ENTRY L0054 19970129 0000L005400000001 SUBENT L0054001 19970129 0000L005400100001 BIB 14 66 L005400100002 INSTITUTE (1USALRL,1CANSAS,1CANTOR,3AULAML) L005400100003 REFERENCE (J,PR/C,27,1,8301) L005400100004 AUTHOR (B.L.BERMAN,J.W.JURY,J.G.WOODWORTH,R.E.PYWELL, L005400100005 K.G.MCNEILL,N.T.THOMPSON) L005400100006 TITLE Photoneutron cross sections for 16O. L005400100007 FACILITY (LINAC,1USALRL) L005400100008 INC-SOURCE (QMPH,ARAD) Positron annihilation in flight. L005400100009 Energy resolution (FWHM) ranged from about 200 keV at L005400100010 E(gamma) = 17 MeV to around 400 keV at 33 MeV. L005400100011 SAMPLE 97.3-g SiO2 sample in a thin-walled Lucite container. L005400100012 Measurements also performed with 51.3 g of metallic L005400100013 silicon in a nearly identical container and with an L005400100014 empty container. L005400100015 DETECTOR (BF3) Neutron 4pi detector, consisting of a 61-cm cube L005400100016 of paraffin containing 48 BF3 tubes arranged in four L005400100017 concentric rings of 12 tubes each. L005400100018 METHOD (EXTB,RINGR) Direct photoneutron detection. L005400100019 Ring-ratio neutron multiplicity measurement. L005400100020 ANALYSIS The oxygen yield was determined by substracting the L005400100021 yield of the silicon metal sample from that of the L005400100022 silicon dioxide sample after sample mass correction. L005400100023 After the recorded neutron events were corrected for L005400100024 pileup in the detector, the neutron backgrounds L005400100025 (annihilation target removed) were substracted for L005400100026 both the positron and electron measurements. L005400100027 Because the energy spectrum of the annihilation-plus- L005400100028 Bremsstrahlung radiation differs from that of purely L005400100029 Bremsstrahlung photons, a measured correction was L005400100030 applied to the ion-chamber (beam monitor) response to L005400100031 normalize the electron data to the positron data. L005400100032 The normalized electron data then were substracted fromL005400100033 the positron data, leaving the neutron counts which L005400100034 result only from the annihilation radiation. L005400100035 The measured sample-blank data, normalized to equal L005400100036 photon flux, were substracted from the target data to L005400100037 give the net target results. L005400100038 After a small correction for the neutron multiplicity L005400100039 in each ring, the data were corrected for the energy- L005400100040 dependent efficiency of the neutron detector using theL005400100041 ring-ratio result for each energy. L005400100042 The data were converted to photoneutron cross sections L005400100043 by applying the measured ion-chamber response per L005400100044 photon, the known number of target nuclei in the beam,L005400100045 and a small correction for the photon attenuation in L005400100046 the sample. L005400100047 A multiplicity analysis of the number of neutrons L005400100048 recordered in each beam burst allows the (gamma,n) andL005400100049 (gamma,2n) yields to be extracted simultaneously and L005400100050 independently. L005400100051 ERR-ANALYS (DATA-ERR) Statistical errors only. L005400100052 CORRECTION Corrected for: L005400100053 - pileup of counts in the detector, L005400100054 - ion-chamber response to electron and positron, L005400100055 produced radiation, L005400100056 - neutron multiplicities in each ring, L005400100057 - photon attenuation in the sample, L005400100058 - silicon and silicon dioxide sample masses. L005400100059 COMMENT Present cross section results agree with the mean of L005400100060 several previous measurements with monoenergetic L005400100061 photons, and resolve a prior discrepancy at 22.1-MeV L005400100062 peak. L005400100063 The measured average photoneutron energy is quite largeL005400100064 in the photon energy region from 26 to 28 MeV, L005400100065 signifying that ground-state transitions dominate the L005400100066 (gamma,n) cross section in this region. L005400100067 HISTORY (891207C) L005400100068 ENDBIB 66 0 L005400100069 NOCOMMON 0 0 L005400100070 ENDSUBENT 69 0 L005400199999 SUBENT L0054002 19970129 0000L005400200001 BIB 2 3 L005400200002 REACTION ((8-O-16(G,N)8-O-15,,SIG)+(8-O-16(G,N+P)7-N-14,,SIG)) L005400200003 Threshold of the reaction (gamma,n+p) is 23. MeV. L005400200004 STATUS Converted from Berman compilation. L005400200005 ENDBIB 3 0 L005400200006 NOCOMMON 0 0 L005400200007 DATA 3 65 L005400200008 EN DATA DATA-ERR L005400200009 MEV MB MB L005400200010 16.966 1.425 0.166 L005400200011 17.157 2.525 0.216 L005400200012 17.347 1.450 0.198 L005400200013 17.538 1.102 0.197 L005400200014 17.728 0.689 0.202 L005400200015 17.918 0.599 0.220 L005400200016 18.109 0.660 0.254 L005400200017 18.299 0.685 0.259 L005400200018 18.490 0.210 0.265 L005400200019 18.680 0.867 0.326 L005400200020 18.870 0.960 0.335 L005400200021 19.061 1.492 0.359 L005400200022 19.251 1.321 0.334 L005400200023 19.442 2.052 0.295 L005400200024 19.632 0.984 0.322 L005400200025 19.822 0.310 0.375 L005400200026 20.013 0.630 0.305 L005400200027 20.203 0.872 0.306 L005400200028 20.394 0.939 0.382 L005400200029 20.584 2.007 0.351 L005400200030 20.774 1.953 0.366 L005400200031 20.965 3.023 0.367 L005400200032 21.155 2.678 0.352 L005400200033 21.346 3.448 0.359 L005400200034 21.563 4.167 0.418 L005400200035 21.726 6.616 0.457 L005400200036 21.917 9.227 0.460 L005400200037 22.107 10.514 0.426 L005400200038 22.298 9.365 0.285 L005400200039 22.488 7.318 0.418 L005400200040 22.678 6.249 0.400 L005400200041 22.869 7.215 0.435 L005400200042 23.059 6.428 0.419 L005400200043 23.250 7.454 0.414 L005400200044 23.440 6.828 0.413 L005400200045 23.630 7.167 0.426 L005400200046 23.821 7.439 0.466 L005400200047 24.035 8.184 0.492 L005400200048 24.202 8.916 0.460 L005400200049 24.392 7.931 0.486 L005400200050 24.535 7.227 0.487 L005400200051 24.725 7.858 0.450 L005400200052 24.916 7.422 0.476 L005400200053 25.106 7.571 0.495 L005400200054 25.296 6.624 0.501 L005400200055 25.487 6.623 0.601 L005400200056 25.677 6.210 0.456 L005400200057 25.868 4.755 0.445 L005400200058 26.058 4.928 0.455 L005400200059 26.248 5.314 0.468 L005400200060 26.439 5.182 0.475 L005400200061 26.629 5.344 0.496 L005400200062 26.820 5.211 0.599 L005400200063 27.010 4.570 0.506 L005400200064 27.391 3.971 0.780 L005400200065 27.772 3.667 0.750 L005400200066 28.152 3.994 0.674 L005400200067 28.533 4.230 0.554 L005400200068 28.914 3.475 0.541 L005400200069 29.295 1.681 0.488 L005400200070 30.056 1.796 0.469 L005400200071 30.818 2.221 0.508 L005400200072 31.580 1.749 0.536 L005400200073 32.341 1.964 0.533 L005400200074 33.103 2.598 0.550 L005400200075 ENDDATA 67 0 L005400200076 ENDSUBENT 75 0 L005400299999 SUBENT L0054003 19970129 0000L005400300001 BIB 2 3 L005400300002 REACTION ((8-O-16(G,N)8-O-15,,INT)+(8-O-16(G,N+P)7-N-14,,INT)) L005400300003 Threshold of the reaction (gamma,n+p) is 23. MeV. L005400300004 STATUS (DEP,L0054002) Taken from text in article L005400300005 ENDBIB 3 0 L005400300006 NOCOMMON 0 0 L005400300007 DATA 4 1 L005400300008 EN-MIN EN-MAX DATA DATA-ERR L005400300009 MEV MEV MB*MEV MB*MEV L005400300010 15.7 30. 54.8 5. L005400300011 ENDDATA 3 0 L005400300012 ENDSUBENT 11 0 L005400399999 ENDENTRY 3 0 L005499999999