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1910J F Clauser and A Shimony3-xOILU Cw1;-8-6-L-2-5676 8A73 SI 5161 fi63 P2IpL358a 1017 fi2537 fiFigure 6.in good agreement with inequality (5.6) but in sharp disagreement with the quantummechanicalprediction. Since this result is very surprising, Holt and Pipkin tookgreat care to check possible sources of systematic error: the contamination of the sourceby isotopes with non-zero nuclear spin, perturbation by external magnetic or electricfields, coherent multiple scattering of the photons (radiation trapping), polarisationsensitivity of the photomultipliers, and spurious counts from residual radioactivityand/or cosmic rays, etc.One such systematic error was found in the form of stresses in the walls of thePyrex bulb used to contain the electron gun and mercury vapour. Estimates of theoptical activity of these walls were then made, and the results were corrected correspondingly.(The values presented above include this correction.) It is noteworthy,however, that only the retardation sum for both windows was measured, for lightentering the cell from one side and exiting through the opposite side. On the otherhand, in the present experiment in which light exits from both windows, the relevantquantitj is the retardation difference.It is also noteworthy that in the subsequent experiment by Clauser (95.3.3), acorrelation was first measured which agreed with the results of Ilolt and Pipkin.Stresses were then found in one lens which were due to an improper mounting.(These were too feeble to be detected by a simple visual check using crossed Polaroids.)The stresses were removed, the experiment was re-performed, and excellent agreementwith quantum mechanics was then obtained. On the other hand, IIolt and Pipkin didnot repeat their experiment when they discovered the stresses in their bulb.
Bell's theorem : experimental tests and implications 191 1A second criticism is that Holt and Pipkin took the solid-angle limit to be thatimposed by a field stop placed outside the collimating lenses. It is possible that lensaberrations may have allowed a larger solid angle than they recognised. A ray-tracingcalculation was in fact performed to assure that this was not the case. However, a solidstop ahead of the lens would have given one greater confidence that this did not, infact, occur.5.3.3. Experiment by Clauser (1976). Clauser (1976) repeated the experiment of Holtand Pipkin, using the same cascade and same excitation mechanism, though with asource consisting mainly of the zero-spin isotope 202Hg. (The depolarisation effectdue to some residual non-zero nuclear spin isotopes was calculated, using some resultsof Fry (1973)) Pile-of-plates polarisers were used with transmittances := 0.965 €ml= 0.011 = 0.972 = 0.008and the half-angle 6 taken to be 18.6". The quantum-mechanical prediction is:[R(3~/8)/Ro -R(T/8)/&]QM= 0.2841.The experimental result, from 412 h of integration, is :[R(3~/8)/& - R(~/8)/Ro]expt = 0,2885 & 0.0093in excellent agreement with the quantum-mechanical prediction, but in sharp disagreementwith inequality (5.6).5.3.4. Experiment by Fry and Thompson (1976). Fry and Thompson (1976) observedthe 4358 A and 2537 A photon pairs emitted by the 73S1+63P1+61So cascade in thezero nuclear-spin isotope ZOOHg. Their experiment is shown schematically in figure 7.Figure 7. Schematic diagram of the experimental arrangement of Fry and Thompson.Polariser plate arrangement is also indicated. Actual polarisers have 14 plates.A, Hg oven; B, solenoid electron gun; C, RCA 8575; D, 4358 A filter; E, 5461 Alaser beam; F, Amperex 56 DUVP/03; G, 2537 A filter; H, focusing lens; I, pileof-platespolariser; J, laser beam trap; K, atomic beam defining slit; L, lightcollecting lens; M, crystal polariser; N, RCA 8850 (figure after Fry and Thompson).
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