222Rn daughters influence on scaler mode of ARGO-YBJ detector

Irene Bolognino,University of Pavia and INFN

E. Giroletti,C. Cattaneo,G. Liguori,P. Salvini,P. Vallania,C. Vigorito

on behalf of the ARGO-YBJ Collaboration

32nd ICRC, Beijing August 13th 2011

ARGO-YBJ detector

Detector layout(5,800 m2)

Active area 93%

Strip = spatial pixelPad = time pixelTime resolution ~1 ns

10 Pads (56 x 62 cm2)for each RPC

8 Strips (6.5 x 62 cm2) for each Pad

78 m

111 m

99 m

74 m

(43 m2)1 CLUSTER = 12 RPC

RPC

+ Analog charge read-out on “Big Pads”

Scaler mode

Cluster counting over 4 channels: Nhit ≥1,≥2, ≥3, ≥4, every 0.5 s, no timing or spatial distribution (Eth > 1 GeV).

detector monitor: influence of meteorological effect, mainly pressure and gas temperature

flaring phenomena (gamma ray bursts, solar flares)

Operation modes

Shower mode

Inclusive Trigger: Npad>20 within 420ns on the central carpet rate ~ 3.6 kHz ( ~220 GBytes/day)

Detection of Extensive Air Showers (direction, size, core …)

cosmic-ray Physics (threshold ~ 1 TeV) VHE g-astronomy (threshold ~ 300 GeV) gamma-ray bursts

Work focused on Scaler mode

Correlation with the environmental parameters

m and b were calculated for different clusters and periods

C ≥ 2, C ≥ 3, and C ≥ 4:m = 0.9-1.2% mbar-1 b = 0.2-0.4% °C-1

C ≥ 1:m= 0.3-0.5% mbar-1 b = 0.2-0.4% °C-1

Barometric, and thermal coefficient depend on the cluster considered and the specifical experimental conditions.

Aielli et al., Astropart. Phys. 30 (2008) 85-95

Radioactive family: Uranium

Radon-222

)()()()(

tCIVtE

dttdC

RnventRnRnRn

Complex time variations in a open building with

ventilation conditions varying during the day

In a stationary state:

CRn(t)= Radon concentration (Bq/m3)

ERn(t)=Radon emission in volume V (Bq/s)

Rn = Radon decay constant (2.110-6 /s)

Ivent= ventilation in (air exchange/s)

Montecarlo simulations in air E (g keV) Simulation with FLUKA using graphics

user interface (GUI) FLAIR.

6·106 gammas launched for each energy

Equilibrium factor = 0.7 0.8 Hz per Bq per m3

Efficiencies check (137Cs, 60Co)

Air

Cluster43 m2

Width (23 m)

Length (17 m)

Deep (m)

Radon enters the Argo hall from soil and cracks (north side) and exits through doors and windows with an ease dependent on ventilation and atmospheric conditions

Bq/m

3

Julian day - offset

30 days, May2010

Radon measurements in air (Lucas Cell)

Average trend of Rn concentration

1st analysis method: the LINEARIZATION

We evaluated: time series (Radon, Scaler1, Pressure, Temperature) at different

seasons of 2010 clusters at North, middle, and South side of the experimental hall normalized time series

Our goal:

C1RESIDUE(t) = k CRn

Quantify the influence of natural radioactivity on C1 counts

Radon Concentration vs Time

Scaler1 vs Time

Pressure vs Time

Gas Temperature vs Time

From 2nd to 15th June 2010, central cluster

C1(t) – [106054 - 114.5 P(t)+ 63.3 T(t)] = C1RESIDUE(t)

correl.coeff.(C1RESIDUE,CRn) = 0.93

MJD, 2010 June from 2nd to 15th

C1RESIDUE(t)

North

South

Middle

Corr coeff is better at the center and worse at the North and South sides.

Worst correlations are obtained in high electric field variation periods (see “Observation of the Effect of the atmospheric electric fields on the EAS with the ARGO-YBJ experiment”, poster of this Conference).

cosmic radon electric fieldbackground

Influence is about 1-3% for radon concentration of 500 Bq/m3

2nd analysis method:PROPORTIONAL Hp: P, and T influence the cosmic rays contribution g1, and the

detector response with the same proportion as in g2, g3, and g4.

kn = <C1/Cn>, n=2,3,4.

North

South

MiddleInfluence is about 1-3% for radon concentration of 500 Bq/m3

~(20±5) kHz

Conclusions Natural radioactivity in air influences the ARGO-YBJ single counting

rates at the level of about 0.5-1.7 Hz per Bq/m3 of 222Rn concentration.

The average radon (500 Bq/m3) influence is ~1-3% of C1 counts according to Fluka simulations.

In general the correlation of the clusters located at the center with CRn is higher than the North and the South ones.

The same methods was applied to C2, C3, and C4 and we didn’t find any radon influence as expected.

Radon gas concentration is monitored in order to perform the best possible correction at the ARGO-YBJ lowest energy threshold.

THANK YOU!

Backup slides

The ARGO-YBJ experiment

• Collaboration between: Istituto Nazionale di Fisica Nucleare (INFN) Accademia Cinese delle Scienze (CAS)

• Site: Observatory for Cosmic Rays of Yangbajing (Tibet), China

High Altitude Cosmic Ray Observatory @ YangBaJingSite altitude: 4,300 m a.s.l., ~ 600 g/cm2

Coordinates: longitude 90° 31’ 50” E, latitude 30° 06’ 38” N

ARGO-YBJ

(Astrophysical Radiation Ground-based Observatory)

Shower mode Space pixel: single strip ( 7×62cm2) Time pixel: pad (56×62 cm2) is the OR of 8 strips, with a resolution of ~ 1 ns

The high granularity , the timeresolution and the full coverage allowreconstruction with unprecedentdetails.

The detailed shower topology is a possible tool for gamma/hadrondiscrimination

222 R

n a

nd

dau

gh

ters

Rad

ioac

tive

fam

ilies

se

cula

r eq

uili

bri

um

BA )()( 2/12/1 BTAT )()( tAtttAtt AB

T1/2 di A = 20 T di B

0

200

400

600

800

1000

1200

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5Tempo, anni

Attività, Bq

0

20

40

60

80

100

120

attività, A

attività, B

Rapporto %, B/A

Radioactive familiessecular equilibrium

CBA

BA )()( tNtN AAB

AB

)()( tAtttAtt AB BAB )()( tAtttN

Complete agreement between simulated and measured efficiencies : 1% for Eg ≈1.25 MeV (60Co source) and 0.5% for Eg of 0.6 MeV (137Cs source)

UM, fluence(e+,e-) [part/primary/cluster]

-0.0005

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0 500 1000 1500 2000 2500 3000

gamma energy, keV

UM

(p

art

/pri

m)

H=1

H=2

H=4

y = 2E-10x2 + 6E-07x - 0.0001

R2 = 0.99

y = 6E-11x2 + 7E-07x - 0.0001

R2 = 0.9865

y = 6E-11x2 + 5E-07x - 0.0001

R2 = 0.9891

Result of volumetric simulation: