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 73 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 II. HARDENING FACILITIES
74 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 II. HARDENING FACILITIES
76 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 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. [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, CERN- PS-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-98-03. [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. II. HARDENING FACILITIES