Nuclear Instruments and Methods in Physics Research A 426 (1999) 72—77
New irradiation zones at the CERN-PS
M. Glaser , L. Durieu , F. Lemeilleur *, M. Tavlet , C. Leroy, P. Roy
ROSE/RD48 Collaboration
CERN, 1211 Geneva 23, Switzerland
University of Montreal, Montreal, Canada
Abstract
After the upgrade of the CERN-PS East Hall, one irradiation zone with 24 GeV/c protons is foreseen to be operational
by the second half of 1998. Another irradiation zone with about 1 MeV neutrons will be commissioned by the first half of
1999. 1999 Elsevier Science B.V. All rights reserved.
1. Introduction
The CERN-PS neutron irradiation facility
(PSAIF) [1] and the PS-T7 proton beam [2] have
been extensively used in the past for testing the
radiation hardness of materials and semiconductor
devices. Both facilities have been closed by December 1996 and September 1997, respectively. Following the strong demand from the R&D projects on
radiation hardness of semiconductor devices and
from the LHC experiments for testing detector
prototypes, two irradiation zones — one with
protons and the other with neutrons — are being
designed using the 24 GeV/c proton primary beam
of the CERN-PS. Fig. 1 shows the general lay-out
of the future beams and experimental areas of the
PS East Hall [3,4], including the proton irradiation
zone on the T7 beam and the neutron irradiation
zone at the end of the T8 beam downstream the
DIRAC experiment. Each irradiation zone will be
* Corresponding author.
equipped with a remote controlled shuttle to move
the samples to be irradiated from the counting
room into the irradiation area. The proton and the
neutron bursts will be delivered during the 14.4 s
supercycle of the PS in 1—3 spills of about 400 ms.
Sections 2 and 3 deal with details on the proton and
neutron irradiation zones including the expected
background contamination, the particle energy
spectra and the particle radial distributions. The
last section discusses the radiation safety operations needed.
2. Proton irradiation zone
The primary 24 GeV/c T7 proton beam is directed using the BZH01 horizontal bending magnet
towards the iron shielding wall upstream of the
DIRAC experiment area as shown in Fig. 2. The
maximal beam intensity is 2—4;10 protons/spill.
A quadrupole system and a frequency program is
spreading out the beam in order to produce a
0168-9002/99/$ — see front matter 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 8 - 9 0 0 2 ( 9 8 ) 0 1 4 7 2 - 7
M. Glaser et al. / Nuclear Instruments and Methods in Physics Research A 426 (1999) 72—77
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Fig. 1. Lay-out of the CERN-PS beam lines and areas in the East Hall after July 1998, showing the proton and the neutron irradiation
areas.
Fig. 2. Lay-out of the proton irradiation zone.
uniform proton irradiation ($10%) over a surface
of several square centimeters. The flux is expected
to be about 2;10 cm\ s\, depending on the
beam profile, with one spill per PS supercycle.
In order to limit the amount of backscattered
particles from the downstream iron shielding wall
where the beam is dumped, a marble absorber with
a size of 80;40;20 cm is placed between the
irradiation area and the iron wall.
Fig. 3. Radial distribution of backscattered particles at a distance of 20 cm from the shielding wall (from bottom to top:
protons, negative pions, positive pions, gammas and neutrons).
The primary beam intensity is 4;10 protons.
A simulation of the backscattered particle background was performed using the MICAP generator
for neutrons with energy below 20 MeV and
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M. Glaser et al. / Nuclear Instruments and Methods in Physics Research A 426 (1999) 72—77
Fig. 4. Energy spectra of backscattered particles at a distance of 20 cm from the shielding wall.
FLUKA for neutrons with energy higher than
20 MeV and for the other particles [5,6]. The energy cuts are 10 keV for neutrons, 14.5 MeV for
the other hadrons and 100 keV for gammas.
Fig. 3 shows the radial distribution of backscattered secondary particles produced by 4;10 incident protons in a plane situated at 20 cm upstream
from the wall, a distance at which the irradiation
will be performed. Fig. 4 shows the energy spectra
of these particles. The neutrons with an energy
larger than 200 keV is estimated to contaminate the
24 GeV/c protons fluence by about 5% at the position of irradiation and the addition of marble reduces the backscattered background by a factor
two. Moving upstream the irradiation point from
the wall could have further reduced this background. But the lay-out of the concrete protection
shielding through which the shuttle conduit is
inserted did not permit it.
The proton shuttle will move on a rail inside an
iron conduit with a section of 40;25 cm and
a length of about 15 m. This conduit, inserted in the
protection shielding, has three chicanes to avoid
secondary particles to come out from the beam
zone. The remote controlled shuttle will support
a container able to handle samples to be irradiated with a maximum area of 10;10 cm
over a longitudinal length of about 15 cm. At the
M. Glaser et al. / Nuclear Instruments and Methods in Physics Research A 426 (1999) 72—77
75
irradiation point, the container will have a vertical
and a horizontal movement covering an area of
10;10 cm in order to align and to displace the
samples in the beam. Samples with a larger size,
such as silicon detector assembled modules, cannot
be irradiated using this remote controlled facility.
In this case, the samples have to be placed manually
into the T7 beam, requiring accesses to the primary
beam area.
A luminescent screen with a camera will be used
to display and optimize the beam profile. A secondary emission chamber (SEC) will provide a
measurement of the proton beam intensity. The
fluence will be measured by activation of the aluminium foils. From the past experience, this technique
should provide fluence measurements with an accuracy of $7%.
3. Neutron irradiation zone
Fig. 5 shows the layout of the neutron irradiation
zone. The irradiation will be performed in a
40;40;40 cm cavity with the secondary particles, produced by the primary T8 24 GeV/c proton beam after crossing a 20;20;50 cm carbon
block and 30 cm of iron from the beam dump.
Fig. 5. Lay-out of the neutron irradiation zone.
Fig. 6. Radial distribution of direct and backscattered particles
in the cavity and in the shuttle access channel after 50 cm
a carbon and 30 cm of iron (bottom curve for protons and pions,
top dashed curves for neutrons and top full curve for gammas).
The primary beam intensity is 4;10 protons.
The simulation [7] of the radial distribution of
the fluences obtained for the direct and backscattered particles in the cavity and in the shuttle access
channel is presented in Fig. 6 for a primary beam
intensity of 4;10 protons, while their energy
spectra is shown in Fig. 7. The energy cuts are
10 keV for neutrons, 14.5 MeV for the other hadrons and 100 keV for gammas.
In the irradiation cavity, a total neutron flux of
about 0.5;10 cm\ s\ (for one spill of 2;10
protons per PS supercycle) is expected among
which about half is for neutrons with an energy
above 200 keV. The total contamination with other
hadrons is of the order of 10% with an average
energy of about 500 MeV. At a distance of 50 cm
from the cavity center, in the vertical access channel, the neutron flux is reduced by a factor two but
the hadron contamination is reduced by two
orders of magnitude. Dosimetric and particle flux
measurements are planned to be performed at the
start of this facility.
The samples to be irradiated will be introduced
in the cavity from the counting room by a remote
controlled shuttle moving into a 40;40 cm
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M. Glaser et al. / Nuclear Instruments and Methods in Physics Research A 426 (1999) 72—77
Fig. 7. Energy spectra of direct and backscattered particles in the neutron irradiation cavity.
conduit with 5 chicanes and a length of about 15 m.
The size of the samples to be irradiated could be
up to 20;20 cm.
4. Safety aspects
The irradiation facilities equipped with shuttles
will allow to irradiate samples without interrupting
the beams for the PS East Hall experiments. Both
facilities will have the possibility of biasing devices
from the counting rooms during irradiation. The
proton irradiation zone will be commissioned in
July 1998 and the neutron irradiation zone is expected to become operational in the spring of 1999.
The operation of these multipurpose irradiation
facilities needs to follow the CERN radiation safety
rules as summarized in Ref. [8]. In particular, the
irradiation experiments must be prepared in agreement with one of the CERN authors of this paper,
and they will be written down in a dedicated logbook. The experimenters must own a valid CERN
access card and must wear their personal film
badge. All samples irradiated with hadrons are
radioactive. The induced radioactivity is to be
checked, the irradiated samples are to be handled,
transported and stored in accordance with the
CERN radiation safety rules. In particular, the persons responsible for the irradiation experiments
must guaranty the traceability of the irradiated
samples. They must ensure that the laboratories
where the post-irradiation measurements are
performed are equipped to handle radioactive
M. Glaser et al. / Nuclear Instruments and Methods in Physics Research A 426 (1999) 72—77
materials, and that the personnel are informed
about their manipulation. And last but not the
least, no irradiated sample shall leave the CERN
sites without the approval of the Radiation-Protection Group.
Acknowledgements
The authors wish to thank J. Y. Hemery who
performed the preliminary Monte Carlo studies
showing the feasibility of neutron production for
irradiation.
References
[1] M. Tavlet, M.E. Leon Florian, PSAIF: The PS-ACOL Irradiation Facility at CERN, IEEE Cat. No 91TH0400-2, 1991.
77
[2] F. Lemeilleur et al., Neutron, proton and gamma irradiations of silicon detectors, IEEE Trans. Nucl. Sci. NS-41 (3)
(1994) 425.
[3] J.Y. Hemery et al., EHNL-5: Proposal for the beam lines
and areas for test and experiments in the East Hall, CERNPS-PA Note, 96-28.
[4] L. Durieu et al., The CERN PS East Area in the LHC Era,
Proc. Physics Accelerator Conf. 1997, Vancouver B.C.,
p. 228.
[5] C. Leroy, P. Roy, Calculation of particle fluxes in the PS
silicon irradiation zone (with marble dump and angle of
incidence), University of Montreal Report, GPP-EXP-9803.
[6] C. Leroy, P. Roy, Calculation of particle fluxes in the PS
silicon proton irradiation zone, University of Montreal Report, GPP-EXP-98-02.
[7] C. Leroy, P. Roy, Calculation of particle fluxes in the PS-T8
silicon neutron irradiation zone, University of Montreal
Report, GPP-EXP-98-01.
[8] Radiation Protection Procedure No 17: Radiation safety
rules for material irradiation at CERN, 1997.
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