instituts-seminar ii. phys. gießen 11.1.12

Instituts-Seminar II. Phys. Gießen 11.1.12

Dr. B. PfeifferII. Physik. Institut, Justus-Liebig-Universität, Gießen

GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt

Beta-delayed neutron emission evaluation for reactor physics and astrophysics

Instituts-SeminarII. Physikalisches Institut, Universität Gießen

11. Januar 2012

Do we need a new evaluation?Can it be done under the auspices of the IAEA?

http://www.gsi.de/

http://www.med.uni-giessen.de/infoweb/allgemein/unisiegel.htm

http://www.uni-giessen.de/cms/fbz/fb07/fachgebiete/physik/einrichtungen/2pi


2

``Reference Data Libraries for Nuclear Applications -- ENSDF''; Report of Technical Meeting of IAEA Nuclear Data Section INDC(NDS)-0543, November 2008, Viennahttp://www-nds.iaea.org/publications/indc/indc-nds-0543.pdf

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''

GSI contributions to data bases

At GSI, many installations are studying nuclear structure. The measured quantitiesare of interest for different fields ranging from basic science to technical applications.A (personally biased) example are the ground-state masses of atoms.

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 complicateddecay chains can result. An alternative technique observes the β-delayed neutronactivity 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.



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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 235U (A.O. Nier, E.T. Booth, J.R. Dunning, A.V. Grosse, Phys.Rev. 57, 546 (1940)).

Discovery of fission



Ewald’s double-focusing spectrograph

Heinz Ewald designed a double-focusing mass spectrograph at the Kaiser-Wilhelm-Institut in the years 1942 – 1944. It accompanied him in all his career and ended at theII. Physikalisches Institut in Gießen. There I saw it as a young student in a dark cellar.Now it is displayed more openly.

Heinz Ewald16.6.1914 –

5.2.1992

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 Mattauchat the Kaiser-Wilhelm-Inst. I could not find a contribution of the Mattauch group to the study of the fission process.

4



Proposal of Ewald for an isotope separator 1942

‡

‡

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 1939-1949“ is reported, that M. von Ardenne picked-up the idea and constructed a proto-type 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.

http://www.petermann-heiko.de/index.php?option=com_content&view=article&id=83&Itemid=96&lang=de

Prof. Ewald was involved with the Uranverein. I could find only one mention.

5



666http://www.phy.ornl.gov/hribf/app/decay/neutrons.shtml

A necessary condition for β-delayed particle emission is that the Q-value issuperior 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 separationenergies decrease.

So, in general, the nuclidesundergoing delayed emissionare situated away from stabilityand have quite low half-lives.

Historically, such nuclides could nearly exclusively be obtainedas products of neutron-inducedfission.Interestingly, the most intensesource for neutrons are nuclearreactors. And for the control ofa reactor, β-delayed neutrons areplaying an essential role.

Therefore, β-delayed neutronswere studied intensively.

Beta-delayed particle emission



7

But although many groups in many countries dedicated much effort in the study of delayed emitters among fission products, there exist elements forwhich not a single Pn value has been reported (see Fig. on next slide).They are mainly situated in the region of symmetric fission with low yieldsand/or are refractory elements not suited for ion sources.

New developments

The data on delayed neutrons collected for reactor applications are nowapplied in totally different fields (partly by the same scientists), as e.g.calculations of the nucleosynthesis in explosive stellar environments‡. Dueto the extremely high neutron fluxes, the properties of very neutron-richisotopes must be obtained.

With the advent of radioactive beam facilities, short-lived neutron- (andproton-) 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:1110.1076Stellar Nucleosynthesis Nuclear Data Mining

New developments



888

NUBASE11

Overview



9

LADY GODIVA

For atomic bombs, reactor and decay heat applications, data on the several hundred individual precursors are notimperitavely 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 shortirradiations with fast neutrons had been studied, p.e.F. de Hoffmann et al., Delayed Neutrons from U-235 After Short IrradiationPhys.Rev. 74, 1330 (1948) .

John Collier (ca. 1898)

D.Loaiza et al., Measurement of Absolute Delayed Neutron Yield and Group Constants in the Fast Fission of U-235 and NP-237Nucl.Sci.Eng. 128, 270 (1998)

9

Chain-reaction assemblies

101010

i Possible precursor nuclei

Mean energy (MeV)

Average half-life of the precursor nuclei (s)

Delayed-neutron fraction (%)

235U 239Pu 233U 235U 239Pu 233U

1 87Br, 142Cs 0.25 55.72 54.28 55.0 0.021 0.0072 0.0226

2 137I, 88Br 0.56 22.72 23.04 20.57 0.140 0.0626 0.0786

3 138I, 89Br, (93,94)Rb 0.43 6.22 5.60 5.00 0.126 0.0444 0.0658

4 139I, (93,94)Kr143Xe, (90,92)Br

0.62 2.3 2.13 2.13 0.252 0.0685 0.0730

5 140I, 145Cs 0.42 0.61 0.618 0.615 0.074 0.018 0.0135

6 (Br, Rb, As etc) - 0.23 0.257 0.277 0.027 0.0093 0.0087

Total0.64 0.21 0.26

Table 2. Parameters of the delayed-neutron groups for three fissile nuclei

http://www.reak.bme.hu/Wigner_Course/WignerManuals/Budapest/DELAYED_NEUTRON.htm

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 fewnuclides with high fission yields.

1957Ke67 Phys.Rev. 107, 1044 (1957) G.R.Keepin, T.F.Wimett, R.K.Zeigler Delayed Neutrons from Fissionable Isotopes of Uranium, Plutonium, and Thorium

The Keepin Groups

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11

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.

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 produceshort-lived fission products.(see, e.g.

The Mainz results have been taken into account in Los Alamos.But what about the many (civilian) data bases?

11

TRIGA-reactor Mainz

K.-L. Kratz, B. Steinmüller, H. Gabelmann, Jahrestagung Kerntechnik, Aachen 1986


http://www.nndc.bnl.gov/nsr/fastsrch_act2.jsp?aname=B.Steinmuller

http://www.nndc.bnl.gov/nsr/fastsrch_act2.jsp?aname=H.Gabelmann

http://www.nndc.bnl.gov/nsr/fastsrch_act2.jsp?aname=K.L.Kratz


12„Atomminister“ Siegfried Balke

Günter HerrmannFrederic de Hoffmann Fritz Straßmann

Ankauf des Mainzer TRIGA-Reaktors

Frederic de Hoffmann, who had worked on delayed neutrons at Los AlamosPhys.Rev. 72, 567 (1947); Phys.Rev. 74, 1330 (1948)later founded in California General Atomic.One of their products is the TRIGA research reactor.

At the on-line separator at thehigh-flux reactor in Grenoble,nuclear structure was studiedby the II. Phys. Inst. in closeinternatonal collaboration.

One of the main researchtopics was the β-delayedneutron emission of short-lived fission products.

The Mainz-group continued their work, especially withthe neutron spectrometers.

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1414

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. 26-30, 1979), IAEA Report INDC NDS-107/G + Special (1979), p. 69

K.-L. Kratz, ibid., p.103http://www-nds.iaea.org/publications/indc/indc-nds-0107.pdf

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 disseminatinginformation relevant to nuclear energy.

Examples are conferences and consultants meetings:

Eisenhower at UNO8. Dezember 1953



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Data on β-decay properties are sought for in many applications. In all laboratoriesone finds a Nuclear Wallet Card.There exist a multitude of compilations for special properties as well as moregeneral overviews, as the long series of „Table of the Isotopes“.

The internationally accepted standard evaluation of decay properties are theNuclear Data Sheets based on the ENSDF, the „Evaluated Nuclear Structure DataFile“ (partly quite outdated; no very light nuclei).

Compilations / evaluations for β-decay properties

I suppose that especially for delayed neutrons there must exist evaluationscollected for the exclusive internal use of research laboratories or enterprisesengaged in the development of nuclear reactors (and weapons).

Neutron data can be found in reaction data bases as EXFOR (Experimental NuclearReaction 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)).



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NUBASE: G. Audi et al., Nucl. Phys. A624, 1 (1997) G. Audi et al., Nucl. Phys. A729, 3 (2003)

The NUBASE Evaluation of Nuclear and Decay Properties

Since 1997, the Atomic Mass Evaluation has been supplemented by dataon decay properties of the ground-state and long-lived isomers as half-lives, spin and parities, delayed emission probabilities.

The main source for the data is ENSDF, but the relevant literature isscanned independently and some data points included in NUBASEare not applied in the Nuclear Data Sheets.

On the web, there are now available intermediate versions of the mass tables and the NUBASE evaluation:

http://amdc.in2p3.fr/masstables/Ame2011int/file1.html

http://amdc.in2p3.fr/nucleus/nucWxp2.exe

It is highly recommented to apply the mass values from the 2011 intermediate release.

Now with collaboration from Gießen/Darmstadt


http://amdc.in2p3.fr/masstables/Ame2011int/file1.html

http://amdc.in2p3.fr/nucleus/nucWxp2.exe


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1989BrZI: Thesis, Texas A-M Univ. (1989); LA-11534-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.

Proc. Int. Conf. Delayed Neutron Properties, Birmingham, England, D.R. Weaver, Ed., (1987)

Recent attempts on dedicated compilations / evaluations (I)

http://www.oecd-nea.org/science/docs/1990/neandc1990-299-u.pdf

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.



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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: http://www.oecd-nea.org/science/wpec/volume6/volume6.pdf andA. 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.

Recent attempts on dedicated compilations / evaluations (II)


http://www.oecd-nea.org/science/wpec/volume6/volume6.pdf


191919

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)

Recent attempts on dedicated compilations / evaluations (III)

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.

(Dedicated experiment at Studsvik and evaluation to be entered in JEFF and ENDF.)



202020

Compilation or evaluation? (I)

With the comments, I would call this an evaluation.



212121

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 T1/2 and Pn of fission products was a comparisonwith the values calculated with different assumptions in order to have an idea whichmodel might be best suited for extrapolations to unknown nuclides. Unfortunately, the editors even cancelled the list of references for the experimentalvalues, and there is no hint at all left to the limited evaluation performed.



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The astrophysics as well as the reactor technology and the nuclear structurecommunities (partly in „Personalunion“) would like to establish a new evaluationencompassing not only the fission product region but also the low- and high-Zprecursors. 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-ordinatedresearch project) a consultants meeting took place at Vienna in October 2011.

Daniel Cano-Ott was participating via video-conference.

Consultant’s meeting


http://www.flickr.com/photos/danielcanoott/


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INDC(NDS)-0599Distr. ….

INDC International Nuclear Data CommitteeSummary Report of Consultants’ Meeting

Beta delayed neutron emission evaluation

IAEA Headquarters, Vienna, Austria10 – 12 October 2011

In p

repar

atio

n !

Will be published onhttp://www-nds.iaea.org/beta-delayed-neutron/#i

Report for IAEA


Prepared byDaniel Abriola

IAEA Nuclear Data SectionVienna, Austria

Balraj SinghMcMaster University

Hamilton, Ontario, CanadaIris Dillmann

Justus-Liebig-UniversitätGiessen, Germany


24Rudstam et al., ADNDT 53,1 (1993)

In summer, Balraj Singh visited us for a preparatory meeting. He had extracted allthe data on T1/2 and Pn 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 yearsand the masses below 40 had not been evaluated by Brookhaven.

Many measurements have been performed long ago. The input parameters appliedmight have changed meanwhile. Can one recalibrate the old data?

During the meeting in Vienna,we wanted to give an overviewof methods to measure Pn valuesand try to describe advantagesand drawbacks of them. Partly we had already problemsto find out how the describedmethods worked [„Ion counting“ wasmeasuring the beam current!].What if future researchers want tostart-up the work again in casethat atomic energy has to be usedin future?

Some remarks on pitfalls for future evaluators



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As a trained nuclear chemist, Karl-Ludwig was personally involved in the measure-ments 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 Pn 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)

A message from a former consultant on delayed neutrons

K.-L. Kratz, Review of delayed neutron energy spectra in Proceedings, Consultants Meeting on Delayed Neutron Properties, Vienna, Austria (Mar. 26-30, 1979), IAEA Report INDC NDS-107/G + Special (1979), p. 103



2626

J.H. Kelley et al., Nucl. Phys. A564, 1 (1993)

1976OH05

17N is the first non-fission emitter discovered 1948. It decays to the stable 17O with fewexcited states. This enables the spectroscopyof the delayed neutron branches.

For the Pn value of 95.1(7)%, only one referenceis cited in NDS: 1976AL02Is this an adequate standard?

Note added in proof: Not evaluated by NDS!

Neutron emitter at the stability line: 17N



2727

3,91(16)*0,90(5)1000(55)*0,068(3)976(53)*0,0076(11)1000(50)*0,0202(10)100.00(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*0,02631000*0,0250(25)20*≈2,30

1982KR11

ENSDF [%]

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)1982KR1171,9(34)26,325.0(25)≈46

Determination of Pn values with absolute γ-intensities



28282828

1995Ok02 Z.Phys. A351, 243 (1995) K.Okano, A.Taniguchi, S.Yamada, T.Sharshar, M.Shibata, K.Yamauchi: “Identification of Beta-Decay of 150La”

As an example, the T1/2 of 150La is given in NUBASE as 510(30) ms,in ENSDF as 860(50) ms:

Whereas NUBASE refers to

E. derMateosian and J. K. Tuli$CIT=NDS 75, 827 (1995); CUT=1-MAR-1995 0.86 S 5 %B-=100$%B-N=2.7 3 (1993RU01) T$from n counting (1993Ru01). Others: ……..

The article was submitted end of January, so it appeared just after the cut-off date.

No update of NDS since 1995!

Differences between ENSDF and NUBASE-2011



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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 forapplications in astrophysics.

Most of the nuclides involved in explosive nucleosynthesis scenarios asthe r-process are not accessible for experimentation, so reliable extrapolationsand calculations have to be developed.

But also new applications in reactor technology and decay heat calculationsdepend on calculated data to complement experimental data, in particular neutron spectra for individuel precursors.

Need for theoretical models



3030

Empirical formulas for Pn values

In the fission product region, there is in general a high level density aboveSn . Therefore one may derive „simple“ expressions to describe thePn values, as

S. Amiel and H. Feldstein, Phys.Lett. 31B, 59 (1970)or

K.-L. Kratz and G.Herrmann, Z. Phys.263, 435

(1973)

Updated parameters in 2002PF04

The results are comparibelto sophisticated calculationsand are used in some data bases (as the new version of ENDF).



3131

More „sophisticated“ calculations ofβ-decay are based on the shell model.Single-particle energies are determinedfor a given nuclear potential, in thiscase a Folded-Yukawa-potential, theparameters of which were adjusted toexperimental decay-schemes.The ground-state deformations weretaken from the fit to nuclear masses.

The influence of the nuclear structureto the β-decay is displayed as thestrength function. The observed β-intensities are obtained by multiplayingwith the Fermi function. From this, thehalf-lives and Pn values are calculated.

Peter Möller assumes that the Gamow-Teller strength is the dominant decaymode for most nuclei, so not taking intoaccount e.g. the first-forbidden strength.

calc. exp.T1/2 76 ms 378 msPn 1.6% 8.7%

QRPA-calculations (I)



3232

1997Mo25 At.Data Nucl.Data Tables 66, 131 (1997) P.Moller, J.R.Nix, K.-L.Kratz Nuclear Properties for Astrophysical and Radioactive-Ion-Beam Applications NUCLEAR STRUCTURE Z=8-136; A=16-339; calculated,compiled total binding energy,one-,two-neutron,proton separation energies,pairing gaps,odd-nucleon parity,spin projection.

Peter Möller has performed these calculations for nearly all possible isotopes.In his approach he obtains wave functions, from which he can calculate notonly masses but in a consistent way separation energies, spin, parities andβ-decay properties as half-lives and emission probabilities:

These data are used for many applications, as the Nuclear Data Sheets.

But there are some problems, especially in calculating T1/2 and Pn.The procedure takes only the Gamow-Teller selection rules into account. This canlead to huge errors, if e.g. the Gamow-Teller decays feed into high-lying levelsand first-forbidden ones near the ground state. The calculated single-particle energies depend on the parameters of the nuclearpotential. There are cases that strong β-branches feed excited states close to theSn value. Tiny changes in the parameters can shift the excited states, so that thecalculated Pn values may be „undetermined“, shifting from 100% to 0%.The article 2002PF04 wanted to look for ways to overcome these deficencies.

QRPA-calculations (II)



33

Warning:This is an unrealistic case for showinga drastic effect! Mother and daughterare deformed in the ground state.

In this model calculation, the mainβ-decay feeds an excited state justabove Sn , so Pn = 100%.With very small changes in the parametersof the nuclear potential and/or the atomicmasses, one can obtain Pn = 0%.

In this case still close to stability, atleast Qβ (9229(20) keV) and Sn (4352(9) keV) are well known.


To account for uncertainties in level and separation energies , we therefore folded all transitions with a Gaussian.

Sn Qβ

Pn=81%; T1/2=350 ms

Pn=9%; T1/2=378 ms exp.


34


S1n S2nS3nQβ

P1n=7%; P2n=84%; P3n=0.02%

P1n=13%; P2n=81%; P3n=0.02%Data base: T1/2=140(4) ms ;P1n=65 %

Although there is in general a goodreproduction of half-lives and Pn-values,there are some striking discrepanciesbetween model predictions and experi-ments. One such case is the very neu-tron-rich 134In.

The model predicts that the β-decay predominantly feeds a level at about8 MeV well above the two-neutronseperation energy, leading to the surpr-isingly high P2n=84 %, whereas theexperimental value is

P. Hoff et al., PRL 77, 1020 (1996)

If this result would be confirmed, theremust be problems with the model:- Ought the shell model parameters be readjusted?- Are the nuclei close to 132Sn deformed?


35

1983Kr11 K.-L.Kratz, H.Ohm, A.Schroder, H.Gabelmann, W.Ziegert, B.Pfeiffer, G.Jung, E.Monnand, J.A.Pinston, F.Schussler, G.I.Crawford, S.G.Prussin, Z.M.de Oliveira The Beta-Decay of 95Rb and 97Rb Z.Phys. A312, 43 (1983)

1982Kr11 K.-L.Kratz, A.Schroder, H.Ohm, M.Zendel, H.Gabelmann, W.Ziegert, P.Peuser, G.Jung, B.Pfeiffer, K.D.Wunsch, H.Wollnik, C.Ristori, J.Crancon Beta-Delayed Neutron Emission from 93-100Rb to Excited States in the Residual Sr Isotopes Z.Phys. A306, 239 (1982)

For applications as reactor technology and decay heat calculations, the energyspectra of the delayed neutrons are essential input parameters, so many studies havebeen undertaken. An overview may be found in http://www-nds.iaea.org/publications/indc/indc-nds-0107.pdf

As examples for this talk, I have chosen spectra taken at the on-line isotopeseparator OSTIS:

Need for neutron spectra



36

(from 1983KR11)

Due to long beam times available atresearch reactors, we could evenperform n-γ-coincidence measurements.

And what could we have done with nowadayselectronics and data handling systems!

Neutron spectra for 95Rb precursor (I)



37

(from 1983KR11) (from 1982KR11)

The measured energy spectra had beencompared to theoretical calculations,applying the latest optical model trans-mission coefficients.It would be interesting to see, if the new CGM-calculations of Los Alamoscan deliver better results.

Neutron spectra for 95Rb precursor (II)



38T. Kawano, P. Möller, W.B. Wilson, Phys. Rev. C78, 054601 (2008)

The neutron and γ decay code CGM (Cascading Gamma and Multiplicity)

In the EXFOR data base, there are only 36 experimental delayed-neutron spectra.With the CGM code, 271 spectra were calculated to be used e.g. in decay heat studies. (They will be applied for ENDF/B-VII-1.)

Calculation of delayed-neutron spectra



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Administrators of data banks at the consultants‘ meeting asked for old neutron spectra which might be digitized and entered into the data bases.

It was questionable if the formats of the data files allow to enterspectra. They were not foreseen in ENSDF, but perhaps with sometricks?

The JEFF files contain less than 50 „spectra“ of individual precursorsin the form of lists of neutron lines.

Call for old data



40By courtesy of Mark A. Kellett, contribution to Consultants‘ Meeting


1982KR11 1983KR11

In JEFF, the few spectra are stored as discrete neutron lines only. They will try to digitize from old publications.

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Original spectra

TOF

3He-spectrometer


By courtesy of Alejandro Sonzogni, contribution to Consultants‘ Meeting42

Example from ENDF/B-VII.1 (December 2011)


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1989HaZC: Particle Emission from Nuclei, Vol.3, p.99, CRC Press, Florida (1989) J.C.Hardy, E.Hagberg Beta-Delayed Proton and Alpha Emission

Beta-delayed charged particle emission and fission

2005Pa06 Nucl.Phys. A747, 633 (2005) I.V.Panov, E.Kolbe, B.Pfeiffer, T.Rauscher, K.-L.Kratz, F.-K.Thielemann Calculations of fission rates for r-process nucleosynthesis NUCLEAR STRUCTURE A=250-320; calculated neutron-induced and beta-delayed fission rates,related features. Astrophysical implications discussed.

For NUBASE, the following article was applied. Are there more recent ones?

For very heavy nuclei, also β-delayed fission and β-delayed n-emission followed byfission has been observed.

Beta-delayed p-emission is interesting for astrophysics, but certainlynot for nuclear reactors, so one will need a separate evaluation.

Beta-delayed α-emission can even „compete“ with neutron emission. In the β-decayof 17N, there is a branching of 2.5(4)*10-5 .


Courtsey Valentina Liberati

Beta- and EC-delayed fission

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Studies of ßDF in the lead region are foreseen for SUPER-FRS.


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Beta-delayed neutron emission evaluation for reactor physics and astrophysics

• Contrary to the development in Germany, nuclear data continues to be collected, evaluated and applied worldwide.• For the planning of reactors of the IVth generation based on fast fission, decay heat, accelerator driven systems data on β-delayed neutron emission are needed.• The existing and especially the future radioactive beam facilities will produce neutron-rich isotopes all over the nuclidic chart. The measurements of T1/2 and Pn values are challenging due to a high background of beam generated high-energy neutrons, but nevertheless many new values will be obtained. Can neutron spectra be measured at these facilities?• Up till now, no evaluation for precursors outside the fission range has been published (at least to my knowledge).• These data will hopefully be applied to develop advanced theoretical models for masses and decay properties.

Résumé


TopicsNuclear reaction data Nuclear structure and decay data Delayed neutrons Fission yields Atomic masses Experimental facilities and detection techniques Nuclear data measurements and analysis Nuclear theories, models and data evaluation Uncertainty quantification and covariances Evaluated nuclear data libraries Nuclear data processing Nuclear data adjustment Validation of evaluated data Integral experiments Cross section and decay standards, Data dissemination and international collaboration

Nuclear Fission (75th anniversary) Nuclear data for reactors Nuclear decay heat Dosimetry and shielding Safeguards and security Criticality safety Homeland security and safety Accelerator related applications Fusion technology Space, cosmic-rays, radiation effects on electronics Astrophysics and cosmology Medical and environmental applications

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instituts-seminar ii. phys. gießen 11.1.12

Documents

nuclear structure

fission products

fission process

fission eventh

physikalisches institut

reference data libraries

technical applications

data basesat gsi