First demonstration of a Compton gamma imager based on silicon photomultipliers

We are developing a rugged and person-transportable Compton gamma imager for use in security investigations of radioactive materials, and for radiological incident remediation. The imager is composed of layers of scintillator with light collection for the forward layers provided by silicon photomultipliers and for the rear layer by photomultiplier tubes. As a first step, we have developed a 1/5th-scale demonstration unit of the final imager. We present the imaging performance of this demonstration unit for Cs-137 at angles of up to 30 degrees off-axis. Results are also presented for Sn-113 and Na-22. This represents the first demonstration of the use of silicon photomultipliers as an embedded component for light collection in a Compton gamma imager.Comment: 19 pages, 6 figure

A Search for the Electric Dipole Moment of the Tau-Lepton

Using the ARGUS detector at the e+e- storage ring DORIS II, we have searched for the real and imaginary part of the electric dipole formfactor d_tau of the tau lepton in the production of tau pairs at q^2=100 GeV^2. This is the first direct measurement of this CP violating formfactor. We applied the method of optimised observables which takes into account all available information on the observed tau decay products. No evidence for CP violation was found, and we derive the following results: Re(d_tau)=(1.6+-.9)*10^(-16) ecm and Im(d_tau)=(-0.2+-0.8)*10^(-16) ecm, where statistical and systematic errors have been combined.Comment: 8 pages, 5 figures (10 subfigures

Monte Carlo modeling of NRC\u2019s primary standard

The BEAMnrc/EGSnrc Monte Carlo code system is employed to develop a model of the National Research Council of Canada primary standard of absorbed dose to tissue in a beta radiation field, comprising an extrapolation chamber and Sr 90 /Y 90 beta source. We benchmark the model against the measured response of the chamber in terms of absorbed dose to air, for three different experimental setups when irradiated by the Sr 90 /Y 90 source. For the first setup, the chamber cavity depth is fixed at 0.2cm and the source-to-chamber distance varied between 11 and 60cm . In the other two cases, the source-to-chamber distance is fixed at 30cm . In one case the response for different chamber depths is studied, while in the other case the chamber depth is fixed at 0.2cm as different thicknesses of Mylar\u2122 are added to the front surface of the extrapolation chamber.Peer reviewed: YesNRC publication: Ye

TH‐C‐T‐617‐08: Monte Carlo Modelling of the Response of NRC's 90Sr/90Y Primary Beta Standard

Purpose: To benchmark an EGSnrc Monte Carlo calculated response against the high quality measured response of an extrapolation chamber used as NRC's primary standard of absorbed dose to tissue in a [formula omitted] beta field. Method and Materials: The BEAMnrc code was used to model the NRC's beta source and indigenously developed extrapolation chamber. The calculated response was compared to the measured response in 3 different series of measurements. An overall scale factor was determined by a global fit. It was used to scale the calculated values to the measured values and was compared to the known activity of the source. A single measurement configuration (30 cm distance, 0.2015 cm chamber depth) was common to all 3 sets of experimental data. Results: The scale factor led to an estimated source activity of 1.237±0.08% GBq which is consistent with the nominal value of 1.2±0.1 GBq. As the source‐detector distance was varied from 11 cm to 60 cm, values of calculated and measured responses agreed within 0.37% for a variation in response by a factor of 29. As chamber depth was varied from 0.05 cm to 0.25 cm the values agreed within 0.4%. As Mylar thicknesses up to 11 mg/cm2 were added to the face of the chamber, the values agreed within 0.2%, and agreed within 1.2% up to 150 mg/cm2. Conclusion: This project demonstrates EGSnrc's ability to calculate the response of extrapolation chamber with a remarkable degree of accuracy. Such high precision comparisons with experimental data are rare. This benchmarking of the Monte Carlo model will allow it to be used to calculate correction factors needed for the NRC's primary standard

Development of a compton imager based on scintillator bars

We are developing a compact, rugged Compton-scatter gamma-ray imager with a large field of view and a low channel count for use in investigations involving radioactive threat material. The two detector planes, (scatterer and absorber), employ bars of NaI(Tl) read out by photomultiplier tubes (PMTs) located at each end. The position of interaction along the bar is reconstructed from the relative pulse heights of the PMTs. We present the imaging performance of a reduced-scale prototype using three bars in the scatter layer and three bars in the absorber layer. A 100 \u3bcCi 662 keV source located 180 cm away from the detector is well localized to within 2\ub0 with 60 s of data over 90% of the time.Peer reviewed: YesNRC publication: Ye

A measurement of the tau lepton lifetime at Argus

Data taken with the ARGUS detector at DESY, Hamburg, specifically #tau# anti #tau# pairs produced from e"+e"- collisions in the energy range (10.4-10.6)GeV, are used to make a precision measurement of the tau lifetime. A new method is introduced which is independent of the beam position and envelope, and applicable to tau events having one-three topology. Applied to ARGUS data the method yields a value for the tau lifetime of #tau#_r=287#+-#11(statistical)#+-#8(systematic) fs. (orig.)SIGLEAvailable from TIB Hannover: RN 9448(1997,06) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

International comparison EUROMET.RI(I)-S2 of extrapolation chamber measurements of the absorbed dose rate in tissue for beta radiation (EUROMET project No 739): final report

For quality assurance in the realization and transfer by the national standard laboratories of the unit of the absorbed dose rate at 0.07 mm tissue depth for beta radiation, comparison measurements among the primary standard facilities are needed. Although some bilateral comparisons have taken place for this quantity, the CCRI decided in May 2003 that a EUROMET supplementary comparison would be appropriate if inclusive of primary standards laboratories of other regional metrology organizations. The operation and results of such a comparison are reported here. A flat ionization chamber and measurement system was used as the transfer instrument. A comparison was made of the calibration coefficients of this transfer instrument in various beta-particle laboratory reference fields (Pm-147, Kr-85, Tl-204 and Sr-90/Y-90) measured by each of the eight participants from France, Italy, Finland, Germany, Russian Federation, USA, Canada and Japan. The PTB was the pilot laboratory and the comparison ran from January 2004 until April 2007 under EUROMET project No 739 and EUROMET.RI(I)-S2. The results for most of the participants are consistent with the stated uncertainties although an extreme deviation is apparent for Pm-147 beta radiation for one participant.Peer reviewed: YesNRC publication: Ye

Reconstruction of an Inaccessible, Large-Area Extended Source with a SCoTSS Compton Gamma Imager

Compton gamma imagers are instruments which use the physics of Compton scattering to locate gamma emitters. This makes Compton gamma imagers useful tools for determining the distribution of radionuclides within an area which has restricted access. Our group has developed a Compton gamma imager which we call the silicon photomultiplier-based Compton telescope for safety and security (SCoTSS). Using a SCoTSS instrument, we made measurements of an extended source of La-140 that lay within an inaccessible area and implemented a tomographic back-projection algorithm to reconstruct the distribution. We demonstrate our metho

Reconstruction of the decay B"-#->#D_1"o(2414)#pi#"-

We present the results of a partial reconstruction of the decay channel B"-#->#D_J"("*")"0#pi#"- performed using the ARGUS detector operating at the e"+e"- storage-ring DORIS II. In the context of this paper, D_J"("*")"0 is an L=1 excited charm meson decaying to D"*"+#pi#"-. The measured product of branching ratios is Br(B"-#->#D_1"0(2414)#pi#"-).Br((D_1"0#->#D"*"+#pi#"-)=(0.17#+-#0.05#+-#0.04)% where the first error is statistical and the second systematic. No evidence for the decay B"-#->#D_2"*"0(2459)#pi#"- is observed. We calculate the upper limit Br(B"-#->#D_2"*"0(2459)#pi#"-).Br(D_2"*"0#->#D"*"+#pi#"-)<0.07% at the 90% confidence level. (orig.)SIGLEAvailable from TIB Hannover: RA 2999(94-069) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman