Safety Report for experiment E1104 : Beamtime Schedule 113 16-31 July 2008 Study of halo effects in the Scattering of 11 Li with heavy targets at energies around the Coulomb Barrier Experiment Leaders : M.J.G. Borge, IEM-CSIC, borge@iem.cfmac.csic.es J. Gomez-Camacho U.Sevilla gomez@us.es I. Martel U. Huelva imartel@uhu.es O. Tengblad, IEM-CSIC, imtot4a@iem.cfmac.csic.es Safety Co-ordinator : Patrick Walden, TRIUMF, mrspi@triumf.ca ext : 7340 Background : The scattering of halo nuclei is strongly affected by coupling to the continuum. At energies below the Coulomb barrier, the dominant effect is that of the dipole Coulomb force that couples the ground state to the low energy continuum. Nuclear effects should also play a role, even at energies below the Coulomb barrier, due to the long range of the halo. A careful analysis of the elastic and break-up cross section of a halo nucleus on a heavy target at energies around the Coulomb barrier should give information on the B(E1) distribution of the halo nucleus, and also about the reaction mechanisms that govern the collisions of halo nuclei. The B(E1) distribution is a measurement of the importance of polarizability. Large B(E1) values at low excitation energies (close to the break-up threshold) indicate that the nucleus is easily polarizable. In terms of the ground state wavefunction, large B(E1) values at energies close to the break-up threshold indicate a large probability that the halo neutrons are in the extreme asymptotic tail. The experiment proposed consists in measuring the elastic differential cross section and the break-up cross sections of 11 Li on 208 Pb at 2.2 and 2.7 MeV/u laboratory energy. We expect to observe and quantify the reduction of the elastic differential cross sections at forward and backward angles compared to the Rutherford cross section. We shall also observe the angular and energy distribution of the 9 Li fragments coming from the projectile break-up. To confirm the correctness of our method of measurement and analysis, and to determine the interactions of the core of the halo nucleus, we will repeat the same measurements using the non-halo nuclei 9 Li on the same target at equivalent energies ( 9 Li at 2.67 and 3,27 MeV/u). Beamline and vacuum chamber: The experiment will be installed at the SEBT2 beam line in between the existing PPAC and the F-cup chamber at the end of the beam line (see photo): 1
Photo of the SEBT2 beam-line with our reaction chamber overlayed. The beam is coming in from the right. We will bring a scattering chamber with dimensions 30x35x35 cm 3 (see attached pdf file for exact measurements of the chamber with beam tube extensions) in which we fit the detector set-up. Appropriate connecting flanges (KF50) to the beam line will also be brought. The beam will pass through two collimators separated by 3 cm, the first of Al with a 5mm hole and the second of Bi with 4 mm hole placed about 8 cm in front of the target position. The beam profile at the target position is expected to be ±1mm based on beam optics simulations Targets : The targets are thin (0,82 mg/cm 2 and 1.2 mg/cm 2 ) foils of Pb and Bi respectively. These targets have been prepared outside TRIUMF at GSI. 2
Fig. 2 Experimental Set-up Safety considerations : Cryogenics : NO cryogenics is needed. Vacuum : The standard turbo pump + scroll pump system being used at the F-cup chamber will be sufficient to also pump our chamber. The chamber is filled with detectors and cables, why standard pressure reached is a few times 10-6 mbar. Radiation : The experiment use beams of 9-11 Li accelerated by ISAC-II to total energy of approximately 24 and 30 MeV. The main beam (90% of the beamtime) is 11Li where no extra radiation is really expected due to the low yield (10 4 ). However, when running the 9Li beams for calibration some neutron activity around the set-up can be expected. But we cannot take to high data rate to avoid dead time (10 6 maximum) so should not exceed 5x10 5 neutrons/s with a spectrum peaking a 680 kev. There is no gamma ray activity expected. Electrical : Electrical power for the vacuum pumps, electronics is installed at the beamline to acceptable industrial and engineering standards. We will use existing TRIUMF VME and NIM crates so NO european 220V will be needed. 3
Addendum to the E1104 Safety Report P. Walden June 23, 2008 Some Quantitative Assessment of the Radiation Fields: The beam fluxes to be requested in this experiment are 10 4 pps of 11 Li and up to 5 10 5 pps of 9 Li. The latter beam will be the most potent source of radiation. It has a high energy β decay with an endpoint energy of 13.6 MeV for decays to the ground state of 9 Be, and 50% of the time an excited 9 Be will decay into a neutron and two alpha particles. The alphas are of no concern as they do not exit the target chamber. However the radiation field from the neutrons needs to be considered. The β field: The β field from 9 Li will be similar to that from 8 Li which also emits a high energy beta (12.96 MeV). Thus fields from 9 Li of similar intensity as that of 8 Li should be equal. Measurements were taken for a beam of 8 Li at TUDA for a beam flux of 2 10 7 pps. The results are given in table I. Table I Collimator FCUP Distance (m) 1700 >2000 contact 50 100 0.5 10 30 1.0 Radiation fields observed around TUDA in μsv/hr for a 8 Li beam flux of 2 10 7 pps. Collimator and FCUP refer to the entrance collimator and exit faraday cup of the TUDA chamber The fluxes for E1104 will be down by a factor of 2 10 7 / 5 10 5 = 40. Rewriting the table to account for this factor gives the results in table II Table II Collimator FCUP Distance (m) 42.5 >50 contact 1.25 2.5 0.5 0.25 0.75 1.0 Radiation field levels in μsv/hr expected in E1104 for the beam fluxes requested With these levels of radiation there is no concern. A sign posted, if required, of a radiation source when beam is on will suffice. The fields indicate full time occupancy will be allowed.
The n field: The n fields from a 9 Li beam have been measured in the case of the Loveland experimental run in ISAC-II at the same location where E1104 is to be run. Surveys conducted during experiment E1023 reported 65 μsv/hr at two meters and zero degrees from the beam stop for a beam of 1.5 ppa of 9 Li. The requested beam flux for E1104 in ppa equivalents is 0.08 ppa. The expected field will then be 65 0.08/1.5 = 3.47 μsv/hr at two meters and zero degrees from the beam stop. If the r 2 law holds true, the expected field at 1m would be 13.9 μsv/hr. These fields are manageable with signs and barriers. Operating Procedure: Once radioactive beam is tuned to the experiment, surveys of β, γ, and n fields will take place. Required barriers and signs will be posted. After delivery of beam, the target chamber will be opened wearing respirators and swipe tests will be conducted before any work commences on the target chamber.