Partridge, Bruce

Stokes, R. A.

Wilkinson, David T.

English

Haverford College: Haverford Scholarship

Haverford College Haverford Scholarship Faculty Publications Astronomy 1967 New Measurements of the Cosmic Microwave Background at lambda=3.2 cm and lambda=1.58 cm -- Evidence in Support of Blackbody Spectrum R. A. Stokes David T. Wilkinson Bruce Partridge Haverford College, bpartrid@haverford.edu Follow this and additional works at: https://scholarship.haverford.edu/astronomy_facpubs Repository Citation (with R. A. Stokes and D. T. Wilkinson) New Measurements of the Cosmic Microwave Background at l = 3.2 cm and l = 1.58 cm—Evidence in Support of a Blackbody Spectrum, Physical Review Letters, Vol. 19, No. 20, 1199, November (1967). This Journal Article is brought to you for free and open access by the Astronomy at Haverford Scholarship. It has been accepted for inclusion in Faculty Publications by an authorized administrator of Haverford Scholarship. For more information, please contact nmedeiro@haverford.edu. Haverford CollegeHaverford ScholarshipFaculty Publications Astronomy1967New Measurements of the Cosmic MicrowaveBackground at lambda=3.2 cm and lambda=1.58cm -- Evidence in Support of Blackbody SpectrumR. A. StokesR. Bruce PartridgeHaverford CollegeDavid T. WilkinsonFollow this and additional works at: http://scholarship.haverford.edu/astronomy_facpubsThis Journal Article is brought to you for free and open access by the Astronomy at Haverford Scholarship. It has been accepted for inclusion in FacultyPublications by an authorized administrator of Haverford Scholarship. For more information, please contact nmedeiro@haverford.edu.Repository Citation(with R. A. Stokes and D. T. Wilkinson) New Measurements of the Cosmic Microwave Background at l = 3.2 cm and l = 1.58cm—Evidence in Support of a Blackbody Spectrum, Physical Review Letters, Vol. 19, No. 20, 1199, November (1967).VQLUME 19,NUMBER 20 PHYSICAL REVIEW LETTERS 13 NOVEMBER 1967NEW MEASUREMENTS OF THE COSMIC MICROWAVE BACKGROUND AT A. = 3.2 cmAND A. = 1.58 cm-EVIDENCE IN SUPPORT OF A BLACKBODY SPECTRUM*R. A. Stokes, R. B. Partridge, and David T. WilkinsontPalmer Physical Laboratory, Princeton University, Princeton, New Jersey(Received 18 September 1967)In an effort to delineate the spectrum of the cosmic blackbody radiation, we havemade more accurate measurements of the intensity at wavelengths of 8.2 and 1.58 cm.The results, combined with that at A, =8.56 mm reported in the preceding Letter, indi-cate that over this wavelength range the spectrum is that of a black body at 2.68 0'&4 K.In particular, a hot greybody spectrum does not fit the results.Dicke et al. ' have suggested that the recent-ly discovered cosmic microwave backgroundradiation' is the remnant radiation from thebig-bang fireball. ~ The decisive tests of thisidea are to measure the spectrum and the iso-tropy of the radiation: The spectrum shouldbe that of a black body and the radiation shouldbe nearly isotropic. Measurements made atPrinceton last year indicate a high degree ofisotropy ', we report here, and in the preced-ing Letter, ' precision measurements of themicrowave background intensity at A. =3.2 cm,A. =l.58 cm, and A. =8.56 mm. The results in-dicate that the radiation is that of a 2.7'K blackbody.To be convinced that one is seeing true black-body radiation, and not that of a hot grey body,it is necessary to go to short wavelengths andlook for the curvature in the spectrum due toquantum effects. The approach which we havetaken is to modify conventional microwave ra-diometer techniques to make absolute measure-ments and to observe from the ground. Themain limitation in pursuing short wavelengthsis atmospheric radiation, which generally in-creases rapidly for wavelengths less than A.= 2 cm. To reduce the atmospheric background,the observations reported here and in Ref. 5were made from an altitude of 12470 ft at theBarcroft facility of the White Mountain ResearchStation, Bishop, California.The technique used in these measurementsis described in the preceding Letter. The op-timum horn antennas were designed to giveabout the same beam width (10 dB down at -4')as that of the 8.56-mm radiometer, so thatthe same reflector could be used in all threemeasurements. All three instruments alsoused the same cold load as a reference source.Since the longer-wavelength antennas neces-sarily have larger apertures, it was necessaryto break the horns at a point in the taper wherethe horn diameter matched the diameter of thecold-load pipe. Then the reference measure-ment was made by removing the large end ofthe horn and coupling the cold load to the smallend. Measurements of the sky were made byreplacing the cold load with the flare whichcompleted the optimum horn. Otherwise, theradiometers are similar to the one sketchedin Fig. 1 of Ref. 5.The results of the 3.2-cm measurements areshown in Table I. Column 3 shows the observedchange in radiometer output when the cold loadreplaces the sky as the radiation source. Col-umn 4 lists the values obtained for the atmo-spheric radiation. Typically, the atmospher-ic temperature is 3'K at sea level for 3.2-cmwavelength. The fifth column shows the con-tribution to cold-load radiation due to reflec-tions from the imperfect absorber. The cold-load absorber was improved after each of thefirst two runs.From other measurements' at 3.2-cm wave-length it was determined that the cold-loadwall emitted at a radiation temperature TWALL=0.16+0.10'K, the aluminum reflector emit-ted at TREF1,=0.08+0.06'K, and the Styrofoamwindow at the top of the cold-load pipe emittedat TgqNDp~ = 0.06 + 0.02'K. Combining thesewith the temperature of boiling helium, THe=3.77'K, we getHe WALL WINDOW REFL= 3.91+0.13 K.Included in the error in Eq. (1) is a possibleerror of +0.02'K due to uncertainties in thebeam angles actually used to measure TA M,and an error of +0.04'K to account for possi-ble deviations of the atmospheric-temperaturemeasurements from the calculated dependenceon zenith angle. Equation (1) is added to theresults of each run in Table I, according to1199VOLUME 19, NUMBER 20 PHYSICAL REVIEW LETTERS 13 NovEMBER 1967Table I. Results of all runs made with the 3.2-mm radiometer.a bAi)prox+ T - T('K)bATM('z)bCLH('x)cB(('z)7/»/ 77/19/o77/2z/677/~3/077/~&/:77/~7/&78/xx/678/11/a78/Zg/678/19/o716:3004:0005:3005:0013:0003:00Oo:3003:0009:304.85 + 0.104.17 + 0.094.06 + 0.056.33 + 0.095.54 + 0.035.32 + 0.024.38 + 0.074.45 + 0.066.19 + 0.106.20 + 0.205.71 + 0.255 75 + 0 155.78 + 0.257.36 + 0.257.08 + 0.256.28 + 0.'076.30 + 0.106.18 + 0.157.68 + 0.257.48 + 0.150 + 0.010 + 0.010 + 0.010 + 0.010 + 0.010 + 0.013 132.412 ~ 272.962.453.030 + 0.01 2.070 + 0.01 2.140 + 0.01 2.500 + 0.01 2.710.260.380.330.260.321.000.530.430.260.26'Declination =- 37 30 ' .".rrors are standard. deviations in the mean, or limit of drift, whichever is larger.Not yet corrected. to thermodynamic ".emyerature.69+0.xe K st ~ 3 2 cmBG ' -0.21 (2)At this wavelength the correction to thermo-dynamic temperature is negligible.The results of the 1.58-cm runs are shownin Table II. The run made on 1 August 1967has been assigned zero weight, primarily be-cause the result is 10 standard deviations fromthe mean. The data indicated that some sys-tematic change took place within the instrumentor in the atmosphere while the TS~-TCL se-ries was in progress.From other measurements at A. =1.58 cm,it was found that TWAI I,=0.21+0.08'K, TREFI,= 0.15+ 0.05'K, and TWINDOW = 0 04 + 0'01 KThus,He WALL WINDOW REFL= 3.87+ 0.11'K. (3)Eq. (3) in Ref. 5, to obtain the values for thebackground temperature in column 6. The weightassigned to each run is derived from the sta-tistical errors in columns 3, 4, and 5. A weight-ed average of the results gives TBG = 2.69+0.09'K,where the error is the weighted standard de-viation in the mean. This statistical errorand the error in Eq. (1) are combined to givea total statistical error of +0.16'K. Includinga possible systematic error of -0.05'K to al-low for beam spilling around the reflector,we get a final result ofFor completeness we list the result from Ref. 5:=2.56 0'~~'K at X =8.56 mm. (5)In Fig. 1 the three results are shown on aplot of monochromatic brightness versus wave-length. Shown also is the spectrum of a 2.7'Kblack body, ' it peaks at about A. = 2 mm. Sincethe above results are in substantial agreementwith EBG=2.7'K, they fit this curve quite well.On this plot the spectrum of a hot grey bodyis a straight line of slope = -2. The dashedline is a greybody spectrum which has beenfitted to the two longer wavelength points. Thisline misses the 8.56-mm result by 2& standarddeviations. We believe that this is good evi-The error includes +0.05'K from uncertaintyin tipping angles and +0.04'K from possibledeviation of tip results from the calculatedtipping law. A weighted average of the valuesin col~m~ 6 gives TBG = 2.79+0.04'K, wherethe error is the weighted standard deviationin the mean. Combining this statistical errorwith the error in Eq. (3) gives a total statisti-cal error of +0.12'K. Adding the possible sys-tematic error of -0.15'K due to beam spill,we get a final error of +0",7 K. A correctionof —0.01'K is made to convert to thermodynam-ic temperature, and the final result is=2.78~0 ~7'K at A. =1.58 cm.1200VOLUME 19,NUMBER 20 P 8YSI CAL RK VI K%' LETTERS 1$ NOVEMBER 1967Table II. The results of all runs made with the 1.58-cm radiometer.7/io/677/18/677/22/677/za/677/&5/677/26/678/z. /678/xz/678/26/678/26/678/27/67aApprox oH. A.18:3005.3023;00j 7:30Q5 e3019.0006:3019:3006:3023 3002:00'bSKY CL( K)1.71 + 0.052.31 + Q. l52.00 + 0.034.07 + 0.08$.49 + 0.053.09 + 0.114.91 + 0.133.66 + 0.071.96 + o.162.91 + 0.132.92 + 0.13ATM('K)2 .83 + o .062 .87 + o .7o339+ 03o4.86 + 0.084.96 + 0.394.25 + 0.464.75 + o.l54.73 + Q. ll3.05 + 0.604.12 + 0.064..13 + 0.07CLH('z)0.03 + 0.010.03 + 0.010.02 + 0.010.02 + 0.010.02 + 0.010.02 + 0,010, 02 + 0.010.03 + 0.010.03 + 0.01Q. Q3 + 0.010.03 + 0.01CBG('K)2.782.503.102.422 734.052.832.812.692.691.000.140.710.270.21Qd,0.630.160.600.57Declination = 37 30'.Errors are standard. deviations in the mean, or limits of drift, , whichever is larger.Not yet corrected. to thermodynamic temperature.W~eight assignecl on basis of large @aviation from mean of' T for this run.dence for spectrum curvature, and argues strong-ly against a hot greybody source.If one adopts the view that the cosmic micro-wave background radiation has a blackbodyspectrum, the above results can be combinedto give an accurate value for the temperature.Averaging the three numbers gives 2.68'K,with a standard deviation of +0.09'K. Addingin the possible systematic error of —0.05'K,common to all measurements, we get a result ofCOV)-ls~BIOI- gs'IhO4PNX EOg EhIO 16OHOT GREYBODY 2.7 KBLACK BODYTE MP.52 cm 2 69 2~ 'K+.l6 oL58 cm 2.78 '1g K.856 c m 2.56+' K—.22This result falls within the error limits of allof the radiometer results' reported to date.We would like to thank Dr. Nello Pace forallowing us to use the facilities of the WhiteMountain Research Station. We are gratefulto Dr. Duane Blume, Mr. Bob Delker, and thestation staff for many services rendered dur-ing our visit. Mr. A. A. Mondelli built and test-ed the 3.2-cm radiometer as part of his seniorthesis work. Finally, we are indebted to Dr.N. J. Woolf for pointing out that the correctionfor atmospheric absorption of the backgroundradiation is contained in our measurement ofTATM and does not need to be made separately.5.0I I2.0 I.OWAVE! ENGTH (cm)I0.5FIG. 1. The results of the measurements reportedin this and the preceding Letter.*Research supported in part by the National ScienceFoundation and by the U. S. Office of Naval Research.)Alfred P. Sloan Foundation Fellow.R. H. Dicke, P. J. E. Peebles, P. G. Roll, and D. T.Wilkinson, Astrophys. J. 142, 414 (1965).2A. A. Penzias and R. W. Wilson, Astrophys. J. 142,VoLUME 19, NUMBER 20 PHYSICAL REVIEW LETTERS 13 NOVEMBER 1967419 (1965); P. G. Roll and David T. Wilkinson, Phys.Rev. Letters 16, 405 (1966); George B. Field and JohnL. Hitchcock, Phys. Rev. Letters 16, 817 (1966);Patrick Thaddeus and John F. Clauser, Phys. Rev. Let-ters 16, 819 (1966); T. F. Howell and J. R. Shakeshaft,Nature 210, 1318 (1966); W. J. Welch, S. Keachie,D. D. Thornton, and G. Wrixon, Phys. Rev. Letters 18,1068 (1967).3R. A. Alpher, H. A. Bethe, and G. Gamo~, Phys.Rev. 73, 803 (1948); R. A. Alpher, Phys. Rev. 74,1577 (1948); G. Gamow, Phys. Rev. 74, 505 (1948);R. A. Alpher and R. C. Herman, Nature 162, 774 (1948);G. Gamow, in Vistas in Astronom+, edited by A. Beers(Pergamon Press, New York, 1956), Vol. 2, p. 1726.4R. B. Partridge and David T. Wilkinson, Phys. Rev.Letters 18, 557 (1967).5David T. Wilkinson, preceding Letter [Phys. Rev.Letters 19, 1195 (1967)].EXPERIMENTAL TEST OF ELECTRON-SCATTERING SUM RULES FOR CARBON*fW. L. Faissler, f. F. M. Pipkin, and K. C. StanfieldCyclotron Laboratory, Harvard University, Cambridge, Massachusetts(Received 17 August 1967)The cross section far scattering of electrons off carbon has been measured at labora-tory angles of 3.3, 6', and 12' for incident energies of 1 to 5 GeV. The measuredcross sections are in good agreement vrith the sum rules describing this process.In an experiment at the Cambridge ElectronAccelerator we have measured the electron-scattering cross section of carbon for incidentelectron energies between 1 and 5 GeV andat labora. tory angles of 3.3', 6', a~d 12'. Thepurpose of the experiment was to determinethe elastic and inelastic carbon form factorsso that one could unambiguously analyze thequantum-electrodynamics experiments performedusing carbon targets. The results of this ex-periment agree with the sum rules for electron-carbon scattering.A half-quadrupole spectrometer was employedto determine the momentum of the electrons.The electrons were identified by a fourfoldscintillation counter telescope, a thresholdgas Cerenkov counter, and a lead-scintillatorshower counter. The acceptance of the systemwas calculated using a ray tracing programand checked by measuring the known hydrogencross section. The carbon targets used were1.1 or 2.2 g/cm' thick. The electron beam wasmonitored with a Faraday cup whose calibra-tion was known to +2 %.For each incident energy and scattering an-gle, the energy spectrum of the scattered elec-trons was measured from well above the elas-tic peak to a point well below the elastic peak.The data, points were corrected for target-outrates ("7 /p), random coincidences (-1 '%%up)& dead-time loss (-8 /p), Cerenkov and shower count-er inefficiency (-0.4%), and pion contamination(-0.15%). The statistical error on most of thedata points was 1% or less and is totally neg-ligible when compared with the uncertaintiesin the corrections.The energy resolution of the apparatus wasinsufficient to resolve the elastic scattering,the inelastic scattering involving nuclear ex-citation, and the quasielastic scattering fromprotons and neutrons in the carbon nucleus.1.0—0,8—0.7—W,0.5—0.4—0.3—0.2—O.I—0.005 O. I 1.0q' IN F10.0 IOOFIG. 1. Experimental and theoretical form factorsversus the four-momentum transfer squared. Drellis an evaluation of the sum rule due to Drell andSchwartz, Elastic is the elastic scattering form fac-tor, Levels is the sum of the inelastic scattering withnuclear level excitation form factors, Quasi is thequasielastic scattering form factor, Sum is the sumof Elastic, Levels, and Quasi. The experimental data,are shown as points.1202

New Measurements of the Cosmic Microwave Background at lambda=3.2 cm and lambda=1.58 cm -- Evidence in Support of Blackbody Spectrum

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New Measurements of the Cosmic Microwave Background at lambda=3.2 cm and lambda=1.58 cm -- Evidence in Support of Blackbody Spectrum

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