Sorption sheet for sorbing a plurality of discrete samples and method of producing such a sorption sheet and use thereof
TECHNICAL FIELD 
     The invention relates to a sorption sheet for sorbing a plurality of discrete samples that simultaneously emit photons or beta particles, the emission thereof to be individually monitored, and a method of producing such a sorption sheet and use thereof. 
     BACKGROUND ART 
     Such a sorption sheet is known, e.g. from U.S. Pat. No. 4,298,796. The sorption sheet or support layer according to that patent comprises a filter mat of nitro-cellulose or glass fibre for supporting a plurality of beta particle emitting samples. This sheet is to be contacted with a scintillant to convert the beta particles into photons to be detected by means of a photodetector. 
     In use of this known sorption sheet radioactivity from one sample may diffuse towards an adjacent sample. Moreover, when the photodetector is monitoring a certain sample, photons from adjacent samples may strike the photodetector and cause an inaccuracy of measurement. This effect is normally called &#34;optical cross-talk&#34;. 
     DISCLOSURE OF INVENTION 
     The object of the invention is to prevent migration or diffusion of the samples into adjacent sample locations and to prevent optical cross-talk between samples when monitored. 
     This is attained in that barriers of a photon and/or beta particle attenuating material extend through at least a portion of the thickness of the sheet which is known per se, to prevent cross-talk between the samples when monitored. 
    
    
     BRIEF DESCRIPTION OF DRAWING 
     The invention will be described more in detail below with reference to the drawing on which 
     FIGS. 1 and 2 show two different embodiments of the sorption sheet according to the invention. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1 and 2 show two different embodiments of a microporous sorption sheet 1 according to the invention for sorbing a plurality of discrete samples (not shown) that simultaneously emit photons or beta particles, the emission thereof to be individually monitored. The sorption sheet as such is known per se and may be made of glass fibre, nylon, nitrocellulose or other polymers. To prevent cross-talk between samples upon monitoring on the one hand and confine each sample to a restricted area on the sheet 1 in order to prevent migration or diffusion of the samples into adjacent sample areas on the other hand, the sorption sheet 1 according to the invention is provided with barriers that extend through at least a portion of the thickness of the sheet. The barriers may extend essentially through the thickness of the sheet. 
     In FIG. 1 these barriers are denoted 2, while in FIG. 2 these barriers are denoted 3. 
     As apparent the barriers 2 in FIG. 1 form a grid pattern, while the barriers 3 in FIG. 2 are annular. In both cases the samples (not shown) will be sorbed on the sorption sheet 1 according to a matrix pattern with e.g. 8 columns as shown and 12 rows. 
     To produce the barriers 2 and 3 a liquid photon and/or beta particle attenuating material, e.g. black ink or resin, is soaked through at least a portion of the thickness of the sheet in the pattern of lines shown, whereupon that material is dried and/or cured to form the barriers 2 and 3, respectively, within the sheet 1. The barriers 2 and 3 according to the invention also prevent migration or diffusion of the samples (not shown). 
     Alternatively, the photon and/or beta particle attenuating material may be a powder which is fused on the sheet. 
     When the samples to be sorbed emit weak beta particles and are to be contacted with a scintillant to cause an indirect emission of photons, the barriers 2 and 3, respectively, may be discontinuous in order for the scintillant to better penetrate the sheet 1. 
     The sorption sheet according to the invention may equally well be used for sorbing samples that directly emit photons, e.g. samples that are luminescent.