The New Set-Up in the Bel Grade Low-Level and Cos Mic-Ray Lab O Ra Tory

A. Dragi}, et al.: The New Set-up in the Bel grade Low-Level and Cos mic-Ray ... Nuclea r Technol ogy & Ra dia tion Pro tection: Year 2011, Vol. 26, No. 3, pp.181-192 181 THE NEW SET-UP IN THE BELGR ADE LOW-LEVEL AND COS MIC-RAY LAB O RA TORY by Aleksandar DRAGI]1*, Vladi mir I. UDOVI^I]1, Radomir BANJANAC1, Dejan JOKOVI]1, Dimitrije MALETI]1, Nikola VESELINOVI]1, Mihailo SAVI]2, Jovan PUZOVI]2, and Ivan V. ANI^IN1 1In sti tute of Phys ics, Bel grade, Ser bia 2Fac ulty of Phys ics, Uni ver sity of Bel grade, Bel grade, Ser bia Sci en tific pa per UDC: 543.428/.429:551.521.6:539.166 DOI: 10.2298/NTRP1103181D The Bel grade un der ground lab o ra tory con sists of two in tercon nected spaces, a ground level labo ra tory and a shal low under ground one, at 25 me ters of wa ter equivalent. The labo ra tory hosts a low-back ground gamma spectros copy sys tem and cos mic-ray muon de tec tors. With the re cently adopted dig i tal data ac qui si tion sys tem it is pos si ble to si mul ta neously study in - de pend ent op er a tions of the two de tec tor sys tems, as well as pro cesses in duced by cos mic-ray muons in ger ma nium spec trom e ters. Char ac ter is tics and po ten tials of the pres ent ex per i men - tal setup, to gether with some pre lim i nary re sults for the flux of fast neu trons and stopped muons, are re ported here. Key words: un der ground lab o ra tory, gamma-ray spec tros copy, low-level mea sure ments, cos mic rays IN TRO DUC TION num ber of years now, while the TL is still not func - tional. The low-level and cosm ic-ray labo ratory in Bel- Con tin u ous mea sure ments of the cos mic-ray grade is ded icated to the measure ment of low ac tiv ities muon flux by means of a pair of small plas tic scinti lla - and cos mic-ray (CR) muon com po nents. At the inter - tors 50 cm ´ 23 cm ´ 5 cm started in the GLL and UL sec tion of the two re search subject s, the study of back in 2002 and lasted for about 5 years. These mea- muon-induced background in gamma spectros copy is sure ments yielded the pre cise val ues of the in tegral CR of par tic u lar in ter est. The lab o ra tory adds to the list of muon flux at ground level and at the depth of 25 m.w.e. rel a tively shal low un der ground lab o ra to ries world- [2]. Dif fer ent anal yses of the time se ries of these mea- wide (see the re cent re view [1]). It is lo cated on the surem ents have also been perform ed [3, 4]. right bank of the river Danube in the Belgrade borough Signif i cant ef forts are being made to contai n of Zemun, on the grounds of the Insti tute of Physics . the low ra don con cen tra tion within the lab o ra tory. The ground level porti on of the labo ratory (GLL), at The UL is com pletely lined with a her meti cally 75 meters above sea level (m.a.s.l), is situ ated at the sealed, 1 mm thick alu minu m foil. The ven tila tion foot of a verti cal loess cliff, about 10 meter s high. The sys tem maintai ns the overpressure of 2 mbar, so as to un der ground part of the labo ratory (UL), use ful area prevent radon dif fu sion from the soil. Fresh air enter - 45 m2, is dug into the foot of the cliff and is ac ces sible ing the lab o ratory is passed through a two-stage fil- from the GLL via a 10 meter s long hori zon tal corri dor ter ing sys tem. The first stage is a mechan i cal fil ter for which also serves as a pressure buffer for a slight dust re moval. The second one is a bat tery of coarse overpressure that is consta ntly maintai ned in the UL and fine char coal ac tive fil ters. The con cen tra tion of (fig. 1). The over burden of the UL is about 12 meter s radon is kept at an aver age value of about 10 Bq/m3. of loess soil, equiva lent to 25 meter s of water . The con - Through out the years, cer tain in ter est ing be hav iors tainer, which is to accom mo date the top labo ratory of the said concen tra tion have also been reporte d [5, (TL), is sit u ated at the top of the cliff, just above the 6]. UL. The GLL and UL have been in some use for a The two lab o ra tory spaces have re cently been furnishe d with a new ex peri m ental set-up which is now ready for rou tine mea sure ments. Here pre sented are some pre lim inary re sults of wider in ter est, ob - * Cor re spond ing au thor; e-mail: [email protected] A. Dragi}, et al.: The New Set-up in the Bel grade Low-Level and Cos mic-Ray ... 182 Nuclea r Technol ogy & Ra dia tion Pro tection: Year 2011, Vol. 26, No. 3, pp. 181-192 Fig ure 1. Cross-sec tion of the low-level and CR labo ra tory at IOP, Bel grade, 44°49'N, 20°28'E, ver ti cal ri gid ity cutoff 5.3 GV tained during the testing period of the new equipm ent tec tor, of 10% ef ficie ncy, is put to use in the GLL. It is and the devel op ment of the needed software. shielded with lead of the same ori gin, parts of a plumb - ing sys tem col lected at a de moli tion site of an old housing es tate. The exact history of this lead is not EX PER I MEN TAL SET-UP known, but all the com po nents are known to be older than two half-lives of Pb-210. The equipm ent now consis ts of two al most iden- At the heart of the data ac qui si tion sys tem are ti cal sets of de tec tors and an a lyz ing elec tron ics, one two flash: ana log to digi tal convert er (ADC), flash an- set sit u ated in the GLL, the other in the UL. Each set is a log to dig i tal con verter (FADC), one in each labo ra- com posed of muon detec tors and a gamma spectrom e- tory, made by CAEN (type N1728B). These are versa - ter. tile in strum ents, capa ble of working in the so-called A pair of plas tic scintillator de tec tors is used for en ergy his to gram mode when per form ing as dig i tal CR muon measure m ents. One of them is a larger spec trom eter s or, in the oscillogram mode, when they 100 cm ´ 100 cm ´ 5 cm detec tor, equipped with four per form as dig i tal stor age os cil lo scopes. In both PMT direct ly coupled to the corners bev eled at 45°, modes, they sam ple at 10 ns in ter vals into 214 channels made by Amcrys-H, Kharkov, Ukraine. The other, a in four in depend ent in puts. The full voltage range is small 50 cm ´ 23 cm ´ 5 cm plas tic scintillator de tec - ±1.1 V. tor, with a sin gle PMT look ing at its lon gest side via a They are capa ble of op erat ing in the list mode, Perspex light guide ta pering to the di am eter of a PMT, when every ana ly zed event is fully re corded by the made by JINR, Dubna, Russia , and as sem bled lo cally. time of its oc currence and its am pli tude. This enable s The smaller detec tor may serve as a check of sta bil ity the corre la ti on of events, both prompt and arbi tra rily of the muon time se ries obtai ned from the larger detec - de layed, at all four in puts with the time res o lu tion of tor, which is im por tant for long term measure m ents. It 10 ns. Sin gle and coin ci dent data can be or ganize d into can also be used (in co in cidence with the larger de tec- time se ries within any inte gra ti on period from 10 ns tor) for measure ments of the lateral spread of par ticles up. The two N1728B units are syn chronize d, enabli ng in CR show ers. Plas tic scin til la tion de tec tors are also co in ci dence/cor re la tion of the events re corded in both em ployed for ac tive shielding of gamma spectrom e- of them.

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