeter was irradiated by the sun during different day hours and during different seasons. The tests were calibrated by a PMA2100 data logger with a PMA2101 and PMA2102 UVB detectors manufactured by the Solar Light Co. The dosimeter's color is not influenced neither after being held in the sun or light without time limitation, or being held in darkness for at least 5-6 hours, nor at the temperature 50 deg.C. This dosimeter reverts its color 200 times without significant fatigue. Example No. 2 The dosimeter is designed for skin type No. 2 and comprises a matrix made of polystyrene. The total thickness of the dosimeter is 1.5 mm. The matrix in the form of a film is cast from the polymer solution. The lower layer of the matrix has a thickness of 1 mm and contains 3 weight percent of an active compound which is 2,2',4,4',5,5'-hexa-p-Chlorophenyl-bis-imidazole . The upper layer has a thickness of 0. 5 mm and distributed therein is 1.5 weight percent of a UV absorber, which is 2,2'-dihydroxy-4,4'-methoxybenzophenone. The dosimeter according to this example refers to an embodiment shown in fig, 5c with an upper layer having a gradient of thickness. The upper layer is cast separately and then attached to the matrix. The dosimeter changes color from transparent to purple after irradiation of 1 MED (of skin type no.2).

The dosimeter was irradiated by the sun during different hours of the day and during different seasons. The tests were calibrated by a PMA2100 data logger with a PMA2101 UVB detector manufactured by Solar Light Co. The dosimeter's color is not influenced neither after being held in the sun or light without time limitation or being held in darkness for at least 6 hours, nor at the temperature 50 deg. C. This dosimeter reverts its color 50 times without significant fatigue. Example No. 3

The dosimeter is designed for skin type No. 3 and has the total thickness 0.5 mm. The matrix in the form of a film is cast from the polymer solution. The lower layer of the matrix is made of PVA and contains 2 weight percent of an active compound which is N-Benzyl-N'-n-Propyl-4,4'-Bipyridinium dichloride . The upper layer with an absorber therein is made of PMMA. It has a maximum thickness of 0.25 mm and distributed therein is 0.25 weight percent of an UV absorber, 2-(2-hydroxy-5-methyl-phenyl)-2H-benzotriazole,. The dosimeter according to this example refers to an embodiment shown in fig. 5b with an upper layer having a gradient of thickness. This layer is cast separately and then is attached to the matrix. The dosimeter changes its color from transparent to blue after irradiation of 1 MED. The dosimeter was irradiated by the sun during different hours of the day and during different seasons. The tests were calibrated by a PMA2100 data logger with a PMA2101 UVB detector manufactured by the Solar Light Co. The dosimeter's color is not influenced neither after being held in the sun or light without time limitation, or being held in darkness for at least 6 hours, nor at the temperature 50 deg.C. This dosimeter revert its color 10 times without significant fatigue.

It should be appreciated that the present invention is not limited to the above-described embodiments and that changes and modifications can be made by one ordinarily skilled in the art without deviation from the scope of the invention, as will be defined in the appended claims.

The dosimeter of the present invention can be used for measuring the UV dose to which not only people but also to which other objects were exposed, for example, plants or animals in agriculture, various sensible equipment to be exploited at the conditions of exposure to UV radiation, etc. It should be appreciated that the features disclosed in the foregoing description, and/or in the following claims, and/or in the accompanying drawings and/or in the accompanying examples may, both separately and in any combination thereof, be material for realizing the present invention in diverse forms thereof.

Claims

Claims;

1. A dosimeter for sun radiation comprising a matrix with at least one active chemical compound distributed therein, capable of changing its original color to a new color due to a chemical reaction induced by exposure to UV radiation, said matrix being made of a material having transparency sufficient for visual detection the change of the original compound's color to the new color, said matrix containing at least one absorbing compound capable of absorbing the UV radiation, said active chemical compound being capable of changing its color after exposure to UV radiation with an efficacy equivalent to at least 1 MED, said UV radiation being accumulated during at least 15 min of exposure.

2. The dosimeter as defined in claim 1, in which said active chemical compound retains its new color during exposure to sun radiation at temperatures up to 50 deg.C, or during exposure to visible light and reverts to its original color only after it has been kept in darkness during 6-10 hours.

3. The dosimeter as defined in claim 2, in which said active chemical compound is capable to change its original color due to said chemical reaction and to revert to its original color at least 10 times without loosing his ability to undergo said chemical reaction.

4. The dosimeter as defined in claim 1, in which said matrix is made of an optically transparent polymeric material chosen from the group comprising polycarbonates, polystyrenes, polyolifines; polyacrylates such as polymethylmethacrylates, polyvinyl derivatives, polyesther derivatives, polyvinyl chloride; and cellulose derivatives such as cellulose acetate, polyurethanes, polyethylene terephthalate, silicone resins, triethylene glycole dimethacrylate, epoxy resins etc. taken alone or in any combination thereof.

5. The dosimeter as defined in claim 2, in which said compound or mixture of capable of absorbing the UV radiation is chosen from the group comprising:

2,4-bis(2,4-dimethylphenyl)-6-(2-hydroxy-4-n-octyl-oxyphenyl)-l,3,5-triazine, 2-hydroxy-4-(N-octoxy)benzophenone,

2-(2-hydroxy-5-methyl-phenyl)-2H-benzotriazole, 2-(2H-benzotriazol-2-YL)-4,6-ditertpentylphenol, 2,2'-dihydroxy-4-methoxybenzophenone. 2,2',4,4'-tetrahydroxybenzophenone. 2,2'-dihydroxy-4,4'-dimethoxybenzophenone. taken alone or in any combination thereof.

6. The dosimeter as defined in claim 1, in which said matrix is formed as a thin layer having thickness of 0.25-5 mm, the amount of said active chemical compound within said matrix layer being 0.1-10 weight percents.

7. The dosimeter as defined in claim 4, in which said matrix is provided with an opaque covering layer capable of preventing the premature exposure of the active chemical compound before the dosimeter is put in use, said covering layer being removable before the dosimeter is put in use.

8. The dosimeter as defined in claim 3, in which said active chemical compound and said absorbing compound are homogeneously distributed within said matrix.

9. The dosimeter as defined in claim 3, in which said absorbing compound is distributed within the matrix so as to create therein an effective gradient of concentration of the absorbing compound, said gradient of concentration being directed from one lateral side of the dosimeter to the opposite lateral side thereof.

10. The dosimeter as defined in claim 3, in which said active chemical compound is distributed within the matrix so as to create therein an effective gradient of concentration of the active compound, said gradient being opposite to the gradient of concentration of said absorbing material.

11. The dosimeter as defined in claim 3, in which said active chemical compound is homogeneously distributed in the lower portion of the matrix and said absorbing compound is distributed within the upper portion of the matrix.

12. The dosimeter as defined in claim 1, in which said chemical reaction is governed by the mechanism chosen from the group comprising photochemical dissociation of carbonyl group, electron transfer, formation of ions, and radical dissociation.

13. The dosimeter as defined in claim 11, in which said active chemical compound is at least one compound chosen from the group comprising Chromium hexacarbonyl, Viologens derivatives, spiropyrans and spirooxazines derivatives, Bis-Imidazoles and bis-pyrroles derivatives