ENTRY 14689 20210309 14821468900000001 SUBENT 14689001 20210309 14821468900100001 BIB 8 13 1468900100002 TITLE Production of Low Energy Neutrons by Filtering 1468900100003 through Graphite 1468900100004 AUTHOR (H.L.Anderson,E.Fermi,L.Marshall) 1468900100005 REFERENCE (J,PR,70,815,1946) 1468900100006 #doi:10.1103/physrev.70.815 1468900100007 INSTITUTE (1USACHI) 1468900100008 FACILITY (REAC,1USAANL) The graphite chain reacting pile. 1468900100009 DETECTOR (BF3) A BF3 proportional counter. 1468900100010 COMMENT Compiler's comment: 1 eV is approximately equal 11600 1468900100011 K or 1 K = 0.0862 meV. This ratio was used to convert 1468900100012 temperatures into neutron energies. Therefore, 18 K 1468900100013 neutron temperature is 1.5516 meV (0.0015516 eV). 1468900100014 HISTORY (20210309C) BP 1468900100015 ENDBIB 13 0 1468900100016 NOCOMMON 0 0 1468900100017 ENDSUBENT 16 0 1468900199999 SUBENT 14689002 20210309 14821468900200001 BIB 4 21 1468900200002 REACTION (6-C-12(N,TOT),,SIG) 1468900200003 SAMPLE Graphite, 12.96 g/cm2. 1468900200004 METHOD (TOF) Neutrons of energy much lower than thermal were 1468900200005 produced by filtering a beam of thermal neutrons 1468900200006 through a block of graphite 23 cm long. In such a 1468900200007 block, Bragg scattering removes the neutrons whose 1468900200008 wave-length is less than the largest Bragg 1468900200009 wave-length in graphite, 6.69 angstroms. Measurement 1468900200010 of the boron absorption of the filtered neutrons 1468900200011 showed that they had an effective wavelength of 7.15 1468900200012 angstroms which corresponds to neutron temperatures 1468900200013 around 18 Kelvin. The whole assembly was isolated 1468900200014 from stray thermal neutrons by the cadmium shield. A 1468900200015 cadmium plate could be inserted above the graphite 1468900200016 filter in order to measure the background. In all 1468900200017 measurements the small background observed with this 1468900200018 cadmium plate in place was always subtracted. 1468900200019 Measurements by the transmission method were made of 1468900200020 the total cross sections of a number of substances 1468900200021 with and without the 23-cm long graphite filter. 1468900200022 STATUS (TABLE) Table I, page 816. 1468900200023 ENDBIB 21 0 1468900200024 NOCOMMON 0 0 1468900200025 DATA 2 2 1468900200026 EN-DUMMY DATA 1468900200027 EV B 1468900200028 0.0253 4.05 1468900200029 0.0015516 0.70 1468900200030 ENDDATA 4 0 1468900200031 ENDSUBENT 30 0 1468900299999 SUBENT 14689003 20210309 14821468900300001 BIB 4 21 1468900300002 REACTION (4-BE-9(N,TOT),,SIG) 1468900300003 SAMPLE Be, 4.52 g/cm2. 1468900300004 METHOD (TOF) Neutrons of energy much lower than thermal were 1468900300005 produced by filtering a beam of thermal neutrons 1468900300006 through a block of graphite 23 cm long. In such a 1468900300007 block, Bragg scattering removes the neutrons whose 1468900300008 wave-length is less than the largest Bragg 1468900300009 wave-length in graphite, 6.69 angstroms. Measurement 1468900300010 of the boron absorption of the filtered neutrons 1468900300011 showed that they had an effective wavelength of 7.15 1468900300012 angstroms which corresponds to neutron temperatures 1468900300013 around 18 Kelvin. The whole assembly was isolated 1468900300014 from stray thermal neutrons by the cadmium shield. A 1468900300015 cadmium plate could be inserted above the graphite 1468900300016 filter in order to measure the background. In all 1468900300017 measurements the small background observed with this 1468900300018 cadmium plate in place was always subtracted. 1468900300019 Measurements by the transmission method were made of 1468900300020 the total cross sections of a number of substances 1468900300021 with and without the 23-cm long graphite filter. 1468900300022 STATUS (TABLE) Table I, page 816. 1468900300023 ENDBIB 21 0 1468900300024 NOCOMMON 0 0 1468900300025 DATA 2 2 1468900300026 EN-DUMMY DATA 1468900300027 EV B 1468900300028 0.0253 3.25 1468900300029 0.0015516 0.73 1468900300030 ENDDATA 4 0 1468900300031 ENDSUBENT 30 0 1468900399999 SUBENT 14689004 20210309 14821468900400001 BIB 4 21 1468900400002 REACTION (4-BE-9(N,TOT),,SIG) 1468900400003 SAMPLE Be, 9.04 g/cm2. 1468900400004 METHOD (TOF) Neutrons of energy much lower than thermal were 1468900400005 produced by filtering a beam of thermal neutrons 1468900400006 through a block of graphite 23 cm long. In such a 1468900400007 block, Bragg scattering removes the neutrons whose 1468900400008 wave-length is less than the largest Bragg 1468900400009 wave-length in graphite, 6.69 angstroms. Measurement 1468900400010 of the boron absorption of the filtered neutrons 1468900400011 showed that they had an effective wavelength of 7.15 1468900400012 angstroms which corresponds to neutron temperatures 1468900400013 around 18 Kelvin. The whole assembly was isolated 1468900400014 from stray thermal neutrons by the cadmium shield. A 1468900400015 cadmium plate could be inserted above the graphite 1468900400016 filter in order to measure the background. In all 1468900400017 measurements the small background observed with this 1468900400018 cadmium plate in place was always subtracted. 1468900400019 Measurements by the transmission method were made of 1468900400020 the total cross sections of a number of substances 1468900400021 with and without the 23-cm long graphite filter. 1468900400022 STATUS (TABLE) Table I, page 816. 1468900400023 ENDBIB 21 0 1468900400024 NOCOMMON 0 0 1468900400025 DATA 2 2 1468900400026 EN-DUMMY DATA 1468900400027 EV B 1468900400028 0.0253 2.82 1468900400029 0.0015516 0.71 1468900400030 ENDDATA 4 0 1468900400031 ENDSUBENT 30 0 1468900499999 SUBENT 14689005 20210309 14821468900500001 BIB 4 21 1468900500002 REACTION (1-H-D2O(N,TOT),,SIG) 1468900500003 SAMPLE D2O, 4.352 g/cm2. 1468900500004 METHOD (TOF) Neutrons of energy much lower than thermal were 1468900500005 produced by filtering a beam of thermal neutrons 1468900500006 through a block of graphite 23 cm long. In such a 1468900500007 block, Bragg scattering removes the neutrons whose 1468900500008 wave-length is less than the largest Bragg 1468900500009 wave-length in graphite, 6.69 angstroms. Measurement 1468900500010 of the boron absorption of the filtered neutrons 1468900500011 showed that they had an effective wavelength of 7.15 1468900500012 angstroms which corresponds to neutron temperatures 1468900500013 around 18 Kelvin. The whole assembly was isolated 1468900500014 from stray thermal neutrons by the cadmium shield. A 1468900500015 cadmium plate could be inserted above the graphite 1468900500016 filter in order to measure the background. In all 1468900500017 measurements the small background observed with this 1468900500018 cadmium plate in place was always subtracted. 1468900500019 Measurements by the transmission method were made of 1468900500020 the total cross sections of a number of substances 1468900500021 with and without the 23-cm long graphite filter. 1468900500022 STATUS (TABLE) Table I, page 816. 1468900500023 ENDBIB 21 0 1468900500024 NOCOMMON 0 0 1468900500025 DATA 2 2 1468900500026 EN-DUMMY DATA 1468900500027 EV B 1468900500028 0.0253 7.65 1468900500029 0.0015516 9.44 1468900500030 ENDDATA 4 0 1468900500031 ENDSUBENT 30 0 1468900599999 SUBENT 14689006 20210309 14821468900600001 BIB 4 16 1468900600002 REACTION (1-H-WTR(N,TOT),,SIG) 1468900600003 SAMPLE H2O, 0.455 g/cm2. 1468900600004 METHOD (TOF) Neutrons of energy much lower than thermal were 1468900600005 produced by filtering a beam of thermal neutrons 1468900600006 through a block of graphite 23 cm long. In such a 1468900600007 block, Bragg scattering removes the neutrons whose 1468900600008 wave-length is less than the largest Bragg 1468900600009 wave-length in graphite, 6.69 angstroms. Measurement 1468900600010 of the boron absorption of the filtered neutrons 1468900600011 showed that they had an effective wavelength of 7.15 1468900600012 angstroms which corresponds to neutron temperatures 1468900600013 around 18 Kelvin. The whole assembly was isolated 1468900600014 from stray thermal neutrons by the cadmium shield. A 1468900600015 cadmium plate could be inserted above the graphite 1468900600016 filter in order to measure the background. 1468900600017 STATUS (TABLE) Table I, page 816. 1468900600018 ENDBIB 16 0 1468900600019 NOCOMMON 0 0 1468900600020 DATA 2 1 1468900600021 EN-DUMMY DATA 1468900600022 EV B 1468900600023 0.0015516 85.8 1468900600024 ENDDATA 3 0 1468900600025 ENDSUBENT 24 0 1468900699999 SUBENT 14689007 20210309 14821468900700001 BIB 4 16 1468900700002 REACTION (1-H-WTR(N,TOT),,SIG) 1468900700003 SAMPLE H2O, 0.265 g/cm2. 1468900700004 METHOD (TOF) Neutrons of energy much lower than thermal were 1468900700005 produced by filtering a beam of thermal neutrons 1468900700006 through a block of graphite 23 cm long. In such a 1468900700007 block, Bragg scattering removes the neutrons whose 1468900700008 wave-length is less than the largest Bragg 1468900700009 wave-length in graphite, 6.69 angstroms. Measurement 1468900700010 of the boron absorption of the filtered neutrons 1468900700011 showed that they had an effective wavelength of 7.15 1468900700012 angstroms which corresponds to neutron temperatures 1468900700013 around 18 Kelvin. The whole assembly was isolated 1468900700014 from stray thermal neutrons by the cadmium shield. A 1468900700015 cadmium plate could be inserted above the graphite 1468900700016 filter in order to measure the background. 1468900700017 STATUS (TABLE) Table I, page 816. 1468900700018 ENDBIB 16 0 1468900700019 NOCOMMON 0 0 1468900700020 DATA 2 1 1468900700021 EN-DUMMY DATA 1468900700022 EV B 1468900700023 0.0015516 82.5 1468900700024 ENDDATA 3 0 1468900700025 ENDSUBENT 24 0 1468900799999 SUBENT 14689008 20210309 14821468900800001 BIB 4 21 1468900800002 REACTION (83-BI-209(N,TOT),,SIG) 1468900800003 SAMPLE Bi, 76.39 g/cm2. 1468900800004 METHOD (TOF) Neutrons of energy much lower than thermal were 1468900800005 produced by filtering a beam of thermal neutrons 1468900800006 through a block of graphite 23 cm long. In such a 1468900800007 block, Bragg scattering removes the neutrons whose 1468900800008 wave-length is less than the largest Bragg 1468900800009 wave-length in graphite, 6.69 angstroms. Measurement 1468900800010 of the boron absorption of the filtered neutrons 1468900800011 showed that they had an effective wavelength of 7.15 1468900800012 angstroms which corresponds to neutron temperatures 1468900800013 around 18 Kelvin. The whole assembly was isolated 1468900800014 from stray thermal neutrons by the cadmium shield. A 1468900800015 cadmium plate could be inserted above the graphite 1468900800016 filter in order to measure the background. In all 1468900800017 measurements the small background observed with this 1468900800018 cadmium plate in place was always subtracted. 1468900800019 Measurements by the transmission method were made of 1468900800020 the total cross sections of a number of substances 1468900800021 with and without the 23-cm long graphite filter. 1468900800022 STATUS (TABLE) Table I, page 816. 1468900800023 ENDBIB 21 0 1468900800024 NOCOMMON 0 0 1468900800025 DATA 2 2 1468900800026 EN-DUMMY DATA 1468900800027 EV B 1468900800028 0.0253 6.68 1468900800029 0.0015516 1.03 1468900800030 ENDDATA 4 0 1468900800031 ENDSUBENT 30 0 1468900899999 SUBENT 14689009 20210309 14821468900900001 BIB 4 21 1468900900002 REACTION (16-S-0(N,TOT),,SIG) 1468900900003 SAMPLE Crystalline, 19.91 g/cm2. 1468900900004 METHOD (TOF) Neutrons of energy much lower than thermal were 1468900900005 produced by filtering a beam of thermal neutrons 1468900900006 through a block of graphite 23 cm long. In such a 1468900900007 block, Bragg scattering removes the neutrons whose 1468900900008 wave-length is less than the largest Bragg 1468900900009 wave-length in graphite, 6.69 angstroms. Measurement 1468900900010 of the boron absorption of the filtered neutrons 1468900900011 showed that they had an effective wavelength of 7.15 1468900900012 angstroms which corresponds to neutron temperatures 1468900900013 around 18 Kelvin. The whole assembly was isolated 1468900900014 from stray thermal neutrons by the cadmium shield. A 1468900900015 cadmium plate could be inserted above the graphite 1468900900016 filter in order to measure the background. In all 1468900900017 measurements the small background observed with this 1468900900018 cadmium plate in place was always subtracted. 1468900900019 Measurements by the transmission method were made of 1468900900020 the total cross sections of a number of substances 1468900900021 with and without the 23-cm long graphite filter. 1468900900022 STATUS (TABLE) Table I, page 816. 1468900900023 ENDBIB 21 0 1468900900024 NOCOMMON 0 0 1468900900025 DATA 2 2 1468900900026 EN-DUMMY DATA 1468900900027 EV B 1468900900028 0.0253 1.66 1468900900029 0.0015516 2.89 1468900900030 ENDDATA 4 0 1468900900031 ENDSUBENT 30 0 1468900999999 SUBENT 14689010 20210309 14821468901000001 BIB 5 22 1468901000002 REACTION (16-S-0(N,TOT),,SIG) 1468901000003 SAMPLE Amorphous, 8.02 g/cm2. 1468901000004 METHOD (TOF) Neutrons of energy much lower than thermal were 1468901000005 produced by filtering a beam of thermal neutrons 1468901000006 through a block of graphite 23 cm long. In such a 1468901000007 block, Bragg scattering removes the neutrons whose 1468901000008 wave-length is less than the largest Bragg 1468901000009 wave-length in graphite, 6.69 angstroms. Measurement 1468901000010 of the boron absorption of the filtered neutrons 1468901000011 showed that they had an effective wavelength of 7.15 1468901000012 angstroms which corresponds to neutron temperatures 1468901000013 around 18 Kelvin. The whole assembly was isolated 1468901000014 from stray thermal neutrons by the cadmium shield. A 1468901000015 cadmium plate could be inserted above the graphite 1468901000016 filter in order to measure the background. In all 1468901000017 measurements the small background observed with this 1468901000018 cadmium plate in place was always subtracted. 1468901000019 Measurements by the transmission method were made of 1468901000020 the total cross sections of a number of substances 1468901000021 with and without the 23-cm long graphite filter. 1468901000022 FLAG (1.) Next day measurement. 1468901000023 STATUS (TABLE) Table I, page 816. 1468901000024 ENDBIB 22 0 1468901000025 NOCOMMON 0 0 1468901000026 DATA 3 3 1468901000027 EN-DUMMY DATA FLAG 1468901000028 EV B NO-DIM 1468901000029 0.0253 3.52 1468901000030 0.0015516 7.06 1468901000031 0.0015516 3.31 1. 1468901000032 ENDDATA 5 0 1468901000033 ENDSUBENT 32 0 1468901099999 SUBENT 14689011 20210309 14821468901100001 BIB 4 14 1468901100002 REACTION (6-C-12(N,TOT),,SIG,,TMP) 1468901100003 SAMPLE Graphite, 15.4 g/cm2. 1468901100004 METHOD To show the effects of the thermal motion of the 1468901100005 atoms in a crystal on the interference conditions, 1468901100006 the scattering cross section for graphite was studied 1468901100007 with filtered neutrons as a function of temperature 1468901100008 of the scatterer. The scatterer was heated with an 1468901100009 oxyacetylene torch and the temperature measured using 1468901100010 a thermocouple. Temperature equilibrium was not 1468901100011 perfectly established in these experiments but the 1468901100012 effect is evident. These experiments show clearly 1468901100013 that the thermal motion of the crystal atoms tends to 1468901100014 destroy the interference conditions. 1468901100015 STATUS (TABLE) Table II, page 816. 1468901100016 ENDBIB 14 0 1468901100017 COMMON 1 3 1468901100018 EN-DUMMY 1468901100019 EV 1468901100020 0.0015516 1468901100021 ENDCOMMON 3 0 1468901100022 DATA 2 5 1468901100023 TEMP DATA 1468901100024 DEG-C B 1468901100025 20.0 0.71 1468901100026 69.0 0.84 1468901100027 117.0 0.97 1468901100028 254.0 1.33 1468901100029 370.0 1.92 1468901100030 ENDDATA 7 0 1468901100031 ENDSUBENT 30 0 1468901199999 ENDENTRY 11 0 1468999999999