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" Faster than light-like-events " in cosmic ray vetoing. I.Bikit*, D.Mrdja*, I.Anicin**, M.Veskovic*, S.Forkapic*. * Department of Physics, Faculty of Sciences ,University of Novi Sad, Serbia and Montenegro

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" Faster than light-like-events "

in cosmic ray vetoing

I.Bikit*, D.Mrdja*, I.Anicin**, M.Veskovic*, S.Forkapic*

* Department of Physics, Faculty of Sciences ,University of Novi Sad,

Serbia and Montenegro

** Faculty of Physics, University of Belgrade,Serbia and Montenegro

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In our attempts to explore and optimize the vetoing effect of the anti muon

shield for low level gamma spectrometry,

we made the observations which involve at first sight the superluminal velocities

●The extended range GMX type gamma spectrometer ( HPGe ) with nominal

efficiency of 32 %, made by ORTEC, was shielded with the cylindrical

lead shield with 12 cm wall thickness

● Above the lead shield , the 0.5 m x 0.5 m x 0.05 m

plastic veto detector

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The coincidence/anticoincidence signal processing NIM electronic

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● In the first runs, the time spectrum from the TAC , had the broad tail on right side , pointing towards slow ( probably neutron induced ) coincidence events

( the coincidence resolving time was 4 μs )

●In order to explore the slow event contribution, we adjust the TFA

amplification and shaping , and the CFD’s delay cables and walk. The TFA settings are presented in Table

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● The GMX energy threshold on the CFD was set to 30 keV ,while on the plastic CFD the threshold was set to 3 MeV ( above environmental gamma rays and far below the muon maximum at 10 MeV )

●These settings improved significantly the time resolution of the coincidence circuit

● In the time spectrum , two almost separated peaks appeared at the

distance of 125 ns

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● The biggest surprise occurred during the test of the system timing with the

10 μCi activity 22Na positron source

● The maximum of the prompt time spectrum was placed on the same channel

as the second maximum of the cosmic coincidence spectrum

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● Similar time spectrum observed by Povinec : " IAEA-MEL system timing with the .s underground counting laboratory (CAVE) for the analysis of radionuclides in the environment at very low-levels" - Journal of Radioanalytical and Nuclear Chemistry, Vol. 263, No. 2 (2005) 441.445

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● This result can be naively explained by superluminal speeds

● The gammas from 22Na ( energies 511 keV and 1275 keV )

have the speed of light and cross the 32 cm detector to detector

distance in about 1.1 ns ( regardless to the source position between the detectors )

defining thus the prompt ( zero ) time between the start and stop pulses

●The pulses below this point on the time spectrum

can be produced by random coincidences ( flat distribution ), electronic noise

( not detected in our experiment ), or by a particle traveling with superluminal speed

from the plastic to the Ge detector.According to the data measured,

the speed of this particle is about 115 c ( c x 125ns/1.1ns)

● In order to explore the interaction of this particle with the Ge detector,

we measured the coincidence spectra with the events of first ( “superluminal “) peak,

and second ( “prompt” )

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● Figure clearly shows that the first time peak triggers high energy GMX events,

while the second , the low energy ones.

● Thus the exotic tachyonic explanation can be replaced by the more realistic

electronic saturation effect.

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● High energy GMX pulses ( from muons and gammas above 1.5 MeV ) saturate in the TFA, yielding much shorter rise time than the non saturated pulses from 22Na

●The saturated events are triggered by the CFD much sooner than the non saturated ones and follow the plastic start signal faster than the "prompt" ones

●The first peak in the time spectrum is the signature of such events

●It looks surprising that the CFD sharply grouped the signals with significantly different rise times and in wide energy ranges acts as a pulse shape discriminator

● Further investigations of this effect are under way

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THANK YOU FOR YOUR ATTENTION MeV ) saturate in the TFA, yielding much shorter rise time than the non saturated pulses from 22Na