Measurement of β-ray maximum energy with an HPGe detector by means of β-annihilation photons coincidence

A β⁺-ray detection system free from summation of annihilation photons has been constructed for the determination of Q_EC-values. It consists of an HPGe β-ray detector and two pairs of BaF₂ scintillation detectors for annihilation photons. A Q_EC-value of 4.83(4) MeV is obtained for ¹²⁶Cs separated with the JAERI on-line isotope separator.     

The new CERN-ISOLDE on-line mass-separator facility at the PS-Booster

The ISOLDE on-line isotope separators have been operated since 1967 at the CERN-SC. This 600 MeV proton synchro-cyclotron had to be shut down in December 1990 after 33 years of service and it was decided to move ISOLDE to a new experimental area. The new on-line mass-separator facility is now under construction at the CERN PS-Booster. This accelerator provides an average current of about 2 μA of 1 GeV protons in very short high intensity pulses at low repetition rate. The beam can hit either one of the two target stations, the general purpose separator (GPS), a reconstructed ISOLDE-2 type machine (which can deliver beams simultaneously into three beam lines), and the high resolution separator (HRS), which is essentially the slightly modified ISOLDE-3 separator. The central GPS beam line and the HRS feed a common beam transport system to which most of the experiments will be connected. The new facility will be taken into operation in spring 1992.     

OPERA: an on-line system of optical pumping in solids for unstable nuclei

An on-line system of optical pumping in solids for the study of unstable nuclei was developed. The system is operated in connection with mass separators on line. The mass-separated unstable isotopes are implanted into a host crystal set at the focal position of the separator and then spin-polarized with laser optical pumping in the crystal. The crystal can be cooled down to 20–100 K with a cold finger attached to a liquid He bath. The achieved nuclear polarization/alignment is detected by observing the asymmetry/anisotropy of the emitted beta-/gamma-radiation with scintillation/Ge counters. Nuclear magnetic resonances are observed by detecting the destruction and/or enhancement of the asymmetry/anisotropy distribution with an applied rf magnetic field. The system has been applied to the study of unstable Tm and Si isotopes. Apparatus and performance of the on-line system are described together with some of the results obtained.     

Status report of the Leuven isotope separator on-line (LISOL)

The mass separator LISOL, on-line to the CYCLONE cyclotron, is described as it is presently configured. The main development has been in the ion-guide operation in conjunction with light-ion induced fusion and fission. The plans to obtain intense (nA) beams of light (A ≤ 30), short-lived nuclei in the framework of the ARENAS³ project are also described.     

Status report of the JAERI on-line isotope separator

A mass separator has been connected on line to the 20 MV tandem accelerator at JAERI/Tokai. Using a thermal ion source, decay spectroscopic studies have been carried out for neutron-deficient isotopes in the mass 120–130 region. A study with collinear laser spectroscopy has begun recently. The present paper describes the status of the mass separator facility together with some experimental results.     

Beam heating and cooling of thick targets for on-line production of exotic nuclei

Calculations have been made of energy deposition distributions for “thick” targets (1 mole/cm²) employed in on-line production of exotic nuclei using the Monte Carlo based LAHET code system for high-energy charged particle transport. A variety of target materials and incident proton beam energies have been examined. For 600 MeV protons, the results are compared to those from a similar study reported in the literature. The agreement between the two studies for total energy deposition is reasonably good for monatomic targets, but the results differ in some details of the energy deposition distributions. Target cooling, both radiative and conductive, is examined to assess the suitability of existing target concepts exposed to bombardment by intense (up to 100 μA), energetic (500 MeV to 1.2 GeV) proton beams to produce exotic nuclei. Implications of cooling requirements to target material selection and design are discussed.     

Upgrade of the TRIUMF on-line isotope separator, TISOL

The operational TISOL thick target, on-line isotope separator at the TRIUMF, 500 MeV proton cyclotron facility has been upgraded to be a production facility with an active experimental program. A new experimental area is now available and modifications are under design to handle remotely the expected radioactively “hot” targets. Two ion source systems are now available, a heated surface of normal design and a new ECR (electron cyclotron resonance) source resulting in ion beams from a wide range of elements. Details of the new upgraded facility will be presented along with its experimental program and plans for the future. The status of the previously proposed accelerated radioactive beams facility, ISAC, for which TISOL is a prototype front-end system, will also be mentioned.     

The Princeton separator, past and future

Some past research applications of the Princeton separator are reviewed. The future program envisaged includes fundamental β decay studies, low temperature nuclear orientation and nuclear astrophysics.     

Status report of the SARA IGISOL used in the study of the U(α 40 MeV, ƒ) reaction

A new ion guide isotope separator on-line (IGISOL), operating with the SARA facility, has been constructed. Using the ²³⁸U(α 40 MeV, ƒ) reaction to produce very neutron-rich radioisotopes, all mass chains from A = 96 to 122 have been scanned by conventional methods of nuclear spectroscopy. Provided the stopping volume is separated from the primary beam, it has been proved that the yield is nearly proportional to the He pressure. In addition to the usual advantages (quasi-independence from physical and chemical properties of elements), this makes IGISOL a powerful technique for high energy recoil products. During the experiments the boundary of known neutron-rich nuclei was reached such as ¹¹⁷Rh(440 ms) and several unknown activities were detected in the range A = 113–118.     

Ion traps — recent applications and developments

Paul and Penning traps are now widely applied in chemistry and physics laboratories. They are used as storage devices, as tools for precision spectroscopy and metrology, and as mass spectrometers. Direct mass measurements of short-lived Rb, Sr, Cs, Ba, Fr and Ra isotopes were performed at the on-line mass separator ISOLDE at CERN, Geneva, by means of a tandem Penning trap system. The ions from ISOLDE are captured and cooled in a first trap and trasnferred to a second trap. Here the mass of the trapped ions is determined by measuring their cyclotron frequency. Resolving powers exceeding m/Δm (FWHM) = 10⁶ could be achieved. Mass values of about 60 isotopes have been determined with accuracies of typically δm/m = 10⁻⁷. For the first time in the history of mass spectrometry the isomeric and ground states of a nucleus have been resolved.     

Ion-optical correction elements for on-line mass separators

To adjust on-line mass separators, variable magnetic or electrostatic multipoles are most desirable. Such elements were built and subsequently included in the ISOLDE-3 on-line mass separator at CERN. In first tests a mass resolving power m/†m > 10 000 (FWHM) was achieved, which allowed the isobaric separation of ³⁷Ca from ³⁷K using a tungsten-surface ionization source.     

Time resolved on-line nuclear orientation (TR-OLNO)

Conventional on-line nuclear orientation (OLNO) involves continuous implantation of unpolarised nuclei which are cooled to milli-Kelvin temperatures by nuclear spin lattice relaxation. Anisotropy of radiation from the cold, polarised nuclei is analysed to yield nuclear moments and decay properties. Incomplete relaxation prior to decay complicates analysis and, as half-lives shorten on moving further from stability, places an ultimate limit on the range of nuclei which can be studied by OLNO. This paper introduces a new method, time resolved on-line nuclear orientation (TR-OLNO) in which the implanted beam is pulsed and study is made of the nuclear relaxation itself to yield nuclear g-factors. Decay scheme parameters can also be extracted when the relaxation is observed. This method has its optimum application as half-life and relaxation time become comparable, thus extending the range of the OLNO technique. The basic principles of the new method are introduced and its application to the study of decay chains of implanted even- and odd-A nuclei is discussed. The ability to deal with “inherited” orientation in a decay sequence is emphasised. Examples are given of existing TR-OLNO studies of light Au isotopes by the NICOLE Collaboration.     

A large solid-angle secondary-beam collector using an axially symmetric superconducting magnetic field

A new type of beam collector for light secondary charged particles (“Large ω” beam course) was designed and constructed at the RIKEN Ring Cyclotron (RRC). It makes use of the focusing properties of an axially symmetric magnetic field produced by three short superconducting coils. The system sees the target at right angles to the primary beam, and covers a solid angle of about 600 msr. It has been used mainly to transport surface muons from the decay of pions produced in nucleus-nucleus collisions. The large collection efficiency of surface muons by this collector helped us to obtain valuable data on the production cross section of low-energy pions (below 10 MeV) in reactions of 135 MeV/u ¹⁴N beam with various target nuclei. Its future development will also be discussed.     

Study of a thick target surface ionizer at INS

A surface-ionization ion source for the use of a thick target has been studied by an isotope separator on-line at INS using the ⁴⁰Ca(p,2pn)³⁸K reaction. The ionization efficiency and release time were measured for CaC₂, CaO and CaF₂ targets. The measured efficiency turned out to be about 20% both for tantalum and platinum surface ionizers. The release time was also deduced for each target at various values of temperature by measuring time distributions of the extracted radioactivity after bombarding the target for a short time.     

Development of uranium carbide targets for the on-line production of neutron-rich isotopes

A number of on-line and off-line tests have been performed at the IRIS (investigation of radioactive isotopes at synchrocyclotron) facility in order to develop uranium carbide targets with a high density (11 g/cm³) for the on-line production of neutron-rich isotopes by fission of ²³⁸U. A 1 GeV proton beam was used to bombard two kinds of targets held at temperatures in the range of 1900–2100 °C. The first one was a target-ion source assembly slightly modified to withstand 3 months of continuous heating at a temperature of about 2050 °C. The second unit was of a new kind, where ionisation takes place in the target volume itself. A comparison of the on-line isotopic yields before and after heating for 3 months is here reported. The yields and release times of Rb, Cs and In are compared with the ones obtained from a standard reference target, as measured in previous experiments.     

The Chalk River high-temperature helium-jet ion source

The Chalk River helium-jet ion source has been upgraded to accommodate a helium transfer-gas flow of 6 std 1/m and operate at 2000°C. It now provides yields exceeding 1000 atoms/s for short-lived isotopes of some refractory elements.     

Present status of singly charged ion ECR sources at the SARA on-line separator

Various 2.45 GHz microwave electron cyclotron resonance (ECR) ion-sources designed with quartz tubes and without hexapole have been developed and tested for production, transport and focalization of singly-charged ions. A first on-line endeavour to separate radioactive isotopes in a He-jet coupled mode has been realized with a capillary skimmer ion-source injection system parallel to the source plasma axis. In order to improve the coupling of a ECR source with the He-jet system, a new compact metallic body ion-source with a skimmer-catcher injection arrangement perpendicular to the plasma has been designed. The layout of this new metallic ion-source is given. The ionization efficiencies have been measured as a function of gas pressure for a complete off-line regime with various support gases and for a dynamical regime induced with an He-jet injection simulating the subsequent on-line coupled mode conditions.     

铀浓度在线分析系统的研制

采用标准加入-γ吸收法原理研制了铀浓度在线分析系统。利用不同厚度金属片对γ射线吸收程度的差异,通过在样品池与放射源之间添加金属片的方式实现固体内标的加入。研究工作中对测量模块的结构、内标材料的选择及在线流路进行了设计,编制了在线分析软件。采用有机相铀溶液对在线分析系统进行了测试,6次测定的平均值与真实值的相对偏差在3%以内,分析系统连续运行72 h的稳定性在1%以内。测试结果表明,铀浓度在线分析系统性能稳定,准确度高,适用于核燃料后处理工艺复杂基体中铀浓度的在线测量。     

Performance of and experiments with the recoil separator CARP at RCNP

A recoil mass separator (CARP) in operation at RCNP is described. The optimization of the operational parameters of the separator has been carried out experimentally. The procedure and the resulting performance of the system are presented. The mass resolution has been observed to be about 800 for the fusion-evaporation residues for a solid angle of 2 msr. The practical solid angle has been found to be limited to about 5.5 msr, due primarily to a presence of one of the third order aberrations. The current experiments with the separator are briefly described.     

粒子望远镜对运动放射源绝对探测效率的研究

文章描述了在延迟粒子谱学研究中所常用的氦喷咀系统的粒子望远镜，并对运动的放射源的绝对探测效率进行计算。考虑具有一定分布的放射性面源，计算光栏和放射源偏离中心位置对探测效率的影响。将计算过程编制成计算机程序以处理实验数据。