Investigation of a fibre-coupled beryllium oxide (BeO) ceramic luminescence dosimetry system

The purpose of this study is to investigate the potential use of a beryllium oxide (BeO) ceramic as a radioluminescence (RL) and optically stimulated luminescence (OSL) probe material for fibre-coupled luminescence dosimetry. A portable dosimetry system, named RL/OSL BeO FOD was developed, consisting of a 1 mm diameter, 1 mm long BeO ceramic cylinder coupled to a silica/silica optical fibre. The reader measures the RL signal and also uses a 450 nm laser diode to stimulate the BeO ceramic. A second background optical fibre is used to remove the stem effect. The RL/OSL BeO FOD was characterised in a solid water phantom, using a 6 MV x-ray beam. The RL was found to be reproducible and have a linear response to doses ranging from 30 cGy–15 Gy and dose rates from 100 cGy/min – 600 cGy/min. The OSL response was linear to doses of 10 Gy, becoming supralinear at higher doses. Measured percentage depth curves using the RL/OSL BeO FOD agreed with those measured using an IC15 ion chamber to within 5%, beyond the build up region. It was also found that the RL from BeO ceramic is unaffected by the delivered dose to the probe and hence, it remains constant for a given dose-rate. The insensitivity of the RL to accumulated dose makes BeO ceramic potentially capable of accurate dose-rate measurements without any corrections for the accumulated dose. This study demonstrates the feasibility of BeO ceramic as a versatile fibre-coupled luminescence dosimeter probe.     

Thermoluminescence characteristics of Na3 SO4 Cl:X (X=Ce,Dy, Mn) phosphor

In the present paper Na₃SO₄Cl:Ce, Na₃SO₄Cl:Dy, Na₃SO₄Cl:Mn, of Na₃SO₄Cl:Ce, Dy and Na₃SO₄Cl:Ce, Mn phosphor were synthesized by the wet chemical method. Thermoluminescence (TL) characteristics of Na₃SO₄Cl:Ce, Na₃SO₄Cl:Dy, Na₃SO₄Cl:Mn, Na₃SO₄Cl:Ce, Dy and Na₃SO₄Cl:Ce, Mn phosphors were studied for 5 Gy γ-ray dose. In TL glow curve, two peaks have been observed at 129°C and 224°C for different concentrations of Ce and Dy, whereas Mn peaks at 212°C. The same host is also tried for Ce, Dy (peaks at 126, 219) and Ce, Mn (248°C). A significant single peak is observed in the case of Na₃SO₄Cl:Mn and Na₃SO₄Cl:Ce, Mn. This may be due to the effect of activators. It is found that intensity tends to be increase with increased concentrations of the activators. The TL glow curves of the phosphors have been recorded and irradiated at a rate of 0.39 kGy h^?1 for 5 Gy γ-rays dose. It is also found that all the phosphors are less sensitive as compared with Thermoluminescence dosimetry-CaSO₄: Dy for the same γ-rays dose. The paper discuses the preliminary TL characteristics and effect of γ-rays on Na₃SO₄Cl:Ce, Na₃SO₄Cl:Dy, Na₃SO₄Cl:Mn, Na₃SO₄Cl:Ce, Dy and Na₃SO₄Cl:Ce, Mn phosphors.     

Response of HD-V2 radiochromic film to argon ions

A two-dimensional dose detector for ion beam is required in many high energy density physics experiments. As a solid detector, the GAFChromic film offers a good spatial resolution and dosimetric accuracy. For an absolute dose measurement, the relative effectiveness, which represents the darkening efficiency of the film to a radiation source, needs to be taken into consideration. In this contribution, the dose-response of HD-V2 to argon ions is presented for the first time. The calibration was taken over the dose range of 65 Gy-660 Gy with 8-keV argon ions. The response of net optical density is from 0.01 to 0.05. Triple-color dose-response functions are derived. The relative effectiveness for the argon ion beams is about 5%, much lower than that of protons and carbon ions. To explain this effect, the inactivation probability based on track theory of ion bombardment is proposed. Furthermore, a theoretical prediction of the relative effectiveness for single ion is presented, showing the dependence of the darkening efficiency on the atomic number and the incident energy of ions.     

Sonochemical dosimetry: A comparative study of Weissler,Fricke and terephthalic acid methods

Acoustic cavitation and sonochemical reactions play a significant role in various applications of ultrasound. A number of dosimetry methods are in practice to quantify the amount of radicals generated by acoustic cavitation. In this study, hydroxyl radical (OH) yields measured by Weissler, Fricke and terephthalic acid dosimetry methods have been compared to evaluate the validities of these methods using a 490 kHz high frequency sonochemical reactor. The OH yields obtained after 5 min sonication at 490 kHz from Weissler and Fricke dosimetries were 200 µM and 289 µM, respectively. Whereas, the OH yield was found to be very low (8 µM) when terephthalic acid dosimetry was used under similar experimental conditions. While the results agree with those reported by Iida et al. (Microchem. J., 80 (2005) 159), further mechanistic details and interfering reactions have been discussed in this study. For example, the amount of OH determined by the Weissler and Fricke methods may have some uncertainty due to the formation of HO₂ in the presence of oxygen. In order to account for the major discrepancy observed with the terephthalic acid dosimetry method, high performance liquid chromatography (HPLC) analysis was performed, where two additional products other than 2-hydroxy terephthalic acid were observed. Electrospray ionization mass spectrometry (ESI-MS) analysis showed the formation of 2,5-dihydroxyterephthalic acid as one of the by-products along with other unidentified by-products. Despite the formation of additional products consuming OH, the reason for a very low OH yield obtained by this dosimetry could not be justified, questioning the applicability of this method, which has been used to quantify OH yields generated not only by acoustic cavitation, but also by other processes such as γ-radiolysis. The authors are hoping that this Opinion Paper may initiate further discussion among researchers working in sonochemistry area that could help resolve the uncertainties around using these dosimetry methods.     

A Conversation with Robert F. Christy – Part II

Robert F. Christy, Institute Professor of Theoretical Physics Emeritus at Caltech, recalls his wartime work at Los Alamos on the critical assembly for the plutonium bomb (“the Christy bomb”); the Alamogordo test, July 16, 1945; the postwar concerns of ALAS (Association of Los Alamos Scientists); his brief return to the University of Chicago and move to Caltech; friendship with and later alienation from Edward Teller; work with Charles and Tommy Lauritsen and William A. Fowler in Caltech’s Kellogg Radiation Laboratory; Freeman Dyson’s Orion Project; work on the meson and RR Lyrae stars; fellowship at Cambridge University; 1950s Vista Project at Caltech; his opposition to the Strategic Defense Initiative; and his post-retirement work for the National Research Council’s Committee on Dosimetry and on inertial-confinement fusion.     

固体核径迹探测器的刻度

为了测量在神舟飞船返回舱内由空间重电离粒子引起的辐射剂量，采用了固体核径迹探测器CR-39来测量飞船飞行期间，返回舱内由重电离粒子引起的能量沉积. 本文介绍了CR-39探测器对能量沉积的响应的刻度.     

Optically Induced Effects in the Thermoluminescence of Dosimetric Anion-Defective Corundum Crystals

This paper considers the influence of light fluxes in the 200–600-nm spectral range on the thermally stimulated luminescence (TL) of TLD-500 radiation detectors based on anion-defective corundum crystals. It has been shown that the luminescent-storing action of light in the above spectral range is due to the optical ionization of F-centers and electronic trapping centers of carriers responsible for the dosimetric peak at 450 K and TL at higher temperatures. The features of the dosimetric information distortion depending on the initial state of population of deep traps and the spectral composition and power of optical radiation are discussed.     

Slow and fast neutron detection using bare CN-85 cellulose nitrate detectors

We report on the application of CN-85 cellulose nitrate track detectors to neutron dosimetry. CN-85 has the ability to register proton tracks and therefore can be used for neutron detection via neutron-induced recoil events within the detector matrix. The CN-85 detectors were used to study the distribution of the weakly moderated spallation neutrons, produced in the irradiation of an extended Pb-target with 1 GeV protons. The results obtained are compared with Monte Carlo simulations using the MCNPX-2.5.c code. The thermal and epithermal neutrons can also be detected by CN-85 detectors without the need for a neutron converter via the ¹⁴N(n, p)¹⁴C reaction, which has a positive Q-value of 626 keV.     

Bismuth-fission detectors for high energy nucleons: II. Proton and neutron responses

A critical requirement for the ²⁰⁹Bi-fission detector is the knowledge of its response as a function of energy for both neutrons and protons. For this reason, stacks of ²⁰⁹Bi-fission detectors have been exposed to proton beams of 100 and 150 MeV at the Paul Sherrer Institute. Similar stacks have been exposed to neutron beams of 100 and 160 MeV at the Svedberg Laboratory from Uppsala University. The calibrations data with neutrons have been compared with those obtained with protons of the same energies. This comparison has proved that the response of ²⁰⁹Bi-fission detector for neutrons is two to three times smaller than that for protons at least in the range of nucleon energy up to 150 MeV.     

Stabilization of Ion-Radicals in the Structure of Calcium Sulfite

Using the EPR- and IR-spectroscopy methods, we studied the conditions of formation of stable ion-radicals in the structure of calcium sulfite and determined the limits of their stability. We detected and identified the ion-radicals SO ₂ ⁻ with g(iso) = 2.0055 in the initial substances, two types of thermally induced SO ₂ ⁻ (with g₁ = 2.0093, g₂ = 2.0045, and g₃ = 2.0020, and g₁ = 2.0104, g₂ = 2.0049, and g₃ = 2.0018) when the substance was heated, and three types of mechanically induced SO ₃ ⁻ (with g_⊥ = 2.0036 and g_‖ = 2.0022, with g(iso) = 2.0033 and ΔH = 0.1 mT and with g(iso) = 2.0031 and ΔH = 0.33 mT) when the substance was ground up. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 3, pp. 391–396, May–June, 2005.