High-energy Accelerator Facilities Research Articles

Deep Multi-task Learning Models for Radiation Estimation at High Energy Accelerator Facility

Deep Multi-task Learning Models for Radiation Estimation at High Energy Accelerator Facility

Radiological Characterization with a Fluence Conversion Coefficients–Based Method: A Practical Example of the Preparatory Studies to the Pilot Beam at the CERN Large Hadron Collider

At high-energy accelerator facilities like the ones that are part of the accelerator complex at the European Organization for Nuclear Research (CERN), Monte Carlo radiation transport codes are widely employed to face the challenges of estimating radionuclide production yields and activities with the aim of performing the radiological characterization of activated components. Indeed, it is of paramount importance to ensure adequate radiation protection during scheduled maintenance, transport, and handling of these components and to establish their proper disposal pathway once they ultimately reach the end of their useful life. This paper summarizes the principles of the fluence conversion coefficients method that was developed as a complementary approach for radiological characterization studies. Then, the Monte Carlo simulations in preparation to the pilot beam run at the Large Hadron Collider at CERN in 2021 are presented as a practical example of possible applications. Finally, the flexibility of the method and the most relevant operational radiation protection implications are discussed in relation to the provided example.

Production of neptunium and plutonium nuclides from uranium carbide using 1.4-GeV protons

Accelerator-based techniques are one of the leading ways to produce radioactive nuclei. In this work, the isotope separation on-line method was employed at the CERN-ISOLDE facility to produce neptunium and plutonium from a uranium carbide target material using 1.4-GeV protons. Neptunium and plutonium were laser-ionized and extracted as 30-keV ion beams. A multireflection time-of-flight mass spectrometer was used for ion identification by means of time-of-flight measurements as well as for isobaric separation. Isotope shifts were investigated for the 395.6-nm ground state transition in ${}^{236,237,239}\mathrm{Np}$ and the 413.4-nm ground state transition in ${}^{236,239,240}\mathrm{Pu}$. Rates of ${}^{235--241}\mathrm{Np}$ and ${}^{234--241}\mathrm{Pu}$ ions were measured and compared with predictions of in-target production mechanisms simulated with geant4 and fluka to elucidate the processes by which these nuclei, which contain more protons than the target nucleus, are formed. ${}^{241}\mathrm{Pu}$ is the heaviest nuclide produced and identified at a proton-accelerator-driven facility to date. We report the availability of neptunium and plutonium as two additional elements at CERN-ISOLDE and discuss the limit of accelerator-based isotope production at high-energy proton accelerator facilities for nuclides in the actinide region.

Evaluation and modelling of the lithium fluoride based thermoluminescent detector response at the CERN-EU high-energy reference field (CERF)

Lithium fluoride (LiF) thermoluminescent detectors (TLDs) are commonly used for measurements in mixed high energy radiation fields such as space, hadron radiotherapy and other high energy accelerator facilities. However, the results of these measurements are often challenging to interpret since the radiation field compositions are not known a priori. The goal of this work was to model and understand the LiF TLD response in the CERN-EU high-energy Reference Field (CERF).Six different LiF TLD types, namely MTS (LiF:Mg,Ti) and MCP (LiF:Mg,Cu,P) TLDs with different Li abundances, were irradiated at CERF. For the modelling of their response, CERF reference fluence energy spectra from FLUKA simulations and TLD relative luminescence efficiencies according to the Microdosimetric d(z) Model were collected from previous works and supplemented with new relative luminescence efficiency calculations for neutrons with energies above 0.01 MeV. Dedicated MCNP6.2 simulations were performed to obtain the required fluence to absorbed dose conversion factors.Results demonstrated that the response of LiF detectors can be well predicted even for complicated, mixed radiation fields. The modelling allowed to assess the dose contributions from different radiation types in mixed fields. Based on the results of this work, a methodology was proposed to perform LiF TLD measurements in well-characterized mixed fields in terms of absorbed dose in water or tissue. In unknown mixed radiation fields MTS-7 TLDs are recommended to assess the non-neutron component of the absorbed dose in water or tissue. Assessing the dose from neutrons requires dedicated neutron detectors.

Optimization of the electron beam dump for a GeV-class laser electron accelerator

The advances of laser-driven electron acceleration offer the promise of great reductions in the size of high-energy electron accelerator facilities. Accordingly, it is desirable to design compact radiation shielding for such facilities. A key component of radiation shielding is the high-energy electron beam dump. In an effort to optimize the electron beam dump design, different material combinations have been simulated with the FLUKA Monte Carlo code in the range of 1–40 GeV. The studied beam dump configurations consist of alternating layers of high-Z material (lead or iron) and low-Z material (high-density concrete or borated polyethylene) in either three-layer or five-layer structures. The designs of various beam dump configuration have been compared and it has been found that the iron and concrete stacking in a three-layer structure with a thick iron layer results in the lowest dose at 1, 10, and 40 GeV. The performance of the beam dump exhibits a strong dependence on the selected materials, the stacking method, the beam dump thickness, as well as the electron energy. This parametric study provides general insights that can be used for compact shielding design of future electron accelerator facilities.

Estimation of cooling water activation in high-energy heavy ion medical accelerator

The estimation of air, material, and cooling water activation is essential for designing a robust nuclear safety protocol for high-energy heavy ion medical accelerators. Demineralized cooling water activation is simulated for the C-12 ion beam medical accelerator (synchrotron) with a maximum energy of 430 MeV/u. Three conservative scenarios are proposed for the estimation of demineralized cooling water activation. Simulations were performed by using a combination of MCNPX2.7.0 and VCINDER codes. Simulation parameters were optimized to match the volume of the cooling water in the accelerator system. The sums of the ratios of specific activities to unrestricted release limits were calculated for the three scenarios as a function of decay time. All activity concentrations are far less than the corresponding unrestricted release limits after a 1-day decay time because the sums of the ratios are all less than 1.0. Noticeable hazardous radioactive elements were found to be H-3, Be-7, and C-11 which have relatively long half-life times. Although hazardous radioactive elements with relatively short half-life times (within 10 min), such as N-13, O-14, and O-15, are also produced in large concentrations, there are no unrestricted release limits specified in the table issued by the National and International Radiation Protection Ordinances. The estimation of cooling water activation is useful for designing a nuclear safety protocol for high-energy heavy ion medical accelerator facilities. Specifically, the results suggest that the direct discharge of the cooling water waste into the environment (in case of an accident or the end of the life cycle of cooling water) must not be permitted. A separate reservoir for cooling water waste collection is recommended with a dedicated real-time measuring equipment to measure the concentrations of H-3, Be-7, C-11, N-13, O-14, and O-15 separately.

Evaluation of Skyshine from an Accelerator Facility: Dependence on Distance and Angle.

Neutron skyshine from Linac Coherent Light Source II 4 GeV electron beam operation at SLAC National Accelerator Laboratory can contribute to prompt radiation exposure to the public at distances far beyond the accelerator tunnel housing. One of the shielding design requirements at SLAC is that the annual dose to a member of the public is no more than 0.05 mSv y. This study uses Monte Carlo code FLUKA to simulate the generation of neutrons from 4 GeV electron beam losses on a thick copper target inside a generalized geometry of the Linac Coherent Light Source II Beam Transport Hall accelerator tunnel section. The effective dose from neutron skyshine was characterized as a function of both distance from the tunnel wall (up to 1 km away) and angle relative to the beam direction (between 0° and 180°). This new methodology for evaluating neutron skyshine dose is applicable to high-energy GeV-range electron accelerator facilities both at SLAC and elsewhere.

Third integer resonance extraction with presence of higher multipoles

The slow resonant extraction of a beam in a storage ring is a very well-established technique. Several high-energy physics accelerator facilities around the world are currently using this technique for high-intensity beam operations. As the demand for beam power is constantly growing, extraction efficiency in many cases is becoming a limiting factor. In this report, we discuss a new effective approach to improving the slow extraction efficiency by using configurations of higher multipoles. We will describe this approach, determine optimal multipole configurations, and present the results of simulations to support the proposed recipe. We found that, with the use of higher multipole field content, the extraction efficiency can be improved, and, therefore, the level of prompt and residual radioactivity in the accelerator components and surrounding buildings can be reduced by as much as 40% or more. We also explored manipulating the higher-order effects produced in the pure sextupole configurations for the same purpose and demonstrated that similar results can be achieved by only rearranging the sextupole magnets in the lattice.

Estimating internal dose coefficients of short-lived radionuclides in accordance with ICRP 2007 recommendations

ABSTRACT For radiation protection in high-energy accelerator facilities, internal dose coefficients of short-lived radionuclides were estimated using the dosimetric methodology in accordance with the International Commission on Radiological Protection (ICRP) 2007 Recommendations. A computational program was developed for estimating the dose coefficients. The program was verified by confirming whether it could reproduce the dose coefficients provided by ICRP for intakes of representative radionuclides. In addition, the estimated dose coefficients of short-lived radionuclides were compared to the values generated by Dose and risk CALculation software (DCAL), which is based on a dosimetric methodology that is in accordance with the ICRP 1990 Recommendations, to discuss the reasons why the dose coefficients were changed by the revision of the dosimetric methodologies. The comparison revealed a decreasing trend of dose coefficients in the case of inhalation upon revision of the dosimetric methodologies. By contrast, in the case of ingestion, the dose coefficients tended to increase.

Prediction of activation products and resulting dose rates for the magnetic septum in heavy-ion medical accelerator

In high-energy heavy-ion medical accelerator facility, the induced activity due to primary and secondary interactions of the lost beams is the most concerned issue in view point of nuclear safety because long-lived radioactive nuclides cause problems of radiation exposure for staff involved in the repair or maintenance work and in decommissioning the facility. This paper presents activation of a thick magnetic septum by modeling the copper coils which are heavily showered by the lost carbon ion beams with the energy of 430 MeV/u. The activation takes place by all possible interaction modes which include direct interaction of the carbon ion beam with the elements, the interaction of backscattered neutrons from the concrete walls, and isotope production as a result of the decay of other isotopes produced in these interactions. The prediction of the radionuclide inventory and induced activation are performed by using the combination of MCNPX2.7.0 and CINDER’90 codes.

Distributed Optical Fiber Radiation Sensing in the Proton Synchrotron Booster at CERN

In this paper, we report on the development and first deployment of a distributed optical fiber radiation sensor (DOFRS) for the online monitoring of radiation levels in the high-energy accelerator facilities of CERN. The DOFRS is composed of two basic parts: a set of suitably chosen radiation sensitive optical fibers (OFs), to be installed in the machine tunnel, and an optical time domain reflectometer (OTDR), to be installed in a radiation-free area. We carried out a calibration of the radiation response of a P-doped multimode OF under 60Co $\gamma $ -rays and in the mixed-field radiation environment of the CHARM facility at CERN. By performing OTDR measurements, we are able to probe the radiation-induced attenuation in the OF along its length and calculate the deposited radiation dose with a spatial resolution of 1 m. In this paper, we describe the main features associated with DOFRS implementation in the proton synchrotron booster (PSB) at CERN. We also report the first results obtained from the monitoring of PSB radiation levels since its recommissioning in April 2017. The performances and advantages of the DOFRS system are discussed.

The CERN-EU high-energy Reference Field (CERF) facility: applications and latest developments

The CERF facility at CERN provides an almost unique high-energy workplace reference radiation field for the calibration and test of radiation protection instrumentation employed at high-energy accelerator facilities and for aircraft and space dosimetry. This paper describes the main features of the facility and supplies a non-exhaustive list of recent (as of 2005) applications for which CERF is used. Upgrade work started in 2015 to provide the scientific and industrial communities with a state-of-the-art reference facility is also discussed.

Optimization of a neutron dosimeter for the high energy accelerators

In high energy accelerator facilities the neutron radiation should be continuously measured during operation to control the ambient dose. This requires a reliable neutron dosimeter in a wide energy range. In this work we present an optimization of a compact cylindrical passive neutron dosimeter for the usage in wide energy neutron fields.

Dose Measurements through the Concrete and Iron Shields under the 100 to 400 MeV Quasi-Monoenergetic Neutron Field (at RCNP, Osaka Univ.)

Shielding benchmark experiments are useful to verify the accuracy of calculation methods for the radiation shielding designs of high-energy accelerator facilities. In the present work, the benchmark experiments were carried out for 244- and 387-MeV quasi-monoenergetic neutron field at RCNP of Osaka University. Neutron dose rates through the test shields, 100-300 cm thick concrete and 40-100 cm thick iron, were measured by four kinds of neutron dose equivalent monitors, three kinds of wide-energy range monitors applied to high-energy neutron fields above 20 MeV and a conventional type rem monitor for neutrons up to 20 MeV, placed behind the test shields. Measured dose rates were compared one another. Measured results with the wide-energy range monitors were in agreement one another for both the concrete and the iron shields. For the conventional type rem monitor, measured results are smaller than those with the wide-energy range monitors for the concrete shields, while that are in agreements for the iron shields. The attenuation lengths were obtained from the measurements. The lengths from all the monitors are in agreement on the whole, though some differences are shown. These results are almost same as those from others measured at several hundred MeV neutron fields.

Adsorption behavior of beryllium(II) on copper-oxide nanoparticles dispersed in water: A model for (7)Be colloid formation in the cooling water for electromagnets at high-energy accelerator facilities.

The adsorption behavior of Be(II) on CuO nanoparticles dispersed in water was studied as a model for colloid formation of radioactive (7)Be nuclides in the cooling water used for electromagnets at high-energy proton accelerator facilities. An aqueous Be(II) solution and commercially available CuO nanoparticles were mixed, and the adsorption of Be(II) on CuO was quantitatively examined. From a detailed analysis of the adsorption data measured as a function of the pH, it was confirmed that Be(II) is adsorbed on the CuO nanoparticles by complex formation with the hydroxyl groups on the CuO surface (>S-OH) according to the following equation: n > S-OH + Be(2+) ⇔ (>S-O)n Be((2-n)+) + nH(+) (n = 2, 3) S : solid surface. The surface-complexation constants corresponding to the above equilibrium, β(s,2) and β(s,3), were determined for four types of CuO nanoparticles. The β(s,2) value was almost independent of the type of nanoparticle, whereas the β(s,3) values varied with the particle size. These complexation constants successfully explain (7)Be colloid formation in the cooling water used for electromagnets at the 12-GeV proton accelerator facility.

The triple GEM detector as stray neutron monitor

A triple GEM detector for low energy neutrons and high rejection of gamma background was tested at the CERF facility at CERN as stray neutron monitor. The detector was exposed to a wide neutron spectrum generated by a 120 GeV/c positively charged hadron beam hitting a copper target. The beam particle rate on target ranged over three orders of magnitude. The neutron count rate measured with the GEM could be linearly correlated with the beam intensity and also compared well with Monte Carlo simulations. The detector performance suggests that it can be used as an independent low energy neutron monitor at high-energy particle accelerator facilities.

Estimation for the intensity of beam loss by the optical fiber based Cherenkov beam loss monitor at SACLA

From the issues of radiation safety and radiation damage of accelerator equipments, it is useful to detect the beam loss immediately at high-energy and high intensity particle accelerator facilities. In the undulator section of Spring-8 Angstrom Compact free electron LAser (SACLA) [1], beam loss monitors have been installed in order to control beam losses and to prevent demagnetization of permanent magnets due to electron hitting [2]. Since the commissioning phase of SACLA, this monitor has been successfully working. This beam loss monitor consists of a quartz fiber with 400 μm core diameter and a photomultiplier tube (PMT) which is connected with the upstream end of the fiber. The Cherenkov radiation which is produced in the fiber due to the passing of secondary electrons and positrons (Cherenkov emitters) is detected by the photomultiplier tube. With the detection time of the monitor signals, the position of the beam loss point can be measured. In addition, the use of two monitors with different gains allows measuring intensity of the beam loss over the wide dynamic range. While it is expected that the waveform of the monitor signal corresponds to the spatial distribution of the electron flux or absorbed dose due to the beam loss, if this monitor is used for the beam loss control, it is necessary to calibrate the magnitude of the monitor signal to a value such as the number of electrons or the absorbed dose in order to set an appropriate threshold level. In this study, the electron beam loss was measured by the beam loss monitor and thermo luminescent dosimeters (TLD), and the correlation among the signal of the beam loss monitor, the absorbed dose and electron flux was investigated.

Evaluation and Measurements of Radioactive Air Emission and Off-Site Doses at SLAC

SLAC, a high-energy (GeV) electron accelerator facility, performs experimental and theoretical research using high-energy electron and/or positron beams that can produce secondary neutron and gamma radiation when beam losses occur. Radioactive gas production (mainly C, N, O, Ar) and release is one of the environmental protection program issues. U.S. DOE Order 458.1 requires that 40 CFR 61 Subpart H's NESHAP requirements be followed. These regulations prescribe a total dose limit of 0.1 mSv y to the Maximally Exposed Individual (MEI) of the general public, a requirement for a continuous air monitoring system if a release point within a facility can cause > 1 × 10 mSv y to the MEI, and a requirement for periodic confirmatory measurements for minor sources which give releases that contribute ≤ 1 × 10 mSv y to the MEI. At SLAC, all air release points for current operations are evaluated to be minor sources. This paper describes SLAC's evaluation following NESHAP requirements; measurements using the Air Monitoring Station (AMS) as periodic confirmatory measurements are also discussed.

Observation of the antimatter partner of Rutherford's α-particle - 4

The antimatter helium-4 nucleus (4, or anti-α) has not been observed previously although the α-particle was identified a century ago by Rutherford. High-energy nuclear collisions recreate energy densities similar to that of the universe microseconds after the Big Bang, and in both cases, matter and antimatter are created with comparable abundances. However, the relatively short-lived expansion in nuclear collisions makes it possible for antimatter to decouple quickly from matter. This makes a high-energy accelerator facility the ideal environment for producing and studying antimatter. In this paper, we report 18 antihelium-4 nuclei discovered by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The measured invariant differential cross section is consistent with expectation from thermodynamics and coalescent nucleosynthesis models, which has implications for future production of even heavier antimatter nuclei, as well as for experimental searches for new phenomena in the cosmos. Future directions of rare and exotic matter searches from STAR will also be discussed.

Design of a high energy neutron dosimeter using CR-39 with multi-layer radiator

Abstract Personal neutron dosimeters are necessary for radiation protection of nuclear workers in high energy accelerator facilities. To improve sensitivity for high energy neutrons above 10 MeV, a new personal neutron dosimeter was designed using a solid state nuclear track detector (CR-39) covered with Multi-Layer radiator consisting of polyethylene, polyamide and iron/aluminum sheets. In this work, we investigated various radiator combinations and thicknesses in order to detect high energy neutrons above 10 MeV. Energy response of each radiator was calculated using the multi-purpose Monte Carlo simulation code, Particle and Heavy Ion Transport System (PHITS). To evaluate the accuracy of our calculations, the energy response of each radiator was measured in a mono-energetic neutron field at the Facility of Radiation Standard (FRS) of the Japan Atomic Energy Agency (JAEA). The energy response of each radiator calculated by PHITS was in good agreement with our experimental results. The results obtained in this research indicate that PHITS is a useful software tool for the design of new personal neutron dosimeters using CR-39 and using Multi-layer radiator approach.