NE213 Organic Liquid Scintillator Research Articles

Analytical modeling of the neutron response function of the NE213 organic liquid scintillator in the energy range of 0.2 MeV to 148 MeV

Determination of the neutron response function is essential for measuring the energy of neutrons emitted from natural and artificial neutron sources and nuclear reactions. This paper presents the calculation procedure of generating a neutron analytical response function for NE213 scintillation detectors in the energy range of 0.2–148 MeV. To obtain the analytical response function, the available neutron experimental response functions were grouped according to their behavior in different energy ranges. Different analytical functions were fitted to the experimental data of the detector response function for each neutron energy range. The function which best fits the experimental data was selected. Then a computer program was written for calculating the parameters of the analytical function by using the fitting functions and their parameters for each desired energy, and generating the analytical response functions. A comparison of the results shows that the analytical response functions are much faster and more consistent with the experimental response functions than the generated response functions of stand-alone codes and general-purpose Monte Carlo codes.

Shielding experiments of concrete and iron for the 244 MeV and 387 MeV quasi-mono energetic neutrons using an organic scintillator (at RCNP, Osaka Univ.)

A shielding benchmark experiment has been performed using a quasi-monoenergetic 7 Li(p,n) neutron source with the peak energies of 244 and 387 MeV at the Research Center for Nuclear Physics (RCNP) of Osaka University, in order to assess the accuracy of nuclear data and calculation codes used in high-energy accelerator shielging design. Energy spectra behind bulk shields of 10- to 100-cm-thick iron, 25- to 300-cm-thick concrete and their composite are measured using a NE213 organic liquid scintillator with a diameter and thickness of 25.4 cm each with a time-of-flight and an unfolding method. The neutron attenuation lengths are illustared for iron and concrete as a function of the incident energy.

Methodology for the neutron time of flight measurement of 120-GeV proton-induced reactions on a thick copper target

A methodology for the time-of-flight measurement of the neutron energy spectrum for a high-energy proton-beam-induced reaction was established at the Fermilab Test Beam Facility of the Fermi National Accelerator Laboratory. The 120-GeV proton beam with 3×105protons/spill was prepared for event-by-event counting of incident protons and emitted neutrons for time-of-flight energy determination. An NE213 organic liquid scintillator (12.7cm in diameter by 12.7cm in length) was employed with a veto plastic scintillator and a pulse-shape discrimination technique to identify neutrons. Raw waveforms of NE213, veto and beam detectors were recorded to discriminate the effects of multi-proton beam events by considering different time windows. The neutron energy spectrum ranging from 10 to 800MeV was obtained for a 60-cm-long copper target at 90° with respect to the beam axis. The obtained spectrum was consistent with that deduced employing the conventional unfolding technique as well as that obtained in a 40-GeV/c thin-target experiment.

Benchmark Experiment of Neutron Penetration through Iron and Concrete Shields for Hundreds-of-MeV Quasi-Monoenergetic Neutrons—II: Measurements of Neutron Spectrum by an Organic Liquid Scintillator

A shielding benchmark experiment has been performed to obtain the spectra of neutrons penetrating 10- to 100-cm-thick iron shields and 25- to 200-cm-thick concrete shields and to investigate the accuracy of various calculation codes using a 137-MeV quasi-monoenergetic neutron source. The source neutrons are produced from a 1.0-cm-thick lithium target bombarded with 140-MeV protons, and the energy spectra are measured with the time-of-flight (TOF) method using a NE213 organic liquid scintillator. The neutrons emitted in the forward direction were collimated with a 150-cm-thick iron collimator with 10- × 12-cm aperture. TOF and unfolding methods are applied to obtain the energy spectra behind the shield for the peak energy region and continuous-energy region, respectively. Monte Carlo calculations with PHITS and MCNPX are compared with the measured data. The comparison shows that the calculated spectra are in good agreement with the measured spectra.

Measurement and calculation of high-energy neutron spectra behind shielding at the CERF 120 GeV/c hadron beam facility

Neutron energy spectra were measured behind the lateral shield of the CERF (CERN-EU High Energy Reference Field) facility at CERN with a 120 GeV/c positive hadron beam (a mixture of mainly protons and pions) on a cylindrical copper target (7-cm diameter by 50-cm long). An NE213 organic liquid scintillator (12.7-cm diameter by 12.7-cm long) was located at various longitudinal positions behind shields of 80- and 160-cm thick concrete and 40-cm thick iron. The measurement locations cover an angular range with respect to the beam axis between 13 and 133°. Neutron energy spectra in the energy range between 32 MeV and 380 MeV were obtained by unfolding the measured pulse height spectra with the detector response functions which have been verified in the neutron energy range up to 380 MeV in separate experiments. Since the source term and experimental geometry in this experiment are well characterized and simple and results are given in the form of energy spectra, these experimental results are very useful as benchmark data to check the accuracies of simulation codes and nuclear data. Monte Carlo simulations of the experimental set up were performed with the FLUKA, MARS and PHITS codes. Simulated spectra for the 80-cm thick concrete often agree within the experimental uncertainties. On the other hand, for the 160-cm thick concrete and iron shield differences are generally larger than the experimental uncertainties, yet within a factor of 2. Based on source term simulations, observed discrepancies among simulations of spectra outside the shield can be partially explained by differences in the high-energy hadron production in the copper target.

Development of a quasi-monoenergetic neutron field using the 7Li(p,n)7Be reaction in the energy range from 250 to 390 MeV at RCNP

A quasi-monoenergetic neutron field using the (7)Li(p,n)(7)Be reaction has been developed at the ring cyclotron facility at the Research Center for Nuclear Physics (RCNP), Osaka University. Neutrons were generated from a 10-mm-thick Li target injected by 250, 350 and 392 MeV protons and neutrons produced at 0 degrees were extracted into the time-of-flight (TOF) room of 100-m length through the concrete collimator of 10 x 12 cm aperture and 150 cm thickness. The neutron energy spectra were measured by a 12.7-cm diam x 12.7-cm long NE213 organic liquid scintillator using the TOF method. The peak neutron fluence was 1.94 x 10(10), 1.07 x 10(10) and 1.50 x 10(10) n sr(-1) per muC of 250, 350 and 392 MeV protons, respectively. The neutron spectra generated from various thick (stopping length) targets of carbon, aluminium, iron and lead, bombarded by 250 and 350 MeV protons, were also measured with the TOF method. Although these measurements were performed to obtain thick target neutron yields, they are also used as a continuous energy neutron field. These neutron fields are very useful for characterising neutron detectors, measuring neutron cross sections, testing irradiation effects for various materials and performing neutron shielding experiments.

Measurement of neutron energy spectra behind shielding of a 120 GeV/ c hadron beam facility

Neutron energy spectra were measured behind the lateral shield of the CERF (CERN-EU High Energy Reference Field) facility at CERN with a 120 GeV/ c positive hadron beam (mainly a mixture of protons and pions) on a cylindrical copper target (7-cm diameter×50-cm long). NE213 organic liquid scintillator (12.7-cm diameter×12.7-cm long) was located at various longitudinal positions behind shields of 80- and 160-cm thick concrete and 40-cm thick iron. Neutron energy spectra in the energy range between 12 and 380 MeV were obtained by unfolding the measured pulse height spectra with the detector response functions which have been experimentally verified in the neutron energy range up to 380 MeV in separate experiments. The corresponding MARS15 Monte Carlo simulations generally gave good agreements with the experimental energy spectra.

Measurement of response functions of organic liquid scintillator for neutron energy range up to 390 MeV

The neutron response functions of 12.7 cm diameter by 12.7 cm long NE213 organic liquid scintillator have been measured in the energy range up to 390 MeV at the Research Center for Nuclear Physics (RCNP) of Osaka University. The continuous energy neutrons were produced by the 392 MeV proton bombardment on a 20-cm thick aluminum target and the response functions of the time-of-flight (TOF)-gated monoenergetic neutrons in a wide energy range up to 390 MeV were simultaneously measured. The quasi-monoenergetic neutrons were also produced via 7Li(p,n) 7Be reaction by the 392-MeV proton beam bombardment on a 1.0-cm thick 7Li target, and the TOF-gated 388-MeV peak neutrons were used to obtain the response function at this energy. The measured results show that the response functions for monoenergetic neutrons below 100 MeV have a recoil proton plateau and an edge around the maximum light output which increases with increasing neutron energy, while on the other hand, for energies above 100 MeV, the plateau and the edge become unclear because the proton range starts to exceed the detector size allowing protons to escape.

Measurements of the response functions of a large size NE213 organic liquid scintillator for neutrons up to 800 MeV

The response functions of 25.4 cm (length) x 25.4 cm (diameter) NE213 organic liquid scintillator have been measured for neutrons in the energy range from 20 to 800 MeV at the Heavy-Ion Medical Accelerator in Chiba (HIMAC) and at the Research Center for Nuclear Physics (RCNP) of Osaka University. At HIMAC, white (continuous) energy spectrum neutrons were produced by the 400 MeV per nucleon carbon ion bombardment on a thick graphite target, whose energy spectrum has already been measured by Kurosawa et al., [Nucl. Sci. Eng. 132, 30 (1999)] and the response functions of the time-of-flight-gated monoenergetic neutrons in a wide energy range from 20 to 800 MeV were simultaneously measured. At RCNP, the quasi-monoenergetic neutrons were produced via 7Li(p,n)7Be reaction by 250 MeV proton beam bombardment on a thin 7Li target, and the TOF-gated 245 MeV peak neutrons were measured. The absolute peak neutron yield was obtained by the measurement of 478 keV gamma rays from the 7Be nuclei produced in a Li target. The measured results show that the response functions for monoenergetic neutrons < 250 MeV have a recoil proton plateau and an edge around the maximum light output, which increases with increasing incident neutron energy, on the other hand > 250 MeV, the plateau and the edge become unclear because the proton range becomes longer than the detector size and the escaping protons increase. It can be found that the efficiency of the 24.5 cm (diameter) x 25.4 cm (length) NE213 for the 250 MeV neutrons is -10 times larger than the 12.7 cm (length) x 12.7 cm (diameter) NE213, which is widely used as a neutron spectrometer.

Sequential Measurements of Cosmic-Ray Neutron Spectrum and Dose Rate at Sea Level in Sendai, Japan

The cosmic-ray neutron energy spectrum and dose rate were measured sequentially for two years from April 2001 up to March 2003 by using three neutron detectors, a 3He-loaded multi-moderator detector (Bonner ball), 12.7 cm diameter by 12.7 cm long NE213 organic liquid scintillator, and high-sensitivity rem (dose equivalent) counter at the Kawauchi campus of Tohoku University in Sendai, Japan of geomagnetic latitude, 29°N, and cutoff rigidity, 10.43 GV. The neutron spectrum has three major peaks, thermal energy peak, evaporation peak around 1 MeV and cascade peak around 100 MeV. The ambient neutron dose equivalent rates measured by the rem counter, and the Bonner ball keep almost constant values of 4.0 and 6.5 (nSv/h), respectively, throughout this time period, after atmospheric pressure correction, and it often decreased about 30% after a large Solar Flare, that is called as the Forbush decrease. The total neutron flux was also obtained by the Bonner ball measurements to be 7.5×10-3 (n cm−2.s−1) in average. The altitude variation of neutron flux and dose was also investigated by comparing the measured results with other results measured at Mt. Fuji area and aboard an airplane, where the cutoff rigidities are similar.

Measurement of neutron activation cross sections for major elements of water, air and soil between 30 and 70 MeV

Neutron activation cross sections between 30 and 70 MeV were measured by the activation method using a semi-monoenergetic neutron field settled at the AVF cyclotron of the Cyclotron and Radioisotope Center(CYRIC), Tohoku University. Natural samples of N, O, Si, Na, Ca and Mg which are the major elements of water, air and soil were irradiated in this neutron field generated through the 7Li(p,n)7Be reaction by 30, 35,40, 50,60 and 70 MeV protons on thin Li target. Neutron yields were measured with the time-of-flight method using a calibrated NE213 organic liquid scintillator. From the induced activities measured with the HPGe detectors, we estimated the excitation functions of 15 cross sections.

Neutron energy and time-of-flight spectra behind the lateral shield of a high energy electron accelerator beam dump. Part I: measurements

Neutron energy and time-of-flight spectra were measured behind the lateral shield of the electron beam dump at the Final Focus Test Beam (FFTB) facility at the Stanford Linear Accelerator Center. The neutrons were produced by a 28.7 GeV electron beam hitting the aluminum beam dump of the FFTB which is housed inside a thick steel and concrete shield. The measurements were performed using an NE213 organic liquid scintillator behind different thicknesses of the concrete shield of 274, 335, and 396 cm , respectively. The neutron energy spectra between 6 and 800 MeV were obtained by unfolding the measured pulse height spectrum with the detector response function. The attenuation length of neutrons in concrete was then derived. The spectra of neutron time-of-flight between beam on dump and neutron detection by NE213 were also measured. The corresponding experimental results were simulated with the FLUKA Monte Carlo code. The experimental results show good agreement with the simulated results.

Measurements of high energy neutrons penetrated through iron shields using the Self-TOF detector and an NE213 organic liquid scintillator

Neutron energy spectra penetrated through iron shields were measured using the Self-TOF detector and an NE213 organic liquid scintillator which have been newly developed by our group at the Heavy-Ion Medical Accelerator in Chiba (HIMAC) of National Institute of Radiological Sciences (NIRS), Japan. Neutrons were generated by bombarding 400 MeV/nucleon C ion on a thick (stopping-length) copper target. The neutron spectra in the energy range from 20 to 800 MeV were obtained through the FORIST unfolding code with their response functions and compared with the MCNPX calculations combined with the LA150 cross section library. The neutron fluence measured by the NE213 detector was simulated by the track length estimator in the MCNPX, and evaluated the contribution of the room-scattered neutrons. The calculations are in fairly good agreement with the measurements. Neutron fluence attenuation lengths were obtained from the experimental results and the calculation.

Measurements of High-Energy Neutrons Penetrated Through Concrete Shields Using Self-TOF, NE213, and Activation Detectors

Neutron energy spectra penetrated through concrete shields were measured using three types of high-energy neutron detectors: the Self-TOF detector, an NE213 organic liquid scintillator, and Bi and C activation detectors, which have been newly developed by a group at the Heavy-Ion Medical Accelerator in Chiba (HIMAC) facility of the National Institute of Radiological Sciences, Japan. Neutrons were generated by bombarding 400 MeV/nucleon C ions on a thick (stopping-length) copper target. The neutron spectra were obtained through an unfolding code with their response functions and compared with LAHET and MCNPX calculations combined with the LA150 cross-section library. The calculations tend to overestimate with increasing the shielding thickness compared to the experimental results. The neutron fluence measured by the NE213 detector was simulated by the track length estimator in the MCNPX code, and the contribution of the room-scattered neutrons was evaluated. The neutron fluence attenuation length was obtained from the experiment for each detector and the calculation in the energy range of 20 to 800 MeV.

Measurements of the response functions of an NE213 organic liquid scintillator to neutrons up to [formula omitted

The neutron response functions of 12.7 cm diameter by 12.7 cm long NE213 organic liquid scintillator have been measured in the energy range from 50 to 800 MeV at the Heavy-Ion Medical Accelerator in Chiba (HIMAC). Neutrons were generated by the 800 MeV/ nucleon Si ion and 400 MeV/ nucleon C ion bombardment on a thick carbon target. Neutron energy was determined by the time-of-flight method with using the beam pick-up scintillator. The maximum light outputs were gradually increased with increasing incident neutron energy and the variation of the response functions have been observed up to 800 MeV . The experimental results show good agreement with other experimental results and the calculated values for incident neutron energy below about 200 MeV .

Development of a quasi-monoenergetic neutron field and measurements of the response function of an organic liquid scintillator for the neutron energy range from 66 to 206 MeV

A quasi-monoenergetic neutron field was developed using a thin 7Li target bombarded by protons in the energy range from 70 to 210 MeV at the RIKEN ring cyclotron facility. The neutron energy spectra were measured with an NE213 organic liquid scintillator using the TOF method. The absolute peak neutron yields were obtained by measurements of 478 keV γ-rays from 7Be nuclei produced in a 7Li target through the 7 Li( p,n) 7 Be (g.s.+0.429 MeV) reaction. Using the neutron field, the absolute values of the neutron response functions of a 12.7 cm diameter by 12.7 cm long NE213 organic liquid scintillator were measured, and were compared with calculations using a Monte Carlo code developed by Cecil et al. The measured response functions without any wall-effect events were also obtained, and compared with calcualtions using a modified Monte Carlo code. Comparisons between a measurement and a calculation both with and without any wall-effect events gave a good agreement.

Absolute measurements of the response function of an NE213 organic liquid scintillator for the neutron energy range up to 206 MeV

The absolute values of the neutron response functions of a 12.7 cm diameter by 12.7 cm long NE213 organic liquid scintillator were measured using a quasi-monoenergetic neutron field in the energy range of 66– 206 MeV via the 7Li(p,n) 7Be reaction in the ring cyclotron facility at RIKEN. The measured response functions were compared with calculations using a Monte Carlo code developed by Cecil et al. The measurements clarified that protons escaping through the scintillator wall induced by high-energy neutrons increase from 6% for 66 MeV neutrons to 35% for 206 MeV neutrons, and that this wall effect causes a difficult problem for n–γ discrimination. Measured response functions without the wall-effect events were also obtained by eliminating the escaping-proton events in the analysis, and compared with calculations using a modified Monte Carlo code. Comparisons between the measurements and calculations both with and without any wall-effect events gave a good agreement, but some discrepancy in the light output distribution could be found, mainly because the deuteron generation process was not taken into account in the calculation. The calculated efficiencies for 10 MeVee threshold, however, also gave good agreement within about 10% with the measurements.

Development of a quasi-monoenergetic neutron field using the [formula omitted](p, n) 7Be reaction in the 70–210 MeV energy range at RIKEN

A quasi-monoenergetic neutron field was developed using the 7 Li (p, n) 7Be reaction in the energy range from 70 to 210 MeV in the ring cyclotron facility at RIKEN. Neutrons were generated from a 10-mm-thick 7 Li target injected by protons accelerated to 70, 80, 90, 100, 110, 120, 135, 150, 210 MeV. The neutron energy spectra were measured with an NE213 organic liquid scintillator using the TOF method. The absolute peak neutron yields were obtained by measurements of 478 keV γ-rays from 7 Be nuclei produced in a 7 Li target through the 7 Li (p, n) 7Be (g.s.+0.429 MeV) reaction. Two relative neutron fluence monitors, which were calibrated to the absolute peak neutron fluences by the 7 Be measurement, were equipped along the neutron beam line during an irradiation experiment. This high-energy neutron field is very useful for neutron cross-section measurements, response measurements of neutron detectors, and shielding experiments.

A performance study on a phoswich detector consisting of an inner NE213 scintillator and an outer CaF 2(Eu) crystal wall

We developed a new phoswich detector. The detector consists of an inner NE213 organic liquid scintillator and an outer thin CaF 2(Eu) crystal which are coupled to a photomultiplier. The charged particles produced in the NE213 scintillator by the interaction of radiation with the detector either stop in the NE213 scintillator or pass through both the NE213 scintillator and the outer CaF 2(Eu) crystal. The fast output pulses of a few ns from the NE213 scintillator can easily be separated from the slow output pulses of about 1 μs from the outer CaF 2(Eu) scintillator. From this difference, the events that the charged particle stops inside NE213 scintillator can be separated out from the events that the charged particle escapes from the inside NE213 detector. The phoswich detector response functions for gamma rays and neutrons measured with the radioactive gamma-ray sources and the neutrons produced by a Be + Cu target bombarded by protons from the cyclotron, and compared with Monte Carlo calculations. It was found that the main characteristics of the NE213 scintillator were not degraded by assembling as a phoswich detector using the CaF 2(Eu) crystal wall. The n-γ discrimination property is slightly degraded but neutrons can be separated from gamma rays. Further we used to test the phoswich detector for neutron measurements under the intense charged particles, mainly protons, with considering the possibility of neutron detection in space crafts. It was shown that the phoswich detector is capable of detecting neutrons in the mixed field.

Absolute calibration of neutron counters on the Compact Helical System

A calibration experiment of the neutron counters of the Compact Helical System (CHS) has been carried out in order to determine the calibration factor which relates the neutron-counter output to the extended neutron source of a torus plasma. The instruments employed in the present experiment include a BF3 proportional counter, a 3He proportional counter, an NE213 organic liquid scintillator. The BF3 counter was installed at the center of the CHS torus and the other two detectors were installed outside the torus. A total of 64 toroidal angles along the magnetic axis of plasma were surveyed by the movement of a 252Cf neutron source. The poloidal cross section of the CHS plasma is elliptical in shape and rotates toroidally with the same period as that of the helical coil. The spatial distribution of 25 local point efficiencies in three poloidal cross sections with elongated orientations of 0°, 45°, and 90° were investigated in order to determine the influence of the plasma profile on the calibration factor. The shadow and scattering effects were clearly observed by the center counter when the source was located behind the helical coil. The calibration factor for the BF3 counter, obtained by averaging the point efficiencies over all the toroidal angles, was 3.6×10−4 counts per neutron, about several ten times greater than those of the counters located outside the torus. Details of the calibration setup and the analysis of experimental results are presented.