Instituts-Seminar II. Physikalisches Institut, Universität Gießen 11. Januar PDF

Instituts-Seminar II. Physikalisches Institut, Universität Gießen 11. Januar 2012 Beta-delayed neutron emission evaluation for reactor physics and astrophysics Dr. B. Pfeiffer II. Physik. Institut, Justus-Liebig-Universität,

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Instituts-Seminar II. Physikalisches Institut, Universität Gießen 11. Januar 2012 Beta-delayed neutron emission evaluation for reactor physics and astrophysics Dr. B. Pfeiffer II. Physik. Institut, Justus-Liebig-Universität, Gießen GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt Do we need a new evaluation? Can it be done under the auspices of the IAEA? GSI contributions to data bases At GSI, many installations are studying nuclear structure. The measured quantities are of interest for different fields ranging from basic science to technical applications. A (personally biased) example are the ground-state masses of atoms. In 2008, European nuclear physics institutions instigated an effort to intensify their participation in the international task of establishing ``Reference Data Libraries for Nuclear Applications'' ``Reference Data Libraries for Nuclear Applications -- ENSDF''; Report of Technical Meeting of IAEA Nuclear Data Section INDC(NDS)-0543, November 2008, Vienna At FRS, decay properties of neutron-rich nuclei are studied. The half-lives can be measured following the β-decays. For nuclei far from stability, quite complicated decay chains can result. An alternative technique observes the β-delayed neutron activity with, in general, less complex decay chains. Browsing the literature, we could not find a recent evaluation of this decay mode. In addition, all evaluations up till now were restricted to fission products. 2 Discovery of fission Already in the first year after the discovery of fission (O. Hahn, F. Straßmann, Die Naturwissenschaften 27, 11 (1939)), it was observed that the fission products have an asymmetric mass distribution ( Kamelhöckerkurve ); more than 1 prompt neutron is emitted per fission event (H. Halban, F. Joliot, L. Kowarski, F. Perrin: J. de phys. et rad. 10, 428 (1939); and Nature 143, 470, 680, 939 (1939); L. Szilard, W. Zinn, Phys.Rev. 55, 799 (1939)), opening the way to chain reactions; delayed neutrons are emitted for 1 ½ min (R.B. Roberts, R.C. Meyer, P. Wang, Phys.Rev. 55, 510 (1939; R.B. Roberts, L.R. Hofstad, R.C. Meyer, P. Wang, Phys.Rev. 55, 664 (1939)), neutrons allowing to control the chain reactions in a nuclear reactor; thermal neutrons fission 235 U (A.O. Nier, E.T. Booth, J.R. Dunning, A.V. Grosse, Phys.Rev. 57, 546 (1940)). 3 Ewald s double-focusing spectrograph A.O. Nier had used a mass spectrometer to separate the Uranium isotopes and irradiated them with neutrons. At the same time, Ewald had joined the group of Mattauch at the Kaiser-Wilhelm-Inst. I could not find a contribution of the Mattauch group to the study of the fission process. Heinz Ewald Heinz Ewald designed a double-focusing mass spectrograph at the Kaiser-Wilhelm- Institut in the years It accompanied him in all his career and ended at the II. Physikalisches Institut in Gießen. There I saw it as a young student in a dark cellar. Now it is displayed more openly. 4 Proposal of Ewald for an isotope separator 1942 Prof. Ewald was involved with the Uranverein. I could find only one mention. Recently, R. Karlsch put forward the hypothesis that the German scientists had made substantial progress on the way to the atomic bomb. In Ewald/Hintenberger is shown a proposal for an isotope separator by Ewald 1942 (see Fig. right). In M. Walker German National Socialism and the Quest for Nuclear Power is reported, that M. von Ardenne picked-up the idea and constructed a prototype in his laboratory. Prof. Schmidt-Rohr presumes that Ardenne built also a fullfledged separator with the Forschungsanstalt der Deutschen Reichspost in a circular bunker near Bad Saarow south of Berlin, as this bunker corresponds to the one constructed for a cyclotron at Miersdorf. 5 Beta-delayed particle emission A necessary condition for β-delayed particle emission is that the Q-value is superior to the binding energy of the last particle, either a neutron or a proton. With increasing distance to the valley of stability, Q-values increase and separation energies decrease. So, in general, the nuclides undergoing delayed emission are situated away from stability and have quite low half-lives. Historically, such nuclides could nearly exclusively be obtained as products of neutron-induced fission. Interestingly, the most intense source for neutrons are nuclear reactors. And for the control of a reactor, β-delayed neutrons are playing an essential role. Therefore, β-delayed neutrons were studied intensively. 6 New developments But although many groups in many countries dedicated much effort in the study of delayed emitters among fission products, there exist elements for which not a single P n value has been reported (see Fig. on next slide). They are mainly situated in the region of symmetric fission with low yields and/or are refractory elements not suited for ion sources. New developments The data on delayed neutrons collected for reactor applications are now applied in totally different fields (partly by the same scientists), as e.g. calculations of the nucleosynthesis in explosive stellar environments. Due to the extremely high neutron fluxes, the properties of very neutron-rich isotopes must be obtained. With the advent of radioactive beam facilities, short-lived neutron- (and proton-) rich nuclides can now be produced for all elements. The past compilations/evaluations comprised mainly fission products, the new developments necessitate also new evaluations. very recent article: B. Pritychenko; rxiv: Stellar Nucleosynthesis Nuclear Data Mining 7 Overview NUBASE11 8 Chain-reaction assemblies For atomic bombs, reactor and decay heat applications, data on the several hundred individual precursors are not imperitavely needed. Aggregate or group data are sufficient and have been measured partly with daring and perilous installations as the fast reactors of the GODIVA type. The first drop-installation The Dragon had already been built by O.R. Frisch end of 1944 at Los Alamos. The time-dependance of delayed-neutrons after short irradiations with fast neutrons had been studied, p.e. F. de Hoffmann et al., Delayed Neutrons from U-235 After Short Irradiation Phys.Rev. 74, 1330 (1948). LADY GODIVA D.Loaiza et al., Measurement of Absolute Delayed Neutron Yield and Group Constants in the Fast Fission of U-235 and NP-237 Nucl.Sci.Eng. 128, 270 (1998) John Collier (ca. 1898) 9 The Keepin Groups For reactor applications, the decay-curve of the delayed neutrons can be approximated according to Keepin with a sum of 6 exponential functions, which depend on a few nuclides with high fission yields. Table 2. Parameters of the delayed-neutron groups for three fissile nuclei i Possible precursor nuclei Mean energy (MeV) Average half-life of the precursor nuclei (s) Delayed-neutron fraction (%) 235 U 239 Pu 233 U 235 U 239 Pu 233 U 1 87 Br, 142 Cs I, 88 Br I, 89 Br, (93,94) Rb I, (93,94) Kr 143 Xe, (90,92) Br I, 145 Cs (Br, Rb, As etc) Total Ke67 Phys.Rev. 107, 1044 (1957) G.R.Keepin, T.F.Wimett, R.K.Zeigler Delayed Neutrons from Fissionable Isotopes of Uranium, Plutonium, and Thorium 10 TRIGA-reactor Mainz For reactor technology, time dependent neutron spectra of the Keepin groups are sought for. Such measurements had also been performed at the TRIGA reactor in Mainz. This pulsed reactor had been chosen by Strassmann as it can produce short-lived fission products. (see, e.g. 1984STZT Inst.fur Kernchemie, Univ.Mainz, Jahresbericht 1983, p.79 (1984) B.Steinmuller, H.Gabelmann, K.-L.Kratz Das Gruppenspektrum β-verzogerter Neutronen der 22-s-Komponente aus der Spaltung von 235U mit Thermischen Neutronen NUCLEAR REACTIONS 235U(n, F), E=thermal; measured fission fragment β-delayed neutron emission probability. K.-L. Kratz, B. Steinmüller, H. Gabelmann, Jahrestagung Kerntechnik, Aachen 1986 The Mainz results have been taken into account in Los Alamos. But what about the many (civilian) data bases? 11 Ankauf des Mainzer TRIGA-Reaktors Frederic de Hoffmann, who had worked on delayed neutrons at Los Alamos Phys.Rev. 72, 567 (1947); Phys.Rev. 74, 1330 (1948) later founded in California General Atomic. One of their products is the TRIGA research reactor. Atomminister Siegfried Balke Günter Herrmann Frederic de Hoffmann Fritz Straßmann 12 At the on-line separator at the high-flux reactor in Grenoble, nuclear structure was studied by the II. Phys. Inst. in close internatonal collaboration. One of the main research topics was the β-delayed neutron emission of shortlived fission products. The Mainz-group continued their work, especially with the neutron spectrometers. 13 Data on β-delayed neutrons are of vital interest for reactor technology, decay heat calculations, weapons safeguard. Therefore, since a long time, the UN agency for atomic energy IAEA (founded in 1957) is engaged in collecting, evaluating and disseminating information relevant to nuclear energy. Eisenhower at UNO 8. Dezember 1953 Examples are conferences and consultants meetings: G. Rudstam, in Proceedings, 2nd IAEA Advisory Group Meeting on Fission Product Nuclear Data, Petten, The Netherlands (Sept. 5-9, 1977), Vol. II, p. 567 G. Rudstam, in Proceedings, Consultants Meeting on Delayed Neutron Properties, Vienna, Austria (Mar , 1979), IAEA Report INDC NDS-107/G + Special (1979), p. 69 K.-L. Kratz, ibid., p Compilations / evaluations for β-decay properties Data on β-decay properties are sought for in many applications. In all laboratories one finds a Nuclear Wallet Card. There exist a multitude of compilations for special properties as well as more general overviews, as the long series of Table of the Isotopes. The internationally accepted standard evaluation of decay properties are the Nuclear Data Sheets based on the ENSDF, the Evaluated Nuclear Structure Data File (partly quite outdated; no very light nuclei). Neutron data can be found in reaction data bases as EXFOR (Experimental Nuclear Reaction Data) and in special data bases as JEFF Decay Data Library (of the OECD), ENDF/B-VII-1 (in December, with values from Pfeiffer et al.(2002)). I suppose that especially for delayed neutrons there must exist evaluations collected for the exclusive internal use of research laboratories or enterprises engaged in the development of nuclear reactors (and weapons). 15 The NUBASE Evaluation of Nuclear and Decay Properties Since 1997, the Atomic Mass Evaluation has been supplemented by data on decay properties of the ground-state and long-lived isomers as half-lives, spin and parities, delayed emission probabilities. NUBASE: G. Audi et al., Nucl. Phys. A624, 1 (1997) G. Audi et al., Nucl. Phys. A729, 3 (2003) The main source for the data is ENSDF, but the relevant literature is scanned independently and some data points included in NUBASE are not applied in the Nuclear Data Sheets. On the web, there are now available intermediate versions of the mass tables and the NUBASE evaluation: It is highly recommented to apply the mass values from the 2011 intermediate release. Now with collaboration from Gießen/Darmstadt 16 Recent attempts on dedicated compilations / evaluations (I) Proc. Int. Conf. Delayed Neutron Properties, Birmingham, England, D.R. Weaver, Ed., (1987) 1989BrZI: Thesis, Texas A-M Univ. (1989); LA T (1989) M.C.Brady Evaluation and Application of Delayed Neutron Precursor Data COMPILATION 79,80,81Ga,85As,87,88,89,90,91,92Br,92,93,94,95,96,97, 98Rb,129,130In,134,135Sb, 136Te,137,138,139,140,141I,141,142,143,144, 145,146,147Cs; compiled,evaluated beta-delayed neutron spectra, precursor data. 1989Br25: Nucl.Sci.Eng. 103, 129 (1989) M.C.Brady, T.R.England Delayed Neutron Data and Group Parameters for 43 Fissioning Systems COMPILATION 227,229,232Th,231Pa,232,233,234,235,236,237,238U,237, 238Np, 238,239,240,241,242Pu,241,242m,243Am,242,245Cm,249,251,252Cf, 254Es,255Fm; compiled,evaluated delayed neutron six-group parameters. STATUS OF DELAYED NEUTRON DATA 1990, J. Blachot et al. NEACRP-L-323, NEANDC-299 U ; OECD Nuclear Energy Agency Mikey Brady Karl-Ludwig Kratz had been consultant at Los Alamos working with Tall England. He made neutron spectra from Mainz, Grenoble, Geneva available for this group. 17 Recent attempts on dedicated compilations / evaluations (II) From 1990 to 2000, the Nuclear Energy Agency (NEA) of the Organisation for Economic Co-operation and Development (OECD) run a Working Party on International Nuclear Data Evaluation Co-operation (WPEC). The Subgroup-6 Delayed Neutron Data published a summary report in 2002: Report NEA/WPEC-6: and A. D Angelo, Prog.Nucl.Energy 41, 5 (2002) Remark: Our evaluation 2002Pf04 appeared in the same volume of Prog.Nucl.Energy and is cited in these reports. 18 Recent attempts on dedicated compilations / evaluations (III) 1993Ru01 G.Rudstam, K.Aleklett, L.Sihver, At.Data Nucl.Data Tables 53, 1 (1993) Delayed- Neutron Branching Ratios of Precursors in the Fission Product Region COMPILATION A=75-150; compiled beta--decay T-1/2,neutron emission probability; deduced average delayed-neutron branching ratios. RADIOACTIVITY 80,81,83,79,82Ga,84Ge,84,85,86,87As,88,89,91,87Se,100, 99,98mY, 100,98Sr,99,98,97,96,95,94,93,92Rb, 91,90,89,88,87Br,129m, 129,130m,131,128m,128,132In,150,149,148,147La,149,148,147,146Ba, 148, 147,146,145,144,143,142,141Cs,139,138,137I,137,136Te,136,135,134Sb, 134,133Sn(beta-n) (Dedicated experiment at Studsvik and evaluation to be entered in JEFF and ENDF.) 2002Pf04 B.Pfeiffer, K.Kratz, P.Möller, Prog.Nucl.Energy 41, 39 (2002) Status of delayed-neutron Precursor Data: Half-Lives and Neutron Emission Probabilities COMPILATION Z=27-63; compiled,analyzed beta-decay T-1/2,neutron emission probabilities, model predictions. 19 Compilation or evaluation? (I) With the comments, I would call this an evaluation. 20 Compilation or evaluation? (II) 2002Pf04: B.Pfeiffer, K.Kratz, P.Möller, Prog.Nucl.Energy 41, 39 (2002) Status of delayed-neutron Precursor Data: Half-Lives and Neutron Emission Probabilities COMPILATION Z=27-63 The primary reason for presenting T 1/2 and P n of fission products was a comparison with the values calculated with different assumptions in order to have an idea which model might be best suited for extrapolations to unknown nuclides. Unfortunately, the editors even cancelled the list of references for the experimental values, and there is no hint at all left to the limited evaluation performed. 21 Consultant s meeting The astrophysics as well as the reactor technology and the nuclear structure communities (partly in Personalunion ) would like to establish a new evaluation encompassing not only the fission product region but also the low- and high-z precursors. Regarding the long history of evaluations under the auspices of the IAEA, the nuclear data section was addressed. In order to prepare a report for an eventual (near) future IAEA CRP (co-ordinated research project) a consultants meeting took place at Vienna in October Daniel Cano-Ott was participating via video-conference. 22 Report for IAEA INDC(NDS)-0599 Distr.. INDC International Nuclear Data Committee Summary Report of Consultants Meeting Beta delayed neutron emission evaluation IAEA Headquarters, Vienna, Austria October 2011 Prepared by Daniel Abriola IAEA Nuclear Data Section Vienna, Austria Balraj Singh McMaster University Hamilton, Ontario, Canada Iris Dillmann Justus-Liebig-Universität Giessen, Germany Will be published on 23 Some remarks on pitfalls for future evaluators In summer, Balraj Singh visited us for a preparatory meeting. He had extracted all the data on T 1/2 and P n contained in the ENSDF as a starting point for an evaluation. But quite a lot of the isobaric chains have not been updated since several years and the masses below 40 had not been evaluated by Brookhaven. Many measurements have been performed long ago. The input parameters applied might have changed meanwhile. Can one recalibrate the old data? Rudstam et al., ADNDT 53,1 (1993) During the meeting in Vienna, we wanted to give an overview of methods to measure P n values and try to describe advantages and drawbacks of them. Partly we had already problems to find out how the described methods worked [ Ion counting was measuring the beam current!]. What if future researchers want to start-up the work again in case that atomic energy has to be used in future? 24 A message from a former consultant on delayed neutrons As a trained nuclear chemist, Karl-Ludwig was personally involved in the measurements of delayed-neutron emission propabilities and the spectroscopy of delayed neutrons. He told me that the evaluators keep in mind that the very early experiments on delayed neutrons were based on chemistry: Typically, uranium samples were irradiated in a reactor and then chemically separated. Then the number of delayed neutrons were determined for the different isotopes. In general, there was no direct measurement of the β-decays preceding the neutrons. The delayed neutron emission probabilities P n were derived from systematics of nuclear-charge distributions of the fission fragments. Unfortunately, the earliest systematics did not take into account the odd-even effect in the distributions. If one wants to use the older evaluations, one must be careful. A.C. Wahl et al., Phys. Rev. 126, 112 (1962) A.C. Wahl, At. Data Nucl. Data Tables 39, 1(1988) K.-L. Kratz, Review of delayed neutron energy spectra in Proceedings, Consultants Meeting on Delayed Neutron Properties, Vienna, Austria (Mar , 1979), IAEA Report INDC NDS-107/G + Special (1979), p Neutron emitter at the stability line: 17 N 17 N is the first non-fission emitter discovered It decays to the stable 17 O with few excited states. This enables the spectroscopy of the delayed neutron branches. J.H. Kelley et al., Nucl. Phys. A564, 1 (1993) Note added in proof: Not evaluated by NDS! 1976OH05 For the P n value of 95.1(7)%, only one reference is cited in NDS: 1976AL02 Is this an adequate standard? 26 Determination of P n values with absolute γ-intensities ENSDF [%] 1982KR11 3,91(16)*0,90(5) 1000(55)*0,068(3) 976(53)*0,0076(11) 1000(50)*0,0202(10) (5)*0,61(4) 100*0,942(9) 100*0,226(12) 100*0,158(7) 100*0,49(3) 100,00(5)*0,780(20) 94,0(30)*0,765(12) 1000*0, *0,0250(25) 20* 2,30 3,52(34) 68.0(67) 7,4(15) 20,2(20) 61,0(71) 94,2(9) 22,6(12) 15,8(7) 49(3) 1982KR11 71,9(34) 26,3 25.0(25) 46 27 Differences between ENSDF and NUBASE-2011 As an example, the T 1/2 of 150 La is given in NUBASE as 510(30) ms, in ENSDF as 860(50) ms: E. dermateosian and J. K. Tuli$CIT=NDS 75, 827 (1995); CUT=1-MAR S 5 %B-=100$%B-N=2.7 3 (1993RU01) T$from n counting (1993Ru01). Others:.. Whereas NUBASE refers to 1995Ok02 Z.Phys. A351, 243 (1995) K.Okano, A.Taniguchi, S.Yamada, T.Sharshar, M.Shibata, K.Yamauchi: Identification of Beta-Decay of 150La The article was submitted end of January, so it appeared just after the cut-off date. No update of NDS since 1995! 28 Need for theoretical models Not all delayed-neutron precursors are available for experimental studies. Missing data have to be derived from systematics and / or calculations. The necessity to develop reliable mathematical schemes is quite obvious for applications in astrophysics. Most of the nuclides involved in explosive nucleosynthesis scenarios as the r-process are not accessible for experimentation, so reliable extrapolations and calculations have to be developed. But also new applications in reactor technology and decay heat calculations depend on calculated data to complement experimental data, in particular neutron spectra for individuel precursors. 29 Empirical formulas for P n values In the fission product region, there is in general a high level density above S n. Therefore one may derive simple expressions to describe the P n values, as S. Amiel and H. Feldstein, Phys.Lett. 31B, 59 (1970) or K.-L. Kratz and G.Herrmann, Z. Phys.263, 435 (1973) The results are comparibel to sophisticated calculations and are used in some data bases (as the new version of ENDF). Updated parameters in 2002PF04
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