Abstract:
A probehead for an electron spin resonance (ESR) dosimeter comprises a resonator and an insert extending into the resonator. The insert has a guide channel for bringing a sample into the resonator. The sample comprises a dosimeter substance. The guide channel is configured for receiving and guiding a test strip. The insert is provided with a first machine-readable code imprint. The insert is provided with at least one reference sample. A pressurized air unit is provided for blowing the sample out of the resonator after completion of a measurement. The insert has an opening on an upper side of the resonator. The opening is openly accessible for manually inserting dosimeter pills thereinto. The insert, further, is provided on the upper side with a pressurized air connector. The pressurized air connector is connected to an orifice via a pressurized air channel within the insert. The orifice is located within a lower, otherwise closed bottom of the guide channel. The sample substance comprises a chromium-doped magnesium oxide (Cr:MgO). The magnesium oxide is doped with the isotope  52 Cr.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention, generally, relates to the field of electron spin resonance (ESR) dosimetry.  
           [0002]    More specifically, the invention relates to a probehead for an electron spin resonance dosimeter reader, comprising a resonator and an insert extending into the resonator having a guide channel for bringing a sample into the resonator, the sample comprising a dosimeter substance.  
           [0003]    Still more specifically, the invention relates to a probehead for an electron spin resonance dosimeter, comprising a resonator, an insert extending into the resonator having a guide channel for bringing a sample into the resonator, the sample comprising a dosimeter substance, and a pressurized air unit for blowing the sample out of the resonator after completion of a measurement.  
           [0004]    Moreover, the invention is related to a sample substance for an electron spin resonance dosimeter, comprising a chromium-doped magnesium oxide (Cr:MgO).  
         BACKGROUND OF THE INVENTION  
         [0005]    A probehead of the type of interest in the present context is disclosed in document JP 01 138 484 A.  
           [0006]    In the industrial practice, it becomes more and more customary to irradiate products of any kind. For example, various products are irradiated for disinfection purposes or for increasing their durability, respectively. A typical example is the field of hygiene articles, for example baby&#39;s diapers. During production, such diapers are packed in batches and are then irradiated batch by batch in order to put them at the customer&#39;s disposal in a germ-free condition. It is common practice to convey the articles to be irradiated batch by batch past a source of irradiation, wherein several passes may be provided in order to achieve a predetermined dose of irradiation.  
           [0007]    Further, it is a well-established practice to irradiate products and articles in order to exterminate unwanted organisms. In practice this happens for example in connection with food-stuffs, for example spices which are sometimes affected by pathogenic germs and, prior to being processed and distributed, must be treated accordingly.  
           [0008]    Still another field of application is the prophylactic irradiation of articles of many kinds in connection with the use of biologic warfare agents if, for example, pieces of mail must be treated as a precautionary measure, because it must be expected that certain pieces of mail containing pathogenic germs are mailed in connection with terrorist attacks.  
           [0009]    In all these and many other applications of irradiation, it is, however, desired to properly measure the amount of irradiation and, as the case may be, to document same. This holds true basically independent of the kind of irradiation (gamma rays, electron rays, etc.).  
           [0010]    For that purpose, corresponding measuring instruments, dosimeter substances, packaging methods for dosimeter substances and pertinent standards have been developed under the general term “dosimetry”. In the U.S., for example, the American Society for Testing and Materials has developed and published a standard E 1607-96 “Standard Practice for Use of the Alanine-EPR Dosimetry System”. Dosimetry methods are today certified by various official and other institutions. For that purpose, it is necessary to be able to follow-back measuring samples, i.e. to provide a complete documentation.  
           [0011]    Conventional dosimeters, as are used, for example, for protecting people in installations where work is done with rays of various kinds, essentially consist of a section of a normal commercial photographic film which becomes blackened under the action of an irradiation. The film sections are developed after a certain period of time has lapsed, and are then evaluated optically, wherein the amount of blackening of the film is a measure for the irradiation dose received. Such film dosimeters are still today used on a broad scale in connection with the measurement of irradiation doses in industrial irradiation processes.  
           [0012]    Film dosimeters, however, have the disadvantage that they are relatively complicated in their handling and evaluation. Further, one has found out that they are not stable over an extended period of time. A fast and reliable measurement of irradiation values is, therefore, as much impossible as a long term storage and documentation of the original dosimeters. Finally, the behavior of a photographic film in the present context does not correspond to the behavior of organic tissue being subjected to an irradiation.  
           [0013]    Therefore, conventional film dosimeters have increasingly been replaced by so-called alanine dosimeters. In this type of dosimeter, the dosimeter substance consists of alanine, i.e. an amino acid, the behavior of which, for example with respect to gamma rays, corresponds to that of organic tissue to a far more extent as is the case for conventional film dosimeters. In the art, alanine dosimeters are, therefore, referred to by the term “tissue equivalent”. Alanine, moreover, is very stable over an extended period of time, so that irradiated alanine may be again measured after a long period of time has lapsed, without any information having gone lost. Typically, doses of irradiation of interest in the present context are within the range of between 400 Gy (Gray) and 100 kGy (Kilogray).  
           [0014]    As already mentioned above in connection with a standard established in the U.S., alanine dosimeters are conventionally measured and evaluated by utilizing the technique of electron paramagnetic resonance (EPR), also referred to as electron spin resonance (ESR). This is because when alanine is irradiated, so-called “free radicals” are generated, which, in the course of an ESR measurement, show a characteristic spectrum in which the amplitude of the primary line within the spectrum is representative for the dose of irradiation.  
           [0015]    Document DE 196 37 471 C2 discloses a dosimeter substance, an alanine dosimeter as well as a method for their production. In this context it is disclosed that alanine dosimeters may be configured for utilizing pill- or film-shaped alanine elements of various geometry.  
           [0016]    Document DE 39 03 113 C2 discloses a dosimeter as used for persons working in an irradiation-protected area. Likewise, alanine pills are used as dosimeter substance. The dosimeter itself consists of a small frame-shaped assembly having a corresponding chamber for receiving the alanine pills.  
           [0017]    Document JP 02 173 589 A discloses still another dosimeter which is adapted to be evaluated by means of ESR. The dosimeter substance in that case has the shape of a strip and is applied to a small frame-shaped assembly.  
           [0018]    Document JP 01 138 484 A mentioned at the outset, discloses a probe feed apparatus for ESR dosimeters. In this prior art apparatus, rod-shaped dosimeter elements are inserted into corresponding, axially extending recesses within a rotating disc, the rotation of which is controlled by means of optical sensors. The rotating disc is located above an ESR sample chamber. By rotating the disc accordingly, various dosimeter elements may be positioned above the ESR sample chamber one after the other and may then be lowered thereinto, where they are held in a reference position by means of appropriate holding elements.  
           [0019]    Pressurized air may be fed to the sample chamber from its lower side in order to be able to blow the dosimeter element out of the sample chamber after completion of the ESR measurement.  
           [0020]    During an ESR measurement, the ESR signal is measured as an electric mistuning of a resonator housing the sample under investigation. During the resonance transition, the sample absorbs energy and, hence, the resonator, having been tuned before, becomes mistuned. For that purpose, the external magnetic field acting on the resonator is conventionally swept slowly so that depending on the sample material and the complexity of the ESR spectrum, one or more resonance lines are generated.  
           [0021]    Classical ESR spectrometry is limited in this context to the analysis of the particular appearance of the spectrum, i.e. the number, position and shape of the spectral lines which are recorded and analyzed. Although signal intensity plays a certain roll in that regard, conventional ESR spectrometers do not allow to measure signal intensity in absolute values. The reason is that the signal amplitude as an absolute value does not only depend on process parameters which may be set reproducibly, for example microwave frequency, the irradiated microwave energy, the scanning modulation amplitude, etc., but also from the type of sample, in particular its dielectric losses, the resonator tuning, the type of resonator used, etc.  
           [0022]    In contrast, ESR dosimetry requires that the signal of the sample comprising the dosimeter substance be determined absolutely, namely with an accuracy of between 1 and 2%. This is impossible with conventional ESR spectrometers.  
           [0023]    In another area of magnetic resonance, namely in the area of nuclear resonance (NMR), it is known to measure absolute signal amplitudes by concurrently measuring the sample under investigation and a so-called “standard”, for example tetramethylsilane (TMS). These “standards” may either be mixed with the sample under investigation (so-called “internal standard”), or they may be arranged separately within the probehead (so-called “external standard”), as the case may be. If the resonance behavior and, in particular, the amplitude of the reference material signal is predetermined, then the signal of the sample under investigation may be calibrated by comparing amplitudes.  
           [0024]    In the context of investigations of solids, in particular of doped solids by means of electron spin resonance, one has to a large extent also made investigations on magnesium oxide with various dotations or contaminations, respectively, for example electron spin resonance of Cr 3+  in MgO. In that context one has also investigated substances in which the chromium ions were present as the isotope  53 Cr. In that case, an isotopic spectrum with particular hyperfine structure was obtained, i.e. a structure having a plurality of spectral lines.  
           [0025]    It is, therefore, an object underlying the present invention to improve a probehead of the type specified at the outset, such that the afore-mentioned disadvantages are avoided.  
           [0026]    In particular, the invention shall make it possible to provide a probehead for an ESR dosimeter allowing a processing of irradiated dosimetry strips in a faster and safer way. In particular, it shall become possible to individually identify dosimeter strips so that a proper documentation of the measurement results is possible, as is described for certain certification processes.  
           [0027]    Still another object underlying the invention is to enable measurements of absolute values quickly and easily so that the irradiation dose may be reliably measured and documented.  
           [0028]    According to another object underlying the invention, an ESR dosimeter shall be provided allowing to process irradiated dosimeter pills quickly and safely, wherein also a manual supply of dosimeter pills to the probehead shall be possible, even by non-skilled persons.  
           [0029]    Finally, it is an object underlying the present invention to provide a sample substance of the type specified at the outset such that the afore-mentioned disadvantages are avoided.  
           [0030]    In particular, the invention shall enable to provide a reference substance for the electron spin resonance dosimetry having only one single characteristic line within the ESR spectrum having a sufficient distance from the resonance of the free electron (g=2) and the ESR behavior of which corresponding essentially to the behavior of the sample under investigation containing the dosimeter substance.  
         SUMMARY OF THE INVENTION  
         [0031]    These and other objects are achieved according to the present invention by a probehead for an electron spin resonance dosimeter, comprising a resonator, and an insert extending into the resonator and having a guide channel for bringing a sample into the resonator, the sample comprising a dosimeter substance, wherein the guide channel is configured for receiving and guiding a test strip.  
           [0032]    By guiding the test strip, the test strip will always be located at a predetermined reference position during the ESR measurement so that the measurement is made under reproducible conditions. This enables faster and safer measurements.  
           [0033]    In a preferred embodiment of the inventive probehead, the test strip consists of a carrier material, and the carrier material is coated with the dosimeter substance at least over a section thereof.  
           [0034]    This measure has the advantage that the test strip may be utilized for various functions.  
           [0035]    This holds true in particular when, according to a further embodiment of the invention, the test strip is provided with a first machine-readable code imprint.  
           [0036]    This measure has the advantage of a reliable identification of any test strip with conventional means, for example with a commercially available bar code reader.  
           [0037]    It is particularly preferred in that context when, further, the insert is provided with a second machine-readable code imprint.  
           [0038]    This measure has the advantage that not only each individual test strip may be automatically identified. Moreover, the particularly used test strip may be allocated to the particularly used insert so that the ESR measurement may be documented extensively.  
           [0039]    For that purpose, it is preferred when the code imprints are located side by side when the test strip is inserted into the guide channel, wherein the insert is configured optically transparent at least in the area of the first code imprint.  
           [0040]    This measure has the advantage that both code imprints may simultaneously be read by means of the same optical reader. Insofar, compact structures become possible.  
           [0041]    According to still another preferred embodiment of the invention, the first code imprint is readable by means of a code reader only when the test strip is in a predetermined position and in a predetermined orientation within the guide channel.  
           [0042]    For that purpose, the optically transparent area is located such that the first code imprint can be read only when the test strip is in a predetermined position and in a predetermined orientation within the guide channel.  
           [0043]    According to still another embodiment of the invention, the guide channel is provided with a stop for the test strip which can preferably be configured by the lower terminal end of the vertically extending guide channel.  
           [0044]    These measures have the advantage, that measurements may be executed extremely simply by manually feeding the insert with test strips. The user of the inventive probehead needs only to insert the test strip from above into the guide channel. When the guide channel extends vertically, the test strip will fall downwardly under the action of gravity, until it comes to rest at the stop with its lower terminal end, namely at the lower bottom of the guide channel. In any event, the test strip has then assumed its predetermined reference position within the probehead.  
           [0045]    The above approach may still further be improved as well for manual as well as for automatic operation when the guide channel is provided with an insertion assisting means for the test strip.  
           [0046]    According to further embodiments of the invention, the insert is provided with at least one reference sample, the reference sample being positioned within the insert such that it is located in the area of the section coated with the dosimeter substance, when the test strip is inserted into the guide channel.  
           [0047]    This measure has the advantage that absolute measurements on test strips become possible because the signal intensity of the dosimeter substance comprised in the measuring sample may be converted into absolute values when their signal is compared to the predetermined signal of the reference sample and an appropriate ratio is computed.  
           [0048]    Within the scope of the present invention, it is particularly preferred to use alanine as dosimeter substance.  
           [0049]    The objects underlying the invention are, further, solved by a probehead for an electron spin resonance dosimeter, comprising a resonator, and an insert extending into the resonator and having a guide channel for bringing a sample into the resonator, the sample comprising a dosimeter substance, wherein the insert is provided within a first machine-readable code imprint.  
           [0050]    If, namely, the insert is provided with a corresponding code imprint, various information may be detected during the measurement and may be stored together with the measurement result of the measuring probe. This type of information comprises, for example, information about the type, size, etc. of the particularly used insert, information about ESR spurious or base signals coming from the insert and being unavoidable to a certain extent, which signals will also be generated during the later ESR measurement but can be eliminated from the measurement on the measuring probe by appropriate computation if these spurious or based signals are known. Finally, the code imprint may provide information about a reference sample integrated into the insert.  
           [0051]    In a preferred embodiment of the invention, a code reader is associated to the first code imprint.  
           [0052]    This measure has the advantage that commercially available instruments may be used at low cost.  
           [0053]    In a further embodiment of the invention, the sample is provided with a second machine-readable code imprint.  
           [0054]    This measure has the advantage that not only characteristic values of the insert but also values of the sample itself may be read prior to the measurement and correspondingly stored. This allows a still more complete documentation of any parameters possibly influencing the measurement.  
           [0055]    The object underlying the invention is further solved by a probehead for an electron spin resonance dosimeter, comprising a resonator, and an insert extending into the resonator and having a guide channel for bringing a sample into the resonator, the sample comprising a dosimeter substance, wherein the insert is provided with at least one reference sample.  
           [0056]    By utilizing a reference sample with an ESR signal of predetermined amplitude, the absolute value for the measuring probe may be determined by comparing the ESR signal of the reference sample on the one hand and of the measuring probe comprising the dosimeter substance, on the other hand. Therefore, via measuring the reference sample, the dose of the irradiation exerted on the measuring sample may be determined with sufficient precision of, for example, 1 to 2%.  
           [0057]    In a preferred embodiment of the inventive probehead, the reference sample is positioned within the insert such that it is located in the area of the volume of the sample to be measured, when the sample is inserted into the guide channel.  
           [0058]    This measure has the advantage that the measuring conditions become reproducible because the measuring sample on the one hand and the reference sample on the other hand are located at approximately the same location within the probehead and, hence, within the resonator, so that the measuring conditions for both samples are practically identical.  
           [0059]    This holds true in particular when the guide channel extends vertically within the insert, and a stop for the sample is provided at the lower terminal end of the guide channel, and the reference sample is arranged in the area of that stop.  
           [0060]    This measure enables in particular to feed the inventive probehead with the dosimeter substance manually because it must only be inserted from above into the guide channel for then automatically falling downwardly under the action of gravity into the area of the stop. This corresponds to a precise reference position.  
           [0061]    In this context, it is further preferred when the reference sample generates an ESR signal having a spectral position distant from the ESR signal of the dosimeter substance.  
           [0062]    This measure has the advantage that both signals may be clearly separated one from the other and, hence, both signals may be evaluated without interfering with each other.  
           [0063]    It is, further, particularly preferred when the reference sample generates an ESR signal having a microwave saturation behavior corresponding to the microwave saturation behavior of the dosimeter substance. The same applies, mutatis mutandis, for the line width, i.e. the modulation saturation behavior, as well as for the temperature coefficient.  
           [0064]    All these measures have the common advantage that with a similar ESR measuring behavior, no error is generated when the measuring conditions are altered which would result in different reactions for the measuring sample on the one hand and the reference sample on the other hand, if their behavior were different.  
           [0065]    The object underlying the invention is, further, solved by a probehead for an electron spin resonance dosimeter, comprising a resonator, an insert extending into the resonator and having a guide channel for bringing a sample into the resonator, the sample comprising a dosimeter substance, and a pressurized air unit for blowing the sample out of the resonator after completion of a measurement, wherein the insert has an opening on an upper side of the resonator, the opening being openly accessible for manually inserting dosimeter pills thereinto, the insert, further, being provided on the upper side with a pressurized air connector, the pressurized air connector being connected to an orifice via a pressurized air channel within the insert, the orifice being located within a lower, otherwise closed bottom of the guide channel.  
           [0066]    With this assembly, even unskilled persons are in a position to insert irradiated dosimeter pills which are supplied to them into the openly accessible opening from which the pills are automatically, i.e. under the action of gravity, conveyed to their measurement position where they may then be measured automatically. After completion of the measurement, the measured dosimeter pills are then disposed off automatically by feeding pressurized air and may, accordingly, be guided to a collecting means in which the dosimeter pills are, for example, packed, marked and documented.  
           [0067]    As the probehead according to the present invention has all inputs, outputs and connectors located on the upper side of the resonator, the probehead may be utilized on commercially available ESR resonators, without the need of modifying the resonator or even the magnet system in which the resonator is located. Moreover, the guide- or convection system for the samples is closed in itself, so that the interior of the resonator is protected against ingression of dust.  
           [0068]    According to a preferred embodiment of the invention, the guide channel has a rectangular cross-section.  
           [0069]    This measure has the advantage that a form-fitting guide for the dosimeter pills is provided within the channel so that reproducible measuring conditions may be guaranteed.  
           [0070]    This holds true in particular when the opening is configured as a slot.  
           [0071]    This has the advantage that the dosimeter pills fed to the insert become oriented already during their insertion into the opening being openly accessible from above.  
           [0072]    According to still another improvement of the invention, the opening is arranged at a lateral distance from the guide channel, and has a transition to the guide channel via a chamfered guide means.  
           [0073]    This measure has the advantage that the opening is very well accessible laterally so that dosimeter pills may be fed manually without problems. The chamfered guide in the transition between the opening in the guide channel guarantees that the dosimeter pills will not become stuck but will safely come to their measurement position.  
           [0074]    In still another group of embodiments, the guide channel has an upper end and a transition into a blow-out channel at the upper end, in particular a 180° elbow.  
           [0075]    These measures have the advantage that the trajectory of the blown-out dosimeter pills is well-defined. Further, the flush arrangement between the guide channel and the blow-out channel has the advantage that the dosimeter pills will safely fly from the guide channel into the blow-out channel during the blowing-out.  
           [0076]    Furthermore, certain embodiments of the invention preferably provide for a reference sample located essentially at the bottom of the insert, wherein also two reference samples with distinct gyromagnetic ratios may be provided essentially at the bottom.  
           [0077]    This measure has the advantage that quantitative measurements, i.e. calibrated amplitude measurements, may be conducted on the dosimeter pills.  
           [0078]    The object is, finally, also solved by a sample substance for an electron spin resonance dosimeter, comprising a chromium-doped magnesium oxide (Cr:MgO), wherein the magnesium oxide is doped with an isotope  52 Cr.  
           [0079]    In the context of the present invention, one has, namely, surprisingly found that  52 Cr:MgO has only one single explicit ESR resonance line being sufficiently distant from g=2 and, further, having ESR properties corresponding essentially to those of the conventional dosimeter substance alanine. This relates to a comparable line width (i.e. modulation saturation behavior), a comparable microwave saturation behavior, a comparable temperature coefficient, an isotropic behavior, etc.  
           [0080]    Although the pertinent literature has already reported on ESR investigations on chromium-doped magnesium oxide, one has never found on Cr:MgO nor on  53 Cr:MgO, also described in the literature, that an ESR spectrum has one single explicit line. In contrast, one has measured an explicit hyperfine structure, i.e. the exact contrary, on  53 Cr:MgO. Moreover, it cannot be taken from the measurements described in the literature that chromium-doped magnesium oxide has similarities with alanine, i.e. an amino acid, for what concerns the ESR behavior.  
           [0081]    In a preferred embodiment of the invention, the isotope  52 Cr is used in an isotope-pure abundance (&gt;95%).  
           [0082]    Furthermore, it is preferred when the fraction of the isotope  52 Cr within the doped magnesium oxide  52 Cr:MgO is between 0.05 and 0.15%.  
           [0083]    These values have shown to be very advantageous in practice.  
           [0084]    In a nutshell, the invention comprises the use of  52 Cr:MgO as a reference substance for the electron spin resonance dosimetry.  
           [0085]    Further advantages will become apparent from the description and the enclosed drawing.  
           [0086]    It goes without saying that the afore-mentioned features and those that will be explained hereinafter, may not only be used in the particularly given combination, but also in other combinations, or alone, without leaving the scope of the present invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0087]    Embodiments of the invention are depicted in the drawing and will be described in further detail throughout the subsequent description.  
         [0088]    [0088]FIG. 1 is a perspective view on a first embodiment of an insert for an electron spin resonance (ESR) spectrometer, adapted to be used for pill-shaped alanine dosimeters;  
         [0089]    [0089]FIG. 2 shows the insert of FIG. 1, in a longitudinal sectional view;  
         [0090]    [0090]FIG. 3 shows an ESR spectrum of a first reference sample;  
         [0091]    [0091]FIG. 4 shows an ESR spectrum of a second reference sample;  
         [0092]    [0092]FIG. 5 shows an ESR spectrum comprising ESR signals of a reference sample as well as of a sample comprising a dosimeter substance;  
         [0093]    [0093]FIG. 6 is an illustration, similar to that of FIG. 1, however, for a second embodiment of an insert for an ESR spectrometer, adapted to be used for strip-shaped alanine dosimeters;  
         [0094]    [0094]FIG. 7 is an illustration, similar to that of FIG. 2, however for the embodiment of FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0095]    In FIGS. 1 and 2, reference numeral  10  as a whole indicates an insert for an electron spin resonance (ESR) spectrometer. Reference numeral  12  schematically indicates a hollow cavity resonator  12  of conventional design. In the embodiment shown, cavity resonator  12  is a rectangular cavity of the TE 102  mode of oscillation.  
         [0096]    Below a flange  14 , insert  10  comprises a lower portion  16  which, in turn, has an upper section  18  and a lower section  20 . A common axis  22  (FIG. 2) extending vertically in the mounting position of FIG. 1 defines the extension of lower portion  16  as well as an upper portion  24  extending upwardly from flange  14 .  
         [0097]    Insert  11  is introduced into cavity resonator  12  in a vertical direction until upper section  18  comes to rest on the upper side of cavity resonator  12 . In this defined position, insert  10  is affixed to cavity resonator  12  in a conventional manner. It goes without saying that this operation may be automatized, i.e. may be executed by means of a robot. Interchanging insert  10  may, hence, be made simple and reproducible.  
         [0098]    Upper portion  24  is subdivided into a vertical section  26  and a horizontal section  28  extending laterally from vertical section  26 . Vertical section  26  has a transition to a tube elbow  30  at its upper side, tube elbow  30  being a 180° elbow in the illustrated embodiment.  
         [0099]    Upper section  18  of lower portion  16  is provided with a lateral surface  32 . A bar code imprint  34  is applied to that surface  32  being preferably a plane surface. Imprint  34  cooperates with a bar code reader  36  as schematically indicated in FIG. 1 by a double arrow. Bar code reader  36  may be an external reader, however, it will also be possible to integrate bar code reader  36  into cavity resonator  12 .  
         [0100]    Bar code imprint  34  contains various information as will be explained in further detail below. In particular, it identifies the particular insert  10  with respect to its design. Further, it may contain information about unavoidable base signals generated by insert  10  during subsequent ESR measurements, in order to make it possible to eliminate such base signal from the measurement on a sample to be measured by computation. Finally, imprint  34  may provide information about a reference sample integrated in insert  10  as will also be described in further detail below. Allocation of this type of information may preferably be effected via a reference data file.  
         [0101]    In the embodiment shown in FIGS. 1 and 2, reference sample  38  is positioned at the lowermost end of lower section  20 . Reference sample  38 , for example, may be configured as a small sphere or as a pill and may be molded within a channel  39 . It is always located in an optimal relative position with respect to the sample under investigation, i.e. the measurement conditions for both samples are as much identical as possible.  
         [0102]    Insert  10  shown in FIGS. 1 and 2 is used for conducting measurements on pill-shaped measuring samples comprising a dosimeter substance. Alanine is preferably used as dosimeter substance, alanine being used in these days in standardized form for measuring irradiation doses (cf. the already abovementioned U.S. standard E 1607-96 from the American Society for Testing and Materials). Alanine pills are commercially available for that purpose. They are affixed to goods which, for the purpose of sterilization or for other purposes are exposed to an irradiation, wherein documentary evidence shall be created with respect to the irradiation dose exerted on these goods.  
         [0103]    Horizontal section  28  on the upper side of insert  10  shown in FIGS. 1 and 2 is provided with an insertion opening  40  being configured as a small vertical slot which, for example, may be provided with a chamfer as a means for assisting insertion. The width of slot  40  is dimensioned such that an alanine pill  60  may just be received by slot  40  in a vertical position. Within vertical section  26  of upper portion  24 , there is a transition from slot  40  configured as a chamfered guide  42  via which alanine pill  60  enters into a vertical narrow, i.e. flat, channel  44 . The radial cross-sectional area of channel  44  essentially corresponds to the cross-sectional area of alanine pill  60  such that alanine pill  60  is guided within channel  44  by positive engagement when it falls downwardly under the action of gravity.  
         [0104]    As indicated at  60   a  in FIG. 2, the alanine pill finally arrives at bottom  46  of channel  44 , serving at the same time as a mechanical stop and, hence, as a reference position.  
         [0105]    Insert  10 , further, may comprise means (not shown in the drawing) allowing to detect whether at the beginning of an ESR measurement there is actually only one alanine pill  60   a  in the reference position or whether there is no pill or a plurality of pills due to some malfunction. As an alternative, this may be detected from a shift of the reference frequency.  
         [0106]    In order to enable a disposal of alanine pill  60   a  via elbow  30  after the completion of the ESR measurement, a transition  47  from the flat to a round cross-sectional shape is provided, extending to an interior space  48  of elbow  30 . In that area, interior space  48  is flush with channel  44  along axis  22 .  
         [0107]    A pressurized air connector  50  is provided in the area of flange  14 . It is connected with a controllable pressurized air unit  51 . Pressurized air connector  50  is connected with an annular space  52  within flange  14 . Annular space  52 , in turn, is connected to a pressurized air channel  54  extending parallel to channel  44  into lower section  20  of lower portion  16 , down to an orifice  56  within bottom  46  of channel  44 .  
         [0108]    The apparatus is operated as follows:  
         [0109]    As already mentioned, alanine pill  60  may be inserted into insertion opening  40  or into the slot in the direction of an arrow  62 , preferably manually. Alanine pill  60  will now fall downwardly within vertical channel  44  in the direction of arrow  64 , until it reaches bottom  46  at  60   a.    
         [0110]    After the completion of the ESR measurement, the pressurized air system is activated and compressed air is guided into annular space  52  and pressurized air channel  54 , respectively. Accordingly, alanine pill  60   a  will be blown upwardly from bottom  46  in a vertical direction, as indicated by arrow  66 . It now flies along axis  22  upwardly into interior space  48  of elbow  33  and is deflected there, as indicated by arrow  68 . The alanine pill within elbow  30  is indicated at  60   b  in FIG. 2.  
         [0111]    As indicated by arrow  70 , it is then again deflected vertically downwardly and then (arrow  72 ) reaches, for example, a collecting container  74  positioned below the exit of elbow  30 . In FIG. 2 this is indicated at  60   c.    
         [0112]    Hence, the guide system for alanine pills  60  is a closed system in itself, so that the interior space of resonator  12  is protected against the intrusion of dust or abraded pill particles.  
         [0113]    As already mentioned above, the ESR measurement on alanine pill  60  is conducted for determining a dose of irradiation to which alanine pill  60  had been exposed before.  
         [0114]    In this connection it is desired that the dose of irradiation be measured with an accuracy of between 1 and 2%. This is not easily possible with conventional ESR measurements because the amplitude of an ESR signal within a broad range depends on the particular measuring conditions. Among these are not only parameters that may be set externally and reproducibly, as the microwave frequency, the microwave intensity, the modulation amplitude, the amplification factor etc., but also other parameters that may much less be set properly or reproducibly, respectively, as is the case with the properties of the particular resonator, its cooperation with the particular measuring probe, the type and the setting of the coupling between the resonator and the microwave line, etc.  
         [0115]    For that reason, insert  10  shown in FIGS. 1 and 2 utilizes a setup with reference sample  38  being utilized as an integrated standard in order to calibrate the measured ESR signal of alanine pill  60 .  
         [0116]    Considering that the dose of irradiation in today&#39;s industrial applications varies in wide ranges in practice, typically between 400 Gy and 100 kGy, reference samples  38  for various ranges of irradiation must be provided. In this context it is also possible to utilize several reference samples of distinct kind in one insert, as will be explained below in connection with FIGS. 6 and 7.  
         [0117]    As has already been mentioned, the material from which all components of insert  10  are manufactured, shall have an intrinsic ESR signal being as small as possible, so that the measurement on the sample is not superimposed by a spurious or base signal.  
         [0118]    Conventionally utilized dosimeter substances, in particular alanine, have an ESR signal in the area of a gyromagnetic ratio of g=2. The material from which insert  10  is made should, therefore, not have a measurable ESR signal in that range. This is the case, for example, for polyester when used as such material.  
         [0119]    The same applies in principle for reference sample  38 . The ESR signal of the reference sample shall be significant, however, it should have a sufficient spectral distance from the ESR signal of the dosimeter substance. Apart from that, the reference sample should as much as possible have the same ESR characteristics as the dosimeter substance, i.e. for example, have a comparable line width (i.e. modulation saturation behavior), a comparable microwave saturation behavior, a comparable temperature coefficient, an isotropic behavior, etc.  
         [0120]    According to the present invention, a chromium-doped magnesium oxide (Cr:MgO) is utilized as a reference sample. The amount of dotation is preferably 0.1%. The chromium cation Cr 3+  may be utilized in natural or in isotope clean abundance, as will be explained below.  
         [0121]    [0121]FIG. 3 illustrates an ESR spectrum of this sample material for a measurement in X-band, i.e. at a microwave frequency of about 9.8 GHz.  
         [0122]    As one may clearly see from FIG. 3, the ESR spectrum of Cr:MgO has a primary line  82  as well as a smaller secondary line  84 . Both lines are sufficiently at a distance from the gyromagnetic ratio g=2, i.e. the resonance position of a free electron.  
         [0123]    The amplitude A 1  of primary line  82 , measured from tip to tip, is about 38×10 3  arbitrary units.  
         [0124]    Within the scope of the present invention, one has now found that a considerable improvement may be achieved insofar when instead of Cr:MgO a reference sample is utilized, in which the chromium ions appear as the isotope  52 Cr. In that case, the chromium cation will be used in its isotope clean abundance (&gt;95%  52 Cr 3+ ).  
         [0125]    [0125]FIG. 4, in an analog illustration as compared to FIG. 3, the ESR spectrum  86  of  52 Cr:MgO is shown. One can see that the spectrum only comprises a primary line  88  but no secondary line. Moreoever, the signal-to-noise ratio is substantially better, as becomes apparent from an amplitude A 2  of main line  88  being equal to 2.8×10 6  arbitrary units. The amplitude ratio A 2 /A 1  is, therefore, about  74 .  
         [0126]    [0126] 52 Cr:MgO is, hence, extremely well suited as a reference sample for measurements of the kind of interest in the present context because it has only one distinct primary line  88  within ESR spectrum  86  being sufficiently at a distance from g=2 and, in relation to the amount of sample substance, has a higher amplitude.  
         [0127]    [0127]FIG. 5 now shows the dosimetry measurement as such, as may be executed with insert  10  of FIGS. 1 and 2, while utilizing a reference sample  38  according to FIGS.  4  or  5 .  
         [0128]    A third ESR spectrum  90  illustrated in FIG. 5 shows on the right hand side a primary line  92  of reference sample  38 , the amplitude of which being indicated with A 3 . Primary line  92 , again, is at a sufficient distance D from position g=2, corresponding to the center of the alanine spectrum  94  which, in turn, consists of a primary line  86  as well as to secondary lines  98   a  and  98   b  being located symmetrically thereto.  
         [0129]    For calibrating the measured alanine signal which, as already mentioned, is in turn a measure for the irradiation dose exerted on the sample, amplitude A 4  of primary line  96  is determined and is set into a relationship to predetermined amplitude A 3  of primary line  92  of reference sample  38 , being stored in bar code imprint  34 . In such a way it is, therefore, possible to calibrate the ESR signal of alanine pill  60  and, hence, determine the dose of irradiation in absolute values (Gy). Further, at this moment in time it is possible to eliminate an intrinsic signal of insert  10 , if necessary, which is also stored in bar code imprint  34 .  
         [0130]    [0130]FIGS. 6 and 7 show still another embodiment of an insert  10  for another application, namely for the use of strip-shaped alanine dosimeters.  
         [0131]    Insert  100  may be introduced in a hollow cavity resonator  101  which, again, is indicated to be a rectangular resonator. In this case, too, insert  100  is provided with a flange  102 .  
         [0132]    A lower portion  104  of insert  100  is again subdivided into an upper section  106  which, when insert  100  is introduced, comes to rest on resonator  101 , and a lower section  108 . The insert  100  may, therefore, be exchanged simply and reproducibly. In the vertical mounting position shown, insert  100  extends along a common axis  110 .  
         [0133]    An upper portion  112  extends upwardly from flange  102 .  
         [0134]    A surface  114  of upper section  106  is again provided with a bar code imprint  116  of the kind already explained.  
         [0135]    Within the upper side of upper portion  112 , there is an insertion opening or assisting means  120  extending to a vertically extending channel  122 . Channel  122 , again, is of a flat shape, i.e. is essentially rectangular in a radial cross-section. Its shape is adapted to the radial cross-section of a test strip  124  which may be introduced into channel  122  from above with the help of assisting means  120 .  
         [0136]    The length of test strip  124  is dimensioned such that when it is entirely introduced, it comes to rest on a stop  125  at a reference position at the lower terminal end of channel  122  (cf. FIG. 7), wherein it still protrudes upwardly from upper portion  112 , such that test strip  124  may be pulled out manually or automatically, after the measurement is completed.  
         [0137]    Within the area of channel  122 , test strip  124  is subdivided into a lower area  126  and an upper area  128 . Within lower area  126 , test strip  124  may be coated with a dosimeter substance, for example an alanine film.  
         [0138]    In contrast, upper area  128  is provided with still another bar code imprint which, for example, may indicate the batch number of the irradiated goods, the composition of the dosimeter substance, etc., i.e. data which are necessary for the archives, in particular in the context of a certification.  
         [0139]    If insert  100 , at least in the area of upper section  106  of lower portion  104 , is configured to be optically transparent, bar code imprint  128  may be read from the exterior. For that purpose, one can either provide a corresponding recess within surface  114  of upper section  106  or one can configure upper section  106  as a whole from a transparent material.  
         [0140]    In a preferred embodiment, first code imprint  116  may only be read by means of a code reader, when test strip  124  is in a predetermined position, i.e. in a vertical position, and in a predetermined orientation, for example front/back, within guide channel  122 .  
         [0141]    For that purpose, the optically transparent area of insert  100  may be configured such that first code imprint  116  may only be read by means of a code reader when test strip  124  is within a predetermined position and orientation within guide channel  122 .  
         [0142]    As one can clearly see from FIG. 6, bar code imprint  128  in the upper area of test strip  124  just lies side-by-side with bar code imprint  116  on upper section  106  of insert  100 , when test strip  124  is in the measuring position. Hence, in that condition one can read both bar code imprints  116  and  128  with one and the same bar code reader, as already indicated above in connection with the embodiment shown in FIG. 1.  
         [0143]    Finally, insert  100  at the lower terminal end of lower section  108  is provided with a reference sample, wherein in the embodiment shown in FIG. 7, two such reference samples  130   a  and  130   b  are provided in an optimum relative position with respect to lower area  126 . These two reference samples may have different amplitudes at different spectral position, in order to be able to use the same insert  100  for test strips  124  of different signal intensity, i.e. different dose of irradiation, for example within a range between 400 Gy and 100 kGy. One has found that in practice for covering this range of doses, two distinctly strong reference samples are sufficient.