ENTRY L0051 19970129 0000L005100000001 SUBENT L0051001 19970129 0000L005100100001 BIB 13 68 L005100100002 INSTITUTE (1USALRL) L005100100003 REFERENCE (J,PR/C,22,2273,8012) L005100100004 AUTHOR (B.L.BERMAN,D.D.FAUL,P.MEYER,D.L.OLSON) L005100100005 TITLE Photoneutron cross sections for He4. L005100100006 FACILITY (LINAC,1USALRL) L005100100007 INC-SOURCE (QMPH,ARAD) Positron annihilation in flight. L005100100008 Photon energy resolution is typical for livermore L005100100009 facility experiments. L005100100010 SAMPLE The 5.55-mole helium gas sample was contained at a L005100100011 pressure of 30.61 mpa (about 300 atm). L005100100012 DETECTOR (BF3) An efficient paraffin-and-BF3-tube neutron 4pi L005100100013 detector. L005100100014 METHOD (EXTB) L005100100015 ANALYSIS After the recorded neutron events were corrected for L005100100016 pileup in the detector, the neutron backgrounds L005100100017 (annihilation target removed) were substracted for L005100100018 both the positron and electron measurements. L005100100019 Because the energy spectrum of the annihilation-plus- L005100100020 Bremsstrahlung radiation differs from that of purely L005100100021 Bremsstrahlung photons, a measured correction was L005100100022 applied to the ion-chamber (beam monitor) response to L005100100023 normalize the electron data to the positron data. L005100100024 The normalized electron data then were substracted fromL005100100025 the positron data, leaving the neutron counts which L005100100026 result only from the annihilation radiation. L005100100027 The measured sample-blank data, normalized to equal L005100100028 photon flux, were substracted from the target data to L005100100029 give the net target results. L005100100030 After a small correction for the neutron multiplicity L005100100031 in each ring, the data were corrected for the energy- L005100100032 dependent efficiency of the neutron detector using theL005100100033 ring-ratio result for each energy. L005100100034 The data were converted to photoneutron cross sections L005100100035 by applying the measured ion-chamber response per L005100100036 photon, the known number of target nuclei in the beam L005100100037 and a small correction for the photon attenuation in L005100100038 the sample. L005100100039 A multiplicity analysis of the number of neutrons L005100100040 recordered in each beam burst allows the (gamma,n) andL005100100041 (gamma,2n) yields to be extracted simultaneously and L005100100042 independently. L005100100043 ERR-ANALYS (DATA-ERR1) Statistical errors only. L005100100044 (DATA-ERR2) There are several possible sources of L005100100045 systematic errors: L005100100046 - uncertainty in the photon flux calibration: no L005100100047 greater than 5% at 22 MeV, but rises to about 10% L005100100048 at 45 MeV. L005100100049 - uncertainty in the neutron-detector efficiency L005100100050 >3% for neutrons of 2 MeV (E(gamma) about 23 MeV), L005100100051 rising to about 5% for E(n) = 14 MeV, and, perhaps, L005100100052 to 8% for E(n) = 18 MeV (E(gamma) about 45 MeV). L005100100053 - uncertaintiy arising from the Bremsstrahlung yield L005100100054 substraction: never more than 2% of the yield, WHIC L005100100055 translates into about 10% of the cross section at L005100100056 35 MeV. L005100100057 - uncertainty arising from the sample-blank yield: L005100100058 could be as much as 15% above 42 MeV. L005100100059 The data points at 25.3, 26.3 MeV, and, perhaps, at L005100100060 28.3 MeV, have systematic uncertainties as large as L005100100061 15%. L005100100062 COMMENT Results agree with earlier monoenergetic-photon and L005100100063 certain photoneutron time-of-flight (liquid-sample) L005100100064 results at the lower energies, and consequently L005100100065 disagree with the results of other experiments at L005100100066 these energies. At the higher energies, however, the L005100100067 present results are essentially in agreement with all L005100100068 previous results. L005100100069 HISTORY (891207C) L005100100070 ENDBIB 68 0 L005100100071 COMMON 1 3 L005100100072 DATA-ERR2 L005100100073 PER-CENT L005100100074 15. L005100100075 ENDCOMMON 3 0 L005100100076 ENDSUBENT 75 0 L005100199999 SUBENT L0051002 19970129 0000L005100200001 BIB 2 3 L005100200002 REACTION ((2-HE-4(G,N)2-HE-3,,SIG)+(2-HE-4(G,N+P)1-H-2,,SIG)) L005100200003 Threshold of the reaction (gamma,n+p) is 26.1 MeV. L005100200004 STATUS Converted from Berman compilation. L005100200005 ENDBIB 3 0 L005100200006 NOCOMMON 0 0 L005100200007 DATA 3 19 L005100200008 EN DATA DATA-ERR1 L005100200009 MEV MB MB L005100200010 18.305 0.02 0.05 L005100200011 20.304 0.08 0.05 L005100200012 21.291 0.29 0.05 L005100200013 22.303 0.55 0.05 L005100200014 23.291 0.82 0.07 L005100200015 24.302 1.09 0.06 L005100200016 25.290 1.09 0.06 L005100200017 26.301 1.00 0.07 L005100200018 28.301 1.05 0.07 L005100200019 29.288 0.88 0.09 L005100200020 30.300 1.02 0.10 L005100200021 31.312 1.06 0.11 L005100200022 32.299 0.98 0.11 L005100200023 33.311 1.20 0.11 L005100200024 35.310 1.07 0.15 L005100200025 38.296 0.78 0.20 L005100200026 41.307 0.86 0.23 L005100200027 44.293 0.77 0.26 L005100200028 47.304 0.62 0.29 L005100200029 ENDDATA 21 0 L005100200030 ENDSUBENT 29 0 L005100299999 SUBENT L0051003 19970129 0000L005100300001 BIB 2 3 L005100300002 REACTION ((2-HE-4(G,N)2-HE-3,,INT)+(2-HE-4(G,N+P)1-H-2,,INT)) L005100300003 Threshold of the reaction (gamma,n+p) is 26.1 MeV. L005100300004 STATUS (DEP,L0051002) Data taken from text in article L005100300005 ENDBIB 3 0 L005100300006 NOCOMMON 0 0 L005100300007 DATA 4 2 L005100300008 EN-MIN EN-MAX DATA DATA-ERR1 L005100300009 MEV MEV MB*MEV MB*MEV L005100300010 20.6 31.4 9. 1. L005100300011 20.6 47.3 23.1 1.6 L005100300012 ENDDATA 4 0 L005100300013 ENDSUBENT 12 0 L005100399999 SUBENT L0051004 19970129 0000L005100400001 BIB 2 3 L005100400002 REACTION ((8-O-16(G,N)8-O-15,,SIG)+(8-O-16(G,N+P)7-N-14,,SIG)) L005100400003 Threshold of the reaction (gamma,n+p) is 23 MeV. L005100400004 STATUS (CURVE) Data read from curve in article L005100400005 ENDBIB 3 0 L005100400006 NOCOMMON 0 0 L005100400007 DATA 3 21 L005100400008 EN DATA DATA-ERR1 L005100400009 MEV MB MB L005100400010 15.3 .05 .05 L005100400011 17. .6 .1 L005100400012 17.1 1.1 .1 L005100400013 17.2 1.6 .1 L005100400014 17.3 1.7 .1 L005100400015 17.4 1.5 .1 L005100400016 17.5 1. .05 L005100400017 17.6 .95 .05 L005100400018 17.7 .9 .1 L005100400019 21.9 7.1 .1 L005100400020 22.1 8.05 .05 L005100400021 22.3 8.3 .1 L005100400022 22.5 7.4 .15 L005100400023 22.7 5.3 .15 L005100400024 24. 7.05 .15 L005100400025 24.1 8. .1 L005100400026 24.3 7.15 .15 L005100400027 24.5 6.2 .1 L005100400028 24.7 6. .1 L005100400029 27.3 3.8 .1 L005100400030 28.9 2.3 .1 L005100400031 ENDDATA 23 0 L005100400032 ENDSUBENT 31 0 L005100499999 ENDENTRY 4 0 L005199999999