Search results for "radioaktiivisuus"
showing 10 items of 12 documents
Järvisedimenttien iänmääritys lyijyajoituksella
2013
Radioaktiivisuudella tarkoitetaan epästabiilin ytimen hajoamista toiseksi ytimeksi. Käytännössä ydin voi hajota kolmella perusprosessilla; alfa-, beeta tai gammahajoamisella, joista gammahajoamisessa virittyneen ytimen viritystila purkautuu emittoimalla gammahiukkasen, fotonin, jonka energia vastaa viritystilan tai viritystilojen välistä energiaa. Lyijyn isotoopin 210Pb (puoliintumisaika noin 22 vuotta) gammahajoamiseen perustuvalla lyijyajoituksella voidaan määrittää järvenpohjien sedimenttikerrosten ikä syvyyden funktiona. Sedimentteihin 210Pb kertyy kahdella tavalla: hajoamalla radioaktiivisesti maaperässä olevasta radiumista sekä ilmakehästä suoraan esimerkiksi sateiden välityksellä tai…
Estimating Mean Lifetime from Partially Observed Events in Nuclear Physics
2022
Abstract The mean lifetime is an important characteristic of particles to be identified in nuclear physics. State-of-the-art particle detectors can identify the arrivals of single radioactive nuclei as well as their subsequent radioactive decays (departures). Challenges arise when the arrivals and departures are unmatched and the departures are only partially observed. An inefficient solution is to run experiments where the arrival rate is set very low to allow for the matching of arrivals and departures. We propose an estimation method that works for a wide range of arrival rates. The method combines an initial estimator and a numerical bias correction technique. Simulations and examples b…
Superallowed α Decay to Doubly Magic 100Sn
2018
We report the first observation of the 108Xe→104Te→100Sn α-decay chain. The α emitters, 108Xe [Eα=4.4(2) MeV, T1/2=58+106−23 μs] and 104Te [Eα=4.9(2) MeV, T1/2<18 ns], decaying into doubly magic 100Sn were produced using a fusion-evaporation reaction 54Fe(58Ni,4n)108Xe, and identified with a recoil mass separator and an implantation-decay correlation technique. This is the first time α radioactivity has been observed to a heavy self-conjugate nucleus. A previous benchmark for study of this fundamental decay mode has been the decay of 212Po into doubly magic 208Pb. Enhanced proton-neutron interactions in the N=Z parent nuclei may result in superallowed α decays with reduced α-decay wi…
Detailed spectroscopy of the neutron-deficient bismuth isotopes ¹⁹³,¹⁹⁵Bi
2015
Two experiments aiming to study the shape coexistence and competing structures in 193Bi and 195Bi isotopes have been performed at the Accelerator laboratory of the University of Jyv askyl a, Finland (JYFL). Many new states have been found, hugely extending the previously known level schemes for both isotopes. The i13=2 bands were extended up to I = 45/2+ in both the 193;195Bi isotopes. In case of 193Bi, the I = 31/2+ member of the i13=2 band was found to de-excite also to a long-lived isomeric state. This link determines the energy of the isomeric state to be 2350(1) keV and suggests a spin and parity of 29/2+. The half-life of the isomeric state was measured to be 85(3) s. A level structur…
γ decay of excited states in 198Rn identified using correlated radioactive decay
1999
The low-lying level structure of the neutron-deficient isotope 198Rn has been studied for the first time, using the 166Er(36Ar,4n) reaction at a beam energy of 175 MeV. Evaporation residues were selected using an in-flight gas-filled separator, RITU, and implanted at the focal plane into a 16-element position-sensitive, passivated ion-implanted planar silicon detector. Prompt γ rays in 198Rn were observed at the target position using the JUROSPHERE array of 24 Compton-suppressed germanium detectors, and were identified by the subsequent radioactive decay of associated recoiling ions in the silicon detector. Isotopic assignments of the nuclei produced were made on the basis of the energy and…
Radiohiiliajoitus
2017
Radiohiiliajoitus on paljon käytetty ajoitusmenetelmä erityisesti orgaanista alkuperää olevien tutkimuskohteiden ajoituksessa. Radiohiili eli hiili-14 (C-14) on radioaktiivinen hiilen isotooppi, jonka puoliintumisaika on noin 5700 vuotta. Radiohiiltä syntyy yläilmakehässä luonnollisin mekanismein kosmisen säteilyn vuorovaikutuksesta ilmakehän partikkeleiden kanssa. Radiohiiltä syntyy myös ihmisen tekojen vaikutuksesta. Aikanaan Ilmakehässä tehdyt ydinasekokeet tuottivat merkittävän määrän radiohiiltä. Myös ydinvoimaloissa syntyy radiohiiltä. Radiohiili reagoi ilmassa olevan hapen kanssa tuottaen ns. raskasta hiilidioksidia. Kasvit käyttävät hiilidioksidia yhteyttämisessä, jolloin radiohiilt…
Women Scientists Who Made Nuclear Astrophysics
2019
Female role models reduce the impact on women of stereotype threat, i.e. of being at risk of conforming to a negative stereotype about one’s social, gender, or racial group (Fine in Delusion of Gender. W.W. Norton & Co. NY, p. 36, 2010 [1]; Steele and Aronson in J Pers Soc Psychol 69:797–811, 1995 [2]). This can lead women scientists to underperform or to leave their scientific career because of negative stereotypes such as, not being as talented or as interested in science as men. Sadly, history rarely provides role models for women scientists; instead, it often renders these women invisible (CafeBabel Homepage [3]). In response to this situation, we present a selection of twelve outst…
Proton radioactivity of 117La
2001
A new more precise measurement of the ground-state proton decay of 117La is presented @Ep 5806(5) keV, t1/2,p526(3) ms#. 117La was produced via the p4n fusion-evaporation channel by bombarding a 64Zn target with 310 and 295 MeV 58Ni beams. The proton decay rate is consistent with emission from a prolate deformed 3/21 or 3/22 Nilsson state. No evidence is found for a previously reported proton decay from a high spin isomer in 117La. An upper limit for the production cross section for proton decay of 116La at a bombarding energy of 325 MeV was established. peerReviewed
Radioaktiivisten jätteiden kartoitus kiihdytinlaboratoriossa
2011
Kiihdytinlaboratoriossa syntyy radioaktiivista jätettä, joka on pääosin tutkimuksessa käytettävien laitteiden osia ja laitteiden huoltojätettä. Aktiivinen jäte tulee luokitella ja käsitellä Suomen lakien määrämällä tavalla. Tässä työssä kartoitettiin jätteestä mahdollisesti löytyviä radioaktiivisia nuklideja ja nuklidien havaitsemiseen sopivaa mittauslaitteistoa. Jäteosia mitattiin gammasäteilyä havaitsevalla mittauslaitteistolla. Osista tunnistettiin radioaktiiviset nuklidit ja laskettiin niiden aktiivisuudet. Näiden määritysten pohjalta päätetään jäteosien jatkokäsittely yhteistyössä viranomaisten kanssa.
Rare beta decays and the spectrum-shape method
2017
This is a thesis consisting of seven publications and an introductory part on theoretical studies on rare single beta decays. Firstly, the theoretical framework is applied to the computation of partial half-lives for few selected cases of rare single beta-decay transitions. This includes the study on a possible ultra-low-Q-value decay branch of 115Cd as well as the highly forbidden beta decays of 48Ca and 50V. The double magic 48Ca is one of the few experimentally verified nuclei that decay via the two-neutrino mode of double beta decay. A theoretical study on the single beta-decay branches was used to inspect the competition between the single and double beta-decay channels. In the case of…