Processing of radiation hard particle detectors on Czochralski silicon

The purpose of this work was to study the radiation hardness of particle detectors. Silicon detectors are cost-effective and have an excellent spatial resolution. Therefore, they are widely used in many high-energy physics experiments. It is known that oxygen improves the radiation hardness of silicon detectors. The natural way to have a high concentration of oxygen in silicon is to use magnetic Czochralski silicon (MCz-Si). MCz-Si has intrinsically a relatively uniform and high level of oxygen (5×1017 cm³) compared to regular float-zone silicon (FZ-Si). Such a level is hard to attain with other methods, namely the diffusion oxygenation of float-zone silicon. In the Large Hadron Collider (LHC) and its potential upgrade, the luminosity and the fluencies of fast hadrons can be so high that detectors made of standard detector-grade FZ-Si might not survive the planned operating period. MCz-Si offers an improvement to the lifetime of particle detectors through improved radiation hardness. This thesis takes a process-oriented view of the potential of the MCz-Si material. The processing of radiation detectors on MCz-Si is described, the process is characterized from the process point of view, and the radiation hardness is studied after irradiations. There is also an emphasis on the intentional introduction of thermal donors (TDs) in high-resistivity MCz-Si material, and specifically on their potential in p-type MCz-Si detectors

Thermal donors formation via isothermal annealing in magnetic Czochralski high resistivity silicon

A quantitative study about the thermal activation of oxygen related thermal donors in high resistivity p-type magnetic Czochralski silicon has been carried out. Thermal donor formation has been performed through isothermal annealing at 430°C up to a total time of 120min. Space charge density after each annealing step has been measured by transient current technique. The localized energy levels related to thermal double donors (TD) have been observed and studied in details by thermally stimulated currents (TSCs) in the range of 10–70K, and activation energies E and effective cross sections σ have been determined for both the emissions TD0∕+ (E=75±5meV, σ=4×10−14cm2) and TD+∕+ (E=170±5meV, σ=2×10−12cm2). The evolution of the space charge density caused by annealing has been unambiguously related to the activation of TDs by means of current deep level transient spectroscopy TSC, and current transients at constant temperature i(t,T). Our results show that TDs compensate the initial boron doping, eventually provoking the sign inversion of the space charge density. TD's generation rate has been found to be linear with the annealing time and to depend critically on the initial interstitial oxygen concentration, in agreement with previous models developed on low resistivity silicon

Maanpuolustuskorkeakoulu teknisten tutkimusmenetelmien käytön murroksessa

Artikkelin johdannon mukaan "Tekniikan tutkimusmenetelmistä ei ole yhtä lähdettä, jossa menetelmät olisi määritelty ja luokiteltu yleisesti hyväksyttävällä tavalla. Toisaalta ei ole yleistä käsitystä siitä, mitä metodeja ylipäätään voidaan määritellä teknisiksi, ja onko siihen edes tarvetta." Näiden ongelmien selvittämiseksi ja opinnäytetöiden ohjaamiseksi on Maanpuolustuskorkeakoulun tekniikan laitoksella tehty tutkimus vuosituhannen vaihteessa Maanpuolustuskorkeakoulussa käytetyistä tutkimusmenetelmistä, jotka on julkaistu tekniikan laitoksen julkaisusarjassa. Saman tutkimuksen tuloksena ovat syntyneet kuvaukset sellaisista teknisistä menetelmistä, joita voidaan käyttää Maanpuolustuskorkeakoulussa. "Tähän artikkeliin on otettu tästä julkaisusta kolme artikkelia. Ensimmäisenä on Tekniikan laitoksen professorin laatima yleiskatsaus tekniikan tutkimuksesta." Seuraavassa kahdessa artikkelissa esitellään kaksi metodia; vaatimusmäärittely ja kenttäkoe. "Nämä on valittu tähän artikkeliin sen vuoksi, että niitä käytetään paljon puolustusvoimissa virkatehtävissä, mutta niiden metodiikkaa ei useinkaan mielletä tutkimusmenetelmäksi." Kirjoittajien mukaan " Kenttäkokeilla on merkittävä osa aselajikoulujen tutkimus- ja kehittämisosastoissa sekä aselajien ampumaleireillä. Kenttäkokeita suunnittelevat ja johtavat upseerit eivät liene olleet useinkaan tietoisia, että he ovat samalla tulleet käyttäneeksi teknistä tutkimusmenetelmää.(..) Vastaavasti materiaalihankkeissa tehdään järjestelmien vaatimusmäärittelyt pääsääntöisesti virkatyötä. Vaatimusmäärittelyäkin voidaan pitää teknisenä tutkimusmetodina."There is summary in English at the end of the article

Behaviour of Metals during Bioheap Leaching at the Talvivaara Mine, Finland

The behaviour of base metals Ni, Zn, Cu, Co, Fe, and Mn, potentially toxic metals Pb, Cr, and Cd, and the radioactive elements, U and Th, in the Talvivaara mining process, Finland has been studied by tracing metal concentrations from the black schist ore, through ores subjected to bioheap leaching of varying duration, to pregnant leach solution (PLS), and solid process waste material deposited on site in gypsum waste ponds. It is apparent that Zn, Cu, Co, and Cd are leached from the ore in a similar manner and recovered efficiently in the PLS; however, Ni, though leached, was also found in the gypsum pond at relatively high concentrations. Relatively little Pb is released from the ore, but the small fraction that is mobilised accumulates in the gypsum pond. Of the radioactive constituents, Th is essentially immobile, whereas U is readily leached from the ore, again accumulating in gypsum pond waste. In addition, a laboratory-based sequential leach test was applied to assess the future leaching potential of metals from residual ore and process waste material under different environmental conditions.Peer reviewe

Radionuclide and heavy metal redistribution at the former pilot-scale apatite plant in Sokli, northern Finland

A new phosphate mine is being planned at Sokli in northern Finland. In the late 1970s, pilot-scale mining and mineral processing took place at the site. The mobilisation of radionuclides and heavy metals from the mill tailings was examined in order to assess the potential environmental impact of past and future mining activities. Given the considerable amount of apatite still present, the waste material does not represent true tailings. Variations in abundance probably represent material discharges to the tailings rather than mobilization of the elements from the tailings themselves. No indication of heavy-metal migration was found. Extraction results suggest that only a small proportion of cadmium is in exchangeable form. Elements that are partly soluble under weakly-acidic conditions include copper, zinc, cadmium, uranium and lead. However, most of the elements are tightly bound to the sample matrix and therefore not easily released to the environment.Peer reviewe

Maternal Depressive Symptoms During and After Pregnancy and Psychiatric Problems in Children

OBJECTIVE: Maternal depressive symptoms during pregnancy are associated with increased risk of psychiatric problems in children. A more precise understanding of the timing of the symptoms during pregnancy and their independence of other prenatal and postnatal factors in predicting child psychopathology risk is needed. We examined whether maternal depressive symptoms during pregnancy predict child psychiatric problems, whether these associations are trimester- or gestational-week-specific and/or independent of pregnancy disorders, and whether maternal depressive symptoms after pregnancy mediate or add to the prenatal effects. METHOD: The study sample comprised 2,296 women and their children born in Finland between 2006-2010, participating in the prospective pregnancy cohort study Prediction and Prevention of Preeclampsia and Intrauterine Growth Restriction (PREDO) and followed up from 1.9 to 5.9 years of age. The women completed the Center for Epidemiologic Studies Depression Scale biweekly between gestational weeks+days 12+0/13+6 and 38+0/39+6 or delivery. In the follow-up, they completed the Beck Depression Inventory-II and Child Behavior Checklist 1½-5. RESULTS: Maternal depressive symptoms during pregnancy predicted significantly higher internalizing (0.28 SD unit per SD unit increase [95% CI = 0.24-0.32]), externalizing (0.26 [0.23-0.30]), and total problems (0.31 [0.27-0.35]) in children. These associations were nonspecific to gestational week and hence pregnancy trimester, independent of pregnancy disorders, and independent of, although partially mediated by, maternal depressive symptoms after pregnancy. Psychiatric problems were greatest in children whose mothers reported clinically significant depressive symptoms across pregnancy trimesters and during and after pregnancy. CONCLUSION: Maternal depressive symptoms during pregnancy predict increased psychiatric problems in young children. Preventive interventions from early pregnancy onward may benefit offspring mental health.Peer reviewe

Release of radionuclides from waste rock and tailings at a former pilot uranium mine in eastern Finland

The Paukkajanvaara mine in Eno, eastern Finland, started to operate in 1959. The mine was a test site for assessing the feasibility of larger-scale uranium extraction. Pilot-scale mining and milling were carried out between 1958 and 1961, and the mine site was rehabilitated in the early 1990s. The aim of this study was to examine the potential for further mobilization of radionuclides after remediation. There are two primary sources of contamination at the site, the waste-rock pile and the tailings. Our study indicates that 226Ra leached from the waste-rock pile and accumulated in surrounding soil. In run-off sediment samples collected from a dry stream bed near the waste-rock pile, the activity concentrations of 226Ra and 238U were higher than in soil samples. From the tailings, radionuclides can leach directly to the lake and to another small stream, which flows to the east of the waste-rock pile. In the water samples collected from this stream, uranium concentrations increased at the outlet to the lake. The results from the soil samples collected between the tailings area and the stream indicate leaching of 238U and 226Ra with the surface flow. Sediment samples collected from the bottom of the lake displayed pronounced uranium series disequilibrium with fractionations of 210Pb and 226Ra relative to the parent 238U. The results therefore indicate that leaching and accumulation of at least 226Ra from the waste-rock pile and possibly tailings is still ongoing.Peer reviewe

Maternal Hypertensive Pregnancy Disorders and Mental Disorders in Children

The associations of maternal hypertensive pregnancy disorders with offspring mental disorders remain unclear. We examined whether maternal hypertensive disorders and maximum blood pressure during pregnancy predict offspring childhood mental disorders, whether the associations are independent of maternal and paternal mental disorders and paternal hypertensive disorders, independent of or additive with maternal early pregnancy overweight/obesity and diabetes mellitus disorders, and mediated or moderated by preterm birth, small-for-gestational-age birth and neonatal intensive care unit admission. Our prospective study comprised 4743 mother-child dyads of Prediction and Prevention of Preeclampsia and Intrauterine Growth Restriction study. Women were recruited to the study in early pregnancy at Finnish maternity hospitals. Children were born 2006 to 2010 and followed-up until December 31, 2016, to ages 6.4 to 10.8 years. Hypertensive pregnancy disorders were identified from medical records, Medical Birth Register, and Care Register for Health Care. Systolic and diastolic blood pressure were measured at antenatal clinics and hospital visits. Mental disorder diagnoses were identified from Care Register for Health Care. Maternal gestational and chronic hypertension, preeclampsia and its severity increased offspring hazard of any childhood mental disorder. The associations of preeclampsia (hazard ratio=1.66 [95% CI, 1.14-2.42]) and severe preeclampsia (hazard ratio=2.01 [95% CI, 1.08-3.73]) were independent of all covariates. Maternal hypertensive and diabetes mellitus disorders and overweight/obesity also additively increased offspring hazard of mental disorders. Preterm and small-for-gestational-age births and neonatal intensive care unit admission partially mediated the effects of any and severe preeclampsia on offspring mental disorders. To conclude, maternal hypertensive pregnancy disorders carry adverse consequences for offspring mental health.Peer reviewe

Maternal depressive symptoms during and after pregnancy are associated with attention-deficit/hyperactivity disorder symptoms in their 3-to 6-year-old children

Maternal depressive symptoms during pregnancy have been associated with child behavioural symptoms of attention-deficit/hyperactivity disorder (ADHD) in early childhood. However, it remains unclear if depressive symptoms throughout pregnancy are more harmful to the child than depressive symptoms only during certain times, and if maternal depressive symptoms after pregnancy add to or mediate any prenatal effects. 1,779 mother-child dyads participated in the Prediction and Prevention of Pre-eclampsia and Intrauterine Growth Restriction (PREDO) study. Mothers filled in the Center of Epidemiological Studies Depression Scale biweekly from 12+0-13+ 6 to 38+0-39+6 weeks+days of gestation or delivery, and the Beck Depression Inventory-II and the Conners' Hyperactivity Index at the child's age of 3 to 6 years (mean 3.8 years, standard deviation [SD] 0.5). Maternal depressive symptoms were highly stable throughout pregnancy, and children of mothers with consistently high depressive symptoms showed higher average levels (mean difference = 0.46 SD units, 95% Confidence Interval [CI] 0.36, 0.56, p <0.001 compared to the low group), and proportion (32.1% vs. 14.7%) and odds (odds ratio = 2.80, 95% CI 2.20, 3.57, p <0.001) of clinically significant ADHD symptoms. These associations were not explained by the effects of maternal depressive symptoms after pregnancy, which both added to and partially mediated the prenatal effects. Maternal depressive symptoms throughout pregnancy are associated with increased ADHD symptomatology in young children. Maternal depressive symptoms after pregnancy add to, but only partially mediate, the prenatal effects. Preventive interventions suited for the pregnancy period may benefit both maternal and offspring mental health.Peer reviewe