Vol. 20 No. 2 - NuPECC

facilities and methodscounts140012001000800600400200012500 12550 12600 12650 12700 12750 12800 12850 12900 12950will enhance the Penning effect orproduce secondary ionizations thatcould lead to gas discharges.This last hypothesis was the originof a diffused urban legend about thepossible sparking and consequentirreversible damage of the expensiveHPGe detectors, when operated instrong magnetic fields [8]. We experiencedhow this common belief tookroot in the community when a loan ofa HPGe Clover was denied for testsinto a magnetic field and when adetector specifically ordered to beused into a magnetic field, with all thecomponents under vacuum (FET,preamplifier, H.V. filter) shielded toreduce the Penning effect, was guaranteedfor operation only up to 0.5 T.The above arguments fully justifiedthe request of an exhaustive R&Dprogram on the behavior of HPGe instrong magnetic fields, supported inchannelsFigure 2. Result of the recovery procedure for the 1173.2 keV peak from 60 Co.The continuous line on the right represents the original spectrum measuredwith B = 0 T, the continuous line on the left the one at 2.5 T and the dashed linerepresents the corrected spectrum. The conversion constant for the abscissascale is 0.0914 keV/channel. (From Ref. [10].)sequence by grants of the EuropeanUnion Integrated Infrastructure Initiative“Hadron Physics” (I3HP), underContract number RII3-CT-2004-506078,Efficiency loss (%)86420−2−4B = 0.7 TB = 1.32 TB = 2.25 TB = 2.50 Tand by Progetti di Ricerca di InteresseNazionale 2005, by the Italian Government(Hypergamma Program).Experimental ResultsThe first campaign of measurements[9] was performed at GSI onVEGA Clover and EUROBALLCluster HPGe detectors. They werecooled with liquid Nitrogen (LN 2 ) andimmersed into the uniform field of theALADiN dipole magnet, varied up to1.6 T. The axis of the detectors wasnormal to the field lines and, due tomechanical reasons, this set-up didnot allow a variation of such an angle.A 60 Co γ-rays source was used for thetest series.The second, more complete, campaignof measurements [10] was performedat Laboratori Nazionali delSud of INFN, by using an ORTECGX10P4-S-PLUS coaxial HPGe n-type crystal, electrically cooled by anORTEC CFG-X-Cool-II-230 device.It was immersed into the uniformfield of the SOLE superconductingsolenoid, varied up to 2.5 T. The angleϑ between the axis of the detector and0 200 400 600 800 1000 1200 1400γ energy peak [keV]Figure 3. g–ray energy dependence of the efficiency loss for different values ofB. (From Ref. [10].)24 Nuclear Physics News, Vol. 20, No. 2, 2010