Transcript Slide 1

Investigation of fast neutron spectra in the uranium
assembly of the experimental set-up "Energy plus
transmutation" in the JINR NUCLOTRON proton
beam at an energy of 1.5 GeV
Yu.A. Batusov1, V. Bradnova1, S.R. Hashemi–Nezhad 2,
V.V. Tereshchenko1 and S.V. Tereshchenko1
1. Joint Institute for Nuclear Research (JINR), Dubna, Russia.
2. School of Physics, University of Sydney, Australia.
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Experimental setup
Energy plus Transmutation (EPT) assembly
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Nuclear Emulsion Chambers and Irradiation
The setup was irradiated with protons of energy 1.5 GeV from the Nuclotron
Accelerator.
Emulsion chambers were exposed to neutrons from the setup for a period of 0.9 s.
Total number of protons on the target was 1.51010.
The Emulsion chambers were composed of 3 plates of
0.6 x 25 x 100 mm in contact with each other
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Y
Emulsion
plates
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After exposure emulsions were developed and fixed in
usual manner.
Y
For more than 5000 recoil proton tracks the track length
and angle with respect to Y-axis were measured.
Emulsion
plates
Only tracks in the middle emulsion plate and within a
volume restricted to the emulsion thickness and within a
width of 1 mm at its center along its length were measured.
This method filters large number of the neutrons that their
direction is not parallel to Y-axis.
From the track lengths the recoil proton energies were
calculated.
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Background neutron measurements
N
Two emulsion
chambers were
exposed to the back
ground neutrons of
irradiation hall and
the EPT setup. Both
in absence of the
proton beam for a
period of 150 times
the when beam was
on.
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Laboratory
U/Pb Setup
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1000
En (MeV)
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En (MeV)
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En (MeV)
Red points outside the assembly
Blue points inside the assembly
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Monte Carlo Simulations (a brief description)

Main Monte Carlo simulations were performed using the MCNPX code.

The EPT setup and the emulsion chambers were built in the code and
the setup was “irradiated” with 1.5 GeV protons along the target axis.
In this series of calculations the following steps were taken
We used the PTRAC card in the MCNPX input file to obtain the neutron
collisions with the nuclei within the emulsion. For the composition of the
emulsion we used that of the Ilford G-5, with a density of 3.907 g.cm-3.

SSW card was used to record the neutrons that enter the emulsion volume
from its different surfaces.

Extra codes were written to analyze the PTRAC and WSSA output files.

A code was written which uses the PTRAC as an input and produces
the recoil events and transports recoil nuclei in the emulsion.

In this program it was assumed that the neutron scattering in the centre of
mass coordinate system is isotropic.

The scattering angles, direction cosines and the recoil nuclei energies were
calculated in the laboratory system.
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EPT setup as seen
by MC- code
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Proton recoil spectrum
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Experiment
Normalised MC
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MC results
agree with the
experiment
within 1-2 .
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Proton recoil energy (MeV)
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Neutron spectrum
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Experiment
Calculation
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En (MeV)
In the calculations
only neutrons that
their direction is
parallel to Y-axis are
taken into account.
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0
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En (MeV)
Experimental and calculated spectra of the neutrons
that have resulted in proton recoils in the emulsion.
The width of the energy bins at neutron energies of
En  40 MeV and 40< En  200 MeV are En = 0.5
MeV and En = 10 MeV respectively.
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Neutron spectrum (continued)
From the figure it is evident that
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Experiment
Calculation
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En (MeV)
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1) At neutron energies of En 
40 MeV the experimental
and calculated spectra of the
colliding neutrons are in
agreement within one
standard deviation for En > 3
MeV.
2) However at neutron
energies of En < 3 MeV the
experimental and the
calculated spectra are not in
agreement.
3) At En > 40 MeV large
discrepancies exist between
the calculated and
experimental spectra.
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In spite of the observed discrepancies, the weighted mean
neutron energies from the measured and calculated spectra
are in agreement.
Weighted mean energy of the neutron spectra for
different energy intervals
Weighted mean energy
(MeV)
Neutron
energy
interval
Experiment
Calculation
1 – 20 MeV
4.7  0.5
4.5 MeV
1 – 40 MeV
6.0  0.5
5.7
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Origins of the observed discrepancies
The observed agreement between the experiment and
calculation in the case of the recoil proton spectrum as
shown in the following figure, indicate that
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The error must have been due to the
measurement related to the recoil angle q .
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Experiment
Normalised MC
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E p  En cos2 q
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In other words some of the measured
angles (with respect to Y-axis) were not the
true recoil angles of the recoil protons with
respect to the neutron direction.
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Proton recoil energy (MeV)
To examine this following calculations were carried out.
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400
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Experiment
Calculation
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The experimental and calculated
energy spectra, obtained with the
assumption that all neutrons
involved in the proton recoil
production have a direction
parallel to the Y-axis
(i.e. same as the experiment
measurements)
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En (MeV)
A perfect agreement (within one standard deviation)
between the calculated and experimental data is obtained
for neutrons of energy En > 1 MeV.
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300
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 = Recoil angle with neutron direction (Calc)
 = Recoil angle with Y-axis (Exp)
 = Recoil angle with Y-axis (Calc)
Recoil protons of E> 200 keV
are taken into account
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0.0
0.1
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0.9
1.0
cos()
The calculated and experimental distributions of the recoil
protons space angles with respect to Y-axis and the calculated
distribution of the recoil protons space angle with respect to the
direction of the incident neutrons.
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Conclusions
The complete agreement between the
calculations and experiment the when the
exact conditions of the experiment was used
in MC-calculation, implies that
If properly collimated neutron beam is used or
much better stray neutron filters is employed
a perfect agreement between the
experimental and calculated high-energy
neutron spectra is expected.
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