Search for Strangelets in Cosmic Rays-a Study with Nuclear Track detectors

Sandhya Dey(Mandal)Research ScientistIRHPA ProjectCentre for Astroparticle Physics and Space Science Bose Institute

Contents of talk

Open air exposure to Nuclear Track detector at different

mountain altitudes to study change in characteristics of detectors.

Study of cosmic radiation at high mountain altitudes with

PET & CR-39.

Special events observed at Darjeeling and Hanle.

Conclusion.

Detectors exposed to cosmic rays.

Darjeeling

Hanle

Ooty

Kolkata

Detectors at mountain altitude.

To detect exotic events strangelets predicted to be present in cosmic radiation at mountain altitude, we have placed plastic detectors (PET) along with CR-39 for preliminary study . The locations have been chosen are

Darjeeling (Latitude- 28° N Longitude-88° E and Altitude 2.13 asl),

Ooty (Latitude- 11.4° N Longitude-76.7° E and Altitude 2.23 asl)

Hanle.(Latitude- 32° 42’N, Longitude- 79° 04’E, Altitude 4.5 asl).

Exposure at Darjeeling

At Darjeeling first cosmic ray exposure was given to plastic detector. Both CR-39 and PET have been used.

Exposure was given to seven sets of detectors. Several different arrangements were made. Horizontal, inclined, bending.

Duration of exposure was around six months for each

exposure. Both CR-39 and PET plates are etched in appropriate

etching condition(6.25N conc and temp 55°C for PET and 70°C) in aqueous solution of NaOH. Duration of etching are 1-12 hours.

Change in bulk etch rate after long exposure in open air.

Solid State Nuclear Track detector is a Z/ß detector and which in turn depends on reduced etch rate Vt/Vb . Bulk etch rate(Vb ) changes after long time exposure in open air.

Vb became more than twice than Vb of unexposed detector after exposure at Darjeeling.

at Ooty it is almost twice. And at hanle it is less than twice. Also bulk etch rate is different for top and bottom side of

the plate after open air exposure.

Observation at Darjeeling on PET

Charge particle flux~1.5x 10-5/(cm2.s.sr) recorded on PET over different sets of exposures of various durations.

Analysis of tracks on PET found at Darjeeling

VT/Vb=2.94±0.42 corresponding to these tracks.

Tracks very short ranged (~10

μm) making particle identification difficult.

Origin of these charged particle tracks on PET not very clear. Characterization will require further studies of local radiation environment of Darjeeling.

Unusual event at Darjeeling

In PET there are only 2% of image frames contains single tracks, 98% are vacant.

But in one particular PET film, a single image frame from first exposure shows six tracks. This is highly unusual. Each fragment idenified as particle of Z~20 and E/m ~1MeV/n.

Tracks on CR-39 at Darjeeling

CR-39

Flux recorded on CR-39 ~ 9.299 x 10-7/(cm2.s.sr)

for non stop tracks

Detectors exposed at Ooty

Charged particle flux recorded with CR-39 detectors

1.954 x 10-6/(cm2.s.sr)

Thorough scanning of PET failed to reveal any charged particle track which we have observed at Darjeeling.

Design of detectors for Hanle

horizontal

Inclined-30°

CR-39

PET

Flux obtained at Hanle

Charged particle flux recorded with CR-39 detectors 2.116x10-7/(cm2.s.sr).

Main contributions are from proton and alpha.

Thorough scanning of PET failed to reveal any charged particle track like those, which we have seen at Darjeeling.

IMPORTANT OBSERVATION AT HANLEY:

One un-usually heavy ion track is observed on the bottom side of a CR-39 plate. Micro photograph of track is shown. It has punched through CR-39 plate and entered to the PET film then stopped after few micron(~33 micron) travel. CR-39 plate was placed on a bunch of PET film. Bunch contained three pet film each of 100 µ thick. Range of the ion in the detector is greater than 700µ. Thickness of the CR-39 detector used was 700µ.From the track parameters of this track on PET it is identified as particle of Z~25±2.

.

Heavy ion track observed in the bottom surface of CR-39

Distribution of Reduced Etch Rate

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.00

2

4

6

8

10

12

14

16

18

20

22

24 Reduced etch rate

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qu

en

cy(n

o.o

f e

ven

ts)

Vt/Vg(reduced etch rate)

Identification of high energy event

Range in PET =33±2 µm Charge response Vt/Vg =6.53+±0.67 Then observed event at Hanle is identified with the help of

calibration curve and dE/dx vs. range relation. dE/dx is determined from our calibration curve and found to be

35.23±5 MeV/mg/cm2.

The event identified as ion of charge (Z)=25±2

Energy of the ion (iron) when it enters to the PET is ~150 MeV. Track length in CR-39 is determined (~24.5±1.75 µ). Then

range from the tip in CR-39 is ~65µ). Energy of ion on CR-39 is determined to be ~2 GeV.

dE/dx vs range curves

Flux of iron at the altitude of Hanley is ~10-20 /cm2/s. Which is less than 1 particle per square km/century.

We have observed it after searching an area of ~100 cm2, which has exposed for ~one year.

Calculated flux over this area is 3.6x10-10

This is a very very rare event

Cosmic ray flux at mountain altitude

Non stop tracks can be considered as cosmic ray particles which have gone through the plate and produces conical tracks.

Flux of such tracks in CR-39 after 6 hour etching.

At Ooty - 1.954x10-7/(cm2.s.sr). At Hanle- 2.116x10-6/(cm2.s.sr). At Darjeeling- 9.299x10-7/(cm2.s.sr).

Conclusion :

Flux obtained at Hanle (Lat- 32° 42’N, Long- 79° 04’E, Alt. 4.5 asl).

=2.23 x flux obtained at Darjeeling (Lat - 28° N Long -88° E and Alt 2.13 asl).

=10.8 x flux obtained at Ooty (Lat - 11.4° N Long -76.7° E and Alt - 2.23 asl).

Flux of non stop particles is changing with altitude and also with

latitude. So we can conclude these are due to cosmic rays.

For large area exposure the site at hanle is ready and further work is in progress .

References

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(SRIM Computer Code), Version:2003.26 .

List of other publications

1. Calibration of a solid state nuclear track detector (SSNTD) with high detection threshold to search for rare events in cosmic rays_ S. Dey, D. Gupta, A. Maulik, Sibaji Raha, Swapan K. Saha, D. Syam, J. Pakarinen, D. Voulot, F. Wenander Astroparticle Physics(2011) 34 / 805–808

2. Characterization and calibration of a SSNTD for heavy-ion detection and strangelet search in cosmic rays_ D. Bhowmik , S. Dey, A. Maulik, Sibaji Raha, S. Saha Swapan K. Saha, D. Syam..Nuclear Instrum. and Meth. B (2011)269 / 197 – 201.

3. Charge response of polyethyelene terephthalate polymers (PET) to light and heavy nuclei _ B. Basu, S. Dey, B. Fischer, A. Maulik, A. Mazumdar, S. Raha, S. Saha, Swapan K. Saha , D. Syam Radiation Measurements(2008) 43 / S95-S97

4. Polyethylene terephthalate polymers at mountain altitude as cosmic ray heavy particle detector _ B. Basu, S. Biswas, S. Dey, A. Maulik, A. Mazumdar, S. Raha, S. Saha, Swapan K. Saha , D. Syam Radiation Measurements(2008)43 / S262-S265

5. Determination of the depth of an etch pit through studies of diffraction rings _ B.Basu, S. Dey, A. Maulik, S. Raha, S. Saha, Swapan K. Saha, D. Syam Radiation Measurements(2009)44 / 359-362

List of publications-continued

Characterization of polyethylene terephthalate (PET) detector to search for rare events in

cosmic rays. – A. Maulik, D. Bhowmik, S. Dey, Sibaji Raha, S. Saha, Swapan K. Saha,

D. Syam. Proceedings of the 31st ICRC (ID 1072)

Multi-pronged events from Coulomb fission of nuclei at very low energies _ B. Basu, S. Dey,

D. Gupta, A. Maulik, Sibaji Raha, Swapan K. Saha, D. Syam [ arXiv:0812.0054]

Observation of a rare cosmic ray events at mountain altitude, B. Basu, S. Biswas

, S. Dey, A. Mazumdar, S. Raha , S .Saha, S.K. Saha , D . Syam will be

resubmitted to Phys. Rev.Let.

A highly unusual cosmic ray event at mountain altitude, B. Basu, S. Biswas , S.

Dey, A. Mazumdar, S. Raha , S .Saha, S.K. Saha , D . Syam , 29th International Cosmic Ray

Conference ,279 Pune (2005)

Characterization of polyethylene terepthalate (PET) detector to search for rare events in

cosmic rays, A. Maulikb, D. Bhowmik a,1 , S. Deyb, S. Rahab,c, S. Sahad, Swapan K. Sahab,c,*, D.

Syame – Proceedings of the 31st ICRC, Ł´OD´Z 2009

THANK YOU