Laser Compton scattering experiments were carried out at the Idaho Accelerator Center (IAC) using the 5-44 MeV linear accelerator (LINAC). LCS X-rays were generated using a 50 ps electron beam colliding with a 4 GW, 250 ps, phase locked Nd:YAG laser. 60 Hz x-rays bursts resulting from the approximate head-on collision of relativistic electrons with the high peak power laser second (532 nm) and fourth harmonic (266 nm) lines were generated respectively. LCS x-rays were used for x-ray fluorescence (XRF) experiments and x-ray transmission/absorption measurements in several foils of different atomic numbers and thicknesses including neodymium (Nd), lead (Pb) and bismuth (Bi). One of the purposes of this work is to use LCS x-rays as a non-invasive means for material identification and quantification. Results from our experiments showed that because of its relatively low spectral bandwidth, energy tunability and low bremsstrahlung background, LCS could be a useful x-ray source for hybrid k-edge densitometry.

A series of experiments dedicated to the monitoring of the reactivity of Accelerator driven subcritical systems were carried out in the thermal subassembly of the Idaho State University. First, it was shown that the pulsed neutron source techniques can be utilized in a thermal subassembly coupled to an electronic linear accelerator in spite of the strong gamma field generated after every accelerator shot. Second, reactivity estimates using the area-ratio method and the beam trip one for a far subcritical level are consistent before applying calculated correction.

An S-band 20 MeV electron linear accelerator formerly used for medical applications has been recommissioned to provide a wide range of photonuclear activation studies as well as various radiation effects on biological and microelectronic systems. Four radiation effect applications involving the electron/photon beams are described. Photonuclear activation of a stable isotope of oxygen provides an active means of characterizing polymer degradation. Biological irradiations of microorganisms including bacteria were used to study total dose and dose-rate effects on survivability and the adaptation of these organisms to repeated exposures. Microelectronic devices including bipolar junction transistors (BJTs) and diodes were irradiated to study photocurrent from these devices as a function of peak dose rate with comparisons to computer modeling results. In addition, the 20 MeV linac may easily be converted to a medium energy neutron source which has been used to study neutron damage effects on transistors.

Laser-Compton scattering (LCS) experiments were carried out at the Idaho Accelerator Center (ICA) using the 5 ns (FWHM) and 22 MeV electron beam. The electron beam was brought to an approximate head-on collision with a 7 ns (FWHM), 10 Hz, 29 MW peak power Nd:YAG laser. We observed clear and narrow X-ray peaks resulting from the interaction of relativistic electrons with the 532 nm Nd:YAG laser second harmonic line on top of a very low bremsstrahlung background. We have developed a method of using LCS as a non-intercepting electron beam monitor. Unlike the method used by Leemans et al. (1996), our method focused on the variation of the shape of the LCS spectrum rather than the LCS intensity as a function of the observation angle in order to extract the electron beam parameters at the interaction region. The electron beam parameters were determined by making simultaneous fits to spectra taken across the LCS X-ray cone. We also used the variation of LCS X-ray peak energy and spectral width as a function of the detector angles to determine the electron beam angular spread, and direction and compared the results to the previous method. Experimental data show that in addition to being viewed as potential bright, tunable and monochromatic X-ray source, LCS can provide important information on electron beam pulse length, direction, energy, angular, and energy spread. Since the quality of LCS X-ray peaks, such as degree of monochromaticity, peak energy and flux, depends strongly on the electron beam parameters, LCS can therefore be viewed as an important non-destructive means for electron beam diagnostics.

Laser-Compton scattering (LCS) experiments were carried out at the Idaho Accelerator Center using the 5 ns (FWHM) and 22 MeV electron beam. The electron beam was brought to an approximate head-on collision with a 29 MW, 7 ns (FWHM), 10 Hz Nd:YAG laser. Clear and narrow x-ray peaks resulting from the interaction of relativistic electrons with the Nd:YAG laser second harmonic line at 532 nm were observed. We have developed a relatively new method of using LCS as a nonintercepting electron beam monitor. Our method focused on the variation of the shape of the LCS spectrum rather than the LCS intensity as a function of the observation angle in order to extract the electron beam parameters at the interaction region. The electron beam parameters were determined by making simultaneous fits to spectra taken across the LCS x-ray cone. This scan method allowed us also to determine the variation of LCS x-ray peak energies and spectral widths as a function of the detector angles. Experimental data show that in addition to being viewed as a potential bright, tunable, and quasimonochromatic x-ray source, LCS can provide important information on the electron beam pulse length, direction, energy, angular and energy spread. Since the quality of LCS x-ray peaks, such as degree of monochromaticity, peak energy and flux, depends strongly on the electron beam parameters, LCS can therefore be viewed as an important nondestructive tool for electron beam diagnostics.

The Idaho National Laboratory has developed prototype shielded nuclear material detection systems based on pulsed photonuclear assessment (PPA) techniques for the inspection of cargo containers. During this work, increased nuclear material detection capabilities have been demonstrated at higher electron beam energies than those allowed by federal regulations for cargo inspection. This paper gives a general overview of a nuclear material detection system, the PPA technique and discusses the benefits of using these higher energies. This paper also includes a summary of the numerical and test results from LINAC operations up to 24MeV and discusses some of the federal energy limitations associated with cargo inspection.

The technique of charged particle radiography has been developed and proven with 800 MeV protons at LANSCE and 24 GeV protons at the AGS. Recent work at Los Alamos National Laboratory in collaboration with the Idaho Accelerator Center has extended this diagnostic technique to electron radiography through the development of an inexpensive and portable electron radiography system. This system has been designed to use 30 MeV electrons to radiograph thin static and dynamic systems. The system consists of a 30 MeV electron linear accelerator coupled to a quadrupole lens magnifier constructed from permanent magnet quadrupoles. The design features and operational characteristics of this radiography system are presented as well as the expected radiographic performance parameters.

High intensity x-ray beams are used in a wide variety of applications in solid-state physics, medicine, biology and material sciences. Synchrotron radiation (SR) is currently the primary, high-quality x-ray source that satisfies both brilliance and tunability. The high cost, large size and low x-ray energies of SR facilities, however, are serious limitations. Alternatively, "novel" x-ray sources are now possible due to new small linear accelerator (LINAC) technology, such as improved beam emittance, low background, sub-Picosecond beam pulses, high beam stability and higher repetition rate. These sources all stem from processes that produce Radiation from relativistic Electron beams in (crystalline) Periodic Structures (REPS), or the periodic "structure" of laser light. REPS x-ray sources are serious candidates for bright, compact, portable, monochromatic, and tunable x-ray sources with varying degrees of polarization and coherence. Despite the discovery and early research into these sources over the past 25 years, these sources are still in their infancy. Experimental and theoretical research are still urgently needed to answer fundamental questions about the practical and ultimate limits of their brightness, mono-chromaticity etc. We present experimental results and theoretical comparisons for three exotic REPS sources. These are Laser-Compton Scattering (LCS), Channeling Radiation (CR) and Parametric X-Radiation (PXR).

Laser-Compton scattering (LCS) experiments were carried out at the Idaho Accelerator Center (IAC). Sharp monochromatic X-ray lines were observed which result from the interaction of the electron beam with the laser optical photons. The back-scattered photons are kinematically boosted to keV X-ray energies. The X-rays were generated by colliding a 20-22 MeV, 5-20 ns electron beam with a 100 MW, 7 ns Nd:YAG laser. We observed low background, sharp LCS X-ray spectral peaks resulting from the interaction of the electron beam with the Nd:YAG laser fundamental and second harmonic lines (1064 and 532 nm). The LCS X-ray energy lines and energy deviations were measured as a function of the electron beam energy and energy-spread respectively. The experimental results showed good agreement with the predicted values. Because LCS X-rays are monochromatic, with energies that are easily tunable, have the same polarization as the laser, and the same time structure as that of the electron beam, LCS could be used as a unique X-ray source with a broad range of applications.

The Idaho Accelerator Center (IAC) has developed new techniques for Positron Annihilation Spectroscopy (PAS) using highly penetrating gamma-rays to create positrons inside the material via pair production. gamma-Ray induced positron annihilation spectroscopy can provide highly penetrating probes for material characterization and defect analysis. Bremsstrahlung beams from small, pulsed electron Linacs (6 MeV) have been used to bombard the materials to generate positrons, which annihilate with the material electrons emitting 511 keV radiation. We have also synchronized bremsstrahlung pulses with laser irradiation pulses to study dynamic structural changes in material. In addition, we have developed another method using (p,gamma) reactions from a 2 MeV proton beam, which induce coincident gamma-rays to perform positron life-time spectroscopy. We have showed the feasibility of extending PAS into thick samples and a wide variety of materials and industrial applications.

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A new nondestructive accelerator based x-ray fluorescence (AXRF) approach has been developed to identify heavy metals in large-volume samples. Such samples are an important part of the process and waste streams of U.S Department of Energy sites, as well as other industries such as mining and milling. Distributions of heavy metal impurities in these process and waste samples can range from homogeneous to highly inhomogeneous, and non-destructive assays and imaging that can address both are urgently needed. Our approach is based on using high-energy, pulsed bremsstrahlung beams (3-6.5 MeV) from small electron accelerators to produce K-shell atomic fluorescence x-rays. In addition we exploit pair-production, Compton scattering and x-ray transmission measurements from these beams to probe locations of high density and high atomic number. The excellent penetrability of these beams allows assays and images for soil-like samples at least 15 g/cm(2) thick, with elemental impurities of atomic number greater than approximately 50. Fluorescence yield of a variety of targets was measured as a function of impurity atomic number, impurity homogeneity, and sample thickness. We report on actual and potential detection limits of heavy metal impurities in a soil matrix for a variety of samples, and on the potential for imaging, using AXRF and these related probes.

LCS experiments were carried out at the Idaho Accelerator Center (IAC); sharp monochromatic x-ray lines were observed. These are produced using the so-called inverse Compton effect, whereby optical laser photons are collided with a relativistic electron beam. The back-scattered photons are then kinematically boosted to keV x-ray energies. We have first demonstrated these beams using a 20 MeV electron beam collided with a 100 MW, 7 ns Nd:YAG laser. We observed narrow LCS x-ray spectral peaks resulting from the interaction of the electron beam with the Nd:YAG laser second harmonic (532 run). The LCS x-ray energy lines and energy deviations were measured as a function of the electron beam energy and energy-spread respectively. The results showed good agreement with the predicted values. LCS could provide an excellent probe of electron beam energy, energy spread, transverse and longitudinal distribution and direction.

Laser-Compton scattering (LCS) experiments were carried out at the Idaho Accelerator Center. A 20MeV electron beam was brought to a head-on collision with a 100MW 7ns Nd:YAG laser. We observed clear narrow LCS X-ray spectral peaks resulting from the interaction of the electron beam with the two Nd:YAG laser photon lines of 1064 and 532nm. The LCS X-ray energy lines and widths were measured as a function of the electron beam energy and energy spread, respectively. The results recorded showed good agreement with the predicted values.

Thick samples of materials have been investigated by the in situ production of positrons arising from β+ decay of neutron deficient positron emitting nuclei photo-induced by high energy γ rays. The Idaho State University–Idaho Accelerator Center (ISU–IAC) possesses an electron LINAC that produces 10–20MeV bremsstrahlung photons when a tungsten target is bombarded with the electron beam. These γ photons induce positron active radio-nuclei in the sample by means of photonuclear reactions. The radio-nuclei subsequently β+ decay via a positron within the sample which can be up to several inches thick. Materials that undergo such positron emitting excitation include most of the metals and semi-conducting elements. Once the positrons are produced within the material they diffuse and thermalize in the normal manner seeking out defects and vacancies deep within the material and further produce the characteristic Doppler broadened annihilation spectra dependent on defect type and environment. As examples of this technique, data are presented for a set of fatigued stainless steels and an aluminum alloy under heat treated aging. Possible applications as a field deployable diagnostic technique will be discussed.

Near-threshold boron neutron capture therapy (BNCT) is an accelerator-based concept that produces neutrons from thick lithium targets using proton beam energies only tens of keV above the Li-7(p,n)Be-7 reaction threshold. Proton energies in this range lead to lower neutron yields than a higher proton energy, such as 2.5 MeV, but lower energy neutrons are produced and hence less moderation is required. This allows thinner moderators that place the patient closer to the neutron source. A summary is presented here of calculations and experiments that have been performed that demonstrate the feasibility of near-threshold neutron sources for BNCT. A model for predicting near-threshold differential neutron yields from thick targets of lithium metal and lithium compounds was developed. Neutron yields from this model were used as neutron sources for Monte Carlo (MCNP) simulations of a head phantom. Calculated dose components were experimentally verified using an acrylic phantom. Initial dose calculations using treatment planning software, which indicate near-threshold neutron sources are competitive with existing reactor BNCT beams, are also presented.