Temperature and magnetic field dependent longitudinal spin relaxation in nitrogen-vacancy ensembles in diamond

We present an experimental study of the longitudinal electron-spin relaxation time (T1) of negatively charged nitrogen-vacancy (NV) ensembles in diamond. T1 was studied as a function of temperature from 5 to 475 K and magnetic field from 0 to 630 G for several samples with various NV and nitrogen concentrations. Our studies reveal three processes responsible for T1 relaxation. Above room temperature, a two-phonon Raman process dominates, and below, we observe an Orbach-type process with an activation energy, 73(4) meV, which closely matches the local vibrational modes of the NV center. At yet lower temperatures, sample dependent cross relaxation processes dominate, resulting in temperature independent values of T1, from ms to minutes. The value of T1 in this limit depends sensitively on magnetic field and can be tuned by more than an order of magnitude.Comment: 5 pages, 3 figures, and 3 pages of supplemental material with additional figure

A novel method for the absolute fluorescence yield measurement by AIRFLY

One of the goals of the AIRFLY (AIR FLuorescence Yield) experiment is to measure the absolute fluorescence yield induced by electrons in air to better than 10% precision. We introduce a new technique for measurement of the absolute fluorescence yield of the 337 nm line that has the advantage of reducing the systematic uncertainty due to the detector calibration. The principle is to compare the measured fluorescence yield to a well known process - the Cerenkov emission. Preliminary measurements taken in the BFT (Beam Test Facility) in Frascati, Italy with 350 MeV electrons are presented. Beam tests in the Argonne Wakefield Accelerator at the Argonne National Laboratory, USA with 14 MeV electrons have also shown that this technique can be applied at lower energies.Comment: presented at the 5th Fluorescence Workshop, El Escorial - Madrid, Spain, 16 - 20 September 200

Temperature and Humidity Dependence of Air Fluorescence Yield measured by AIRFLY

The fluorescence detection of ultra high energy cosmic rays requires a detailed knowledge of the fluorescence light emission from nitrogen molecules over a wide range of atmospheric parameters, corresponding to altitudes typical of the cosmic ray shower development in the atmosphere. We have studied the temperature and humidity dependence of the fluorescence light spectrum excited by MeV electrons in air. Results for the 313.6 nm, 337.1 nm, 353.7 nm and 391.4 nm bands are reported in this paper. We found that the temperature and humidity dependence of the quenching process changes the fluorescence yield by a sizeable amount (up to 20%) and its effect must be included for a precise estimation of the energy of ultra high energy cosmic rays.Comment: presented at the 5th Fluorescence Workshop, El Escorial - Madrid, Spain, 16 - 20 September 2007, to appear in Nuclear Instruments and Methods

Beam Transport Testing for the Production Accelerator Arrangement

This describes the beam transfer system about the electron beam into the target

Hydrogen atoms in radiolysis of liquids, solids and ordered systems: Zeolites and mesoporous solids

Hydrogen atoms are ubiquitous species in radiolysis of many liquid and solid systems. They serve a very important role in passivation of solid-state defects in silica-based devices and there is concern about the role of radiolytic generation of molecular hydrogen in radioactive waste storage. The authors have made extensive studies of H atoms in water, ice and amorphous silica using conventional and time-resolved magnetic resonance. H atoms are exquisite probes of reaction dynamics and phase structure in these systems. Furthermore, via the study of Chemically Induced Dynamic Electron Polarization (CIDEP), additional insights into the mechanisms of radiolytic generation of H atoms and their fate can be obtained. With this considerable experience they embarked on the study of H atoms in zeolites and mesoporous solids to address the following questions: (1) What is the source of H atoms--bound hydroxyls or confined water? (2) Do the H atom dynamics in the water-saturated powders exhibit kinetics and spin relaxation that is similar to that in bulk silica, liquid water or ice? (3) What are the formation and destruction pathways of H atoms? This could be important for understanding radiolysis in silica-water systems, e.g., nuclear waste

Radiation effects on transport and bubble formation in silicate glasses

Advanced Electron Paramagnetic Resonance spectroscopy (pulsed EPR, time-resolved EPR, high-frequency EPR, ENDOR) has been used to structurally characterize metastable point defects in irradiated alkali borate, silicate, and borosilicate glasses and to study mobile interstitial H atoms. In addition, the yield of radiolytic oxygen has been determined by outgassing. Several mechanisms for the defect formation in oxide glasses have been established