The “Beta-Delayed Neutrons at RIKEN” project (BRIKEN): conquering the most exotic beta-delayed neutron-emitters

Among the main missions of modern radioactive isotope facilities is the exploration of properties of yet unknown isotopes on the neutron-rich side of the chart of nuclides. However, going more neutron-rich also means that the neutron separation energy decreases until it reaches the dripline at Sn = 0 MeV. If the neutron separation energy gets lower than the ß-decay energy window (Qß value), a new decay mechanism can occur: the emission of neutrons after ß-decay. These “ß-delayed neutron” (ßn) emitters play a crucial role in nuclear structure, nuclear astrophysics, and for nuclear reactor applications.Postprint (published version

Neutron capture on ^{205}Tl: depicting the abundance pattern of lead isotopes in s-process nucleosynthesis

Proposal: Neutron capture on 205Tl: depicting the abundance pattern of lead isotopes in s-process nucleosynthesisWe propose to use the TOF technique to measure the neutron capture cross section of 205Tl(n,gamma) over the full energy range of stellar interest. An accurate measurement of this cross section is needed for a complete and consistent understanding of the s-process nucleosynthesis of the heaviest nuclei which are produced in low-mass and low metallicity AGB-stars. The only previous TOF measurement has yield only a partial information, insufficient for a reliable analysis of the complex branching pattern around 205Pb and 205Tl. Furthermore, there is also a discrepancy of 40% between the two previous activation measurements made at kT=24 keV. The cross section of 205Tl(n,gamma) is particularly relevant because it affects the equilibrium that is established in some stellar conditions between the 205Tl -> 205Pb bound-state Beta-decay and the 205Pb -> 205Tl E.C. decay. This effect induces a complex interplay which influences the final s-process abundance of both nuclei. We propose to measure accurately and with high resolution the 205Tl(n,gamma) cross section by using a set of four C6D6 detectors in combination with the pulsed neutron-source of CERN n_TOF.Preprin

The BRIKEN Project: extensive measurements of ß-delayed neutron emitters for the astrophysical r process

An ambitious program to measure decay properties, primarily ß-delayed neutron emission probabilities and half-lives, for a significant number of nuclei near or on the path of the rapid neutron capture process, has been launched at the RIKEN Nishina Center. We give here an overview of the status of the project.Postprint (published version

Preliminary results on the 233U capture cross section and alpha ratio measured at n_TOF (CERN) with the fission tagging technique

233U is of key importance among the fissile nuclei in the Th-U fuel cycle. A particularity of 233U is its small neutron capture cross-section, which is on average about one order of magnitude lower than the fission cross-section.The accuracy in the measurement of the 233U capture cross-section depends crucially onan efficient capture-fission discrimination, thus a combined set-up of fission and ¿-detectors is needed. A measurement of the 233U capture cross-section and capture-to-fissionratio was performed at the CERN n_TOF facility. The Total Absorption Calorimeter (TAC) of n_TOF was employed as ¿-detector coupled with a novel compact ionization chamber as fission detector. A brief description of the experimental set-up will be given, and essential parts of the analysis procedure as well as the preliminary response of the set-up to capture are presented and discussedPostprint (published version

Measurement of the 235U(n,f) cross section relative to the 6Li(n,t) and 10B(n,a) standards from thermal to 170 keV neutron energy range at n_TOF

The 235U(n,f) cross section was measured in a wide energy range at n_TOF relative to 6Li(n,t) and 10B(n,alpha), with high resolution and in a wide energy range, with a setup based on a stack of six samples and six silicon detectors placed in the neutron beam. This allowed us to make a direct comparison of the reaction yields under the same experimental conditions, and taking into account the forward/backward emission asymmetry. A hint of an anomaly in the 10÷30 keV neutron energy range had been previously observed in other experiments, indicating a cross section systematically lower by several percent relative to major evaluations. The present results indicate that the evaluated cross section in the 9÷18 keV neutron energy range is indeed overestimated, both in the recent updates of ENDF/B-VIII.0 and of the IAEA reference data. Furthermore, these new high-resolution data confirm the existence of resonance-like structures in the keV neutron energy region. The new, high accuracy results here reported may lead to a reduction of the uncertainty in the 1÷100 keV neutron energy region. Finally, the present data provide additional confidence on the recently re-evaluated cross section integral between 7.8 and 11 eV.Preprin

Conceptual design of the BRIKEN detector: A hybrid neutron-gamma detection system for nuclear physics at the RIB facility of RIKEN

BRIKEN is a complex detection system to be installed at the RIB-facility of the RIKEN Nishina Center. It is aimed at the detection of heavy-ion implants, ß-particles, ¿-rays and ß-delayed neu- trons. The whole detection setup involves the Advanced Implantation Detection Array (AIDA), two HPGe Clover detectors and a large set of 166 counters of 3He embedded in a high-density polyethy- lene matrix. This article reports on a novel methodology developed for the conceptual design and optimisation of the 3He-tubes array, aiming at the best possible performance in terms of neutron detection. The algorithm is based on a geometric representation of two selected parameters of merit, namely, average neutron detection efficiency and efficiency flatness, as a function of a reduced num- ber of geometric variables. The response of the detection system itself, for each configuration, is obtained from a systematic MC-simulation implemented realistically in Geant4. This approach has been found to be particularly useful. On the one hand, due to the different types and large number of 3He-tubes involved and, on the other hand, due to the additional constraints introduced by the ancillary detectors for charged particles and gamma-rays. Empowered by the robustness of the al- gorithm, we have been able to design a versatile detection system, which can be easily re-arranged into a compact mode in order to maximize the neutron detection performance, at the cost of the gamma-ray sensitivity. In summary, we have designed a system which shows, for neutron energies up to 1(5) MeV, a rather flat and high average efficiency of 68.6%(64%) and 75.7%(71%) for the hybrid and compact modes, respectively. The performance of the BRIKEN system has been also quantified realistically by means of MC-simulations made with different neutron energy distributions.Postprint (published version

Elämyksiä ja kohtaamisia Hopeatien palvelutalon aistihuoneessa

Opinnäytetyön tavoitteena oli selvittää ikäihmisten kokemuksia aistihuoneen käytöstä ja kartoittaa, miten he voivat hyötyä aistihuoneesta. Apuvälineyritys Haltija Groupin SHX-aistihuoneen elementit siirrettiin Helsingin kaupungin Hopeatien palvelutaloon testikäyttöön kolmeksi kuukaudeksi. Opinnäytetyö pohjautuu Gary Kielhofnerin inhimillisen toiminnan malliin “Model of Human Occupation (MOHO)” ja sen keskeiset käsitteet ohjasivat tutkimusaineiston tiedon keruuta sekä sen analysointia. Opinnäytetyön muu teoreettinen perusta muodostui ikääntymisen tarkastelusta toimintakyvyn ja aistien näkökulmasta sekä multisensorisen toiminnan perusteista. Opinnäytetyö perustui laadullisen tutkimuksen periaatteisiin ja siinä oli kaksi työelämäkumppania: Helsingin kaupungin Hopeatien palvelutalo ja Haltija Group. Tutkimusmenetelmiksi valittiin aistihuoneen käyttäjille suunnattu kyselylomake sekä hoitohenkilökunnalle suunnattu ryhmämuotoinen teemahaastattelu. Kirjallinen raporttiosuus sisältää teoreettisen perustan, opinnäytetyön toteutuksen kuvauksen, aineiston analyysin, johtopäätökset ja pohdinnan. Tässä opinnäytetyössä asiakaslähtöisyys ja aistihuoneen esteettömyys nousivat seikoiksi, jotka vaikuttivat myönteisesti ikääntyneen osallistumiseen aistihuoneessa. Asiakkaan elämänhistorian ja mielenkiinnon kohteiden tunteminen sekä yksilöllisen tahdon ja suorituskyvyn huomioiminen koettiin tärkeiksi. Onnistuneeseen käyntiin aistihuoneessa vaikuttivat orientaatio ja henkilökunnan taito käyttää aistihuoneen tekniikkaa. Asiakkaiden kokemukset aistihuoneesta olivat pääosin miellyttäviä, jopa rentouttavia. Tämän opinnäytetyön tulokset ovat yhtenäisessä linjassa verrattuna aiempiin tutkimuksiin aistihuoneista ja niiden vaikutuksista. Opinnäytetyön perusteella aistihuoneen käyttö ikääntyneiden arjessa voi tarjota positiivisia vaikutuksia ikääntyneen psyykkiseen ja sosiaaliseen toimintakykyyn. Huolellinen suunnittelu, esteettömyys ja vahva asiakastuntemus mahdollistavat asiakkaan osallistumisen terapeuttiseen toimintaan aistihuoneessa. Aistihuoneen vaikuttavuudesta pitkällä aikavälillä tarvitaan lisää tutkimustietoa, jota voisi hyödyntää myös suunniteltaessa tulevaisuuden palveluja ikääntyneille.The object of the Bachelor’s thesis was to provide the elderly in the Hopeatie service house in Helsinki with the SHX multisensory elements for trial use. The purpose of this study was to find out experiences of elderly people in the multisensory room and analyze how they can benefit from the multisensory activities in their rehabilitation. The theory is based on Gary Kielhofner’s Model of Human Occupation (MOHO) and its essential concepts that steer the data gathering and analysis. The fundamental aspects of multisensory activities and ageing accompanied by changes in performance and impaired senses are also observed. This thesis is a qualitive study executed in collaboration with two working life partners: the city of Helsinki and Haltija Group, which is a Finnish company for assistive devices, welfare technology and rehabilitation. The thematic group interview of six employees of the service house and a client questionnaire were chosen as research methods. This thesis consists of theory, description of the implementation, data analysis, results of the study, and conclusions and discussion. The results show that the client-centered approach and the accessibility to the multisensory room had an influence on participation of the elderly in the multisensory room. Successful visits of the multisensory room were enabled by employees’ skills to prepare the client for the visit and their skills to master the technology of the room. The experiences of the elderly in the multisensory room were mainly pleasant, some even relaxing. The results of this study are consistent with previous research on the effects of a multisensory room. This study proves that the use of the multisensory room in the elderly people’s daily lives may have a positive effect on their mental and social performance. Thorough planning of therapy intervention, easy access to the multisensory room and strong client knowledge enable committed client participation. More research is needed for long-term effects of multisensory room in order to benefit from the results for planning services for the elderly in the future

(n,cp) reactions study at the n_TOF facilitty at CERN: results for the cosmological lithium problem

The Big Bang Nucleosynthesis describes the production of the lightest nuclides from deuterium to Li at the early stages of the Universe. While a general good agreement is found for most of the isotopes involved in the synthesis, a serious discrepancy between the predicted abundance of 7Li and the related experimental observations is still present. This discrepancy has been referred since several decades as Cosmological Lithium Problem. In one last attempt to find nuclear solutions to this longstanding conundrum, the 7Be(n,alpha)4He and 7Be(n,p)7Li reactions, that affect predominantly the production of 7Li via the destruction of his parent nucleus 7Be, have been studied. Here we present the 7Be(n,a)4He and 7Be(n,p)7Li reaction crosssection measurements performed at the high-resolution n_TOF facility using the time-of-flight technique and high purity samples. The result of the experiments definitely rules out neutron induced reactions as a solution to the puzzle, thus indicating that explanations have to be sought out in other Physics scenarios.Postprint (published version

New accurate measurements of neutron emission probabilities for relevant fission products

We have performed new accurate measurements of the beta-delayed neutron emission probability for ten isotopes of the elements Y, Sb, Te and I. These are fission products that either have a significant contribution to the fraction of delayed neutrons in reactors or are relatively close to the path of the astrophysical r process. The measurements were performed with isotopically pure radioactive beams using a constant and high efficiency neutron counter and a low noise beta detector. Preliminary results are presented for six of the isotopes and compared with previous measurements and theoretical calculations.Postprint (published version