DOCSLIB.ORG

Neutron Activation and Radioactive Decay Neutron Activation and Radioactive Decay

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Trent Physics 203H Lab Neutron Activation and Radioactive Decay Neutron Activation and Radioactive Decay Introduction In this experiment indium foils are activated by irradiation with thermal neutrons. The resulting radioactivity is measured as a function of irradiation time and the decay of the radioactivity after irradiation is followed to find the half-life of a metastable state of In116 . Theory Only a small fraction of the known isotopes are stable. Some unstable naturally occurring isotopes (e.g. 40K, uranium isotopes, etc.) appear stable but actually have very long half-lives ( ≈ 109 years). Often unstable isotopes can be made by irradiating stable elements. A common method of producing radioactive isotopes is by neutron activation: the addition of an extra neutron forms a heavier isotope which is (usually) unstable against radioactive decay. In this experiment foils of the stable element 49 In115 are bombarded by neutrons produced in a radioactive source (described below). The reaction is 0 n1 + 49 In115 →49 In116,m The m indicates that the In116 nuclei are formed in metastable states. These states could in principle decay by prompt emission of gamma rays leading to lower excited states of In116 . Normally such gamma emission would very quickly leave the nucleus in its ground state which could then decay by β − emission to states of 50 Sn116 . However the first excited state of In116 has a very low probability of gamma-emission. This is because it is only slightly more energetic than the ground state (0.127 MeV) and the difference in spins is + + rather large (5 →1 ). Therefore this state decays instead by β − emission to excited states of 50 Sn116 . The half-life for this decay is about 54 minutes. The amount of radioactivity produced by a foil bombarded with neutrons depends on the number of atoms of the required type in the foil, the probability of absorption of a neutron by the foil, and the flux of neutrons incident on the foil. Let P be the rate of production of radioactive atoms (per second). The atoms formed are unstable and decay with a half life τ. The number decaying in 1 second is proportional to the number N present. Therefore, the change in the number of radioactive atoms per unit time is dN = −λN + P (1) dt where, from the definition of half-life ln2 λ = (2) τ Solving differential equation (1) with the boundary condition that no radioactive atoms were present initially, the number of atoms present after an exposure time te is 1 Trent Physics 203H Lab Neutron Activation and Radioactive Decay P N(t ) = (1− e −λte ) (3) e λ Sketch N(te) as a function of te and include this in your laboratory report. If one wishes to measure the radioactivity induced, the sample is withdrawn from the neutron source and placed in a counter which detects the gamma rays emitted. The number of disintegrations per second is equal to λN , but the detector efficiency is less than 1 (say k), so the measured number of counts per second is the activity: −λte A(te ) = kλN(te ) = kP(1− e ) (4) This is the activity that would be measured immediately after exposure. In practice, a finite time, tw, elapses between the end of the exposure and the beginning of the activity measurement. Moreover the activity is not measured instantaneously, but counts are accumulated for a finite time tc. The number of counts recorded will be given by: tw +tc C = A(t )e−λt dt ∫ e (5) tw By doing this integral show that: λCeλtw A(te ) = (6) 1− e−λtc You should include this derivation as an appendix in your lab report – either handwritten or using a word processor’s Equation Editor. Apparatus Neutron Source: The irradiation facility provided is called a neutron howitzer. It consists of a radioactive neutron source in a tank of water. The neutron source consists of a quantity of plutonium intimately mixed with beryllium. Alpha particles emitted by the radioactive plutonium interact with beryllium nuclei to produce fast neutrons ranging in energy up to 10 or 12 MeV. The probability of neutron absorption by indium is largest for "thermal neutrons" (energy of the order of 1/40 eV). The water in the tank serves as a moderator - the energies of the neutrons are reduced, by successive collisions with hydrogen nuclei, to thermal energies. Racks are provided for lowering the indium foils to a position near the neutron source. For each irradiation a foil is inserted in a slot in the rack which is then lowered to a platform in the tank. After the desired exposure time the rack is withdrawn and the foil may be removed for activity determination. The irradiated foil MUST be handled with tweezers. To protect the soft metal of the foil, wrap the ends of the tweezers with tape. NOTE: The neutron source is very radioactive and must not be removed from the water tank. The water in the tank serves as an adequate shield but it is only common sense to keep your radiation exposure to a minimum by staying away from the tank except when the sample is being inserted or removed. The room in which the source is stored must be locked unless someone is present in the adjacent laboratory. 2 Trent Physics 203H Lab Neutron Activation and Radioactive Decay Counting Apparatus: A scintillation detector (NaI-Tl) is provided. For each activity measurement, the radioactive foil is to be placed near the detector in such a manner that the detector efficiency k will be the same for each measurement. The amplifier output from the detector system is fed to a single channel analyzer (SCA) and scalar, and also to a multichannel analyzer so that the spectrum of the radioactive source may be observed. Experiments: A: An indium foil has been placed in the tank for an irradiation time of a few hours. The instructor will remove this foil and prepare it for counting. Examine the spectrum of the emitted gamma rays and be sure that the amplifier gain is set so that most of the radiation results in pulses less than 10 V in height. (Full scale on the PHA corresponds to 10 V.) Remove the radioactive foil (using tweezers) and examine the spectrum of the background radiation. Much of this is low energy gamma rays. You can avoid counting them by adjusting the baseline of the SCA to the level indicated by the PHA spectrum. When this has been done measure the background count rate. Return the activated foil to the counter. At 5 minute intervals record the counts for a fixed time (30 sec or 1 min). Continue for about two half-lives. Correct the activity for background. Construct a plot of ln(counts) versus time. The points should fall on a straight line whose slope is -λ where λ = ln2 /τ . Hence determine the half-life of the radioactivity. This is the half-life of the first excited state of the In116 nucleus. B: Several indium foils are provided, each with its mass (accurate to 0.1 mg) stamped on them. Place a foil in a slot in the rack provided. (Mark the slot so that the same one is used each time.) Carefully but quickly lower the rack onto the platform in the water tank, placing the foil as close to the neutron source as possible. Start a stopwatch as soon as the foil is in position. After a time te has elapsed, remove the rack. Use tweezers to take the foil (it may be dried by patting it with a paper towel) to the counting apparatus. Start the counter when a fixed time tw (1 minute should be long enough) has elapsed since removing the foil from the tank. Count for a fixed time, tc, e.g. 1 minute . Correct the counts for background and standardize to a foil mass of 1 g. Use equation (6) to calculate the activity A(te). This should be done for exposure times te = 2, 5, 10, 20, 35, 60 and 120 minutes. Plot A(te) versus te. Questions: 1. What is the maximum activity obtainable? Why is it limited? Why doesn’t it just keep increasing? 2. There are two naturally occurring isotopes of indium (95.7% In115 , 4.3% In113 ). What is the justification for neglecting activity induced in the lighter isotope? 3.
Recommended publications
  • HISTORY Nuclear Medicine Begins with a Boa Constrictor

    HISTORY Nuclear Medicine Begins with a Boa Constrictor

    HISTORY Nuclear Medicine Begins with a Boa Constrictor Marshal! Brucer J Nucl Med 19: 581-598, 1978 In the beginning, a boa constrictor defecated in and then analyzed the insoluble precipitate. Just as London and the subsequent development of nuclear he suspected, it was almost pure (90.16%) uric medicine was inevitable. It took a little time, but the acid. As a thorough scientist he also determined the 139-yr chain of cause and effect that followed was "proportional number" of 37.5 for urea. ("Propor­ inexorable (7). tional" or "equivalent" weight was the current termi­ One June week in 1815 an exotic animal exhibi­ nology for what we now call "atomic weight.") This tion was held on the Strand in London. A young 37.5 would be used by Friedrich Woehler in his "animal chemist" named William Prout (we would famous 1828 paper on the synthesis of urea. Thus now call him a clinical pathologist) attended this Prout, already the father of clinical pathology, be­ scientific event of the year. While he was viewing a came the grandfather of organic chemistry. boa constrictor recently captured in South America, [Prout was also the first man to use iodine (2 yr the animal defecated and Prout was amazed by what after its discovery in 1814) in the treatment of thy­ he saw. The physiological incident was common­ roid goiter. He considered his greatest success the place, but he was the only person alive who could discovery of muriatic acid, inorganic HC1, in human recognize the material. Just a year earlier he had gastric juice.
  • Neutron Scattering Facilities in Europe Present Status and Future Perspectives

    Neutron Scattering Facilities in Europe Present Status and Future Perspectives

    2 ESFRI Physical Sciences and Engineering Strategy Working Group Neutron Landscape Group Neutron scattering facilities in Europe Present status and future perspectives ESFRI scrIPTa Vol. 1 ESFRI Scripta Volume I Neutron scattering facilities in Europe Present status and future perspectives ESFRI Physical Sciences and Engineering Strategy Working Group Neutron Landscape Group i ESFRI Scripta Volume I Neutron scattering facilities in Europe - Present status and future perspectives Author: ESFRI Physical Sciences and Engineering Strategy Working Group - Neutron Landscape Group Scientific editors: Colin Carlile and Caterina Petrillo Foreword Technical editors: Marina Carpineti and Maddalena Donzelli ESFRI Scripta series will publish documents born out of special studies Cover image: Diffraction pattern from the sugar-binding protein Gal3c with mandated by ESFRI to high level expert groups, when of general interest. lactose bound collected using LADI-III at ILL. Picture credits should be given This first volume reproduces the concluding report of an ad-hoc group to D. Logan (Lund University) and M. Blakeley (ILL) mandated in 2014 by the Physical Science and Engineering Strategy Design: Promoscience srl Work Group (PSE SWG) of ESFRI, to develop a thorough analysis of the European Landscape of Research Infrastructures devoted to Neutron Developed on behalf of the ESFRI - Physical Sciences and Engineering Strategy Scattering, and its evolution in the next decades. ESFRI felt the urgency Working Group by the StR-ESFRI project and with the support of the ESFRI of such analysis, since many reactor-based neutron sources will be closed Secretariat down in the next years due to national decisions, while the European The StR-ESFRI project has received funding from the European Union’s Spallation Source (ESS) in Lund will be fully operative only in the mid Horizon 2020 research and innovation programme under grant agreement or late 2020s.
  • Uses of Isotopic Neutron Sources in Elemental Analysis Applications

    Uses of Isotopic Neutron Sources in Elemental Analysis Applications

    EG0600081 3rd Conference on Nuclear & Particle Physics (NUPPAC 01) 20 - 24 Oct., 2001 Cairo, Egypt USES OF ISOTOPIC NEUTRON SOURCES IN ELEMENTAL ANALYSIS APPLICATIONS A. M. Hassan Department of Reactor Physics Reactors Division, Nuclear Research Centre, Atomic Energy Authority. Cairo-Egypt. ABSTRACT The extensive development and applications on the uses of isotopic neutron in the field of elemental analysis of complex samples are largely occurred within the past 30 years. Such sources are used extensively to measure instantaneously, simultaneously and nondestruclively, the major, minor and trace elements in different materials. The low residual activity, bulk sample analysis and high accuracy for short lived elements are improved. Also, the portable isotopic neutron sources, offer a wide range of industrial and field applications. In this talk, a review on the theoretical basis and design considerations of different facilities using several isotopic neutron sources for elemental analysis of different materials is given. INTRODUCTION In principle there are two ways to use neutrons for elemental and isotopic abundance analysis in samples. One is the neutron activation analysis which we call it the "off-line" where the neutron - induced radioactivity is observed after the end of irradiation. The other one we call it the "on-line" where the capture gamma-rays is observed during the neutron bombardment. Actually, the sequence of events occurring during the most common type of nuclear reaction used in this analysis namely the neutron capture or (n, gamma) reaction, is well known for the people working in this field. The neutron interacts with the target nucleus via a non-elastic collision, a compound nucleus forms in an excited state.
  • H*(10) Y Fluencias En Un Irradiador De Neutrones Con Una Fuente De Ra-Be

    H*(10) Y Fluencias En Un Irradiador De Neutrones Con Una Fuente De Ra-Be

    ISSSD 2020 ONLINE _________________________________________________________________________________ H*(10) y fluencias en un irradiador de neutrones con una fuente de 226Ra-Be Bedher O. Vega-Cabrera1,*, Héctor René Vega-Carrillo2, Víctor M. Viera Castillo1, César J. Guevara Pillaca1, Patrizia E., Pereyra Anaya1 María E. López Herrera1, Daniel F. Palacios Fernández1 1Pontificia Universidad Católica del Perú, Sección de Física. Av. Universitaria 1801, Apartado 1761, Lima – Perú. 2Universidad Autónoma de Zacatecas, Unidad Académica de Estudios Nucleares, C. Ciprés 10, Fracc. La Peñuela, 98068 Zacatecas, Zac. México. * E-mail: [email protected] Resumen Un irradiador de neutrones es un moderador con una fuente isotópica que es usado para enseñanza, entrenamiento y actividades de investigación. Normalmente, el moderador tiene puertos de irradiación radial y/o axial. Con el fin de utilizar el irradiador de neutrones de forma segura y óptima, deben conocerse los niveles de dosis y el espectro de la fluencia de neutrones. En este trabajo se utilizaron métodos Monte Carlo para estimar las fluencias de neutrones en tres rangos de energías: térmicos, epitérmicos y rápidos en siete puertos de un irradiador de neutrones con una fuente 226Ra-Be. El irradiador revestido de plomo contiene parafina wax como medio moderador de neutrones y sus puertos están asignados a diferentes distancias de la fuente de neutrones. El equivalente de dosis ambiental, debido a los neutrones, se estimó a 100 cm lateralmente y a 10 cm por encima del irradiador de neutrones.
  • PGNAA Neutron Source Moderation Setup Optimization

    PGNAA Neutron Source Moderation Setup Optimization

    Submitted to ‘Chinese Physics C PGNAA neutron source moderation setup optimization Zhang Jinzhao1（张金钊）Tuo Xianguo1（庹先国） (1.Chengdu University of Technology Applied Nuclear Techniques in Geoscience Key Laboratory of Sichuan Province，Chengdu 610059，China) Abstract: Monte Carlo simulations were carried out to design a prompt γ-ray neutron activation analysis (PGNAA) thermal neutron output setup using MCNP5 computer code. In these simulations the moderator materials, reflective materials and structure of the PGNAA 252Cf neutrons of thermal neutron output setup were optimized. Results of the calcuations revealed that the thin layer paraffin and the thick layer of heavy water moderated effect is best for 252Cf neutrons spectrum. The new design compared with the conventional neutron source design, the thermal neutron flux and rate were increased by 3.02 times and 3.27 times. Results indicate that the use of this design should increase the neutron flux of prompt gamma-ray neutron activation analysis significantly. Key word: PGNAA; neutron source; thermal neutron; moderation; reflection 1. Introduction study, Monte Carlo calculation was carried out for the Prompt gamma ray neutron activation analysis design of a 252Cf neutron source moderation setup for the (PGNAA) is a rapid, nondestructive, powerful analysis cement samples[7]. The model of Monte Carlo multielemental analysis technique, large samples of some simulation was verified by experiment[8, 9].We improve minor, trace light elements and is used in industrial the thermal neutron source yield rate of 252Cf neutron by control[1-5]. In a PGNAA analysis, the sample nuclear the PGNAA neutron source structure to the design. The composition is determined from prompt gamma rays calculation results for the new design were compared which produced through neutron inelastic scattering and with the previous, example: themal neutron flux rate, fast thermal neutron capture.
  • Sonie Applications of Fast Neutron Activation Analysis of Oxygen

    Sonie Applications of Fast Neutron Activation Analysis of Oxygen

    S E03000182 CTH-RF- 16-5 Sonie Applications of Fast Neutron Activation Analysis of Oxygen Farshid Owrang )52 Akadenmisk uppsats roir avliiggande~ av ilosofie ficentiatexamen i Reaktorf'ysik vid Chalmer's tekniska hiigskola Examinator: Prof. Imre PiAst Handledare: Dr. Anders Nordlund Granskare: Bitr. prof. G~iran Nyrnan Department of Reactor Physics Chalmers University of Technology G6teborg 2003 ISSN 0281-9775 SOME APPLICATIONS OF FAST NEUTRON ACTIVATION OF OXYGE~'N F~arshid Owrang Chalmers University of Technology Departmlent of Reactor Physics SEP-1-412 96 G~iteborg ABSTRACT In this thesis we focus on applications of neutron activation of oxygen for several purposes: A) measuring the water level in a laboratory tank, B) measuring the water flow in a pipe system set-up, C) analysing the oxygen in combustion products formed in a modern gasoline S engine, and D) measuring on-line the amount of oxygen in bulk liquids. A) Water level measurements. The purpose of this work was to perform radiation based water level measurements, aimed at nuclear reactor vessels, on a laboratory scale. A laboratory water tank was irradiated by fast neutrons from a neutron enerator. The water was activated at different water levels and the water level was decreased. The produced gamma radiation was measured using two detectors at different heights. The results showed that the method is suitable for measurement of water level and that a relatively small experimental set-up can be used for developing methods for water level measurements in real boiling water reactors based on activated oxygen in the water. B) Water flows in pipe.
  • Radiation Safety Training

    Radiation Safety Training

    Radiation Safety Training …it concerns your health! 8/30/2006 Charlie Freeman, RSO Slide #1 SUNY Genseseo Atomic Structure Nucleus Orbiting Electrons – Contains Protons and – “Cloud” of orbiting Neutrons electrons surrounds nucleus – Cloud is relatively large – Small Size (~1E-14 m) (~1E-10 m) – Relatively Large Mass – Low mass – Extremely Large Density – Small amount of Stored – Large amount of Stored Energy Energy – Responsible for Chemical Bonds 8/30/2006 Charlie Freeman, RSO Slide #2 SUNY Genseseo Nomenclature • Element Designation A – “X” = Element Symbol X – “Z” = # protons in nucleus Z • “Atomic #” (each element has a unique Z, see periodic For Example table) 16 – “N” = # neutrons 8 O = O-16 = Oxygen 16 – Atomic mass # = “A” 17 • A = Z + N 8 O = O-17 = Oxygen 17 • Isotope: same Z, different N 197 and A 79 Au = Au-197 = Gold 197 8/30/2006 Charlie Freeman, RSO Slide #3 SUNY Genseseo Example: P-32 • 15 protons 32 • 17 neutrons P • A = 32 15 • Z =15 8/30/2006 Charlie Freeman, RSO Slide #4 SUNY Genseseo Ion • In an electrically neutral atom or molecule, the number of electrons equals the number of protons • Any atom or molecule with an imbalance in electrical charge is called an ion • Ions are chemically unstable, and will seek electrical neutrality by reacting with other atoms or molecules. 8/30/2006 Charlie Freeman, RSO Slide #5 SUNY Genseseo Radioactivity • Definition: A collection of unstable atoms that undergo spontaneous transformation that result in new elements. The degree of radioactivity is given by the number of decays that occur per unit time (decays per minute) • Units of measure: – Dpm, dps – Curie (Ci): 1 Ci = 3.7E10 dps – Bequerel (Bq): 1 Bq = 1dps 8/30/2006 Charlie Freeman, RSO Slide #6 SUNY Genseseo Half-Life & Decay Law • The activity of a sample of radioactive 225 200 atoms decreases over 175 150 time 125 100 75 Activity (Curies) • Half-life: how long it 50 25 takes for activity of 0 0 1 2 3 4 5 6 7 sample to decrease by Time (hours) a factor of ½.
  • Neutron Capture Cross Sections of Cadmium Isotopes

    Neutron Capture Cross Sections of Cadmium Isotopes

    Neutron Capture Cross Sections of Cadmium Isotopes By Allison Gicking A thesis submitted to Oregon State University In partial fulfillment of the requirements for the degree of Bachelor of Science Presented June 8, 2011 Commencement June 17, 2012 Abstract The neutron capture cross sections of 106Cd, 108Cd, 110Cd, 112Cd, 114Cd and 116Cd were determined in the present project. Four different OSU TRIGA reactor facilities were used to produce redundancy in the results and to measure the thermal cross section and resonance integral separately. When the present values were compared with previously measured values, the differences were mostly due to the kind of detector used or whether or not the samples were natural cadmium. Some of the isotopes did not have any previously measured values, and in that case, new information about the cross sections of those cadmium isotopes has been provided. Table of Contents I. Introduction………………………………………………………………….…….…1 II. Theory………………………………………………………………………...…...…3 1. Neutron Capture…………………………………………………….….……3 2. Resonance Integral vs. Effective Thermal Cross Section…………...………5 3. Derivation of the Activity Equations…………………………………....…..8 III. Methods………………………………………………………….................…...…...12 1. Irradiation of the Samples………………………………………….….....…12 2. Sample Preparation and Parameters………………..………...………..……16 3. Efficiency Calibration of Detectors…………………………..………....…..18 4. Data Analysis…………………………………...…….………………...…..19 5. Absorption by 113Cd……………………………………...……...….………20 IV. Results………………………………………………….……………..……….…….22
  • Determination of Uranium and Thorium by Neutron Activation Analysis Applied to Fossil Samples Dating

    Determination of Uranium and Thorium by Neutron Activation Analysis Applied to Fossil Samples Dating

    2011 International Nuclear Atlantic Conference - INAC 2011 Belo Horizonte,MG, Brazil, October 24-28, 2011 ASSOCIAÇÃO BRASILEIRA DE ENERGIA NUCLEAR - ABEN ISBN: 978-85-99141-04-5 DETERMINATION OF URANIUM AND THORIUM BY NEUTRON ACTIVATION ANALYSIS APPLIED TO FOSSIL SAMPLES DATING Regina B. Ticianelli 1, Ana Maria Graciano Figueiredo 1, Guilherme S. Zahn 1, 2,3 2 Angela Kinoshita , Oswaldo Baffa 1 Instituto de Pesquisas Energéticas e Nucleares –IPEN-CNEN/SP, C.P. 11049, 05422-970, São Paulo, SP. [email protected] 2 Departamento de Física, FFCRLP- USP, Ribeirão Preto, SP 3 Universidade Sagrado Coração, Bauru, SP ABSTRACT Electron Spin Resonance (ESR) dating is based on the fact that ionizing radiation can create stable free radicals in insulating materials, like tooth enamel and bones. The concentration of these radicals - determined by ESR - is a function of the dose deposed in the sample along the years. The accumulated dose of radiation, called Archeological Dose, is produced by the exposition to environmental radiation provided by U, Th, K and cosmic rays. If the environmental dose rate in the site where the fossil sample is found is known, it is possible to convert this dose into the age of the sample. The annual dose rate coming from the radioactive elements present in the soil and in the sample itself can be calculated by determining the U, Th and K concentration. Therefore, the determination of the dose rate depends on the concentration of these main radioactive elements. Neutron Activation Analysis has the sensitivity and the accuracy necessary to determine U, Th and K with this objective.
  • LENS Report Low Energy Accelerator-Driven Neutron Sources

    LENS Report Low Energy Accelerator-Driven Neutron Sources

    LENS Report Low Energy Accelerator-driven Neutron Sources LENS Ad-hoc Working Group CANS Nov. 2020 2 www.lens-initiative.org Table of Content 1 Foreword ................................................................................................................................6 2 Executive summary .................................................................................................................8 3 Neutrons for science and industry ......................................................................................... 12 4 Neutron production and landscape of neutron Infrastructures in Europe .............................. 16 4.1 Neutron production ........................................................................................................... 16 4.2 Situation in Europe ............................................................................................................ 16 4.3 Situation outside Europe ................................................................................................... 18 5 Capabilities of CANS .............................................................................................................. 22 5.1 What is a CANS ? ............................................................................................................... 22 5.2 What are the different types of facilities that can be considered? ...................................... 22 5.3 What performances can be achieved on a CANS for neutron scattering ............................. 23 6 Advantages / limitations
  • Activation Analysis - Nuclear Chemical Research * Radiochemical Separations

    Activation Analysis - Nuclear Chemical Research * Radiochemical Separations

    DEPARTMENT OF CHEMISTRY UNIVERSITY OF MICHIGAN ANN ARBOR, MICHIGAN . ACTIVATION ANALYSIS - NUCLEAR CHEMICAL RESEARCH * RADIOCHEMICAL SEPARATIONS PROGRESS REPORT 9 November 1, 1960 Supported by DEPARTMENT OF CHEMISTRY MICHIGAN MEMORIAL-PHOENIX PROJECT UNITED ST ATES ATOMIC ENERGY COMMISSION PROJECT NO. 7, CONTRACT NO. AT (11-1)-70 DEPARTMENT OF CHEMISTRY U N I V E R S I T Y O F M I C H I G A N Ann Arbor, Michigan PROGRESS REPORT 9 November 1959 - October 1960 ACTIVATION ANALYSIS NUCLEAR CHEMICAL RESEARCH RADIOCHEMICAL SEPARATIONS Edited by R. S. Maddock and W. W. Meinke, (Project Director) November 1, 1960 Supported by Department of Chemistry Michigan-Memorial Phoenix Project Project No. 7 Contract No. AT(ll-1)-70 U. S. Atomic Energy Commission The following is a report of the work completed on Project No. 7, Contract No. AT(ll-1)-70 during the year of November 1, 1959 to October 31, 1960. Previous progress reports are listed below: Progress Report 1 Novemb er 1952 Progress Report 2 November 1953 Progress Report 3 November 1954 Progress Report 4 (AECU-3116) November 1955 Progress Report 5 (AECU-3375) November 1956 Progress Report 6 (AEcU-3641) November 1957 Progress Report 7 (AEcu.-3887) November 1958 Progress Report 8 (AECU-4438) November 1959 ii FOREWARD A word is perhaps in order about the philosophy of these progress reports which are issued yearly from our laboratories. In any research program a large amount of information is obtained and techniques developed which never find their way into the literature. This includes the "negative results" which are so disappointing and unspectacular but which can often save others considerable work.
  • Instrumental Neutron Activation Analysis (INAA)

    Instrumental Neutron Activation Analysis (INAA)

    Instrumental Neutron Activation Analysis (INAA) Overview: Unlike most analytical techniques INAA requires no chemical processing of the samples, therefore it is described as Instrumental NAA rather than radiochemical NAA. This characteristic has several advantages: (1) Rapid, i.e., less labor required to prepare samples. (2) Precludes the possibility of contaminating the samples. As shown in Fig. 1 (Periodic Table), in terrestrial sediments INAA typically obtains precise abundance data (i.e. duplicate analyses agree within 5%) for many elements, typically occurring as trace elements in the parts per million (by weight) range. The concept of INAA is to produce radioactive isotopes by exposing the samples to a high flux of neutrons in a nuclear reactor. These isotopes typically decay by beta decay and in the process gamma rays (electromagnetic radiation) with discrete energies are emitted). These discrete energies are the fingerprint for an isotope. Note that this technique determines abundance of isotopes, but because isotopic abundances of most, at least high atomic number, elements are constant in natural materials, isotopic abundance is readily translated to elemental abundances. Gamma rays arise from transitions between nuclear energy levels whereas X-rays arise from transitions between electron energy levels. An advantage of gamma rays is that many are much more energetic than X-rays; therefore gamma rays are less readily absorbed and matrix corrections (see lecture on electron microprobe) are not usually important. 1 Periodic Table