Monitor Count Research Articles

Can we properly model the neutron monitor count rate?

AbstractNeutron monitors provide continuous measurements of secondary nucleonic particles produced in the atmosphere by the primary cosmic rays and form the main tool to study the heliospheric modulation of cosmic rays. In order to study cosmic rays using the world network of neutron monitor and needs to be able to model the neutron monitor count rate. Earlier it was difficult because of the poorly known yield function, which has been essentially revisited recently. We have presented a verification of the new yield function of the standard neutron monitor (NM) using a recently released data on the direct in situ measurements of the galactic cosmic rays energy spectrum during 2006–2009 (the period of the record high cosmic ray flux) by Payload for Antimatter Matter Exploration and Light‐nuclei Astrophysics spaceborne spectrometer, and on NM latitude surveys performed during the period of 1994–2007, including periods of high solar activity. We found a very good agreement between the measured count rates of sea level NMs and the modeled ones in very different conditions: from low to high solar activity and from polar to tropical regions. This implies that the count rate of a sea level neutron monitor can be properly modeled in all conditions, using the new yield function.

Solar cycles and depositional processes in annual 10Be from two varved lake sediment records

Beryllium 10 concentrations (10Becon) were measured at annual resolution from varved sediment cores of Lakes Tiefer See (TSK) and Czechowskie (JC) for the period 1983–2009 (∼solar cycles 22 and 23). Calibrating the 10Becon time-series against complementing proxy records from the same archive as well as local precipitation and neutron monitor data, reflecting solar forced changes in atmospheric radionuclide production, allowed (i) identifying the main depositional processes and (ii) evaluating the potential for solar activity reconstruction. 10Becon in TSK and JC sediments are significantly correlated to varying neutron monitor counts (TSK: r=0.5, p=0.05, n=16; JC: r=0.46, p=0.03, n=22). However, the further correlations with changes in organic carbon contents in TSK as well as varying organic carbon and detrital matter contents in JC point to catchment specific biases in the 10Becon time-series. In an attempt to correct for these biases multiple regression analysis was applied to extract an atmospheric 10Be production signal (10Beatmosphere). To increase the signal to noise ratio a 10Be composite record (10Becomposite) was calculated from the TSK and JC 10Beatmosphere time-series. 10Becomposite is significantly correlated to variations in the neutron monitor record (r=0.49, p=0.01, n=25) and matches the expected amplitude changes in 10Be production between solar cycle minima and maxima. This calibration study on 10Be from two sites indicates the large potential but also, partly site-specific, limitations of 10Be in varved lake sediments for solar activity reconstruction.

Measurement and simulation of neutron monitor count rate dependence on surrounding structure

AbstractNeutron monitors are the premier instruments for precise measurements of time variations (e.g., of solar origin) in the galactic cosmic ray (GCR) flux in the range of ∼1–100 GeV. However, it has proven challenging to accurately determine the yield function (effective area) versus rigidity in order to relate a neutron monitor's count rate with those of other monitors worldwide and the underlying GCR spectrum. Monte Carlo simulations of the yield function have been developed, but there have been few opportunities to validate these observationally, especially regarding the particular environment surrounding each monitor. Here we have precisely measured the count rate of a calibration neutron monitor near the Princess Sirindhorn Neutron Monitor (PSNM) at Doi Inthanon, Thailand (18.59∘N, 98.49∘E, 2560 m altitude), which provides a basis for comparison with count rates of other neutron monitors worldwide that are similarly calibrated. We directly measured the effect of surrounding structure by operating the calibrator outside and inside the building. Using Monte Carlo simulations, we clarify differences in response of the calibrator and PSNM, as well as the calibrator outside and inside the building. The dependence of the calibrator count rate on surrounding structure can be attributed to its sensitivity to neutrons of 0.5–10 MeV and a shift of sensitivity to nucleons of higher energy when placed inside the building. Simulated calibrator to PSNM count rate ratios inside and outside agree with observations within a few percent, providing useful validation and improving confidence in our ability to model the yield function for a neutron monitor station.

Biocorrosion Study of Mild Steel in Dumpsite Leachates

Biocorrosion due to dumpsite leachates can lead to rupture and failure of engineering materials such as mild steel. This study was carried out to assess the effect of dumpsite leachates in corrosion process of mild steel. Mild steel coupons were prepared and immersed completely in leachates from Olusosun dumpsite (A), Ewu Elepe dumpsite (B) and Abule Egba dumpsite (C). The following parameters were measured at regular interval in each of the leachate: Total Dissolved Solids (TDS), Conductivity, pH, Temperature and Dissolved Oxygen (DO) using a multi – parameter water quality monitor and Total Bacterial Count (TBC) using standard method for biological analysis of water flood injection water. The corrosion rate was determined using weight loss method. The results revealed that the weight loss varied between 0.27 and 0.58 g in leachate A, between 0.05 and 0.29 g in leachate B and between 0.02 and 0.50 g in leachate C. Corrosion rate varied between 2.35 and 7.61 mm/yr in leachate A, between 1.15 and 1.48 mm/yr in leachate B and between 1.48 and 7.03 mm/yr in leachate C. Leachate A has the highest range of TDS ranging between 18, 686 and 125, 856 mg/L as well as highest range of Conductivity ranging between 8.62 and 57.75 µS/cm. Moreover, leachate A has the highest range of pH ranging between 5.11 and 5.34 while it has the least range of DO varying between 2.94 and 3.59 mg/L. Leachate B has the highest range of temperature varying between 27.60 and 32.30°C. Leachate C has the least range of TBC ranging between 100 x 103 and 126 x 103 Cfu/ml. The leachates from dumpsites have the potential to cause corrosion of mild steel due to the presence of bacterial in the leachates. It was recommended that dumpsites should not be cited where there are pipelines.

Galactic cosmic rays in the heliosphere

Simon R Thomas, Mathew J Owens and Mike Lockwood discuss how neutron monitor counts can help map space weather. This won the 2014 Rishbeth Prize for the best student talk at the Hot Spring MIST Meeting in Bath, April 2014.

International key comparison of neutron fluence measurements in monoenergetic neutron fields: CCRI(III)-K11

To ensure the validity of their national standards, National Metrology Institutes (NMIs) participate regularly in international comparisons. In the area of neutron metrology, Section III of the Consultative Committee for Ionizing Radiation is in charge of the organization of these comparisons. From September 2011 to October 2012, the eleventh key comparison, named CCRI(III)-K11, took place at the AMANDE facility of the LNE-IRSN, in France. Participants from nine NMIs came with their own primary reference instruments, or instruments traceable to primary standards, with the aim of determining the neutron fluence, at 1 m distance from the target in vacuum, per monitor count at four monoenergetic neutron fields: 27 keV, 565 keV, 2.5 MeV and 17 MeV.The key comparison reference values (KCRV) were evaluated as the weighted mean values of the results provided by seven participants. The uncertainties of each KCRV are between 0.9% and 1.7%. The degree of equivalence (DoE), defined as the deviation of the result reported by the laboratories for each energy from the corresponding KCRV, and the associated expanded uncertainty are also reported and discussed.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Continued decline of South Pole neutron monitor counting rate

AbstractThe counting rate of a neutron monitor at South Pole, Antarctica, displays a long‐term decline over the 49 year span from March 1964 to the present. The counting rate follows an 11 year cycle with maxima at times of low solar activity. However, after adjusting for the unusually high overall cosmic ray fluxes in 2009, we find that the 2009 peak rate (based on 27 day averages) was approximately 10% lower than the 1965 peak rate. This change is much larger than that recorded by any other neutron monitor. We suggest that the South Pole monitor, owing to its unique position at both high latitude and high altitude may have a hitherto unsuspected sensitivity to secular changes in the magnetic field of the Earth.

Record neutron monitor counting rates from galactic cosmic rays

AbstractNeutron monitors have recorded the flux of high‐energy Galactic cosmic rays for more than half a century. During the recent, prolonged, deep minimum in solar activity, many sources indicate that modulated Galactic cosmic rays have attained new Space Age highs. However, reported neutron monitor rates are ambiguous; some record new highs while others do not. This work examines the record of 15 long‐running neutron monitors to evaluate cosmic ray fluxes during the recent extraordinary solar minimum in a long‐term context. We show that ground‐level neutron rates did reach a historic high during the recent solar minimum, and we present a new analysis of the cosmic ray energy spectrum in the year 2009 versus year 1987. To do this, we define a reference as the average of eight high‐latitude neutron monitors, four in the Northern Hemisphere (Apatity, Inuvik, Oulu, Thule) and four in the Southern Hemisphere (Kerguelen, McMurdo, Sanae, Terre Adelie). Most stations display changes in sensitivity, which we characterize by a simple linear trend. After correcting for the change in sensitivity, a consistent picture emerges. With our correction, all stations considered display new highs at the recent solar minimum, approximately 3% above the previous record high. These increases are shown to be consistent with spacecraft observations.

Space weather driven changes in lower atmosphere phenomena

During a period of heliospheric disturbance in 2007–9 associated with a co-rotating interaction region (CIR), a characteristic periodic variation becomes apparent in neutron monitor data. This variation is phase-locked to periodic heliospheric current sheet crossings. Phase-locked electrical variations are also seen in the terrestrial lower atmosphere in the southern UK, including an increase in the vertical conduction current density of fair weather atmospheric electricity during increases in galactic cosmic ray-induced neutron monitor count rate at the surface and energetic proton count rates measured by geosynchronous spacecraft. At the same time as the conduction current increases, changes in the cloud microphysical properties lead to an increase in the detected height of the cloud base at Lerwick Observatory, Shetland, with associated changes in surface meteorological quantities. As electrification is expected at the base of layer clouds, which can influence droplet properties, these observations of phase-locked thermodynamic, cloud, atmospheric electricity and solar sector changes are not inconsistent with a heliospheric disturbance driving lower troposphere changes.

Observable Effects of Interplanetary Coronal Mass Ejections on Ground Level Neutron Monitor Count Rates

In this work, non-recurrent Forbush decreases (FDs) triggered by the passage of shock-driven interplanetary coronal mass ejections (ICMEs) have been analyzed. Fifty-nine ICMEs have been studied but only the 25% of them were associated to a FD. We find that shock-driving magnetic clouds (MCs) produce deeper FDs than shock-driving ejecta. This fact can be explained regarding to the observed growing trends between decreases in neutron monitor (NM) count rate and MC/ejecta speed and its associated rigidity. MCs are faster and have higher associated rigidities than ejecta. Also the deceleration of ICMEs seems to be a cause in producing FDs as can be inferred from the decreasing trend between NM count rate and deceleration. This probably implies that the interaction between the ICME traveling from the corona to the Earth and the solar wind can play an important role to produce deeper FDs. Finally, we conclude that ejecta without flux rope topology are the less effective in unchaining FDs.

A ready-to-use galactic cosmic ray model

Galactic cosmic ray nuclei close to Earth are of great importance in different fields of research. By studying their intensity in near-Earth interplanetary space and modeling their modulation in the heliosphere it is possible to gain knowledge both about the structure of the heliosphere and the transport processes within. Additionally, secondary phenomena like cloud formation, ionization processes in the atmosphere, cosmogenic nuclide production and radiation exposure in space and at aviation altitudes are related to the intensity of the galactic cosmic rays and their modulation in the heliosphere. In order to improve the knowledge about these processes and underlying mechanisms it is often beneficial to perform numerical simulations. A necessary prerequisite for such simulations is a model describing the galactic cosmic ray intensities for all particle types and energies of importance. Several of these models exist in the literature. However, many of these do not provide essential characteristics like the description of heavier nuclei or it is difficult to associate them to recent or actual solar modulation conditions. In this work a model is presented which describes the galactic cosmic ray spectra of nuclei based on a single parameter. The values of this parameter for different solar modulation conditions are derived from measurements of the Advanced Composition Explorer (ACE) spacecraft and Oulu neutron monitor count rates. Comparing the galactic cosmic ray spectra predicted by the model to a comprehensive set of experimental data from literature shows very good agreement.

Reliability of Pedometers to Measure Step Counts in Patients With Chronic Respiratory Disease

There are a variety of devices currently available to measure physical activity. Activity monitors are technologically advanced and provide complex data, leading to higher costs. Pedometers are simple, inexpensive devices that provide easy-to-view data. The aim of this study was to determine the reliability of pedometer step counting during slow walking speeds, typical of patients with chronic respiratory disease. The reproducibility of 8 pedometers was initially determined at slow walking speeds in a healthy individual. Thereafter, pedometer step counting was compared with an activity monitor and visual step counts in 9 healthy subjects and 48 patients with chronic respiratory disease. Pedometers were reproducible on the same wearer, on consecutive occasions, although they were not interchangeable. During healthy subject walking, there were no significant differences between the pedometer and activity monitor at all speeds. However, both significantly undercounted steps at slower walking speeds (P < .01). At slow and medium walking speeds with patients with chronic respiratory disease, both the pedometer and activity monitor significantly undercounted steps (P < .001 for both pedometer and activity monitor at slow and P < .003 for pedometer and P < .004 for activity monitor at medium speeds) compared with visual counts. Pedometers are an inexpensive and simple alternative to activity monitors and appear to be reliable during faster walking in both healthy subjects and patients with chronic respiratory disease. However, caution should be applied during slow walking speeds because of undercounting steps, causing misleading data that could become demotivating when used as a training adjunct.

Examination of Dual vs. Single Monitor Use during Common Office Tasks

Previous studies have found that using multiple monitors increases productivity, but there are also documented drawbacks to increased monitor count and/or size. The purpose of this study was to determine whether increases in productivity hold true with newer technology, like wide flat-screens, in the multitasking context. Sixty participants were asked to complete several tasks commonly completed in an office environment. These tasks were performed on four different monitor configurations: a single and dual 17” monitor(s) and single and dual 22” monitor(s). Participants located information from several documents and compiled this information into a new document. Dependent variables measured included efficiency, effectiveness, and satisfaction. Results indicated a performance benefit for dual monitor usage, regardless of monitor size. Participants most preferred using dual 22” monitors and least preferred a single 17” monitor.

On the role of radiation monitors on board LISA Pathfinder and future space interferometers

LISA (Laser Interferometer Space Antenna) and its precursor mission LISA Pathfinder (LISA-PF) will carry particle monitors for noise diagnostics. It was proposed to build and place radiation detectors on board the ASTROD missions as well. We present here a study of the solar energetic particle (SEP) events that the LISA-PF radiation monitors are able to detect above the galactic cosmic-ray (GCR) background predicted at the time of the mission data taking in 2015. In order to optimize the correlation between radiation monitor measurements and gravitational sensor test-mass charging, the energy threshold for particles traversing both detectors should be approximately the same. In LISA-PF, the radiation monitor particle energy cut-off was conservatively set at 75 MeV per nucleon (MeV/n) for protons and ion normal incidence, while the minimum energy of the same particles reaching the test masses is 100 MeV/n. We find that SEP events detectable on LISA-PF are characterized by peak fluxes and fluences at energies >75 MeV/n larger than about 45%, on average, with respect to those at energies >100 MeV/n. We conclude that for an accurate correlation between radiation monitor count rates and test-mass charging, it is mandatory to benefit from absolute flux measurements of both galactic and high-energy solar particles provided by experiments carrying magnetic spectrometers in space at the time of LISA-PF (PAMELA, AMS). On the other hand, the role of the radiation detectors on board LISA-PF is crucial allowing for SEP event onset and dynamics monitoring.

Wrist activity monitor counts are correlated with dynamic but not static assessments of arm elevation exposure made with a triaxial accelerometer

There is evidence in the literature of a link between workplace arm elevation exposure and atraumatic shoulder injuries. However, there are several methods that can be used to assess this exposure. The goal of the present study was to compare the outcomes of an activity monitor attached to the wrist and a triaxial accelerometer mounted on the humerus. Twenty-one workers wore both sensors over the course of a full workday. While the activity monitor data was not significantly correlated with any static humeral parameters, it was strongly correlated with all dynamic parameters. The use of a simple, commercially available activity monitor might offer an inexpensive alternative for the assessment of a large number of subjects over multiple workdays to determine the relationship between dynamic motion and occupation shoulder injuries in the future. Practitioner Summary: Arm overuse has been linked to occupation-related shoulder injuries. An activity monitor attached to the wrist and a triaxial accelerometer mounted on the humerus were compared in a field trial. The results demonstrate that, under certain conditions, a commercially available activity monitor might be a useful tool for exposure assessment.

ESTIMATION OF HIGH-LEVEL, RAPIDLY-CHANGING CONCENTRATIONS USING MOVING-FILTER CONTINUOUS PARTICULATE AIR MONITORS

A previously published mathematical model for the dynamic response of moving-filter continuous particulate air monitors has been enhanced to extend that model to include decay chains. During this work, it was observed that a quantitative relationship appeared to exist between the monitor count rate and the time-dependent particulate airborne radioactive material concentration if, and only if, the filter (tape) speed was much faster than the nominal 2.54 cm h(-1) (1 in h(-1)). The extended model demonstrated that operating moving-filter monitors at this nominal filter speed does not provide a quantitative measurement of a changing airborne particulate concentration of a fission product or other contaminant. By contrast, at faster filter speeds [e.g., 76.2 or 152.4 cm h(-1) (30 or 60 in h(-1))], numerical experimentation with this model showed that the count rate trace has essentially the same shape as the concentration profile. It was then found that a quantitative relationship applies, but only when the filter speed is sufficiently fast so that a Taylor series expansion of the monitor count rate can be reasonably well truncated at the first-order term. This mode of operation, which does not require any new monitor hardware, is capable of tracking rapidly changing concentrations. Since the fast filter speed also reduces the monitor's count rate, all else being equal, the approach will best be used for relatively high-level concentrations, such as may occur in abnormal or "accident" conditions. The count rate suppression may also be useful for reducing the detector saturation that can occur with higher levels of airborne particulate radioactivity in post-accident situations.

Evaluation of internal contamination levels after a radiological dispersal device incident using portal monitors

Following a radioactive dispersal device (RDD) incident, it may be necessary to evaluate the internal contamination levels of a large number of potentially affected individuals to determine if immediate medical follow-up is necessary. Since the current laboratory capacity to screen for internal contamination is limited, rapid field screening methods can be useful in prioritising individuals. This study evaluated the suitability of a radiation portal monitor for such screening. A model of the portal monitor was created for use with models of six anthropomorphic phantoms in Monte Carlo N-Particle Transport Code Version 5 (MCNP) X-5 Monte Carlo Team (MCNP-A General Monte Carlo N-Particle Transport Code Version 5. LA-CP-03-0245. Vol. 2. Los Alamos National Laboratory, 2004.). The count rates of the portal monitor were simulated for inhalation and ingestion of likely radionuclides from an RDD for each of the phantoms. The time-dependant organ concentrations of the radionuclides were determined using Dose and Risk Calculation Software Eckerman, Leggett, Cristy, Nelson, Ryman, Sjoreen and Ward (Dose and Risk Calculation Software Ver. 8.4. ORNL/TM-2001/190. Oak Ridge National Laboratory, 2006.). Portal monitor count rates corresponding to a committed effective dose E(50) of 10 mSv are reported.

Calibration and absolute normalization procedure of a new Deep Inelastic Neutron Scattering spectrometer

We describe the calibration process of a new Deep Inelastic Neutron Scattering (DINS) spectrometer, recently implemented at the Bariloche Electron LINAC (Argentina), consisting in the determination of the incident neutron spectrum, dead-time and electronic delay of the data acquisition line, and detector bank efficiency. For this purpose, samples of lead, polyethylene and graphite of different sizes were employed. Their measured spectra were corrected by multiple scattering, attenuation and detector efficiency effects, by means of an ad hoc Monte Carlo code. We show that the corrected spectra are correctly scaled with respect to the scattering power of the tested materials within a 2% of experimental error, thus allowing us to define an experimental constant that links the arbitrary experimental scale (number of recorded counts per monitor counts) with the involved cross-sections. The present work also serves to analyze the existence of possible sources of systematic errors.

Respiratory rate measurement: a comparison of methods

The value of monitoring respiratory rate as a key vital sign to detect early changes in the health status of critically ill patients has been well documented. However, although pulse oximetry has been a major advance in bedside monitoring, it has not been demonstrated to be an indicator of serious illness. Arterial blood oxygen saturation appears to be poorly understood by hospital staff and lacks specificity as a monitoring tool. Therefore, the primary objective of this study was to demonstrate an equivalence between the respiR8™ respiratory rate monitor and manual counting methods, defined as a difference within ±2 breaths per minute. Secondary objectives of this study were to assess the respiR8™ performance from the end-user perspective, analysing respiR8™ alarm activations, corresponding pulse rate and SpO2 readings (sub-group), and to assess repeatability of both manual and digital readings using a Bland-Altman analysis (describe).

Galactic Cosmic Ray Modulation Up to Recent Solar Cycles

Galactic Cosmic Ray Modulation Up to Recent Solar Cycles Cosmic ray neutron monitor counts obtained by different ground-based detectors have been used to study the galactic cosmic ray modulation during the last four solar activity cycles. Since long, systematic correlative studies have been per-formed to establish a significant relationship between the cosmic ray intensity and different helio-spheric activity parameters, and the study is extended to a recent solar cycle (23). In the present work, the yearly average of 10.7 cm solar radio flux and the interplanetary magnetic field strength (IMF, B) have been used to find correlation of the yearly average cosmic ray intensity derived from different neutron monitors. It is found that for four solar cycles (20-23) the cosmic ray intensity is anti-correlated with the 10.7 cm solar radio flux and the IMF, B value with some discrepancy. However, this is in a good positive correlation with the flux of mentioned wavelength for four different solar cycles. The IMF, B shows a weak correlation with cosmic rays for solar cycle 20, and a good anti-correlation for solar cycles 21-23.