NEWS BIOPHYSICS Antiprotons could help fight against cancer A pioneering experiment at CERN with 120 6 MV photons potential for cancer therapy has produced its 100 protons first results. Exploiting the unique capability 150 MeV antiprotons 80 of CERN’s Antiproton Decelerator to produce an antiproton beam at the right energy, 60 the Antiproton Cell Experiment (ACE) has dose (%) 40 shown that antiprotons are four times more 20 effective than protons for cell irradiation. 0 Cancer therapy is about collateral 0 2 4 6 8 10 12 14 16 18 20 damage: destroying the tumour while depth in water (cm) avoiding the healthy tissue around it. Physical dose deposition by X-rays, protons Unwanted exposure of healthy tissue and antiprotons, as calculated using the could cause side effects and result in a Monte Carlo simulation code FLUKA, clearly reduced quality of life. It is also believed to demonstrates the reduction of dose outside increase the chances of secondary cancers the target area for protons and antiprotons developing. In radiation therapy there is an Michael Holzscheiter, ACE spokesperson compared with X-rays. Antiprotons are ongoing quest to reduce the radiation level (left), retrieves an experimental sample also expected to enhance the biological to tissue outside the primary tumour volume. after irradiation with antiprotons, while effective dose in the Bragg peak, rendering In hadron therapy, which began in Niels Bassler (centre) and Helge Knudsen the difference between protons and 1946 with Robert Wilson’s seminal paper, from the University of Aarhus look on. antiprotons even more significant. “Radiological Use of Fast Protons”, the dose profile of heavy charged particles (hadrons) about a 2 cm range in water. After irradiation the enhanced energy deposition in the does not irradiate healthy tissue because the gelatine is extruded from the tubes and vicinity of the annihilation point and the most of the energy is deposited at the end cut into 1 mm slices. These are then dissolved higher biological effectiveness of this extra of the flight path of the particles – the Bragg in growth medium and the cells are placed in energy (delivered by nuclear fragments). peak – with little before and none beyond Petri dishes in an incubator. After a few days The experiment demonstrates a significant (see p17). However, the question remains of the naked eye can see that some of the cells reduction of the damage to the healthy cells how to maximize the concentration of energy have produced healthy offspring. This gives along the entrance channel of a beam for onto the target. a measure of the survival of cells along the antiprotons compared with protons. The first speculations that antiprotons beam path for the different dose levels. Cell While antiprotons may seem unlikely could offer a significant gain in targeting survival is plotted for the entrance and the candidates for cancer therapy, the initial tumours through the extra energy released Bragg-peak regions as a function of particle results from ACE indicate that these by annihilation date back more than 20 years fluencies, and the ratio of dose for a 20% antimatter particles could lead to more (Gray and Kalogeropoulos 1984). Now the survival in these two regions is extracted. effective radiation therapy. There is no ACE collaboration has tested this idea by Comparing beams of protons and doubt, however, that the first clinical directly comparing the effectiveness of cell antiprotons that cause identical damage at application is still at least a decade away. irradiation using protons and antiprotons. the entrance to the target, the results of the To simulate a cross-section of tissue inside experiment show that the damage to cells Further reading a body, the experiment uses tubes filled with inflicted at the end of the beam is four times L Gray and T E Kalogeropoulos 1984 live hamster cells suspended in gelatine. higher for antiprotons (Holzscheiter et al. Radiation Research 97 246. These are irradiated with beams of protons 2006.) The method directly samples the total M H Holzscheiter et al. 2006 Radiother. or antiprotons at a variety of intensities with effect of the beams on the cells, combining Oncol. doi:10.1016/j.radonc.2006.09.012. Sommaire Les antiprotons – un nouveau traitement pour le cancer? 5 CDF trouve de premiers baryons contenant des quarks b 9 ALICE: l’installation des détecteurs va de l’avant 6 KEDR vise toujours plus de précision pour ses mesures Une cible en cristal de tungstène crée un faisceau intense de de la masse 11 positons au KEKBt 7 La cape d’invisibilité grâce à la magie des méta-matériaux 13 AD: Vers une chimie des antiprotons 8 La vitesse limite des positons galatiques 14 CERN Courier December 2006 CCDecNews5-9.11.indd 5 15/11/06 09:03:13 NEWS LHC EXPERIMENTS ALICE forges ahead with detector installation Two sections of the High Momentum Particle Identification Two installed supermodules of the Time of Flight and the Detector remain visible as it is inserted into the ALICE magnet. Transition Radiation Detector. (Courtesy Antonio Saba for CERN.) When it starts up the ALICE experiment University and INFN, CERN (PH-DT1, -DT2 (0.4 mm thick) and spacers, with 96 readout will observe collisions of heavy ions in and -AIT groups) and the Institute for Nuclear pads, each 3.5 cm × 2.5 cm. The full CERN’s Large Hadron Collider (LHC), where Research, Moscow, is approximately 8 m detector, which contains 138 MRPC strips “fireballs” of extremely hot and dense matter wide by 8 m tall, and weighs about 5 t. It with a total of 157 248 readout channels, will be fleetingly made. Up to 20 000 tracks comprises seven identical modules shaped covers a cylindrical surface of about 150 m2 will emerge from each fireball, and one of to fit against two sides of ALICE’s octagonal at 3.7 m from the beamline, and weighs 25 t. the challenges for ALICE will be to identify magnet. The modules, fully equipped with It is the responsibility of the INFN sections in different particles among this veritable electronics, were individually transported to Bologna and Salerno, in collaboration with “haystack” (CERN Courier September 2003 ALICE and mounted on a support structure. the Institute for Theoretical and Experimental p20). Different elements in the armoury The complete HMPID was then lowered Physics, Moscow, and Kangnung National of particle identification for ALICE are now into the cavern and inserted inside the University, Republic of Korea. arriving in the experiment’s underground magnet. Three months of preparation by The TRD must identify high-energy electron cavern, beginning with the High Momentum CERN (PH-DT1 and AIT) and Bari groups, pairs generated in the fireballs. It comprises Particle Identification Detector (HMPID), and the help of the CERN transport service, 18 supermodules that form a cylinder around which was installed inside the solenoid ensured that transport and installation were the large Time Projection Chamber in the magnet on 23 September. This was soon accomplished within a few hours. central barrel of the ALICE experiment. followed by the first elements of the Time With an active area of about 11 m2 Each supermodule is about 7 m long and of Flight (TOF) system and the Transition covered with CsI, the HMPID is the largest comprises 30 drift chambers in six layers. The Radiation Detector (TRD). application of this technology. Development construction of the modules is a collaboration The HMPID will extend hadron identification began at CERN in the RD2 project, and between the Universities of Frankfurt and in ALICE up to 5 GeV/c, complementing the it took 15 years for the method to reach Heidelberg, GSI Darmstadt, the National reach of the other particle-identification the current scale and efficiency. The full Institute of Physics and Nuclear Engineering, systems. It is a ring-imaging Cherenkov production of the 42 photocathodes Bucharest, and the Joint Institute for Nuclear detector in a proximity-focusing configuration, required to equip the detector, from CsI Research, Dubna, with the radiators produced which uses liquid CF14 as the radiator deposition to quality control, was done by at the University of Munster. medium, while a 300 nm layer of caesium the groups at CERN. During the summer the drift chambers iodide (CsI) on the cathode of a multiwire The first week of October saw the for the first supermodule were equipped proportional chamber converts the Cherenkov installation of the first two supermodules for with readout electronics and inserted into photons into electrons. This layer is divided the TOF system, which will be used to identify the supermodule hull at the University of into 11 280 pads, each 8 mm square, which the thousands of pions, kaons and protons Heidelberg. After transportation to CERN on are individually read out by two ASIC chips, produced in each fireball. Its basic element 27 September, the module was tested on GASSIPLEX and DILOGIC, developed with the is a multigap-resistive-plate-chamber (MRPC) the surface using cosmic rays before being Microelectronics Group at CERN. strip, with a 120 cm × 7.4 cm active area lowered into the ALICE cavern on 9 October. The complete HMPID, realized by Bari made of a sandwich of resistive glass sheets The final installation took place a day later. CERN Courier December 2006 CCDecNews5-9.11.indd 6 15/11/06 09:03:43 NEWS POSITRONS Tungsten-crystal target boosts positron intensity at KEKB linac 1200 new tungsten crystal target (10.5mm thick) 0.040 previously used tungsten target (14mm thick) tungsten crystal 0.035 1000 standard tungsten plate 800 0.030 600 0.025 400 0.020 0.015 number of beam pulses 200 0.010 0 0 0.14 0.18 0.22 0.26 relative positron yield (arbitrary units) 0.005 conversion efficiency (Ne+/Ne–) 0 Fig.