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New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
NEW TREATMENT FOR NEUTRON MULTIPLICITY SORTING AND
PARTIAL PHOTONEUTRON REACTIONS CROSS SECTIONS EVALUATION
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Skobeltsyn Institute of Nuclear Physics,
Lomonosov Moscow State University
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
1
Title
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
The talk is focused on the problem
as old and well-known as modern and actual –
the problem of reliability of data
for partial photonuclear
(primarily, photoneutron) reactions data.
Data were obtained many years ago (~ 1960 – 2000)
and are included into various reviews, atlases, databases
(for example, into “NUCLEAR REACTION DATABASE (EXFOR) of
the MSU SINP Centre for Photonuclear Experiments Data (CDFE):
http://cdfe.sinp.msu.ru
Practically we have no modern data.
Data are widely used in many fields of research and applications.
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
2
Focus
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Main fields of partial photoneutron reactions data using:
•
•
•
•
•
competition of various Giant Dipole Resonance (GDR) decay channels;
competition of direct and statistical processes in decays of highly-excited nuclear states;
GDR configurational splitting effects;
GDR isospin splitting effects;
…. many other traditional fields;
• monitoring of the beam luminosity in ultra-relativistic heavy-ion colliders by measuring
neutron emission rates in mutual electromagnetic dissociation of colliding nuclei – neutron
emission (primarily (,n) and (,2n)) rates in mutual electromagnetic dissociation of colliding
nuclei.
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
3
Main fields
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
, mb
159Tb
(,xn) = (,n) + 2(,2n) + 3(,3n) + …
(,sn) = (,n) + (,2n) + (,3n) + …
(,n)
(,2n)
(,3n)
E, MeV
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
4
Xn-sn-n-2n-3n
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Many experimental data data for partial photonuclear reaction cross sections are published.
Majority was obtained at Livermore (USA) and Saclay (France)
using neutron multiplicity sorting methods:
Atlas of Photoneutron cross sections obtained with monoenergetic photons
(S.S.Dietrich, B.L.Berman. Atom. Data and Nucl. Data Tables, 38 (1988) 199.
The main problem:
if data were obtained at both labs there are significant discrepancies between those.
Simply in general: all ((,n) reaction cross sections are larger at Saclay but all (,2n) reaction cross
sections – vise versa at Livermore.
Other - 13
For each nucleus – cross sections:
Livermore - 86
Both – 42
Saclay - 79
(,xn) = (,n) + 2(,2n) + 3(,3n)
(,sn) = (,n) + (,2n) + (,3n)
(,n)
(,2n)
Many bremsstrahlung data
Main problem
For many nuclei:
(,3n)
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
5
Main problem
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Main problem: many significant ( till 60 %!) disagreements were found out
between data from two laboratories;
(,n) – (,2n) disagreements between Saclay and Livermore data –
integrated cross sections ratios “S / L”
159Tb
Rint = intS/intL (arb. units)
“Special cases”
“Ideal cases”
Squares
- ratios for (,n)
reactions – are
larger than 1.0
Triangles -  ratios for (,2n)
reactions – are
smaller than 1.0.
Mass number A
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
6
Systematics
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Both Labs neutron multiplicity sorting using measurements of neutron kinetic energies.
Basic supposition of neutron multiplicity sorting methods – unique neutron from (,n)
reaction has energy more than both neutrons from reaction (,2n).
Methods for neutron energy measurements are different:
- at Saclay the large Gd-loaded liquid scintillator was used;
- at Livermore so-called “ring-ratio” method was used (concentric rings of counters in
paraffin moderator): low-energy neutrons (from reaction (,2n)) should have enough time
for moderation in the way to inner ring but high-energy neutrons (from reaction (,n))
should go to the outer ring passing inner ring.
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
7
Methods
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
In special experimental investigation
(E.Wolynec and M.N. Martin. Revista Brasiera de Fisica, 17 (1987) 56)
it was shown that the reason is incorrect procedure for neutron multiplicity sorting used at Saclay
– (,2n) data are clear underestimated.
(,2n), mb
Conclusion:
(,2n) data
at Livermore are “good”
181Ta
Final nucleus activity
(reaction is identified via radioactive decay)
Livermore neutron sorting
Saclay neutron sorting (reaction is identified
via mean neutron kinetic energy)
but those
at Saclay are “bad”
because underestimation
(part of neutrons were
unreliably transported
from “2n” channel into
“1n” one).
E, MeV
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
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181Ta-gn- en
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
That conclusion led to the clear method of joint data corrections:
transportation of extra part of neutrons from “1n” Saclay channel back into the “2n” one
using the normalization of total neutron yield reaction (,xn) cross sections.
Total photoneutron reaction cross section in GDR energy region
(,xn) = (,n) + 2(,2n).
Ratio R (“Saclay/Livermore” normalization) for all reactions cross
sections
R = xnS/xnL = nS/nL = 2nS/2nL = (nS + 22nS)/(nL + 22nL),
xnS = (nS + 22nS) = RxnL = R(nL + 22nL) .
Saclay corrected 2nS* must be equal to Livermore corrected: 2nL* =
R2nL ,
therefore:
2nL* = 2nS* = R2nL = 2nS + ½(nS - RnL)
Saclay
(,n) reaction cross section part ½(nS - RnL) is “transmitted back” to
Saclay (,2n) reaction cross section 2nS.
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
9
“n-2n” correction formulae
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
(,n) and (,2n) reaction data
159Tb
 before
and
 after
joint correction procedure of
recalculation from incorrect
Saclay data to correct
Livermore ones
Data for 19 nuclei (51V, 75As, 89Y, 90Zr, 115In, 116,117,118,120,124Sn, 127I, 133Cs, 159Tb, 165Ho, 181Ta, 197Au, 208Pb, 232Th,
238U) were corrected and the problem seemed to be solved.
It was recommended to use “good” Livermore data and do not use “bad” Saclay ones,
but…
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
10
“Before” and “after”
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Livermore - 86
Both – 42
Saclay - 79
But the question remains:
What we must to do if data are
obtained only at one Lab?
The objective criteria of data reliability were needed!
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
11
Main problem1
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Simple clear objective absolute criterion of “correct” data reliability!
(,2n)
F2 = ________________________ < 0.5 (!)
(,n) + 2(,2n) + 3(,3n) +…
B3n
Calculations in
the frame of
modern
photonuclear
reaction model
for
Because F2 is ratio of (,2n) to
itself twice with additions of
(,n) and (,3n) it should not
have values larger 0.5: larger
values mean physically incorrect
data.
Deviation from “0.5” at low
energies is because of (,n) tail.
Deviation from “0.5” at high
energies is because of (,3n)
beginning.
even-evenSn
The results of new data reliability criterion application to
experimental data were unexpected and very impressive!
B2n
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
12
F2-Sn
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
159Tb
116Sn
2.0!
181Ta
(,n) = 0 ?
17 МэВ
Physically not reliable behavior
of Livermore (, n) cross sections
Dramatic
correlated with F 2 > 0.5!
disagreements:
F2 = 1.5 – 2.0!
F2 = (,2n)/(,xn)
Additional criteria:
F1 = (,n) / (,xn)
F3 = (,3n) / (,xn)
F4 = (,4n) / (,xn)
F5 = (,5n)
/ (,xn)
7/21/2015
< 1/1 = 1.00,
< 1/3 = 0.33,
< 1/4 = 0.25,
< 1/5 = 0.20 …
(,2n)
= ________________________ < 0.5
(,n) + 2(,2n) + 3(,3n) +…
Dramatic
disagreements:
F2 > 0.6!
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
13
Tb-Sn-Ta
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Non-physical negative values
> 0.50
> 0.50
> 0.50
> 0.33
91Zr
94Zr
188Os
> 0.33
189Os
Disagreements “ZOO”
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
14
Zoo
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
New experimentally-theoretical method of evaluation
using modern model of photonuclear reactions
initial data – experimental (,xn) reaction cross section
exp(,xn) free from the neutron multiplicity sorting problems;
-
sorting neutrons for multiplicity based on theoretical model.
Theoretically calculated transitional multiplicity functions
Fitheor = theor(,in)/theor(,xn)
are used for cross section evaluation by the following way
eval(,in) = Fitheor(,in)  exp(,xn).
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
15
Method
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
That treatment means:
i)
the competition of partial reactions is in accordance with
equations of model;
ii)
the sum of evaluated partial reaction cross sections
[(,n) + 2(,2n) + 3(,3n)] .
is equal to the experimental exp(,xn).
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
16
Method
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Model:
B.S.Ishkhanov and V.N.Orlin. Physics of Particles and Nuclei 38, 232 (2007),
B.S.Ishkhanov and V.N.Orlin. Physics of Atomic Nuclei 71, 493 (2008):
semiclassical exciton preequilibrium model of photonuclear
reactions based on nuclear level densities calculated in Fermigas model and taking into account effects of nuclear deformation
and GDR isospin splitting
M.B. Chadwick et al., Phys. Rev. C 44, 814 (1991).
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
17
Модель
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Theory-model
Born cross section description (,lpkn):
i – one of 4-components (2 isospin - T0 and T0 + 1 и 2 directions of vibration),
GDR – Lorentz lines with
where
W – decay probability (recurrentional formulae):
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
18
Теория
New
treatment for neutron multiplicity sorting159Tb
(,xn)
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
(,sn)
int, MeV mb
(,n)
Livermore
data are
“bad” because
overestimated
(,2n)
1950
1642
1390
870
715
610
Livermore
 30 %
Saclay
data are
“bad” because
underestimated
7/21/2015
(,3n)
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
int(γ,2n)/int(γ,n)
 27 %
Saclay
19
159Tb-eval.
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Data for 115In:
significant
disagreement
between
Saclay and Livermore data for F1, both of
them differ from theoretical data;
Livermore F1 are in the field of
physically unreliable negative values;
significant
disagreements
between
Saclay and Livermore F2 data; Livermore
F2 are in the field of physically unreliable
values F2 > 0.5;
- Livermore F3 are in the field of
unreliable negative values.
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
20
115In
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Comparison of evaluated
and experimental
(Saclay, Livermore)
reaction cross sections
for 115In.
(,xn)
(,sn)
Squares - [exp(,n) - eval(,n)]
Circles - [eval(,2n) - exp(,2n)]
(,n)
F2 > 0.5
(,n)
(,3n)
Squares - [exp(,2n) - eval(,2n)]
Circles - [eval(,3n) - exp(,3n)]
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
21
Disagreements
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
For 13 nuclei investigated
(90Zr, 115In, 159Tb, 112,114,116,117,118,119,120,122,124Sn, 197Au)
the reason of “not physically reliable” behavior of Livermore F2 > 0.5 data
is underestimation of (,2n) reaction cross section:
(,2n) is not reliable and therefore (,n) is also not reliable.
But for 181Ta situation is quite different:
(,2n) is reliable, but (,n) is “very (!) bad”.
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
22
Ta –2n
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
F
1
181Ta
F1 = (,n) / (,xn)
Not typical case!
F
2
No neutrons from (,n) reaction at E > 17.5 MeV?!
F2 = (,2n) / (,xn):
are Livermore
data really «good»?
(,3n) reaction
F
3
cross section–
negative values
F3 = (,3n) / (,xn)
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
E, MeV
Russia
23
181Ta-F1,2,3.
New treatment for neutron multiplicity sorting 181Ta
, mb
and partial
photoneutron reactions cross sections evaluation
-25 %
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
(,n)/[(,n) + 2(,2n)]
, mb
(,n)/[(,n) + (,2n)]
, mb
(,n)/(,n)
, mb
(,n)/0
For all cross sections
in which the (,n)
contribution
presents, significant
disagreements with
evaluated cross
sections take places
increasing in
accordance with
(,n) contribution
rise
-30 %
-46 %
-5 %
, mb
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
24
E, MeV
Ta –xn,sn,n,2n,3n
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Integrated cross sections int ratios obtained up to energy Eint = 25 MeV
for total and partial reactions evaluated, Saclay and Livermore data
Reaction
inteval/intSaclay
inteval/intLivermore
(,xn)
1
1.25 (3813.8/3068.3)
(,sn)
0.96 (2867.3/2998.4)
1.30 (2867.3/2199.7)
(,n)
0.88 (1922.4/2189.5)
1.46 (1922.4/1315.7)
(,2n)
1.16 (929.1/797.9)
1.05 (929.1/887.0)
Step (,xn)  (,sn)  (,n) is accompanied by decrease of (,2n) reaction part and
increase of part of «bad» (,n) reaction cross section:
1.25  1.30  1.46 !
But in the next step (,n)  (,2n) ratio is equal to 1.05.
181Ta
data situation significantly complicates the problem of partial reaction data reliability!
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
25
181Ta-table
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
F
2
Comparison of 181Ta experimental data obtained using methods
of neutron multiplicity sorting and induced activity
with evaluated data for (γ,n), (γ,2n) and (γ,3n) reactions.
V.V. Varlamov, V.N. Orlin, N.N. Peskov, T.S. Polevich. MSU SINP Preprint-2012-1/879,
B.S. Ishkhanov, V.N. Orlin, S.Yu. Troshchiev, PAN 75, 253 (2012).
Ratios
Experiment
Saclay
Livermore
of cross sections
(,2n) / (,n)
0.36
(797.4 / 2189.5)
0.67
(887.0 / 1315.7)
of yields
Y(,2n) / Y(,n)
0.24
0.42
of cross sections
(,3n) / (,n)
0.063
(137.4 / 2189.5)
yields
Y(,3n) / Y(,n)
0.02
*) our estimation of the yields using cross sections data.
EMIN-2012
7/21/2015
Evaluation
Induced activity
Our data
0.49
(958.3 / 1956.3)
0.34 ± 0.07
20 – 23 September 2012, INR RAS, Moscow,
Russia
0.33 *)
0.055
(107.3 / 1956.3)
0.023 – 0.025
0.018*)
26
Induced activity
F New treatment for neutron multiplicity sorting
1
208Pb
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
One more
Physically unreliable
behavior (F2 > 0.5) of
Livermore data:
both (,2n) and
(,n) are «bad».
not typical case!
F
2
Physically reliable
Saclay data:
both (,2n) and
(,n) are «good».
Saclay data for
(,3n)
F
3
at E > 26 MeV:
no (,n) and
(,2n) ?
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
E, MeV
Russia
27
Pb-F1,2,3
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
New evaluated cross
sections
disagree with «bad»
Livermore data
, mb
, mb
, mb
, mb
208Pb
(,xn)
(,sn)
New evaluated cross
sections
agree with «good»
Saclay data
(,n)
(,2n)
data situation complicates(,3n)
the
problem of data reliability much more:
208Pb
, mb
7/21/2015
differ from situation for other nuclei
EMIN-2012
20 – 23
September
2012,
INR RAS, Moscow,
E, MeV
Saclay
data
are Russia
reliable!
28
208Pb-eval.
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Results of partial photoneutron reaction cross sections data investigation for
15 nuclei (90Zr, 115In,159Tb, 181Ta, 112,114,116,117,118,119,120,122,124Sn, 197Au, 208Pb)
obtained using various experimental methods mean that:
• at Saclay for all nuclei except 208Pb in accordance with F1,2,3 functions
behavior (,n) are over- but (,2n) - underestimated; for 208Pb competition
of both is reliable;
• at Livermore for all nuclei except 181Ta in accordance with F1,2,3 behavior
vise versa (,2n) are under- but (,n) - overestimated; for 181Ta (,2n) small
(5 %) underestimation is correlated with significant (46 %) (,n)
underestimation;
• for 181Ta data evaluated using new experimentally-theoretical method
proposed disagree with unreliable (F2 < 0.5) data obtained neutron
multiplicity sorting between “1n” and “2n” channels but agree with data
obtained using method of induced activity.
7/21/2015
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29
Results
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
At Saclay for neutron energy measurement the large Gd-loaded liquid scintillator
was used.
Because of formation of two neutrons in reaction (,2n) is realized at short nuclear
time at poor time resolution of detection system there is definite opportunity for
small pulses pile-up that certainly must lead to increasing the number of neutrons in
“1n” channel in comparison to that of “2n” channel.
At Livermore so-called “ring-ratio” method was used (concentric rings of counters
in paraffin moderator): low-energy neutrons (from reaction (,2n)) should have
enough time for moderation in the way to inner ring but high-energy neutrons (from
reaction (,n)) should go to the outer ring passing inner ring. But because of multiple
scattering the neutron way certainly should not be as straight line – there is definite
opportunity that neutron will go back to inner ring.
That will certainly increase the number of neutrons in “2n” channel in comparison
of that in “1n” channel.
7/21/2015
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30
Methods
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Neutron “1n” - “2n” - “3n” channels sorting unreliability directly depends on energy of
photons and therefore on neutron spectra – degree of disagreements under discussion and
neutron multiplicities obtained depend on individual features of neutron spectra.
That can be connected with that correlation between spectra of 1-st and 2-nd neutrons
contradict to the basic supposition of both Saclay and Livermore neutron multiplicity sorting
methods – unique neutron from (,n) reaction has energy more than both neutrons from
reaction (,2n).
Neutron “energy – multiplicity” connection is not really simple and direct. It was shown
(B.S. Ishkhanov, V.N. Orlin, S.Yu. Troshchiev, PAN 75, 253 (2012) ) that mean energy of the
first neutron from reaction (,2n) is much more than that of second neutron (for example for
181Ta at photon energy 25 MeV first neutron has mean energy 4.0 MeV, but second one – 1.4
MeV);similar situation takes place for 2-nd and 3-d neutrons from (,3n) reaction.
Additionally: in reaction (,n) after escape of unique neutron and in reactions (,2n) and
(,3n) after escape of first chance neutron the same nucleus is formed .
Moreover the same nucleus is formed in reaction (,np).
7/21/2015
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31
n-2n-np
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
MAIN CONCLUSIONS:
Practically all investigations using objective criteria show that neutron multiplicity sorting was
carried out incorrectly and data obtained are not reliable.
Systematical disagreements of data obtained using various neutron multiplicity sorting methods
appear from the neutron kinetic energy measurement shortcomings because connection between
multiplicity of neutron and its kinetic energy is complex and not direct.
Experimental data on partial photoneutron reactions cross sections should be remeasured and
reevaluated.
For reliable determination of partial photoneutron reactions cross sections the methods of direct
reaction identification – detection of final nucleus of induced activity or of outgoing neutrons in
coincidences – should be used.
Proposed experimentally-theoretical method of partial photo
neutron reactions cross sections evaluation based on joint using of experimental data for total
(,xn) and equations of modern model of photonuclear reactions give results in agreement to
those obtained using the method of induced activity.
7/21/2015
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32
Conclusions
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
New treatment for neutron multiplicity sorting
THANKS A LOT
and partial photoneutron reactions cross sections
evaluation
B.S.Ishkhanov,
V.N.Orlin, and V.V.Varlamov!
FOR
ATTENTION
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
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33
Thanks!
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Systematics of Saclay – Livermore disagreements between (,n) and (,2n)
(
51V, 75As, 89Y, 90Zr, 115In, 116,117,118,120,124Sn, 127I, 133Cs, 159Tb, 165Ho, 181Ta, 197Au, 208Pb, 232Th, 238U)
give to one opportunity to talk about general reasons.
Rint = intS/intL (arb. units)
“Special cases”
“Ideal cases”
Mass number A
Both at Saclay and Livermore neutron multiplicity was obtained from neutron kinetic energy on the base of
hypothesis about that both neutrons from “2n”-channel have energy smaller than one neutron from “1n”-channel,
but the number of neutrons with small energy is underestimated at Saclay but overestimated at Livermore.
Such disagreements should be connected with the neutron registration method.
7/21/2015
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34
General reasons
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
, mb
Significant disagreements – 25 %!
(,xn)
(,sn)
(,n)
(,2n)
(,3n)
7/21/2015
181Ta
, mb
, mb
, mb
“Bad” Saclay data are overestimated ( 12 %),
“Very bad” Livermore data are significantly
(46 %) underestimated
“Bad” Saclay data are underestimated (16%),
“Good” Livermore data are slightly (5 %) underestimated
, mb
EMIN-2012
20 – 23 September 2012, INR RAS,
Moscow,
E, MeV
Russia
35
181Ta –eval.
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Joint correction of both (,n) and (,2n) reaction cross sections of Saclay and Livermore for 208Pb
Part of “incorrect”
overestimated Saclay
(,n) cross section
must be transported
back into (,2n)
cross section
7/21/2015
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20 – 23 September 2012, INR RAS, Moscow,
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36
(,n) – (,2n) correction
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
159Tb
Reaction
Center of gravity
Ec.g., MeV
Integrated cross
section int,
MeVmb
Integrated cross
section int,
MeVmb
New evaluated data
Center of gravity
Ec.g., MeV
decreased for 27 %.
Saclay data
(,xn) *)
16.84
3200
3200
(,sn)
15.78
2383
2557
(,n)
14.04
1642
1950
14.6
(,2n)
19.04
714
610
19.9
(,3n)
26.29
26
16
26.8
7/21/2015
int(γ,2n)/int(γ,n)
16.84
Decrease for 9 %!
Decrease for 19 %!
Increase for 15 %!
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
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37
159Tb-data
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Disagreements (Saclay/Livermore)
of amplitudes – absolute values – integrated cross sections
5 clear cases (from “Atlas…” of S.S.Dietrich and B.L.Berman, Atomic Data and Nuclear Data
Tables, 38 (1988) 199) of int disagreements for appropriate integration energy limits Emax :
Nucleus
Eint-max
(MeV)
int
 s/int.L
51
V
27.8
27.8
689/654 = 1.06
75
90
As
Zr
26.2
25.9
29.5
27.6
1306/1130  1.16 1309/1158  1.13
133
Cs
24.2
29.5
2484/2505  1
165
Ho
26.8
28.9
3667/3385  1.08
The values obtained at Saclay are higher than that obtained at Livermore for about 6 – 16 %.
Explanation of the reasons (B.L.Berman, et al., Phys.Rev., C36 (1987) 1286): “… an Livermore
experiments error either in the photon flux determination or in the neutron detection efficiency or in
both”.
5 nuclei “S/L”
7/21/2015
EMIN-2012
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38
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Systematic of integrated cross section ratios “All other/Livermore” for about 500 total
photoneutron reaction (,xn) cross sections.
6,7
16
O
63,65
Cu
141
Pr
208
Integrated cross section ratio Rintsyst (arb. units)
Li
Pb
Rintsyst = 1.12
.
Target nucleus mass number A
7/21/2015
EMIN-2012
20 – 23 September 2012, INR RAS, Moscow,
Russia
Int. cross. sect.
ratios
39
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Important results:
•
clear data discrepancies force one to use data existed strongly individually;
•
quasimonoenergetic photons-data are strongly (3 – 4 times) over-smoothed and must be additionally
reprocessed to take into account real shape of apparatus function (effective photon spectrum);
•
Livermore total photoneutron reaction (,xn) cross sections have in general absolute values smaller
then that obtained at various other laboratories; the reason: “… an Livermore experiments error either in
the photon flux determination or in the neutron detection efficiency or in both”; therefore Livermore (,xn)
cross sections data of for 19 nuclei studied specially must be multiplied by appropriate coefficients
Rint(,xn) and for others – by <Rintsyst> = 1.12 at least;
•
Saclay partial photoneutron reactions (,n) and (,2n) cross sections are not correct and consistent each
other because of incorrect neutron multiplicity sorting procedure used and must be recalculated;
•
Livermore neutron multiplicity sorting procedure at the same time is correct and therefore Livermore
(,n) and (,2n) cross sections are in consistence with each other and with (,xn) cross sections and both can
be used but again only multiplied by coefficients Rint(,xn) or <Rintsyst>.
Important
results
7/21/2015
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20 – 23 September 2012, INR RAS, Moscow,
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40
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
3 important physical consequences:
•
GDR structure (resonances with width ~ hundreds of keV) exists; BR-data look like preferable for GDR
structure detailed study because QMA-data are strongly over-smoothed;
•
E1 GDR decays dominantly statistically - Saclay interpretation of high-energy tails of (,n) reaction
cross sections as contributions of high-energy neutrons from GDR nonstatictical direct decay (those
contributions evaluated to be about 17 - 30 %) because of small decreasing of (,n) reaction cross sections
for energies higher than (,2n) reaction threshold B(2n) looks like as very doubtful; Saclay (,n) data
corrections described decrease those and put them into accordance with Livermore data: direct decay
contributions are not more than 10 - 12 %;
•
big extra integrated cross section int(,abs)  1.3 – 1.5 60NZ/A (MeVmb) became doubtfully being all
due to effective mass of nucleon changing because of the effect of exchange forces; Saclay data correction
described affects photoabsorption cross section evaluation using cross section data combinations (,abs) =
(,sn) + (,p) and (,sn) = (,xn) - (,2n); mistake in (,2n) reaction data produces the mistakes in both (,sn)
and (,abs) reaction data; correction described do them noticeably smaller.
Physical
consequences
7/21/2015
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20 – 23 September 2012, INR RAS, Moscow,
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41
New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
Neutron multiplicity sorting procedure test:
Twice measurement of
181Ta(e,2n)180Ta
cross section s(e,2n) = ½(s(e,xn) - s(e,n)):
1.
1(e,n) – neutron multiplicity sorting measurement;
2.
 2(e,n) – measurement of induced activity (decay 180Ta  180Hf , 93.3 keV, Ge-Li).
Mean-square ratio < 1(e,n)/ 2(e,n)> = 1.057 ± 0.023 means high reliability of
multiplicity sorting procedure.
Comparison of (e,n) and (,n) data show that Saclay data for (,2n) reaction are
underestimated and correspondingly that for (,n) reaction – vise versa
overestimated.
Multiplicity
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20 – 23 September 2012, INR RAS, Moscow,
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New treatment for neutron multiplicity sorting
and partial photoneutron reactions cross sections evaluation
B.S.Ishkhanov, V.N.Orlin, V.V.Varlamov
CDFE services statistics:
January 2012
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Statistics
43