Preliminary analysis of neutron time-delay histograms from Changvan latitude surveys

Abstract

The name “Changvan” is given to a transportable neutron monitor, modernized by researchers in Thailand and housed inside a standard-size shipping container. It contains three neutron-sensitive proportional counters, which contain enriched 10BF3 gas, to detect cosmic ray showers. Primary cosmic rays are high-energy particles arriving from outer space. By colliding with atoms in the atmosphere, they produce a shower of sub-atomic particles, called secondary particles. Some particles can reach the Earth’s surface, including neutrons. The Changvan is designed to measure atmospheric neutrons during a latitude survey. The side counter tubes are ringed with lead producer to produce evaporation neutrons when secondary particles collide with it. The center counter lacks the lead producer but can receive neutrons from nearby counters. The reflector and moderator made from polyethylene thermalize the evaporation neutrons and protect against disturbance by external low-energy neutrons. In this work, we pursue methods to determine spectral changes in Galactic cosmic rays using data from the Changvan, avoiding the systematic inconsistencies of cross-station comparisons. We examine neutron time delay histograms from the three counter tubes, as recorded by specially designed readout electronics, where the time delay refers to the time interval between consecutive neutron detections in one counter. We perform a preliminary analysis of such histograms to measure the leader fraction (L) of neutrons that do not follow a previous neutron from the same primary cosmic ray. The electronic dead time will be considered in the L calculation.

Simulations of the Yield Functions of a Semi-Leaded Neutron Monitor from Latitude Surveys.

“…We used the count rate data provided in [8] for the southbound data in 2019. Additionally, we obtained supplementary data from the same survey year from [9].…”

“…The Changvan consists of three neutron-sensitive proportional counters assembled according to the standard NM64 design, with the exception that the middle counter lacks the lead producer. We refer to this modified design as a "semi-leaded neutron monitor" [7][8][9][10]. The Changvan incorporates BF 3 gas to induce nuclear fission through the reaction 10 B (n, 𝛼) 7 Li.…”

Response functions of semi-leaded neutron monitor count rates and leader rates from latitude surveys during 2019-2020

“…By using time delay histograms from a neutron monitor can accurately track time variations in the flux of Galactic cosmic rays (GCRs). We analyze hourly time-delay histograms collected by Changvan neutron monitor during the 2019 and 2020 survey years to calculate the leader fraction ( ) [6]. The data acquisition system produces time delay histograms for each counter over short and long timescales.…”

“…− , from 5 ms to before the last time bin (excluding the overflow time bin) [6] is shown in red. The amplitude of exponential tail gives the rate of "leaders" arriving by chance, not "following" in temporal association with preceding count.…”

“…As such the SLNM/NM64 ratio will allow us to study spectral variations in a way related to the standard Bare/NM configuration but with a different response. The main purpose of the Changvan mobile monitor is -in the sense of the "Calmon [1]" -to tie together fixed neutron monitor stations measuring the "leader fraction [2,[4][5][6]." Latitude surveys are also useful in detecting short-time variations in the Galactic cosmic ray spectrum.…”