Review 7 PapeB . rMb STATUS OF BETA- AND GAMMA-DECAY AND SPONTANEOUS- FISSION DATA FROM TRANSACTING ISOTOPESt C. W. Reich Idaho National Engineering Laboratory Aerojet Nuclea. Co r Idaho Falls, Idaho U.S.A. Abstract Several categoriey-related an - 6 f do s deca e transyth datr -fo a actinium isotopes are assessed in the light of their potential use in applied areas e statuf AugustTh o . s a s , 1975 f thes,o e dat sums i a - 2 transactiniumarize14 r fo d m nuclides with 228<A<25 e listinth y f 7b o g experimental values and errors where known. Several useful compilations f transact!'niurn-isotopo e decay date discussedar a . Recent developments relateyielde th d energo an t sd y distribution f prompo s d delayean t d neutrons from spontaneous fissio e brieflar n y treated. Commentd an s observations abou e interrelatioth t e importanth f o n t nuclear-data activities of measurement, compilation and evaluation and needs assess- mene given ar te applications-oriente Th . d fil f decao e y data prepared at our laboratory for ENDF/B is discussed. Finally, a summary by G. Rud- OSIRIe statue th th sta f f So so m wor n delayed-neutroo k n energy spectra f individuao l precursor s includedi s . 1. INTRODUCTION In this paper e revie,w d summarizan w e currenth e t statua f o s broad range of categories of decay data for the transactinium nuclides (Z>90) selectioe Th .specifie th f no c type decaf so y data whice ar h treated here was based on a consideration of their general importance for various applications of decay data. For each individual nuclide, measured values (and, where reported, their uncertainties) of these chosen decay parameters are listed. This compilation of measured values provides a convenient means of assessing the adequacy of the present data for use in specific applications. It should be emphasized that these t constitutvalue f evaluateno o o d t s se r a "recommendedeo d " values. Mork performed under the auspices of the U.S. Energy Research and Development Administration. 265 e inclusioTh f decao n subjece y th dat n i at matte f thiro s meet- ing, the first one of international scope on the subject of transactiniurn- isotope nuclear data, provides another illustratio e increasinth f o n g recognitio e importancth f o n f radioactive-nuclido e e decaye on dat s a categor f "Nucleayo r Data." While data from radioactive-decay studies have contribute e dbasi th muc o ct h concept f nucleaso r physics, their relevance to a number of applied problems i.s now becoming more widely appreciated. For example, decay data for fission products constituted a major topi r discussiofo c e IAEth A t a nPane l Meetin n Fission-Produco g t Nuclear Data [1]. Also, the scope of the Evaluated Nuclear Data File (ENDF/B w beeno ns expande)ha o incorporatt d e such data, partl responsn i y e o theit r obvious importanc assessmene th r fo e f certaito n safety questions in nuclear reactors e recentlTh . y release de firs th Versio s ti versioV I n n f ENDF/o o contait B detailea n f decao t y se ddat a [2]. Wite increasth h - ing interest in assessing the impact of radioactivity on the environment, attentio s beini n g focuse monitorine th t onl no n do y f radioactivo g e effluents associated with the operation of nuclear power plants but also n alo l aspecte nucleath f o s r fuel cycle, includin e managementh g e th f to waste productsafeguardine th d e an reprocesses th f o g d fuel material. Among the components of such an assessment are the identification of the important radioactive nuclides and the establishment of a commonly accepted and utilized base of relevant, evaluated decay data. In some cases, this evaluatio a vigorou e neer y th poinfo d ma nt sou t progra f experimentao m l measurements to provide such data where they are either nonexistent or not of the required accuracy. Through its subject matter and organization, the present meeting represents e transactiniurth r ,fo n nuclides e ste,on p toward the effective use of nuclear decay data in the solution of import- ant problems of both an applied and a basic character. 1.1. Applications o providT framewora e discussioe th decae r th fo k yf o ndat o t a e treatedb appropriats i t ,i o e applicationpoint e th t som f tou o e f o s such data. Since detailed discussions of the applications of these data appea a numbe n i r f paperro s presente t thia d s meeting e giv,w e here only a brief listing. In reactor-related applications, decay data are needed e propeth r r fo assessmen e impacth f f radioactivitto o environe th n o y - ment from all components of the fuel cycle, from the mine through the reprocessing plant, and including the accounting for and safeguarding e fissionablth f o e material. Important operational problems include not only monitoring of the effluents from the nuclear-power plants, but 266 alse storagth o d handlin e an spen th f to g fuel n long-terI . m operation of fast reactors, there is a considerable build-up of transactinium isotopes, leading to the accumulation of a sizeable inventory of nuclides r whicfo h spontaneous fissio a significan s i n t decaye modeth d ;an evaluatio e neutroth f o nn source ter sucn i m h systems following shutdown is an important problem. Biomedical applications represent another area where decay data have an important impact. In calculations of the absorbed dose, for example s necessari t i , o knot yt onl e energno w th y y releas n radioi e - active decay, but also the form in which this energy is emitted (e.g., conversion electrons, x-rays, 3 and y radiation and a particles). To o thid s realistically require a quits e detailed knowledg e decath yf o e e quantitativschemeth n I . e assa f radioactivityo o determint y e amounth e t of a given radioactive nuclide present, a knowledge of the nuclide half- e energieth lif d d absolutan ean s e intensitie e radiationth f o s s being measured in the analysis is necessary. Because of the widespread use of Y-ray spectroscopy employing Ge(Lt) spectrometers to do such assays, Y-rae th y absolute intensities represen ta particularl y important subset of decay data. 1.2. Special features of transactinium-nuclide decay data Experimentally, the study of the decay properties of the trans- actinium nuclide mann i ys i sway s little different froy m an tha f o t other clas f nucleio s . However e transactiniu decae th ,th f yo m muclei exhibit muca s h richer variet f phenomeno y e th e casar th tha fo es i n nuclides commonly encountere e regioth n i dn below (and slightly above) e 1=82th magic number r exampleFo . d electron addition an ,i - 3 o t -n capture (and $+) decay, a-particle emissio spontaneoud an n s fission-- with promp d delayean t d neutron emission—occur. Furthermore, these nuclides frequentl r threo yo edecatw differenta vi y , competing processes. The relative probabilities (branching ratios f thes)o e decay modee ar s important. Finally, internal conversion and its associated phenomena assum n importanea t rol transactinium-nuclidn i e e decay data because of the large internal-conversion coefficients that result from the large Z-valuee generallth d an s y lower energie j-raye th f o s transitions. Con- sequently e discret,th e electron e x-rayth d s an scontai a significann t fraction of the energy associated with the Y-decay process. Knowledge 267 of the conversion-electron spectrum may be important in its own right or for the determination of absolute y-ray intensities for some appli- cations. Taken together, this increased variety of modes of decay provides e measureth r with valuable additional informatio r gaininfo n g insight inte make-uth o f theso p e nuclides greatlt i t bu ,y complicate e probth s - lem f dato s a compilatio d evaluationan n , particularly when datr varioufo a s application e desiredar s . 1.3. The role of theory in transactim'um-nuclide decay data 1.3.1. Nuclear model r stronglfo s y deformed nuclei The transactinium nuclides are all included in the general cate- gory of "strongly deformed" nuclei, in that their equilibrium shapes e characterizear y relativelb d y large axially symmetric deformations. Because of this, the coupling scheme which describes their elementary mode motiof o s n assum a ebasi c simplicity (see,e.g., [3])exampler Fo . , their energy-level schemes exhibi a numbet f strikino r g features such as the existence of a well-developed rotational-band structure. The spins (and parities f thes)o e observed rotational state n frequentlca s e b y deduced from energy-spacing considerations alone. From such considerations and data on the within-band y-ray intensities, one can extract multi- polarity information concerning these transitions. Furthermore, the ordering and properties of the "single-particle" states in the strongly deformed nuclei can be calculated fairly simply [4], and such calculations e foun ar o givt d a gooe d descriptio e propertie th f mano nf o y f theso s e states, particularly of those that lie at fairly low (£0.5 MeV) excitation energies r thesFo .e deformed nuclei, nuclear physicists with experience in nuclear-structure studie n frequentlca s e thesus y e various calculational tools and arguments based on "systematics" to make accurate state assign- ments and transition-probability estimates on the basis of rather frag- mentary data.