Novel Compton suppression equipment in γ-ray spectrometry with list mode data acquisition.

A novel Compton suppression device has been developed at the Radiation and Nuclear Safety Authority of Finland to improve the sensitivity of measurements in the Gamma Laboratory. It utilizes γ-γ anticoincidence, but operates as a full coincidence system. Specific software has been developed for the sorting, visualization and analysis of list mode data produced by the multi-detector list-mode devices in the Gamma Laboratory. By utilizing the software, the coincidence data can be accessed and the true-coincidence losses of photo-peaks of multiple gamma-ray-emitting nuclides restored in the analysis. This simplifies data analysis and further increases the sensitivity of the device in low count-rate gamma spectrometry. A detailed Geant4 simulation model of the device was developed and used to optimize the device as well as to support calibrations and complex analysis tasks. The setup has been integrated to current laboratory information management system used in the Gamma Laboratory. Compton suppression reduces the continuous background seen by the high-purity germanium detector by a factor of 3-10, in addition to comparable reduction in the Compton continuum of any peaks in the spectrum. A comparison with the results of conventional gamma-ray spectrometry is presented.

How do children and adolescents of separated parents sleep? An investigation of custody arrangements, sleep habits, sleep problems, and sleep duration in Sweden.

OBJECTIVES: An increasing number of children and adolescents divide their time between their separated parents' homes. Although marital conflict is disadvantageous for children's sleep, little is known about how children of separated parents sleep. The objective was to investigate the association between children's custody arrangements and sleep habits and sleep initiation difficulties. DESIGN: Cross sectional nationally representative samples of adolescents from the WHO study Health Behaviour in School-aged Children (HBSC) (n = 11,802). SETTING: Sweden in 2013/2014 and 2017/2018. PARTICIPANTS: Adolescents in grades 5, 7, and 9 from Swedish compulsory comprehensive school. MEASUREMENTS: The survey included questions on sleep behaviors including bedtime, wake-up time and frequency of sleep onset problems. The analysis methods used were ordinary least squares and logistic regression. RESULTS: The results show differences by custody arrangement, but they are not uniform across the dependent variables. Children and adolescents in sole maternal custody were less likely to sleep as much as recommended (P < .001), more likely to have late bedtimes (P < .001), report sleep initiation difficulties (P < .01) and to report social jetlag between school mornings and weekends (P < .05) compared to those in 2-parent families. Shared physical custody was associated with a higher likelihood of late bedtimes (P < .05) and sleep initiation difficulties (P < .05) compared to those in 2-parent families, but not of sleeping less than recommended or reporting social jetlag. Less-than-equal sharing was generally associated with worse sleep than in 2-parent families. CONCLUSIONS: As custody arrangements seem to be associated with sleep, it is important to understand the mechanisms behind the findings.

Psychological complaints among children in joint physical custody and other family types: Considering parental factors.

AIMS: Increasing proportions of Scandinavian children and children in other Western countries live in joint physical custody, moving between parents' homes when parents live apart. Children and parents in non-intact families are at risk of worse mental health. The potential influence of parental ill-health on child well-being in the context of differing living arrangements has not been studied thoroughly. This study investigates the psychological complaints of children in joint physical custody in comparison to children in sole parental care and nuclear families, while controlling for socioeconomic differences and parental ill-health. METHODS: Data were obtained from Statistics Sweden's yearly Survey of Living Conditions 2007-2011 and child supplements with children 10-18 years, living in households of adult participants. Children in joint physical custody (n=391) were compared with children in sole parental care (n=654) and children in nuclear families (n=3,639), using a scale of psychological complaints as the outcome measure. RESULTS: Multiple regression modelling showed that children in joint physical custody did not report higher levels of psychological complaints than those in nuclear families, while children in sole parental care reported elevated levels of complaints compared with those in joint physical custody. Adding socioeconomic variables and parental ill-health only marginally attenuated the coefficients for the living arrangement groups. Low parental education and parental worry/anxiety were however associated with higher levels of psychological complaints. CONCLUSIONS: Psychological complaints were lower among adolescents in joint physical custody than in adolescents in sole parental care. The difference was not explained by parental ill-health or socioeconomic variables.

Novel Equipment for In Situ Alpha Spectrometry with Good Energy Resolution.

An approach for in situ alpha spectrometry that allows one to measure the spectra with good energy resolution at ambient air pressure has been developed recently. Here, novel equipment is introduced for in situ measurements. Neither vacuum pumps nor radiochemical sample processing are necessary. Flat and smooth surfaces are ideal sources provided that the radionuclide contamination represents a thin layer on the surface. Other sources, such as air filters or evaporation residues, are also possible. Alpha particle collimation is used to obtain good energy resolution, but the equipment can also be used without collimation. An estimation of the detection efficiency with and without collimation is given using an extended area source containing 241Am.

Determination of (235)U, (239)Pu, (240)Pu, and (241)Am in a nuclear bomb particle using a position-sensitive α-γ coincidence technique.

A nuclear bomb particle containing 1.6 ng of Pu was investigated nondestructively with a position-sensitive α detector and a broad-energy HPGe γ-ray detector. An event-mode data acquisition system was used to record the data. α-γ coincidence counting was shown to be well suited to nondestructive isotope ratio determination. Because of the very small background, the 51.6 keV γ rays of (239)Pu and the 45.2 keV γ rays of (240)Pu were identified, which enabled isotopic ratio calculations. In the present work, the (239)Pu/((239)Pu+(240)Pu) atom ratio was determined to be 0.950 ± 0.010. The uncertainties were much smaller than in the previous more conventional nondestructive studies on this particle. Obtained results are also in good agreement with the data from the destructive mass spectrometric studies obtained previously by other investigators.

Simulated and measured spectral characteristics of 137Cs reference radiation beams.

137Cs sources are widely used in calibrations of radiation protection dosimeters and doserate meters. In these calibrations, conversion coefficients from the air kerma to various dose equivalent quantities are needed. These conversion quantities are functions of photon energy. In this work, Monte Carlo simulations and measurements are used for quantifying the energy distributions of the photon fluence from two 137Cs sources used for calibration purposes. The results indicate that the standard set of conversion coefficients, obtained from a monoenergetic spectrum, do not sufficiently take into account the scattered radiation (most of which is scattered by the source itself): For the large (14x15.6 mm) and small (3.5x3 mm) 137Cs sources, the simulated values for the conversion coefficients H'(0.07)/Ka and H*(10)/Ka (which were nearly equal for the both quantities) showed around 1.0 and 1.5% deviations from the ISO standard value 1.20 (for the large and small sources, respectively). Similarly, the conversion coefficient Hp(10)/Ka showed around 1.5 and 2.5% deviations from the ISO standard value 1.21 for the large and small 137Cs sources, respectively, whereas Hp(0.07)/Ka had the values 1.22 and 1.23. The amplitude of the variation of the conversion coefficients due to varying 137Cs source size did not exceed 1%. Thus, the overall uncertainty (with coverage factor k=2) due to varying source size for the average values of the conversion coefficients can be estimated as low as 0.6%.