BELEN-20 neutron detector at IGISOL facility (University Jyväskylä, Finland)

BELEN-48 neutron detector at IGISOL facility (University Jyväskylä, Finland)

BRIKEN detector at RIKEN facilities (Japan)

BELEN Detector and BRIKEN experiment. Beta delayed neutron emission measurements

The aim is to determine nuclei properties experimentally, focusing on beta delayed neutron emission probabilities of exotic nuclei in the neutron rich region.

Among the main missions of modern radioactive isotope facilities, is the exploration of properties of yet unknown isotopes on the neutron-rich side of the chart of nuclides. However, going more neutronrich also means that the neutron separation energy decreases until it reaches the dripline at Sn = 0 MeV. If the neutron separation energy gets lower than the b-decay energy window (Qβ value), a new decay mechanism can occur: the emission of neutrons after β-decay.

These “β-delayed neutron” (βn) emitters play a crucial role in:

Nuclear structure: For neutron-rich nuclei far from stability, β-delayed neutron emission becomes the dominant decay process. The neutron emission probability (Pn value) helps to verify the modeled β-strength distribution and the level structure of the daughter nucleus. Also the β-decay half-life of the parent nucleus can be determined via β-delayed neutron emission

Nuclear astrophysics: An accurate knowledge of the neutron-branching ratio and half-lives of as many bn emitters as possible, is a crucial prerequisite for improving theoretical models to achieve a better understanding of r-process nucleosynthesis models process that are responsible for the creation of about half of the stable isotopes beyond iron.

Nuclear reactor applications: In fission reactors the longer response time of βn allows keeping the system in a controlled subcritical state. Although their number (delayed neutrons per fission event) is only in the order of 1% of the total neutron yield, they have a long enough effective lifetime to insert or withdraw rods containing neutron absorbing materials to control the reactor.

Our group has developed a high efficiency neutron detector called BELEN detector that consist on a set of proportional neutron counters (³He filled) embedded in a poliethylene matrix to moderate neutrons to be measured. We have developed some prototypes with 20, 30 and 48 proportional counters that has participated in measuring campaigns at GSI - Darmstadt (Germany), and IGISOL facility at Jyväskylä (Finland).
Based on the sucessful achievements of BELEN detector, our group has participated in the design, construction and exploitation of the world’s most efficient neutron detector array at the presently most powerful facility (RIKEN-Japan) to produce neutron-rich isotopes. The neutron detector array, called BRIKEN detector, contains up to 179 ³He tubes from UPCBarcelona, IFIC-Valencia, GSI-Darmstadt, Oak Ridge National Laboratory, JINR Dubna, and RIKEN.

Front view of miniBELEN detector at UPC

miniBELEN installed at the CMAM accelerator facility

MANY project. Measurements of alpha neutron yields

Neutron Spectrometry Array at Astun, Huesca (2100 m)

Neutron Spectrometry Array at ETSEIB, Barcelona (120 m)

Neutron Spectrometry Array at LSC facilities (Canfranc, Huesca)

Neutron Spectrometry Array located at the tunnel of LSC (Canfranc, Huesca)

HENSA project. High Efficiency Neutron Spectrometry Array.

The aim is to measure the neutron flux from cosmic rays in different areas of Spain. This flow of particles is associated with failures in microcomputer systems that can affect telecommunications of navigation. The first measuremet campaing was carried out from june-2020 to october-2020 in many spanish locations as, Astun sky resort (2100 m high), Canfranc Underground Laboratory (LSC) headquartersand, Cantabria Physics Institute (Santander) , Sierra nevada Observatory (Granada - 2896 m high), Astronomical Observatory of Javalambre (Teruel -1957 m high), Complutense University of Madrid (Madrid), and Universitat Politecnica de Catalunya (Barcelona)

 Experimental area

4π calorimeter at the n_TOF experimental area

n_ToF project

The main goal of this project is the study of neutron-induced reactions related with many research areas as basic nuclear physics, nuclear astrophysics, and nuclear technology. n_TOF is an experimental facility established in 2001 at CERN , the European Organization for Nuclear Research, with the aim of producing pulsed neutron beams for cross section measurements of neutron induced nuclear reactions, mainly capture (n,γ) and fission (n,f). The n_ToF (neutron Time-of-Flight) facility consist on a pulsed neutron source that generates a wide energy range of neutrons (up to 20 GeV) at high intensities.

The cross section of a nuclear reaction is the physical magnitude that expresses the probabilty of a certain nuclear reaction to occur. This type of nuclear data is fundamental in all the fields where detailed knowledge of neutron induced reactions is needed, as in the development of new and safer nuclear techonolgy, or in the field of astrophysics which studies the production of the heavy (>Fe) elements in stars, called stellar nucleosynthesis.

At n_TOF, the energy of the neutrons employed to measure reactions is determined with the time-of-flight technique, which consists in measuring the time neutrons take to travel a fixed distance. The neutron beams produced at n_TOF are characterized by a high instant flux, a very high neutron energy resolution and a broad range in neutron energy, which all combined makes it one of the best suited facilities in the world for the study of neutron induced reactions.

In the last years our group has been directly involved in several experiments with applications in stellar nucleosynthesis. In the year 2015, the UPC group was one of the leading institutions in an international collaboration to measure, for the first time ever, the capture cross section of the highly interesting thallium radioactive isotope ²⁰⁴Tl at n_TOF. This cross section is crucial to better establish the isotopic abundance pattern at the endpoint of the s-process, and has a strong influence in the final value of the ²⁰⁵Pb/²⁰⁴Pb abundance ratio. This ratio could be used to estimate the time span since the last s-process events that contributed to the Solar System elemental abundance distribution.

Finally, in 2018 our group proposed and led the measurement of the capture cross seciton of ²⁰⁵Tl, which also affects strongly the ²⁰⁵Pb/²⁰⁴Pb ratio, and will further contribute to the understanding of the nucleosynthesis production of the s-process endpoint.

SANDA project

Supplying Accurate Nuclear data for energy and non-energy Applications

Neutron dosimetry

The radiological dose is a magnitude that estimates the eect of ionizing radiation on the human body. Installations that use this type of radiation, such as tumor treatment centers (radiotherapy) or nuclear power plants, must have devices that precisely measure the dose, so that the limits considered safe are not exceeded. The neutron dosimetry is more difficult to perform than other ionizing radiations. Current neutron dosimeters show some limitations to measure high-energy neutrons. In this sense, our research group is developing a REM neutron counter to improve the limitations of dosimetry for high-energy and pulsed neutrons.

Nuclear instrumentation

Detectors of ionizing radiation are electrical transducers; the signal generated with the interaction of radiation in the detector must be first conditioned in order to be processed and analyzed later. The conditioning and processing of the signal are carried out by specific electronic circuits and encompassed under the name of Nuclear Instrumentation. The signal conditioning is performed by analogical preamplifiers, the signal processing can be digital, analogical or a combination of both.

Our group has carried out charge and current sensitive preamplifiers specifically designed for determined applications of neutron detection and voltage sensitive preamplfiers for scintillation detectors. Nowadays the projects under development are: a neutron dosimeter for continuous fields; an preamplifier for the detection of pulsed fields of neutrons; development of models of charge preamplifiers; design of power supply systems for portable instrumentation and filters for pulses generated in high-noise conditions. We are developing a digital system for the shaping and analysis of pulses for dosimetry in pulsed or continuous neutron fields.

Our skills in Nuclear Instrumentation are:

• Design and implementation of ad-hoc specific instrumentation.
• Implementation of radiation detection systems for specific applications.