Cosmic Ray Testing of the Micro-Modular Neutron Array

R. E. Turner R. E. Turner aa, M. R. Evanger , M. R. Evanger aa, M. Rajabali M. Rajabali aa, B. Luther , B. Luther aa, T. Baumann , T. Baumann cc, Y. Lu , Y. Lu bb, M. Thoennessen , M. Thoennessen b,cb,c, E. , E. Tryggestad Tryggestad cc

aa Concordia College, Moorhead, MN Concordia College, Moorhead, MN bb Michigan State University , East Lansing, MI Michigan State University , East Lansing, MI

c c National Superconducting Cyclotron Laboratory, East Lansing, MINational Superconducting Cyclotron Laboratory, East Lansing, MI

This work supported in part by grants from the National Science Foundation.

ABSTRACTEight of the 144 detector modules comprising the Modular Neutron Array (MoNA), a large-area neutron detector, were tested with cosmic rays at the National Superconducting Cyclotron Laboratory. Each module consisted of a 200 x 10 x 10 cm^3 bar of BC-408 organic plastic scintillator with photomultiplier tubes mounted on each end. The eight bar setup dubbed Micro-MoNA (MoNA) was arranged in two different configurations. One consisted of four vertically stacked horizontal planes of two modules while the other configuration was comprised of two vertically stacked horizontal planes of four modules. Both configurations were tested with cosmic rays to determine position and time resolution. The results and response characteristics of each MoNA setup will be presented.

This is a pictorial example of one layer of four bars in the vertical configuration. To be considered as a valid hit and recorded, each and every phototube must fire and the signal must correspond with a start in the veto detector.

veto

MoNA will be a large-area neutron detector located at the NSCL. MoNA will have a front area of 160 x 200 cm2.

MoNA tests were conducted to determine if the MoNA bars detected neutrons properly and to find horizontal position resolution, energy deposition, and neutron energy.

A more detailed description of MoNA can be found on poster 5P1.071, P.J. Van Wylen et. al., in this session.

Summary: MoNA showed that it is feasible to calibrate the entire MoNA detector with cosmic rays.

MoNA showed that cosmic-ray energy deposition, and position can be effectively measured with the MoNA bars.Thirty-two MoNA bars were

assembled and tested at the NSCL.

This is an example of the horizontal configuration, in which the spectra is indicating each bottom bar being gated by each top bar, with the cuts as shown.

A pictorial example of the bottom bars being gated by the front, top bar.

A 2-dimensional graph of the x-position spectra for a top bar versus its corresponding bottom bar in the horizontal configuration. The strong diagonal line indicates cosmic ray strikes while the off-diagonal is the background noise.

The vertical configuration. The horizontal configuration.

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Position spectra in the vertical configuration. Each bar is being gated on those above it, with the very last spectra indicating those hits that passed through all four bars and were recorded. The five graphs line up very nicely, indicating good position data from the cosmic ray strikes. This was expected and is very encouraging when considering the feasibility of calibrating the MoNA detector.

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Position Spectra

The cosmic ray testing is essential to the MoNA project because current plans involve calibrating the entire MoNA detector using the results from the cosmic ray test.

© T. Baumann 2001

MoNA

The two Configurations

Top Bar 1

Top Bar 2

Top Bar 3

Top Bar 4

Bottom Bars 1-4

The cosmic ray muon flux provides a spatially uniform background for our detectors.

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Energy Spectra

The muons have an extremely high kinetic energy and therefore have a relatively low specific energy loss (dE/dx). The energy distribution of the muon flux gives a peak in the energy deposition at 2.0 MeV*g ¹ *cm². With a density of 1.032g/cm³ and a thickness of 10 cm per bar, this yields a peak of 20.7 MeV in the detector bars.