Transcript Folie 1 - uni

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?
Instituts-Seminar II. Phys. Gießen 11.1.12
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
http://www-nds.iaea.org/publications/indc/indc-nds-0543.pdf
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.
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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 235U
(A.O. Nier, E.T. Booth, J.R. Dunning, A.V. Grosse, Phys.Rev. 57, 546 (1940)).
Instituts-Seminar II. Phys. Gießen 11.1.12
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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
16.6.1914 –
5.2.1992
Heinz Ewald designed a double-focusing mass spectrograph at the Kaiser-WilhelmInstitut in the years 1942 – 1944. 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.
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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 1939-1949“ 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.
‡
http://www.petermann-heiko.de/index.php?option=com_content&view=article&id=83&Itemid=96&lang=de
‡
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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.
http://www.phy.ornl.gov/hribf/app/decay/neutrons.shtml
Therefore, β-delayed neutrons
were studied intensively. 6
Instituts-Seminar II. Phys. Gießen 11.1.12
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 Pn 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:1110.1076
Stellar Nucleosynthesis Nuclear Data Mining
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Overview
NUBASE11
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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) .
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)
LADY GODIVA
John Collier (ca. 1898)
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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
(%)
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
139I, (93,94)Kr
0.62
2.3
2.13
2.13
0.252
0.0685
0.0730
4
143Xe, (90,92)Br
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
.64
0.21
0.26
Total
0
http://www.reak.bme.hu/Wigner_Course/WignerManuals/Budapest/DELAYED_NEUTRON.htm
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
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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?
Instituts-Seminar II. Phys. Gießen 11.1.12
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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.
Günter Herrmann
„Atomminister“ Siegfried Balke
Frederic de Hoffmann
Fritz Straßmann
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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.
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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. 26-30, 1979),
IAEA Report INDC NDS-107/G + Special (1979), p. 69
K.-L. Kratz, ibid., p.103
http://www-nds.iaea.org/publications/indc/indc-nds-0107.pdf
Instituts-Seminar II. Phys. Gießen 11.1.12
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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).
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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:
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
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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-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
„Mikey“ Brady
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.
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.
STATUS OF DELAYED NEUTRON DATA – 1990, J. Blachot et al.
NEACRP-L-323, NEANDC-299"U“; OECD Nuclear Energy Agency
http://www.oecd-nea.org/science/docs/1990/neandc1990-299-u.pdf
Instituts-Seminar II. Phys. Gießen 11.1.12
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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:
http://www.oecd-nea.org/science/wpec/volume6/volume6.pdf
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.
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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.
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Compilation or evaluation? (I)
With the comments, I would call this an evaluation.
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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 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.
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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 2011.
Daniel Cano-Ott was
participating via
video-conference.
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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
10 – 12 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
http://www-nds.iaea.org/beta-delayed-neutron/#i
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Some remarks on pitfalls for future evaluators
In summer, Balraj Singh visited us for a preparatory meeting. He had extracted all
the 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 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 Pn 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?
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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 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)
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
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Neutron emitter at the stability line: 17N
17N
is the first non-fission emitter discovered
1948. It decays to the stable 17O 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 Pn value of 95.1(7)%, only one reference
is cited in NDS: 1976AL02
Is this an adequate standard?
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Determination of Pn values with absolute γ-intensities
ENSDF
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*0,0263
1000*0,0250(25)
20*≈2,30
1982KR11
Instituts-Seminar II. Phys. Gießen 11.1.12
[%]
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
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Differences between ENSDF and NUBASE-2011
As an example, the T1/2 of 150La is given in NUBASE as 510(30) ms,
in ENSDF as 860(50) ms:
E. derMateosian and J. K. Tuli$CIT=NDS 75, 827 (1995); CUT=1-MAR-1995
0.86 S 5 %B-=100$%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!
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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.
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Empirical formulas for Pn values
In the fission product region, there is in
general a high level density above
Sn . Therefore one may derive „simple“
expressions to describe the
Pn 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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QRPA-calculations (I)
More „sophisticated“ calculations of
β-decay are based on the shell model.
Single-particle energies are determined
for a given nuclear potential, in this
case a Folded-Yukawa-potential, the
parameters of which were adjusted to
experimental decay-schemes.
The ground-state deformations were
taken from the fit to nuclear masses.
T1/2
Pn
calc. exp.
76 ms 378 ms
1.6% 8.7%
The influence of the nuclear structure
to the β-decay is displayed as the
strength function. The observed βintensities are obtained by multiplaying
with the Fermi function. From this, the
half-lives and Pn values are calculated.
Peter Möller assumes that the GamowTeller strength is the dominant decay
mode for most nuclei, so not taking into
account e.g. the first-forbidden strength.
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QRPA-calculations (II)
Peter Möller has performed these calculations for nearly all possible isotopes.
In his approach he obtains wave functions, from which he can calculate not
only masses but in a consistent way separation energies, spin, parities and
β-decay properties as half-lives and emission probabilities:
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.
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 can
lead to huge errors, if e.g. the Gamow-Teller decays feed into high-lying levels
and first-forbidden ones near the ground state.
The calculated single-particle energies depend on the parameters of the nuclear
potential. There are cases that strong β-branches feed excited states close to the
Sn value. Tiny changes in the parameters can shift the excited states, so that the
calculated Pn values may be „undetermined“, shifting from 100% to 0%.
The article 2002PF04 wanted to look for ways to overcome these deficencies.
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Warning:
This is an unrealistic case for showing
a drastic effect! Mother and daughter
are deformed in the ground state.
Pn=81%; T1/2=350 ms
Pn=9%; T1/2=378 ms exp.
In this model calculation, the main
β-decay feeds an excited state just
above Sn , so Pn = 100%.
With very small changes in the parameters
of the nuclear potential and/or the atomic
masses,
one can obtain Pn = 0%.
In this case still close to stability, at
least 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
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Instituts-Seminar II. Phys. Gießen 11.1.12
P1n=7%; P2n=84%; P3n=0.02%
S1n
S2n
Qβ S3n
Although there is in general a good
reproduction of half-lives and Pn-values,
there are some striking discrepancies
between model predictions and experiments. One such case is the very neutron-rich 134In.
The model predicts that the β-decay
predominantly feeds a level at about
8 MeV well above the two-neutron
seperation energy, leading to the surprisingly high P2n=84 %, whereas the
experimental value is
Data base: T1/2=140(4) ms ;P1n=65 %
P1n=13%; P2n=81%; P3n=0.02%
If this result would be confirmed, there
must be problems with the model:
- Ought the shell model parameters be
readjusted?
- Are the nuclei close to 132Sn deformed?
P. Hoff et al., PRL 77, 1020 (1996)
Instituts-Seminar II. Phys. Gießen 11.1.12
34
Need for neutron spectra
For applications as reactor technology and decay heat calculations, the energy
spectra of the delayed neutrons are essential input parameters, so many studies have
been 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 isotope
separator OSTIS:
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)
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)
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Instituts-Seminar II. Phys. Gießen 11.1.12
Neutron spectra for 95Rb precursor (I)
(from 1983KR11)
Due to long beam times available at
research reactors, we could even
perform n-γ-coincidence measurements.
And what could we have done with nowadays
electronics and data handling systems!
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Instituts-Seminar II. Phys. Gießen 11.1.12
Neutron spectra for 95Rb precursor (II)
(from 1983KR11)
(from 1982KR11)
The measured energy spectra had been
compared to theoretical calculations,
applying the latest optical model transmission coefficients.
It would be interesting to see, if the new CGM-calculations of Los Alamos
can deliver better results.
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Instituts-Seminar II. Phys. Gießen 11.1.12
Calculation of delayed-neutron spectra
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.)
T. Kawano, P. Möller, W.B. Wilson, Phys. Rev. C78, 054601 (2008)
Instituts-Seminar II. Phys. Gießen 11.1.12
38
Call for old data
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 enter
spectra. They were not foreseen
in ENSDF, but perhaps with some
tricks?
The JEFF files contain less than
50 „spectra“ of individual precursors
in the form of lists of neutron lines.
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Instituts-Seminar II. Phys. Gießen 11.1.12
By courtesy of Mark A. Kellett, contribution to Consultants‘ Meeting
Instituts-Seminar II. Phys. Gießen 11.1.12
40
Original spectra
In JEFF, the few spectra are stored as discrete neutron
lines only. They will try to digitize from old publications.
3He-spectrometer
TOF
1982KR11
1983KR11
Instituts-Seminar II. Phys. Gießen 11.1.12
41
Example from ENDF/B-VII.1 (December 2011)
By courtesy of Alejandro Sonzogni, contribution to Consultants‘ Meeting
Instituts-Seminar II. Phys. Gießen 11.1.12
42
Beta-delayed charged particle emission and fission
For NUBASE, the following article was applied. Are there more
recent ones?
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 p-emission is interesting for astrophysics, but certainly
not for nuclear reactors, so one will need a separate evaluation.
Beta-delayed α-emission can even „compete“ with neutron emission. In the β-decay
of 17N, there is a branching of 2.5(4)*10-5 .
For very heavy nuclei, also β-delayed fission and β-delayed n-emission followed by
fission has been observed.
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.
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Instituts-Seminar II. Phys. Gießen 11.1.12
Beta- and EC-delayed fission
Studies of ßDF in the lead region are foreseen for SUPER-FRS.
Courtsey Valentina Liberati
Instituts-Seminar II. Phys. Gießen 11.1.12
44
Résumé
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.
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Instituts-Seminar II. Phys. Gießen 11.1.12
Topics
Nuclear 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