MEASUREMENT OF RADON BY GRAPES-3 PLASTIC SCINTILLATOR DETECTORS

Meeran Zuberion behalf of GRAPES-3 collaboration, Cosmic Ray Laboratory, Ooty

THE GRAPES–3 EXPERIMENT• Located at Ooty, India at 11.4oN latitude,

76.7oE longitude and an altitude of 2.2 kmamsl.

• 400 (1m2) plastic scintillation detectorswith 8 m inter–detector separation.

• Tracking muon telescope (560m2).

• Total area covered 25,000m2.

• ∼3 million air shower events/day.

12 SEPTEMBER 2018 EVENT

Time (min)

500 1000

Avg C

oun

t In

cre

ase (

%)

2 −

0

2

4

Unfiltered Combined

• During rain episode, a sudden in-crease is observed in all scintilla-tor detectors.

• In addition to that, all scintillatordetector rates undergo dailyvariations due to change in atmo-spheric temperature and pressure.

• These daily variations (back-ground) are successfully modeledand removed by using higherorder polynomial.

0 200 400 600

Avg

Co

un

t In

cre

ase

(%

)

0

2

4

6

8

Time (min)0 200 400 600

Ra

in (

mm

)

0

1

2

3

Set­1

Set­2

Set­3Set­4

0 200 400 600A

vg

Co

un

t In

cre

ase (

%)

0

2

4

6

Time (min)0 200 400 600

Ra

in (

mm

)

0

1

2

3

Cone Type

Fiber Type

0 500

Tota

l C

ounts

Incre

ase

0

2

4

6

Time (min)0 500

Rain

(m

m)

0

1

2

3

Combined

• Half-life(T 12

) is calculated for dif-ferent combination of detectors byfitting it with exponential func-tion.

• T 12

for four equal detector sets;Set-1 = 21.8 min, Set-2 = 28.1 min,Set-3 = 32.5 min, Set-4 = 25.3 min.

• T 12

for different detector type ;Cone = 29.3 min, Fiber = 24.9 min.

• T 12

for all detectors combined;Combined = 26.6 min.

SCINTILLATOR DETECTORS

Cone Type

Fiber Type

RADON DECAY CHAIN• Radioactive decay is governed by

N = N0 e−λt

λ (decay constant) = 0.693T 1

2

SUMMARY• The observed half-life clearly indicates the presence of radon decay products such as lead

and bismuth isotopes.

• The observed data from both cone and fiber type detector show consistent results. However,the cone detector data show an extra feature during decay period of the event which is underinvestigation.

• The study of more such events observed by GRAPES-3 plastic scintillator detectors couldlead to a better understanding of radon decay products by using more realistic decay fittingmodels and hence they can be used as an inexpensive alternative to the inorganic crystalscintillators.

REFERENCES

[1] S.K. Gupta et al., Nuclear Instruments and Methods in Physics Research A, 540, 311 (2005).

[2] Y. Hayashi et al., Nuclear Instruments and Methods in Physics Research A, 545, 643 (2005).

[3] P.K. Nayak et al., Astroparticle Physics, 32, 286 (2010).

[4] P.K. Nayak et al., Astroparticle Physics, 72, 55 (2016).