Search for Strangelets in Cosmic Raysa Study with Nuclear Track detectors
Sandhya Dey(Mandal)
Research Scientist
IRHPA Project
Centre 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
Ooty
Hanle
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
to these tracks.
corresponding

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
CR-39
horizontal
Inclined-30°
PET
Flux obtained at Hanle
 Charged
particle
flux
recorded
with
CR-39
detectors
2.116x107/(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
Reduced etch rate
24
22
20
frequency(no.of events)
18
16
14
12
10
8
6
4
2
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Vt/Vg(reduced etch rate)
3.5
4.0
4.5
5.0
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
This is a very very rare event
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
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 Hanle2.116x10-6/(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
2.13 asl).
=10.8
(Lat - 28° N Long -88° E and Alt
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 .
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List of other publications
1.
2.
3.
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
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.
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
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