Measurements of the neutron yields from 7Li(p,n)7Be reaction (thick target) with incident energies from 1.885 to 2.0 MeV

Using a Tandem Pelletron accelerator to produce a thermal neutron beam for detector testing purposes

Active thermal neutron detectors are used in a wide range of measuring devices in medicine, industry and research. For many applications, the long-term stability of these devices is crucial, so that very well controlled neutron fields are needed to perform calibrations and repeatability tests. A way to achieve such reference neutron fields, relying on a 3 MV Tandem Pelletron accelerator available at the CNA (Seville, Spain), is reported here. This paper shows thermal neutron field production and reproducibility characteristics over few days.

Revisiting the (7)Li(p,n)(7)Be reaction near threshold

In this work we review all the available experimental neutron data for the (7)Li(p,n) reaction near threshold which is necessary to obtain an accurate source model for Monte Carlo simulations in Boron Neutron Capture Therapy. Scattered published experimental results such as cross sections, differential neutron yields and total yields were collected and analyzed, exploring the sensitivity of the fitting parameters to the different possible variables and deriving a consistent working set of parameters to evaluate the neutron source near threshold.

High-power liquid-lithium jet target for neutron production

A compact liquid-lithium target (LiLiT) was built and tested with a high-power electron gun at the Soreq Nuclear Research Center. The lithium target, to be bombarded by the high-intensity proton beam of the Soreq Applied Research Accelerator Facility (SARAF), will constitute an intense source of neutrons produced by the (7)Li(p,n)(7)Be reaction for nuclear astrophysics research and as a pilot setup for accelerator-based Boron Neutron Capture Therapy. The liquid-lithium jet target acts both as neutron-producing target and beam dump by removing the beam thermal power (>5 kW, >1 MW/cm(3)) with fast transport. The target was designed based on a thermal model, accompanied by a detailed calculation of the (7)Li(p,n) neutron yield, energy distribution, and angular distribution. Liquid lithium is circulated through the target loop at ~200 °C and generates a stable 1.5 mm-thick film flowing at a velocity up to 7 m/s onto a concave supporting wall. Electron beam irradiation demonstrated that the liquid-lithium target can dissipate electron power areal densities of >4 kW/cm(2) and volume power density of ~2 MW/cm(3) at a lithium flow of ~4 m/s while maintaining stable temperature and vacuum conditions. The LiLiT setup is presently in online commissioning stage for high-intensity proton beam irradiation (1.91-2.5 MeV, 1-2 mA) at SARAF.

Development of a low-energy monoenergetic neutron source for applications in low-dose radiobiological and radiochemical research

The McMaster University 3 MV KN Van de Graff accelerator facility primarily dedicated to in vivo neutron activation measurements has been used to produce moderate dose rates of monoenergetic fast neutrons of energy ranging from 150 to 600 keV with a small energy spread of about 25 keV (1sigma width of Gaussian) by bombarding thin lithium targets with 2.00-2.40 MeV protons. The calculated dose rate of the monoenergetic neutrons produced using thin lithium targets as functions of beam energy, target thickness, lab angle relative to beam direction, and the solid angle subtended by the sample with the target has also been reported.

Lithium target performance evaluation for low-energy accelerator-based in vivo measurements using gamma spectroscopy

The operating conditions at McMaster KN Van de Graaf accelerator have been optimized to produce neutrons via the (7)Li(p, n)(7)Be reaction for in vivo neutron activation analysis. In a number of earlier studies (development of an accelerator based system for in vivo neutron activation analysis measurements of manganese in humans, Ph.D. Thesis, McMaster University, Hamilton, ON, Canada; Appl. Radiat. Isot. 53 (2000) 657; in vivo measurement of some trace elements in human Bone, Ph.D. Thesis. McMaster University, Hamilton, ON, Canada), a significant discrepancy between the experimental and the calculated neutron doses has been pointed out. The hypotheses formulated in the above references to explain the deviation of the experimental results from analytical calculations, have been tested experimentally. The performance of the lithium target for neutron production has been evaluated by measuring the (7)Be activity produced as a result of (p, n) interaction with (7)Li. In contradiction to the formulated hypotheses, lithium target performance was found to be mainly affected by inefficient target cooling and the presence of oxides layer on target surface. An appropriate choice of these parameters resulted in neutron yields same as predicated by analytical calculations.

Monte Carlo design study for in vivo bone aluminum measurement using a low energy accelerator beam

The need for aluminum monitoring exists in occupational medicine, as well as for the clinical monitoring of patients with renal dysfunction. After the development of an appropriate neutron source card, Monte Carlo simulations were made to design moderator/reflector assembly consisting of a polyethylene moderator (2 cm) and graphite reflector (30 cm), surrounded by a boronated (5%) wax (20 cm) and lead (1 cm) shield. This design should allow for the bone aluminum measurement of healthy subjects, but prior to that detailed microdosimetry is necessary to address a noticed disagreement between theoretical and experimental dose data.

Study of moderator thickness for an accelerator-based neutron irradiation facility for boron neutron capture therapy using the 7Li(p,n) reaction near threshold

Accelerator neutron sources for epithermal neutron capture therapy utilizing the 7Li(p,n) nuclear reaction will require a moderator even in the threshold range of 1.89 to 1.95 MeV. The corresponding neutron energies allow for a thinner reflector and moderator, with less reduction of the epithermal flux. To estimate the useful neutron flux within the epithermal range (4 eV-40 keV), the optimal thickness of a heavy water moderator was determined using the two-dimensional neutron transport S(N) code DORT. Optimized results are compared with the epithermal fluxes reported for the higher proton energy range, and are found to be inferior. Thus, this study supports the 2.5-3.0 MeV proton energy range for accelerator boron neutron capture therapy.