Method and Apparatus for Detecting Counterfeit Articles

1. Field of the Invention:

The present invention is directed to a method and apparatus for authenticating legitimate articles and for detecting counterfeit articles. More particularly, the present application is directed to a method and apparatus for authenticating a legitimate article and detecting a counterfeit article in which the legitimate article has a label which includes an isotope which is enriched to a predetermined amount. The label is subjected to gamma radiation and the radiation is measured with the source of radiation being stationary and then with the source of radiation being vibrated. The measurements are then compared in order to determine the authenticity of the article.

2. Description of the Prior Art:

As a result of technology advances in copying techniques and reproduction techniques, many articles are becoming very vulnerable to being counterfeited. This problem is becoming particularly acute in items such as credit cards, video tapes, cassette tapes, designer fashion accessories and clothing. In addition, an even more serious problem is occurring with regard to the counterfeiting of currency and other financial paper. A related problem is the unauthorized use of a financial item, such as a credit card, registered security or identity document.

Many techniques have been developed for labeling articles to prevent counterfeiting or fraudulent use. Techniques such as holograms on credit cards and magnetic coding on various articles have been in use for some time. These prior art techniques have been less than fully effective either because the counterfeiters have found ways to duplicate the label, or the apparatus for detecting the label and verifying its authenticity, has been too expensive to be utilized in the quantities necessary for preventing counterfeiting.

It is the primary object of the present invention to provide a method and apparatus for determining whether an article is authentic.

It is another object of the present invention to provide a method and apparatus for determining if an article is authentic in which a label for the article is inexpensive to manufacture, and the apparatus for detecting the label is relatively inexpensive.

It is another object of the present invention to provide a label for an article for the purposes of authenticating the article when the label is invisible and will in no way interfere with the text, logo, or design of the article, and wherein the label cannot be transferred from one article to another without destroying the usefulness of the label.

It is another object of the present invention to provide a label which not only determines the authenticity of the article, but which also carries additional stored data. A suitable apparatus for either reading or confirming this data is a further object of this invention.

The present invention is directed to a counterfeit detecting apparatus for detecting the authenticity of an article having a label containing an isotope of a chemical element enriched to a predetermined amount. The apparatus comprises a housing, a source of gamma radiation positioned in the housing, and a gamma radiation detector positioned in the housing for detecting the radiation from the source. The gamma radiation source is selected to emit radiation which can stimulate a selected nuclear transition in the label material in the known manner of the Mossbauer effect. Structure is provided in the housing for receiving the article and positioning at least a portion of the article in the housing such that the label is positioned between the source and the detector. A vibrating member vibrates the source such that the frequency of the gamma radiation therefrom is shifted. A calculating device, such as a microprocessor, is coupled to the detector for calculating the ratio of the number of gamma rays counted by the detector during a predetermined period of time when the article is not in position near the receiving member (N.sub.O) to the number of the gamma rays counted by the detector during a period of time equal to the predetermined period when the article is positioned near the receiving member (N.sub.R), and for calculating the ratio of the number of gamma rays counted by the detector during the period of time when the article is not in position near the receiving member (N.sub.O) to the number of gamma rays counted during a period of time equal to the predetermined period when the source is vibrated by the vibrating device (N.sub.E) and for calculating the ratio (N.sub.R /N.sub.O)/(N.sub.E /N.sub.O) and thus N.sub.R /N.sub.E. An output device provides an output indicating whether or not N.sub.R /N.sub.E and N.sub.E /N.sub.O are within a predetermined range.

The present invention is also directed to a method of reading a label on an article where the label includes an isotope of a chemical element enriched by a predetermined amount. The method comprises steps of counting the number of gamma rays received from a source of gamma rays by a gamma ray detector during a predetermined period of time (N.sub.O) and then placing the article between the source of gamma radiation and the gamma radiation detector. The gamma rays received by the detector are counted for a period of time equal to the predetermined period of time (N.sub.R) and then a relative vibrating movement is established between the source and the detector. The gamma rays received by the detector are again counted for a period of time equal to the predetermined period of time while there is relative vibrating movement between the source and the detector (N.sub.E). The ratios N.sub.R /N.sub.O, N.sub.E /N.sub.O, and N.sub.R /N.sub.E are calculated, and then an indication is provided as to whether the ratio N.sub.R /N.sub.E and N.sub.E /N.sub.O are within one of several predetermined ranges.

Also, the present invention is directed to an article capable of being authenticated, in which the article comprises a non-metallic body and a label fixed to the body. The label includes an isotope of a chemical element enriched to a predetermined amount.

FIG. 1A is a graph showing the gamma ray absorption spectrum of the label of the present invention.

FIG. 1B is a graph showing the gamma ray spectrum of the source of the present invention.

FIG. 2 illustrates a credit card incorporating a label of the present invention.

FIG. 3 is a block diagram of the apparatus of the present invention.

The present invention is based upon the principal that one can measure nuclear resonant absorption (known as the Mossbauer effect) relative to standard electronic absorption with a material having an element enriched with an isotope capable of resonantly absorbing gamma rays. While the electronic absorption of gamma rays determines the amount of a given chemical element in the sample, the nuclear absorption determines the amount of a particular isotope in the sample. There is no way to simulate the relative absorption N.sub.R /N.sub.E for a given N.sub.E /N.sub.O, that is the ratio of nuclear plus electronic to electronic absorption in the sample, without the use of an enriched isotope material. Thus the ratio N.sub.R /N.sub.E for chemical elements is different for a material enriched in one of its isotopes than it would be for the natural unenriched material. Further, a given ratio obtained using an enriched material cannot be duplicated using an unenriched material or a material enriched in a different amount.

In the present invention, a label containing the enriched material is positioned between a suitable source which admits a substantially single energy gamma ray, i.e., a gamma ray spectrum of extremely well defined energy or frequency, and a suitable gamma ray detector. Electronic absorption plus nuclear absorption (N.sub.R) is measured by measuring the decrease in the number of gamma ray photons reaching the detector when the label is positioned between the source and the detector as compared with the number of gamma ray photons reaching the detector from the source in the absence of the label (N.sub.O) for the same time interval. Electronic absorption (N.sub.E) is then measured by displacing the energy of the gamma ray from the energy of the gamma ray resonance in the label. This is accomplished by vibrating the source in order to create a Doppler shift in the gamma radiation. See G. K. Wertheim, "Mossbauer Effect, Principles and Applications", Academic Press, New York and London, 1964.

Referring to FIGS. 1A and 1B, FIG. 1A shows the number of counts of gamma rays absorbed as a function of frequency or photon energy level by the enriched isotope in the label. As can be seen at frequency R, absorption is the greatest since the absorption is both electronic absorption and nuclear absorption. The area in which there is electronic absorption and nuclear absorption is a relatively narrow frequency range. FIG. 1B shows the number of gamma rays generated by the source as a function of frequency. As can be seen, the gamma rays are generated at a particular resonant frequency. The isotopes selected for use with the present invention have a very narrow resonant frequency range. When the source is vibrated there is a Doppler shift of the resonant frequency. As can be seen in comparing FIGS. 1A and 1B, the Doppler shift of the source moves the frequency of the gamma rays outside of the range of nuclear absorption of the label. Thus, when the gamma rays from the source undergo the Doppler shift, there is no nuclear absorption of the photons by the label and the number of counts is significantly higher.

By way of example, the present invention will be described for use with a credit card made of a plastic material. However, the label of the present invention can also be used in paper articles such as currency, passports, financial documents, identifying labels, etc. The material for the label will include a particular isotope enriched over its natural abundance in a material such as a metal oxide of the element. The enriched material is prepared as a uniform suspension in a plastic sheet such as lucite or polyvinyl chloride, or as a suspension in printing ink. A typical label will be approximately 1 cm.times.1 cm.times.0.025 cm and the label will contain typically about 6 milligrams of the particular enriched isotope. Referring to FIG. 2, the label is sealed into the credit card 1 in such a way that no strongly absorbing material interfers with the passage of gamma rays through the card and the internally sealed label 3. No metal tabs should be sealed into the card at the location of the label and the label should probably not be positioned in an area where there is embossing since the variable thickness of the embossed area could influence the measurements. Also, the label should be positioned in an area away from the magnetic tape which is used in some credit cards. Ideally the position of the label would be in the center of the card so that the card can be inserted into the detection device in any orientation. However, as the position of the label cannot be detected without use of the detection apparatus described here, the position itself can be one form of imbedded data.

The enriched isotopes to be used in the labels could, for example be iron-57 (.sup.57 Fe), europium-151 (.sup.151 Eu), and tin-119 (.sup.119 Sn) as absorbers. These are all stable, non-radioactive isotopes which pose no health or environmental risk if they are introduced widely into credit cards which will be held on the person of each cardholder. In conjunction with the enriched isotopes used in the label, a corresponding gamma ray source for these isotopes is used as the gamma ray source in the detector apparatus. In particular, the isotopes are cobalt-57 (.sup.57 Co), samarium-151 (.sup.151 Sm), and tin-119-metastable (.sup.119m Sn), respectively. The level of radioactivity of these sources is at a low enough level so that with the shielding provided by the encapsulation of the source itself, and with the metallic housing of a closed chamber containing the detection apparatus, the radioactivity of these devices would be at a level below of that of natural radioactive sources and therefore, well within government mandated standards for the introduction of radioactive substances into general circulation.

One example of absorber for a label and a source is .sup.151 Eu as the absorber and .sup.151 Sm as the source. The .sup.151 Eu would be enriched above its natural abundance level (47.8%) to make it impossible for a counterfeiter to introduce his own labels made with natural europium. The precise level of enrichment above the 47.8% is not critical, but the greater the enrichment, the larger will be the difference in the signal as compared with the unenriched material and the faster and/or cheaper will be the detection. The europium could be used in an oxide form, such as Eu.sub.2 O.sub.3, which is the chemical form in which it is usually furnished. The .sup.151 Sm used as the source is available inexpensively as a fission-fragment. The source and absorber should be of the same composition, i.e., Sm.sub.2 O.sub.3 and Eu.sub.2 O.sub.3. Other chemical forms are also possible.

The samarium oxide .sup.151 Sm.sub.2 O.sub.3 is a fission product available at an activity level of about 25 Curies/gm. The half-life for the source is 90 years so that its decay would not require source replacement in the detection apparatus during the useful lifetime of the apparatus. .sup.151 Sm decays to .sup.151 Eu by beta decay with the emission of an electron. Only about 0.06% of the nuclear decays involve the emission of a gamma ray. The gamma ray energy is 21.7 keV. Only the gamma ray escapes the sealed encapsulation of the source with the decay electron being absorbed in the source window, and thus, the source poses no hazard to the user. A 5 mg sample of .sup.151 Sm.sub.2 O.sub.3 (total activity 125 mCi) will emit 2.25.times.10.sup.6 gamma ray photons/sec. Self absorption in the source will be about 50%. The fraction of all photons leaving the source which will fall in the gamma ray detector will be about 10% of the total leaving the source. This is because the detector only subtends about 0.4.pi. steradians of source solid angle. Absorption by the sample itself will be about 30% of the photons passing through it. The effective efficiency of the detector after introducing an energy filtering window will be about 60%. Thus the average number of gamma ray photons falling on the detector per second will be about 5.times.10.sup.4 photons/sec. In a 10 second counting time, the accuracy in the recorded number of counts will then be 0.15% according to well known rules of statistics which govern radioactive decays. Should the credit card have higher absorption, or the source have weaker intensity such that the counting rate is reduced to only 10.sup.4 photons/sec, the accuracy of the measurement will be reduced by 0.30%. This accuracy would also be achieved if the counting time were reduced to 2 seconds.

The counterfeit detection apparatus of the present invention is described with reference to FIG. 3. The credit card 1 with label 3 is positioned between a detector 11 and gamma ray source 13 through a slot in the housing of the apparatus. The detection apparatus can include a switch 15 which is turned on by the insertion of the credit card 1, or alternatively, a manual or automatic type of switch can be used to turn on the apparatus. The detector 11 is a gamma ray counting device comprising a scintillation crystal mounted on a photomultiplier tube. The crystal could typical be sodium-iodide NaI(T1). Gamma ray counting devices of this type are commercially available. High voltage power supply 17 is used to energize the photomultiplier in the detector 11. The output of the detector 11 is applied through amplifier 19 to a single channel analyzer 21. The single channel analyzer 21 accumulates only the counts corresponding to the energy of the gamma ray from the source. The device functions as an energy window for the detection of gamma rays, thus reducing interference from background radiation and other sources of stray photomultiplier pulses. The output of the single channel analyzer is applied to scaler 23 which counts the number of pulses from the single channel analyzer in the predetermined time intervals. The output of the scaler is applied to memory and control device 25. The memory in control device 25 stores the accumulated counts during the three stages of measurement. The device is capable of performing the numerical operations such as adding, subtracting, and dividing the numerical counts to compare numbers and to make logical decisions and includes a clock for counting predetermined periods of time. Furthermore, the device controls the sequence of operations of the detector. The output of the memory in control device 25 is applied to an indicator 27 which provides an indication as to whether the credit card is authentic or not.

The gamma ray source 13 is physically connected to the moving core of a loudspeaker coil 29 such as shown in G. K. Wertheim, page 22. The loudspeaker coil vibrates the gamma ray source at the AC line frequency of 50-60 Hz for a predetermined period of time during the measurement process. This vibration causes Doppler shifts in the frequency or energy level of the emitted gamma rays. This shift causes the gamma radiation to shift from the resonant frequency of the enriched isotope in label 3. In other words, the vibration of the gamma ray source 13 by the loudspeaker coil 29, detunes the source away from the nuclear resonance of the .sup.151 Eu in the label.

In performing the method of the present invention, as for example with a credit card to test the authenticity of the credit card, the number of photons reaching the detector is counted for a predetermined period of time, e.g., 10 seconds. The card containing a label composed of Eu.sub.2 O.sub.3 is then introduced into a slit in the detector enclosure, such as a metal box. The card is positioned between the radioactive source Sm.sub.2 O.sub.3 and the detector NaI(T1). The number of photons reaching the detector (N.sub.R) is counted for the predetermined period of time of 10 seconds. The source is then vibrated by the loudspeaker at a velocity of 3 cm/sec peak velocity at a frequency of 50 Hz with an amplitude of 0.1 mm, and the number of photons reaching the detector (N.sub.E) in 10 seconds is counted. The memory in control circuit 25 then compares both N.sub.R and N.sub.E with N.sub.O, the number of photons reaching the detector without the label in place. This number, N.sub.O, has been stored in the memory from a count during 10 seconds prior to inserting the card to be tested.

The electronic circuitry in device 25 calculates the ratios N.sub.E /N.sub.O and N.sub.R /N.sub.O. The ratio N.sub.E /N.sub.O expresses the reduction of gamma rays due to the electronic absorption and thus measures the quantity of europium and other chemicals in the label. The second ratio, N.sub.R /N.sub.O, expresses the fractional reduction of gamma radiation due to both electronic absorption and nuclear resonant absorption (i.e., the Mossbauer effect). The ratio N.sub.R /N.sub.E expresses the reduction due to pure nuclear absorption. For a predetermined total amount of europium (expressed by N.sub.E /N.sub.O), this value will depend upon the degree of enrichment of the .sup.151 Eu isotope in the material used in the label. There is no way for a given value of this ratio to be obtained using only natural europium, which contains two isotopes .sup.151 Eu and .sup.153 Eu.

As an illustrative example, a credit card having a label which includes .sup.151 Eu.sub.2 O.sub.3 is enriched to 95%. In the apparatus, N.sub.O equals 400,000. With a sample of 5 mg/cm.sup.2 of .sup.151 Eu.sub.2 O.sub.3 sealed into polyvinyl chloride of 0.05 cm thickness, the ratio N.sub.E /N.sub.O equals 0.730.+-.0.002, and the ratio N.sub.R /N.sub.O equals 0.6931.+-.0.002, and thus N.sub.R /N.sub.E equals 0.950.+-.0.002. A label such as that produced by a counterfeiter using natural unenriched europium would have the same N.sub.E /N.sub.O for the same amount of europium, however, N.sub.R /N.sub.O equals 0.712.+-.0.002 such that N.sub.R /N.sub.E equals 0.975.+-.0.002. The control device 25 and indicator 27 are programmed to pass a card with ratios N.sub.E /N.sub.O and N.sub.R /N.sub.O within predetermined ranges of the calibrated values for enriched europium in the label, say below 0.960. Thus, the ratio N.sub.R /N.sub.E in the counterfeit card would not fall within the predetermined range passed by the control device and indicator. Of course with no label on the card at all, the detector would find N.sub.R /N.sub.E =1, which is also ouside of the acceptable range.

In addition to the above example, labels with varying degrees of europium enrichment can be used, for example 60%, 72%, and 84%. In these cases, the ratio N.sub.R /N.sub.E would be 0.968.+-.0.002, 0.962.+-.0.002, and 0.956.+-.0.002 respectively. Using a plurality of labels of different enrichments, the detector device could be used to yield additional information. For example, a particular percentage of enrichment could indicate the year of issue of the credit card, or the color of eyes or hair of the card holder. Furthermore, combinations of labels of different enrichments could provide coded data depending upon the particular label and its position relative to the other labels. This arrangement would be similar to a coded bar arrangement in a sequential scan.

The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are, therefore, to be embraced therein.