The FRIBs@LNS facility produces Radioactive Ion Beams (RIBs)

at intermediate energies, by projectile fragmentation. The possibility of using the produced RIBs as secondary beams in nuclear physics experiments by applying the tagging technique, i.e. the identification, event-by-event, in charge, mass and energy of each ion of the RIBs cocktail selected by the fragment separator, before it interacts with the secondary target, has been demonstrated. In 2010 an upgrade of the facility has been performed. Status and perspectives of the FRIBs@LNS facility are discussed

Agodi, C.

Calabretta, L.

Cardella, G.

De Napoli, M.

Giacoppo, F.

Raciti, G.

Rapisarda, E.

Sfienti, C.

English

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DOI 10.1393/ncc/i2011-11067-8Colloquia: IFAE 2011IL NUOVO CIMENTO Vol. 34 C, N. 6 Novembre-Dicembre 2011Past, present and future of radioactive ion beams producedIn-Flight at LNSM. De Napoli(1), G. Raciti(1)(2), C. Agodi(1), L. Calabretta(1),G. Cardella(1), F. Giacoppo(1), E. Rapisarda(1) and C. Sfienti(1)(2)(1) INFN, Laboratori Nazionali del Sudvia S. Sofia 62, 95123 Catania, Italy(2) Dipartimento di Fisica e Astronomia, Universita` di Cataniavia S. Sofia 64, 95123 Catania, Italy(ricevuto il 29 Luglio 2011; pubblicato online il 6 Dicembre 2011)Summary. — The FRIBs@LNS facility produces Radioactive Ion Beams (RIBs)at intermediate energies, by projectile fragmentation. The possibility of using theproduced RIBs as secondary beams in nuclear physics experiments by applyingthe tagging technique, i.e. the identification, event-by-event, in charge, mass andenergy of each ion of the RIBs cocktail selected by the fragment separator, before itinteracts with the secondary target, has been demonstrated. In 2010 an upgrade ofthe facility has been performed. Status and perspectives of the FRIBs@LNS facilityare discussed.PACS 29.38.-c – Radioactive beams.PACS 25.70.Mn – Projectile and target fragmentation.PACS 29.30.Aj – Charged-particle spectrometers: electric and magnetic.1. – IntroductionThe study of nuclei far from the valley of stability has introduced new dimensionsof nuclear physics. The merits of exotic nuclear beams have been demonstrated withexciting new discoveries, particularly near the borderlines of particle stability, where newcharacteristics of nuclear structure and decay have been found. Presently, the produc-tion of exotic beams is realized either by applying nuclear production mechanisms atintermediate-relativistic energies and in-flight separation (In-Flight method) or by usingthe isotope separator online (ISOL) method in combination with a post-accelerator. Thesuccess of the present exotic nuclear beam facilities is the motivation for new projectsand plans for next-generation devices. However, at present, only few facilities produceRIBs at intermediate energies. This circumstance has motivated the development of theIn-Flight FRIBs@LNS facility at the Laboratori Nazionali del Sud in Catania (Italy).c© Societa` Italiana di Fisica 350PAST, PRESENT AND FUTURE OF RADIOACTIVE ION BEAMS ETC. 351Fig. 1. – Layout of the Laboratori Nazionali del Sud. The position of the FRIBs@LNS fragmentseparator is indicated.2. – The FRIBs@LNS facilityThe production of RIBs at intermediate energies at LNS was achieved by the In-Flightmethod, using primary stable beams accelerated by the Superconductive Cyclotron (SC)at energies between 62 and 40A MeV. In order to optimize the RIBs production, wehave used a Be, 500μm thick, and Al, 100μm thick, production targets for the light andheavier projectiles, respectively. Targets have been set in a rotating holder just at theexit of the SC whose extraction line was used as an achromatic fragment separator (FRS)(fig. 1).Different neutron- and proton-rich nuclei have been produced by using, for example,12C, 20Ne, 40Ar and 58Ni projectiles and individual rate up to 105 ions/s were measuredfor primary beam currents up to 500 enA [1]. In order to discriminate the number of nucleiat the exit of the fragment separator, the leading idea of the FRIBs@LNS project wasto apply the tagging technique: namely, the identification, on an event-by-event basis, ofeach nucleus of the secondary beam cocktail, before it impinges on the secondary target.The tagging detector must, obviously, not stop the incoming ions and should modifyas less as possible their characteristics. Therefore, we applied the ΔE-ToF method toidentify each incident fragment using the energy loss (ΔE) signal from a silicon detectorand the time of flight measured from the same signal generated by the silicon detectorwith respect to the radiofrequency signal supplied by the accelerator (fig. 2).3. – Tagged RIBs induced reactionsDue to the Bq acceptance, many different isotopes are transmitted through the frag-ment separator. The main idea behind the FRIBs@LNS project is then to keep all thefragments transmitted through the FRS and to tag them on an event-by-event basis,before they interact with a secondary target. It is then possible to relate the detectedreaction products with only one tagged projectile, among the incoming RIBs cocktail.352 M. DE NAPOLI, G. RACITI, C. AGODI, ETC.Fig. 2. – Left: ΔE-ToF identification from the Si-Strip detector. Right: Particle IDentificationSpectrum on the Si-Strip detector.This technique avoids the reduction of the RIBs intensities and it is particularly conve-nient for systematic studies since several projectiles are available at the same time. Wehave demonstrated the feasibility of measurements with tagged RIBs by performing aseries of experiments devoted to nuclear structure studies of exotic nuclei: among themare the Diproton [2] and Flubber experiments [3]. The first aimed to search and studydiproton decay of 18Ne excited states [2], the second addresses the study of Coulomb andNuclear Breakup in 17F and its astrophysical implications [3].Primary beams of 45A MeV 20Ne interacting with a 9Be production target has leadto the formation of a radioactive cocktail containing 18Ne and 17F (right plot of fig. 2)of about 30A MeV. For the selected RIBs the measured rates at the tagging detector (a24 × 24 Double-sided Silicon Strip Detector (DSSD) detector) were of the order of 5 ×105 pps. Here again we would like to point out the uniqueness of the tagging method, i.e.the possibility to simultaneously carry out a variety of experiments with different exoticnuclei, by selecting offline the isotope of interest before it impinges on the interactiontarget.4. – The FRIBs@LNS upgradeThe In-Flight technique joint with the tagging method, introduced at LNS by Gio-vanni Raciti, has proved the capability to provide useful rates of radioactive beams fornuclear physics experiments at LNS. The international relevance of some results obtainedby using the beams delivered by the FRIBs@LNS facility stimulated the management ofINFN to approve an upgrade [4] of the facility that has been performed in 2010. Thebeam line that transports the beam extracted from the cyclotron up to the Switchingmagnet inside the accelerator room has been fully dismounted and rebuilt in the periodSeptember-December 2010. The main changes performed to the beam line involved theinsertion of 4 new magnetic quadrupoles and 2 new magnetic sextupoles, the removing oftwo existing magnetic quadrupoles and the repositioning of the existing 13 quadrupoles.PAST, PRESENT AND FUTURE OF RADIOACTIVE ION BEAMS ETC. 353Fig. 3. – Layout of the extraction line from the cyclotron exit to the switching magnet, beforeAugust 2010 and after December 2010.Figure 3 shows the layouts of the previous extraction beam line and of the new one.It is evident that the positions of the three main dipole magnets were unchanged. Butall the other magnetic quadrupoles were moved. Also the steering dipole and the twoquadrupoles, near the cyclotron, called, respectively, EXT, EQ1 and EQ2 were shiftedof about 10mm in horizontal plane, just to reduce the 5–10% beam losses detected inthis region. Also the last two quadrupoles Q16 AND q17, after the dipole ED3, wererealigned.Another possibility to increase the FRIBs@LNS yields is based on the reduction of thebeam emittance of the FRIBs@LNS line, without reduction of angular acceptance. Toachieve this result we need to shrink as much as possible the beam size at the productiontarget position on a spot smaller than 3mm in diameter. On the other side, when thecyclotron beam is focused on such a small beam spot, a lot of power has to be dissipatedin a small volume. This can be a serious problem for a beam power of 100W or more,even if not all the power will be dissipated in the target. To solve this problem a newwater-cooled and moving target has been constructed. With the new production targetbeam power up to 600W could be used.354 M. DE NAPOLI, G. RACITI, C. AGODI, ETC.5. – OutlooksThe FRIBs@LNS facility upgrade has been successfully achieved in 2010. The newconfiguration should allow to increase the yields of the produced radioactive beams bya factor about 20 to the final users. Really this goal will be fully achieved when all the30mm diameter beam collimators, installed along the beam lines, are removed. Thesecollimators, installed in front of the Faraday cups of safety controlled by the healthsafety service, have the scope to prevent that the beam could reach accidentally theexperimental area. In the near future the present Faraday cups will be replaced by newones with larger size and larger coarseness made by us. These new Faraday cups, wheninserted, fully fill the beam pipeline, so the collimators will be unnecessary.REFERENCES[1] Raciti G. et al., Nucl. Instrum. Methods B, 266 (2008) 4632.[2] Raciti G. et al., Phys. Rev. Lett., 100 (2008) 192503.[3] Sfienti C. et al., Int. J. Mod. Phys. E, 20 (2011) 831.[4] Calabretta L., Cardella G. and Raciti G., A new FRIBs configuration, LNS (2009).

Past, present and future of radioactive ion beams produced

In-Flight at LNS

http://eprints.bice.rm.cnr.it/17612/1/ncc10119.pdf

Past, present and future of radioactive ion beams produced In-Flight at LNS

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