Neutron dose assessment in laser-generated ultra-short pulsed fields.

ELI Beamlines is one of the pillars of the Extreme Light Infrastructure European Research Infrastructure Consortium (ELI ERIC), the European project aiming at building the next generation of high power lasers for fundamental research and industrial applications. Several high-power lasers are hosted by the ELI Beamlines facility. Even at a power lower than the nominal one, when interacting with a target, the laser can generate mixed ionizing radiation fields of unique nature. One of the major laser systems, High-repetition-rate advanced petawatt laser system (HAPLS) was already used in commissioning experiments. Detecting the neutrons generated during these experiments has been a challenging task, since certain difficulties were faced. First, the experimental conditions were frequently altered during the commissioning phase (such as laser beam parameters, experimental geometry or target type). Next, the extremely short duration of the ionizing radiation pulse generated by the laser (~10-14 s) complicated the correct interpretation of the data provided by the detectors designed and calibrated in standard fields. Here, one commissioning experiment is described, together with the means of addressing the problem of the detection of the ionizing radiation and the lessons learned in this endeavour.

Proton Bragg curve and energy reconstruction using an online scintillator stack detector.

Real-time measurement and characterization of laser-driven proton beams have become crucial with the advent of high-repetition-rate laser acceleration. Common passive diagnostics such as radiochromic film (RCF) are not suitable for real-time operation due to time-consuming post-processing; therefore, a novel approach is needed. Various scintillator-based detectors have recently gained interest as real-time substitutes to RCF-thanks to their fast response for a wide range of dose deposition rates. This work introduces a compact, scalable, and cost-effective scintillator-based device for proton beam measurements in real-time suitable for the laser-plasma environment. An advanced signal processing technique was implemented based on detailed Monte Carlo simulations, enabling an accurate unfolding of the proton energy and the depth-dose deposition curve. The quenching effect was accounted for based on Birks' law with the help of the Monte Carlo simulations. The detector was tested in a proof-of-principle experiment at a conventional cyclotron accelerating protons up to 35 MeV of energy. The signal comparison with a standard RCF stack was also performed during the test of the device, showing an excellent agreement between the two diagnostics. Such devices would be suitable for both conventional and laser-driven proton beam characterization.

COMPARISON OF OSL AND TL DOSEMETERS WITH DATA COLLECTED AT THE MT25 CYCLIC ELECTRON ACCELERATOR.

The Microtron MT25 is a cyclic electron accelerator with a Kapitza resonator, maximum beam energy of 25 MeV, standard repetition frequency of 423 Hz, pulse length of 3.5 µs and mean current of 30 µA. Studies at conventional particle accelerators allow to understand the response of dosemeters in known and controllable radiation fields. Subsequently, it is possible to develop models and predict their behavior in complex radiation fields, such as those generated at laser and FLASH facilities. Therefore, response of thermally and optically stimulated luminescence detectors outside of the beam was studied at the Microtron MT25. The detectors were placed on a Plexiglas phantom inside a lead and iron bunker to shield-off background radiation. In addition, GAFChromic™ films and track detectors were used. Two irradiations were performed: with and without an 8-cm thick polyethylene moderator. This paper presents a comparison of the responses of the different detection systems.

The European Joint Research Project UHDpulse - Metrology for advanced radiotherapy using particle beams with ultra-high pulse dose rates.

UHDpulse - Metrology for advanced radiotherapy using particle beams with ultra-high pulse dose rates is a recently started European Joint Research Project with the aim to develop and improve dosimetry standards for FLASH radiotherapy, very high energy electron (VHEE) radiotherapy and laser-driven medical accelerators. This paper gives a short overview about the current state of developments of radiotherapy with FLASH electrons and protons, very high energy electrons as well as laser-driven particles and the related challenges in dosimetry due to the ultra-high dose rate during the short radiation pulses. We summarize the objectives and plans of the UHDpulse project and present the 16 participating partners.

Monte Carlo simulation of activity measurement of 123I, 111In and 153Sm with a radionuclide calibrator.

The response of radionuclide calibrators for radionuclides with high abundances of high energy X-rays is very sensitive to changes in the source geometry. The magnitude of this effect was explored for Bqmetr (Konsorcium BQM, CR) calibrators with (123)I, (111)In and (153)Sm in several vial and syringe geometries. Dependencies of chamber responses on solution volume and container position were calculated using MCNP transport code. The possibility of usage of an additional copper filter to reduce chamber sensitivity was studied and found to be suitable.

National comparison of 131I measurement among nuclear medicine clinics of eight countries.

A generally applicable protocol for organizing comparisons among nuclear medicine clinics created within the IAEA project CRP E2.10.05 was tested in Brazil, Cuba, Czech Republic, India, Iran, Republic of Korea, Romania and Turkey in 2007. Comparisons of measurement of (131)I were organized by local pilot laboratories with different backgrounds and levels of experience in this field. The results and experiences gained were compared and analyzed. A majority of results in each national comparison were within 10% of the reference value.

Monte Carlo calculations of calibration and geometry correction factors of a radionuclide calibrator.

The activity of radioactive pharmaceuticals administered to patients in nuclear medicine is usually determined using well-type high-pressure ionization chambers. For the Bqmeter chamber (Consortium BQM, Czech Republic) a Monte Carlo model was created using the MCNP4C2 code. Basic chamber characteristics for two sample containers of various geometry (a vial and an ampoule) were calculated and compared with measurements. As the pharmaceuticals are often measured in various syringes, the chamber response for samples in syringes was also studied.

Activity measurements with radionuclide calibrators in the Czech Republic.

Since radionuclide calibrators are used in nuclear medicine for the determination of the activity of radiopharmaceuticals administered to patients, it is important to ensure their long-term accuracy. Results of the checks performed in the Czech Republic during the year 2002 are given, together with a short overview of previous years. For the CMI 4pigamma ionization chamber, against which all the calibrators are checked, we calculated the response function and basic characteristics by a Monte Carlo method, using the MCNP4C code.