Escape of photons and electrons from an HPGe detector at 81 keV

Escape of Ge K x‐rays, Compton‐scattered incident radiation and photoelectrons from an HPGe detector was investigated for 81 keV incident photons. All three escape mechanisms were observed in the same experiment. Experimental escape fractions were compared with the results from Monte Carlo simulations. Good agreement was obtained for the escape of photons. However, the simulations underestimated the escape of photoelectrons. Copyright © 2005 John Wiley & Sons, Ltd.     

An experimental study on cross-section ratio of coherent to incoherent scattering for 145 keV incident gamma photons

The coherent (Rayleigh) to incoherent (Compton) scattering cross-section ratio of elements, in the range 6 ≤ Z ≤ 82, are determined experimentally for 145 keV incident gamma photons. An HPGe (High purity germanium) semiconductor detector is employed, at scattering angle of 50°, 70° and 90°, to record the spectra originating from interactions of incident gamma photons with the target under investigation. The intensity ratio of Rayleigh to Compton scattered peaks observed in the recorded spectra, and corrected for photo-peak efficiency of gamma detector and absorption of photons in the target and air, along with the other required parameters provides the differential cross-section ratio. The measured values of cross-section ratio are found to agree with theoretical predictions (corresponding to 4.939, 6.704 and 8.264 Å⁻¹ photon momentum transfer) based upon non-relativistic form factor, relativistic form factor, modified form factor and S-matrix theory.     

4H-SiC探测器的γ辐照影响研究

为研究4H-SiC探测器的抗γ辐照性能,使用40万Ci级的⁶⁰Co源对4H-SiC探测器进行了数次辐照,累积辐照剂量最大为1 MGy(Si),并在辐照后对4H-SiC的性能进行了测试。随着累积辐照剂量增加,4H-SiC探测器的正向电流增大,而反向电流恰好相反;根据4H-SiC探测器的正向I-V曲线可提取理想因子和肖特基势垒,理想因子从1.87增加到2.18,肖特基势垒从1.93 V减小至1.69 V;4H-SiC探测器对²⁴¹Am源产生的α粒子进行探测时,探测器的电荷收集率从95.65%退化到93.55%,测得能谱的能量分辨率由1.81%退化到2.32%。4H-SiC探测器在受到1 MGy(Si)的γ辐照后,与未受到辐照时相比,在探测能量为5.486 MeV的α粒子时能量分辨率和电荷收集率仅退化了28.18%和2.2%,仍具备优良的探测性能。     

Energy shift effect of exciting gamma line on perturbed angular distribution of resonantly scattered photons

The effect of the exciting gamma line energy shift on the resonant scattering of 129.4 FeV gamma rays of Ir-191 was observed. It was found that the rotation angle of the nuclear precession in the magnetic field depended on this shift. It manifested as a variation with the scattering angle of the shape of the carve, which describes the scattered photon intensity as a function of the shift.     

Effect of absorption of multiply scattering media on the degree of residual polarization of backscattered light

The effect of absorption in a scattering medium on the degree of residual polarization of backscattered radiation is studied in the case of probing of multiply scattering media by a linearly polarized light. An approximate expression describing the dependence of the degree of residual linear polarization of the backscattered radiation on the optical characteristics of a multiply scattering medium is derived within the framework of the phenomenological approach, based on the concept of the distribution of the optical paths of partial components of the scattered optical field under the conditions of multiple scattering, and with the use of the ideas about the similarity of statistical moments of the multiply scattered optical fields. The cut-off of the partial components, characterized by a large value of the optical path, because of their absorption, results in a substantial increase of the degree of residual polarization for the bands of the selective absorption caused by the presence of chromophores in the scattering medium. The results of experiments with model scattering media (whole milk) and biological tissues (human skin in vivo) are presented.     

Study on collimation and shielding of the back-streaming neutrons at the CSNS target

The back-streaming neutrons from the spallation target at CSNS are very intense,and can pose serious damage problems for the devices in the accelerator-target interface region. To tackle the problems,a possible scheme for this region was studied,namely a specially designed optics for the proton beam line produces two beam waists,and two collimators are placed at the two waist positions to maximize the collimation effect of the back-streaming neutrons. Detailed Monte Carlo simulations with the beams in the two different CSNS phases show the effectiveness of the collimation system,and the radiation dose rate decreases largely in the interface section. This can ensure the use of epoxy coils for the last magnets and other devices in the beam transport line with reasonable lifetimes,e.g.,thirty years. The design philosophy for such an accelerator-target interface region can also be applicable to other high-power proton beam applications.     

Study on collimation and shielding of the back-streaming neutrons at the CSNS target

The back-streaming neutrons from the spallation target at CSNS are very intense, and can pose serious damage problems for the devices in the accelerator-target interface region. To tackle the problems, a possible scheme for this region was studied, namely a specially designed optics for the proton beam line produces two beam waists, and two collimators are placed at the two waist positions to maximize the collimation effect of the back-streaming neutrons. Detailed Monte Carlo simulations with the beams in the two different CSNS phases show the effectiveness of the collimation system, and the radiation dose rate decreases largely in the interface section. This can ensure the use of epoxy coils for the last magnets and other devices in the beam transport line with reasonable lifetimes, e.g., thirty years. The design philosophy for such an accelerator-target interface region can also be applicable to other high-power proton beam applications.     

Total photon interaction cross sections for photons of energies between 60 and 1,333 keV

Total photon interaction cross sections at 10 energies between 59.6 and 1,332.5 keV have been determined for the elements V, Cu, Mo, Sn and U. Measurements were performed with the transmission technique using a high energy resolution Ge(Li) detector in a “good geometry” arrangement.     

Path-length distribution and path-length-resolved Doppler measurements of multiply scattered photons by use of low-coherence interferometry

We report first results of measurements by low-coherence Doppler interferometry of the path-length distribution of photons undergoing multiple scattering in a highly turbid medium. We use a Mach-Zehnder interferometer with multimode graded-index fibers and a superluminescent diode as the light source. The path-length distribution is obtained by recording of the heterodyne fluctuations that arise from the Brownian motion of particles in an Intralipid suspension as a function of the optical path length. The experimental path-length distribution is in good agreement with predictions of Monte Carlo simulations. In the heterodyne spectrum, an increase of the mean Doppler frequency with path length is observed.     

Gray whale target strength measurements and the analysis of the backscattered response

One of the current Integrated Marine Mammal Monitoring and Protection System (IMPAS) directions is concentrated on the design and development of the active sonar modality representing just one component of the global system. The active sonar was designed, built, and tested during the Marine Mammal Active Sonar Test (MAST 04), producing whale detections and whale tracks. The experiment was conducted in January 2004 off the coast of California. One of the objectives of the current work is to distinguish whale backscattered responses from the ones generated by the environmental clutter in a waveguide. Furthermore, the work aims to identify and analyze the target signature features that are necessary for enhanced active sonar detection and classification of marine mammals. Over the years there have been very few documented attempts to capture and analyze the backscattering response of whales using an active sonar system. Nevertheless, whales, mostly owing to their size, their motion, and the aspect dependence of their backscattered field, possess desirable properties that help distinguish their scattered response from clutter and other environment related false alarms. As an initial step, data collected during the MAST 04 experiment are presented, and gray whale target strength measurements are obtained. Results are compared to the previously published whale target strengths. Additionally, an investigation is conducted in an effort to provide whale feature identification points suitable for automated detection and classification, as means of relating gray whale active acoustic signatures to their inherent characteristics and their motion.     

Goldanskii effect in quadrupole Mössbauer spectra of the 89 keV gamma ray of 156Gd

Unusual relative line intensities in the recoilless absorption spectra of the 89 keV gamma ray of ¹⁵⁶Gd in Gd₂Ti₂O₇ have been observed at various temperatures. The results prove that the unusual intensities are mainly due to lattice vibrational anisotropy.     

The effect of gamma irradiation on the activation energy of bulk and track etching in Lexan track detector

Various studies have been performed to determine the response of Lexan polymer to gamma irradiations. The track recording properties of certain polymers are changed under the influence of electromagnetic radiations and environmental conditions. In the present work, the effect of gamma irradiation on the activation energies of bulk and track etching in case of Lexan samples have been investigated. The attempt has also been made to study the influence of temperature on the bulk and track etch rates of gamma irradiated polymer. The studies reveal an increase in the bulk and track etches rates with gamma-dose. However, the activation energy associated with track and bulk etch rates at a given temperature and at a constant concentration decreases with gamma-dose.     

用于质子和伽马射线探测的金刚石薄膜探测器的辐照性能

 研制出CVD金刚石薄膜探测器,在国家串列加速器和⁶⁰Co稳态辐射源上分别完成了该探测器对9 MeV质子束流和1.25 MeV γ射线的辐照性能研究。结果表明:该探测器在9 MeV质子照射累积强度达到10¹³ cm^-2时,探测器信号电荷收集效率减小量低于3.5%,辐照前后探测器暗电流没有明显变化。计算得到9 MeV质子对该探测器的损伤系数为1.3×10^-16 μm^-1·cm²。由于γ射线与金刚石作用产生的电子起到了填补缺陷的作用,探测器信号电荷收集效率随γ射线照射剂量的增加略有增加,在γ射线累积照射量达到10.32 C/kg时,其增幅小于0.7%。说明金刚石薄膜探测器具有较高耐辐照强度,适用于高强度辐射测量领域。     

用于质子和伽马射线探测的金刚石薄膜探测器的辐照性能

研制出CVD金刚石薄膜探测器,在国家串列加速器和60Co稳态辐射源上分别完成了该探测器对9 MeV质子束流和1.25 MeV γ射线的辐照性能研究。结果表明:该探测器在9 MeV质子照射累积强度达到1013 cm-2时,探测器信号电荷收集效率减小量低于3.5%,辐照前后探测器暗电流没有明显变化。计算得到9 MeV质子对该探测器的损伤系数为1.3×10-16 μm-1·cm2。由于γ射线与金刚石作用产生的电子起到了填补缺陷的作用,探测器信号电荷收集效率随γ射线照射剂量的增加略有增加,在γ射线累积照射量达到10.32 C/kg时,其增幅小于0.7%。说明金刚石薄膜探测器具有较高耐辐照强度,适用于高强度辐射测量领域。     

Optical and electrical properties of gamma irradiated PADC detector

PADC (Polyallyldiglycol carbonate) detector subjected to gamma rays undergoes change in optical and electrical properties. The optical band-gap is determined using Tauc's plot. The band-gap is found to be unchanged up to the dose of 10³ Gy, and then starts decreasing with increasing dose. The band-gap is lowered from 4.04 eV for the pristine material to 2.46 eV for the highest dose (10⁶ Gy). The dielectric constant of the detector is influenced due to the gamma exposure. At lower doses (up to 10⁴ Gy), the detector seems to be not polarised, so no change in dielectric constant is observed. But at the dose of 10⁵ Gy, the value is increased slightly while at the highest dose (10⁶ Gy), the dielectric constant of the detector is found to be enhanced significantly. The results indicated a decrease in track registration sensitivity with increase in gamma dose.     

Escape of photoelectrons and Compton‐scattered photons from an HPGe detector

The response function of a planar HPGe detector due to escape of photoelectrons and Compton‐scattered photons was studied for a point source with 59.5 keV energy. It was shown that both mechanisms, in addition to Ge x‐ray escape, leading to partial deposition of energy, could be observed in the same experiment. A Monte Carlo program was used to investigate these components of the response function. The results indicate that although the escape of scattered photons and Ge x‐rays are of the same magnitude, the escape of photoelectrons plays a more important role in the efficiency of a detector. Copyright © 2003 John Wiley & Sons, Ltd.     

Charge states of 25–150 keV H and 4He backscattered from solid surfaces

Measurements have been made of the ion-fractions of H and ⁴He backscattered with energies of 25–160 keV from Cu, Au, and Si surfaces which were etched and washed but not atomically clean. The ion-fractions for H range from 0.37 at 25keV to 0.92 at 160 keV, and for ⁴He from 0.10 at 30keV to 0.58 at 150 keV, depending to a small extent on the target material. Where comparisons can be made the data agree rather closely with results of others for particles traversing thin foils. The data are useful for calibration of an electrostatic analyzer in surface analysis. Plots of ion-fraction against particle velocity show a primary dependence on velocity, as expected, but there is a small difference in slope between the H and He curves. Charge states of particles scattered from surface impurities did not deviate significantly from those of particles scattered from the substrate at the same energy.     

Differential incoherent scattering of 279.2 keV photons by Zr,Sn, Ta,Pb and U

Differential incoherent scattering cross-section ratios of 279.2 keV photons by zirconium, tin, tantalum, lead and uranium elements are experimentally determined by comparing the peak areas under the degraded photon energy with that of an equivalent aluminium foil employing a high resolution 35 c.c. coaxial Ge(Li) detector. Studies have been made in single configuration in an angular range of 20° to 115°. The results are compared with theoretical values obtained from the non-relativistichfs model of Hubbell and co-workers. The cross-section ratios decrease as the atomic number increases for a given scattering angle.     

Inelastic and elastic scattering differential cross‐sections of 59.5 keV photons for Cu and Zn targets

Differential cross‐sections for incoherent and coherent scattering of 59.54 keV photons were measured for Cu and Zn targets at scattering angles of 40–135° in a reflection geometry setup with a graded shielding arrangement. The ratio of these cross‐sections, which can be determined with higher precision than absolute values, is given. A method was used to determine differential incoherent and coherent scattering cross‐sections of elements. This method is based on simultaneous measurement of fluorescence radiation and scattered radiation, thus avoiding problems with measuring source strength and source‐to‐detector solid angle. The measurements were performed using a point source of Am‐241 radioisotope and an Si(Li) detector. The experimental results, which complement earlier results, were compared with the theories of incoherent scattering function and form factor. Copyright © 2004 John Wiley & Sons, Ltd.