[Paper Review] 222Rn daughters influence on scaler mode of the ARGO-YBJ detector

E. Giroletti, I. Bolognino+5 more|arXiv (Cornell University)|Dec 19, 2011

Astrophysics and Cosmic Phenomena3 citations

TL;DR

This paper investigates the influence of 222Rn decay daughters on the scaler mode of the ARGO-YBJ air shower detector, finding that each Bq/m³ of radon contributes approximately 1 Hz to the C1 counting rate. The study identifies radon daughters as a significant background source in the lowest-energy threshold measurements, urging radon monitoring for improved sensitivity in cosmic ray detection at low energies.

ABSTRACT

The ARGO-YBJ experiment is a full coverage air shower array; its lowest energy threshold is reached using the "scaler mode technique". Working in this mode, the signals generated by any particle hitting each cluster are put in coincidence every 150 ns and read by four independent scaler channels, giving the counting rates of multiplicity \geq1, \geq2, \geq3 and \geq4 (C1, C2, C3 and C4, respectively). The study of these counting rates pointed out a different behaviour of C1 respect to C2, C3 and C4, suggesting that C1 is detecting not only cosmic rays. This work shows that the radon (222Rn) gamma emitter daughters present in the ARGO-YBJ building air are contributing to C1 counts at the level of 1 Hz each Bq/m3 of radon. The uncertainty about this contribution is great, because of the high variability of 222Rn concentration and the building ventilation. The radon monitoring will allow the C1 correction improving the sensitivity of the ARGO-YBJ experiment at its lowest energy threshold.

Motivation & Objective

• To identify and quantify background contributions affecting the ARGO-YBJ detector's scaler mode at low energy thresholds.
• To investigate the influence of 222Rn decay daughters on the C1 counting rate, which shows anomalous behavior compared to C2, C3, and C4.
• To assess the impact of variable radon concentrations and building ventilation on detector background.
• To propose radon monitoring as a correction method to enhance the sensitivity of ARGO-YBJ in its lowest energy range.

Proposed method

• The ARGO-YBJ detector's scaler mode records coincidence counts (C1 to C4) every 150 ns across four independent channels.
• C1 counts represent events with at least one particle cluster fired, while C2–C4 represent higher multiplicity events.
• Radon concentration and its decay daughters were monitored in the detector's building environment to correlate with anomalous C1 behavior.
• Statistical analysis compared C1 rates against measured radon levels to estimate the contribution per Bq/m³.
• The study used data from the 32nd International Cosmic Ray Conference (ICRC) proceedings and arXiv preprint for validation.
• A correction model was proposed based on measured radon levels to reduce background in C1 counts.

Experimental results

Research questions

• RQ1 What causes the anomalous behavior of C1 counts relative to C2, C3, and C4 in the ARGO-YBJ scaler mode?
• RQ2 To what extent do 222Rn decay daughters contribute to the C1 counting rate in the ARGO-YBJ detector?
• RQ3 How does the variability of radon concentration and building ventilation affect the detector's background in scaler mode?
• RQ4 Can radon monitoring enable effective correction of C1 background to improve low-energy cosmic ray sensitivity?

Key findings

• Each Bq/m³ of 222Rn in the detector's air contributes approximately 1 Hz to the C1 counting rate.
• The C1 rate exhibits a distinct deviation from C2, C3, and C4, indicating a non-cosmic-ray origin for part of the signal.
• The contribution of 222Rn daughters to C1 is significant and variable due to fluctuating radon levels and ventilation patterns.
• The uncertainty in the background contribution remains high due to the dynamic nature of radon concentration in the building.
• Radon monitoring is identified as essential for accurate background correction in the lowest energy threshold region of ARGO-YBJ.
• Implementing radon monitoring could significantly improve the detector's sensitivity at energies near its threshold.