Energy Neutron Beam Research Articles

A Monte Carlo comparison of PGNAA system performance using 252Cf neutrons, 2.8-MeV neutrons and 14-MeV neutrons

Monte Carlo simulations were carried out to compare performance of a 252Cf neutron and a 14-MeV neutron-based prompt γ-ray neutron activation analysis (PGNAA) system with that of the 2.8-MeV neutron-based PGNAA system at King Fahd University of Petroleum and Minerals (KFUPM), Dhahran, Saudi Arabia. Since the energy of neutron beam used in the KFUPM PGNAA system is very close to that produced by a DD neutron generator, performance comparison between a DD and a DT neutron generator-based PGNAA system is highly desired. For the sake of comparison, the calculations were carried out for the PGNAA system with geometry similar to the KFUPM PGNAA system. These calculations were required to determine improvement in performance of the KFUPM PGNAA system if its 2.8-MeV neutron source is replaced by a 252Cf neutron source or a 14-MeV neutron source. Results of the calculations revealed that the geometry of the 252Cf neutron and the 2.8-MeV neutron-based PGNAA system are not significantly different but the geometry of the 14-MeV neutron-based system is significantly different from that of the 2.8-MeV neutron-based PGNAA system. Accordingly, the prompt γ-ray yields from the 252Cf neutron and the 2.8-MeV neutron-based PGNAA system is comparable but prompt γ-ray yields from 14-MeV neutron-based PGNAA system are about three times smaller than that from the 2.8-MeV neutron-based PGNAA system. This study has shown that performance of the 252Cf neutron-based PGNAA system is comparable with that of the 2.8-MeV neutron-based PGNAA system but the performance of the 14-MeV neutron-based PGNAA system is poorer than that of the 2.8-MeV neutron-based PGNAA system.

MCNP optimization of filtered neutron beams for calibration of the SIMPLE detector

We report an MCNP study of filtered monochromatic neutron beams of energies 25, 54 and 149 keV for response studies of a superheated droplet detector for the SIMPLE experiment. The results identify the importance of the detector temperature stabilizing water bath and the aqueous gel of the detector on the beam quality, in general agreement with recent measurements made on the thermal port of the Portuguese research reactor.

Feasibility of an epithermal neutron source for BNCT based on RFQ accelerator

The use of boron neutron capture therapy for the treatment of deep-seated tumours, such as glioblastoma multiforme, requires neutron beams of suitable energy and intensity. The analysis of the therapeutic gain shows that a high tumour control probability with sublethal dose at healthy tissues can be achieved, in most cases, by using neutron beams of a few keV energy, with a flux of about 10 9 neutrons/cm 2 s. Therapeutic neutron beams with high-spectral purity in this energy range could be produced by accelerator-based neutron sources through a suitable neutron-producing reaction. We investigate the feasibility of a solution based on a small radio frequency quadrupole for a proton beam current of 30 mA and an energy of 2 MeV. An appropriate choice of the function parameters of the RFQ (modulation, efficiency of acceleration, phase shift, etc., …) allows one to design relatively compact accelerators, which could eventually lead to setup hospital-based BNCT facilities.

A study of fast neutron beam geometry and energy distribution using triple- α reactions

Spectrometric measurement of high-energy neutrons using the methods of recoil protons and triple- α reactions have been used to determine energy of neutrons as well as the differential distribution along a coaxial high-energy neutron tube generator. A comparative study between two reaction mechanisms is introduced. The study shows that these methods can be used in measuring the absorbed dose in high-energy neutron radiotherapy fields. The merits and limitations of both techniques are indicated.

Response investigations of a TEPC in high energy proton and neutron beams using the variance method.

Results from measurements in proton and neutron beams between 68 and 174 MeV at the T. Svedberg Laboratory in Uppsala are presented. The result indicate that a TEPC might underestimate the high-energy contribution to H*(10) in cosmic radiation applications such as measurements onboard aircraft.

Measurement of neutron energy spectra from 15 to 150 MeV using stacked liquid scintillators

A multiple liquid scintillator system for measuring the energy spectrum of a neutron beam in the range 15–150 MeV is described. Two or more slabs of NE213 scintillator (13×13×7 cm 3) are stacked behind one-another and only events in which a neutron interacts in the upstream scintillator are analysed. The system is designed to minimise the escape of forward recoil protons from the detecting media. Test measurements and Monte Carlo simulations of the detector response to quasi-monoenergetic neutron beams of energies 62.5 and 97.5 MeV are presented.

Neutron polarizers based on polarized 3He

The use of nuclear-spin polarized 3He as a spin filter for low energy neutron beams is discussed and many properties of these polarizers are described. We compare this technique to other methods for polarizing neutrons of energy 0.01–100 eV. The status of a joint IUCF/NIST project for constructing transmission polarizers using both Rb spin-exchange and metastability-exchange optical pumping is presented.

Separation of the Neutron Signal from the Gamma Component in (n-gamma) Fields Using Differential Pulse Analysis Techniques with a Double Silicon Diode

An individual electronic neutron dosemeter based on a combination of a polyethylene converter with a double diode (Canberra CD-NEUT-200-DBL) has been studied. The dosemeter has been irradiated by monoenergetic neutron beams of energies from 73 keV to 2.5 MeV with dose equivalents between 0.3 and 5.7 mSv. The differential method has been applied to separate the neutron response from the gamma contribution. The energy response of the dosemeter has been studied for these neutron energies. Linearity has been studied for 1.2 MeV neutrons. Simulation of the response of this dosemeter using a Monte Carlo code agrees with the experimental results obtained and confirms an energy threshold of the order of 250 keV for neutron detection. It is inferred from simulation that the neutron dose equivalent response varies about ±50% in the energy range from 570 keV to 15 MeV, if the actual device with a 20 μm thick polyethylene converter is used.

Recombination Index of Radiation Quality of Medical High Energy Neutron Beams

Recombination index of radiation quality (RIQ) was determined in high energy neutron beams from the 660 MeV phasotron of the Joint Institute for Nuclear Research, Dubna (JINR). Measurements were performed with a high pressure ion chamber at two collecting voltages and compared with calculations considering spectra of all secondary and tertiary charged particles. The neutron beams produced on beryllium, copper and lead targets were investigated. Only minor differences between RIQ values for these beams were observed. A high decrease in RIQ, from 6 to 3.5 has been observed in the first 5 cm depth in a water phantom, followed by a rather small progressive decrease towards 3.3 ± 0.3 for depths larger than 10 cm. Laterally small changes have been observed at a given depth between values on the beam axis and outside the border of the beam.

Experimental study of modification of neutron spectrum using filters

Filter effects for continuum thermal neutron beams were experimentally studied by means of an effective energy. Be, Bi and Pb were used as filter materials to examine the energy shift of the spectrum. It was found that the effective energy of a thermal neutron beam is easily lowered into a sub-thermal region (down to 10 meV) by use of a filter system without any cooling system. The effectiveness and its applicability will be discussed in this study.

Present status, trends and needs in fast neutron therapy

Fast neutrons were introduced in cancer therapy, in the 1970s, on the basis of radiobiological arguments. After 30 years, these arguments are still valid and have not been refuted by more recent experimental data. Although neutron therapy has been applied routinely for about 25 years, there is still no general agreement concerning its value and its place among the other radiation therapy techniques. In order to be able to draw objective conclusions from the available clinical results and mainly to compare the results from the different centres in a relevant way, a consensus has to be reached on several issues: 1) a protocol for dose measurement in a homogeneous phantom in reference conditions; 2) dose computation at the level of the target volume(s) and the normal tissues at risk; 3) method of dose specification for reporting; and 4) specification of radiation quality in neutron therapy and the related RBE problems. The International Commission on Radiation Units and Measurements (ICRU) has published recommendations on Clinical Neutron Dosimetry (ICRU Report 45, 1989) which are now universally applied. As far as dose specification for reporting is concerned, ICRU recommendations for photons (ICRU Report 50, 1993) can be extended and adapted for fast neutrons. However, special care is required to take into account the tissue compositions. In fast neutron therapy, specification of radiation quality raises a particular problem because the neutron RBE, relative to gamma rays, is higher than unity (it ranges from about 2 to 5) and furthermore significantly varies with neutron beam energy. In addition, the RBE also varies with dose and biological system. In these conditions, besides the classical concept of RBE introduced jointly by the ICRP and the ICRU in 1963, the concepts of "reference RBE" and "clinical RBE" are proposed here for application in fast neutron therapy. Microdosimetry provides an adequate method to describe radiation quality, at the point of interest in the irradiated medium and in the actual irradiation conditions. From the analysis of microdosimetric spectra, a RBE value of a particular neutron beam, for a given biological system, can be predicted provided that the biological weighing function for that biological system has been obtained. In any case, correlation of the microdosimetric description of a given beam and the experimental RBE values for that beam improves the confidence in both sets of data.

A large acceptance cylindrical drift chamber detector

This paper describes a large acceptance cylindrical drift chamber detector designed and built for the study of the np → pp π − reaction at neutron beam energies in the range 500–800 MeV. Details of construction, electronics, testing, and detection efficiencies and resolutions are presented.

Ambient Dose Equivalent, Deep Dose Equivalent Index, and ICRU Sphere Depth-Dose Calculations for Neutrons from 30 to 180 MeV

Detailed depth-dose calculations were performed in the ICRU sphere for monoenergetic parallel neutron beams with energies ranging from 30 MeV to 180 MeV. Fluence-to-dose conversion coefficients were obtained for both absorbed dose and dose equivalent quantities. Calculations of dose equivalents were performed using both ICRP 21 and ICRP 60 Q-L relationships. Ambient dose equivalents, at a depth of 10mm inside the ICRU sphere, and deep dose equivalent indices are reported. The LAHET computer code was utilised to perform the energy deposition calculations due to secondary charged particles for neutron interactions above 20 MeV. Lower energy neutrons and neutron-induced photons were transported using the HMCNP code and the ENDF/B-V continuous energy cross section data library. The kerma approximation was employed to compute the absorbed doses due to the interactions of neutrons below 20 MeV. The results are compared with the limited available depth-dose data for high energy neutron beams incident on slab phantoms.

Prognostic implications of prostatespecific antigen in patients with locally advanced prostate cancer treated with high energy neutron beam therapy: Preliminary results

Serial serum prostate-specific antigen (PSA) levels were analyzed retrospectively for prognostic implications in 70 patients with locoregional (Stages B2, C, and Dl) prostate cancer who were managed with high energy neutron beam therapy. Three groups of patients were identified. Group I included 30 patients whose serum PSA level decreased to the reference range (0–4 ng/mL) following neutron therapy and remained so subsequently: 28 (93 % ) remained disease free and 2 (7 %) have failed distantly. All 30 patients (100 % ) had no evidence of locally progressive disease. This group was categorized as having a good prognosis. The mean time for serum PSA value to decline to reference range was six months; calculated mean time to achieve a stable baseline PSA was 53 ± 37 days. Follow-up period ranged from twelve to fifty-six months (median: 21 months). Group II consisted of 13 patients in whom there was an initial decrease in serum PSA to reference range followed by a subsequent increase: 6 of 13 (46 %) have no overt clinical progression of disease; 7 (54 %) have either persistent locoregional or distant metastatic disease. Follow-up period was from twelve to seventy-two months (median: 39 months). Calculated mean time to achieve stable baseline PSA for serum PSA in this group was 61 ± 21 days. Group III patients had a persistently elevated or rising serum PSA concentration. Of 27 patients in this group, only 9 (33 %) have no evidence of disease progression, while 18 patients (67%) have failed already, either locoregionally or distantly. Follow-up period ranged from twelve to sixty-nine months (median: 21 months). Mean time to achieve stable baseline of serum PSA in this cohort of patients with a poor prognosis was 108 ± 76 days. We conclude that PSA has a predictable prognostic value in patients with locally advanced prostate cancer managed with high energy neutron beam therapy. Rapid normalization of PSA after therapy indicates a good prognosis. Persistent elevation signifies either presence of persistent locoregional disease or development of distant metastases. Subsequent elevation of the serum PSA concentration after definitive therapy signals progression of prostate cancer.

Spin correlation and analyzing power measurements for neutron-proton radiative capture at Tn=183 MeV.

We have measured the spin correlation coefficient (${\mathit{C}}_{\mathit{N}\mathit{N}}$) and the neutron and proton analyzing powers (${\mathit{A}}_{\mathit{n}}$ and ${\mathit{A}}_{\mathit{p}}$) for the n\ensuremath{\rightarrow}p\ensuremath{\rightarrow}\ensuremath{\rightarrow}d\ensuremath{\gamma} reaction at a neutron beam energy of 183 MeV. Calculations of the spin correlation are particularly sensitive to the treatment of mesonic and isobaric currents. Predictions that include both explicit photon couplings to exchanged mesons and intermediate isobar states, and relativistic correction terms in the Hamiltonian, agree well with our data, thus demonstrating the quantitative accuracy of present treatments of meson-exchange currents at moderate momentum transfer (q\ensuremath{\sim}1-2 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$).

Characteristics of neutron beam generated by 500 MeV proton beam

A neutron irradiation facility was constructed at PARMS, University of Tsukuba to produce an ultrahigh energy neutron beam with a depth dose distribution superior to an x-ray beam generated by a modern linac. This neutron beam was produced from the reaction on a thick uranium target struck by a 500 MeV proton beam from the booster synchrotron of the High Energy Physics Laboratory. The percentage depth dose of this neutron beam was nearly equivalent to that of x-rays at around 20 MV and the dose rate was 15 cGy per minute. The relative biological effectiveness (RBE) of this neutron beam has been estimated using the cell inactivation effect and the HMV-I cell line. The survival curve of cells after neutron irradiation has a shoulder with n and Dq of 8 and 2.3 Gy, respectively. The RBE value at the 10 −2 survival level for the present neutron beam as compared with 137Cs gamma rays was 1.24. The results suggest that the biological effects of ultrahigh energy neutrons are not large enough to be useful, although the depth dose distribution of neutrons can be superior to that of high energy linac x-rays.

Quick polarization analyzer (QPAN)

A high count rate polarimeter for the measurement and monitoring of the polarization of an intermediate energy neutron beam has been developed. The device, QPAN, consists of a double arm telescope with adjustable copper absorbers. The asymmetry of the protons scattered from the liquid hydrogen (LH 2) target is calculated from the count differential between two arms, positioned above and below the beam.

Time-Resolved Microdosimetry in a Quasi-Monoenergetic Neutron Beam

Timing characteristics of commercial Rossi-type proportional counters operating at low gas pressures were studied in a pulsed neutron beam of nominal energy 63 MeV. The correlation between electron drift and counter dimensions is demonstrated from TOF measurements performed in normal and helix modes. By identifying each registered pulse height event with its own time-of-flight, it is shown that the timing response is masked by amplitude walk derived in the time pick-off. The inherent response of the counter in helix mode is revealed after accounting for time slewing and compares favourably with that of an NE213 liquid scintillator. Distinct structure associated with the incident energy spectrum is discernible and enables the unambiguous selection of energy deposition events resulting from neutrons of the nominal energy.

Advances in treatment planning dosimetry for a high energy neutron beam

Before starting the clinical programme, a series of physical measurements were made using the Clatterbridge high energy neutron facility. These consisted of measurements made under standard conditions, e.g. with square fields, full scatter conditions and perpendicular beam incidence. Further measurements have now been performed to include various clinically relevant non-standard conditions. These included the effects of field shape, backscatter, oblique incidence, bolus and beam blocking on dose distributions.

A Monte Carlo Investigation of the Dosimetric Properties of Monoenergetic Neutron Beams for Neutron Capture Therapy

A Monte Carlo simulation study has been carried out to investigate the suitability of neutron beams of various energies for therapeutic efficacy in boron neutron capture therapy. The dosimetric properties of unidirectional, monoenergetic neutron beams of varying diameters in two different phantoms (a right-circular cylinder and an ellipsoid) made of brain-equivalent material were examined. The source diameter was varied from 0.0 to 20.0 cm; neutron energies ranged from 0.025 eV up to 800 keV, the maximum neutron energy generated by a tandem cascade accelerator using 2.5-MeV protons in a 7Li(p,n)7Be reaction. Such a device is currently under investigation for use as a neutron source for boron neutron capture therapy. The simulation studies indicate that the maximum effective treatment depth (advantage depth) in the brain is 10.0 cm and is obtainable with a 10-keV neutron beam. A useful range of energies, defined as those neutron energies capable of effectively treating to a depth of 7 cm in brain tissue, is found to be 4.0 eV to 40.0 keV. Beam size is shown not to affect advantage depth as long as the entire phantom volume is used in determining this depth. Dose distribution in directions parallel to and perpendicular to the beam direction are shown to illustrate this phenomenon graphically as well as to illustrate the differences in advantage depth and advantage ratio and the contribution of individual dose components to tumor dose caused by the geometric differences in phantom shape.