Rahmat Aryaeinejad

Using the Cockroft-Walton voltage multiplier with small photomultipliers

A variation of the basic Cockroft-Walton (C-W) voltage multiplier circuit design may be used to generate multiple voltages at sufficient currents to drive the dynodes of a photomultiplier tube. In a battery-operated handheld device, the current draw on the batteries must be kept to a minimum. Several other parameters must be considered carefully during the design as well. Components must be chosen based on size restrictions, expected load current, expected output voltage range, and the maximum allowable ripple in the output voltage. A prototype surface mount C-W board was designed and tested to power two photomultipliers. The whole system, including the detectors, draws less than 15 mA of supply current with the outputs at 1000 Vdc.

Using the Cockroft-Walton voltage multiplier design in handheld devices

A variation of the basic Cockroft-Walton (C-W) Voltage Multiplier circuit design may be used to generate multiple voltages at sufficient currents to drive the dynodes of a photomultiplier tube. In a battery-operated handheld device, the current draw on the batteries must be kept to a minimum. Several other parameters must be considered carefully during the design as well. Components must be chosen based on size restrictions, expected load current, expected output voltage range, and the maximum allowable ripple in the output voltage. A prototype surface mount C-W board was designed and tested to power two photomultipliers. The whole system, including the detectors, draws less than 15 mA of supply current with the outputs at 1000 VDC.

Comparison between digital and analog pulse shape discrimination techniques for neutron and gamma ray separation

Recent advancements in digital signal processing (DSP) using fast processors and a computer allows one to envision using it in pulse shape discrimination. In this study, we have investigated the feasibility of using a DSP to distinguish between neutrons and gamma rays by the shape of their pulses in a liquid scintillator detector (BC501). For neutron/gamma discrimination, the advantage of using a DSP over the analog method is that in an analog system, two separate charge-sensitive ADCs are required. One ADC is used to integrate the beginning of the pulse rise time while the second ADC is for integrating the tail part. In DSP techniques the incoming pulses coming directly from the detector are immediately digitized and can be decomposed into individual pulses waveforms. This eliminates the need for separate ADCs as one can easily get the integration of two parts of the pulse from the digital waveforms. This work describes the performance of these DSP techniques and compares the results with the analog method.

Development of a handheld device for simultaneous monitoring of fast neutrons and gamma rays

Currently at the Idaho National Engineering and Environmental Laboratory, a handheld device is being developed to measure fast neutrons and gamma rays using a single detector. The handheld detection system presented uses a single 12.7 mm (diameter) by 12.7 mm (length) liquid scintillator detector (BC501). The detection system can be made small and light. A small and light device can be used in several applications such as customs inspection, border security, and environmental radiation monitoring. The use of only one detector requires that the neutrons and gamma rays be distinguished by the shape of their pulses in the detector. Two methods of pulse shape discrimination (PSD) are presented: charge integration and zero crossing. Figures of merit were calculated for both methods for a threshold energy range of 50-600 keVee. Results show that the zero crossing method gives much better PSD for 100 keVee and lower, whereas the charge integration method leads. to better separation above 100 keVee. However, the neutrons and gamma rays are totally separated for energies of 100 keVee and above in both techniques. We are currently designing a miniaturized electronic system to be incorporated into the handheld device.

Pocket dual neutron/gamma radiation detector

A pocket radiation detection system has been developed at the Idaho National Engineering and Environmental Laboratory for homeland security applications. It can detect both neutrons and gamma rays instantaneously. This sensor has been designed with an emphasis on compactness, recognizing the widespread need for a radiation detection instrument that could provide both neutron and gamma-ray detection in a single, portable unit. It is very small, extremely sensitive, versatile, and easy to operate. It can detect gamma rays and neutrons in a radiation field as low as 10 /spl mu/R/h above the ambient background, which makes it ideal for use in national security applications. The detection system is based on a technique of using a combination of two sensors made of lithium isotopes /sup 6/Li and /sup 7/Li. It operates on one rechargeable Li-ion battery and is small enough to be put in a pocket or clipped to a belt. In this paper, the detection technique used in developing this prototype sensor as well as its performance will be presented.

Advanced Test Reactor Core Modeling Update Project Annual Report for Fiscal Year 2010

Legacy computational reactor physics software tools and protocols currently used for support of Advanced Test Reactor (ATR) core fuel management and safety assurance and, to some extent, experiment management are obsolete, inconsistent with the state of modern nuclear engineering practice, and are becoming increasingly difficult to properly verify and validate (V&V). Furthermore, the legacy staff knowledge required for application of these tools and protocols from the 1960s and 1970s is rapidly being lost due to staff turnover and retirements. In 2009 the Idaho National Laboratory (INL) initiated a focused effort to address this situation through the introduction of modern high-fidelity computational software and protocols, with appropriate V&V, within the next 3-4 years via the ATR Core Modeling and Simulation and V&V Update (or “Core Modeling Update”) Project. This aggressive computational and experimental campaign will have a broad strategic impact on the operation of the ATR, both in terms of improved computational efficiency and accuracy for support of ongoing DOE programs as well as in terms of national and international recognition of the ATR National Scientific User Facility (NSUF).

Network-oriented radiation monitoring system (NORMS)

We have developed a multi-functional pocket radiation monitoring system capable of detecting and storing gamma ray and neutron data and then sending the data through a wireless connection to a remote central facility upon request. The device has programmable alarm trigger levels that can be modified for specific applications. The device could be used as a stand-alone device or in conjunction with an array to cover a small or large area. The data is stored with a date/time stamp. The device may be remotely configured. Data can be transferred and viewed on a PDA via direct connection or wirelessly. Functional/bench tests have been completed successfully. The device detects low-level neutron and gamma sources within a shielded container in a radiation field of 10 uR/hr above the ambient background level.

High-resolution Compton-suppressed CZT and LaCl/sub 3/ detectors for fission products identification

Room-temperature semiconductor CdZnTe (CZT) detectors are currently limited to total detector volumes of 1-2 cm/sup 3/, which is dictated by poor charge transport characteristics. Because of this size limitation, one of the problems in accurately determining isotope identification is the enormous background from Compton scattering events. Eliminating this background will not only increase the sensitivity and accuracy of measurements, but will also help to resolve peaks buried under the background and peaks in close vicinity to others. We are currently developing a fission products detection system based on Compton-suppressed CZT and LaCl/sub 3/ (Ce) detectors. In this application, the detection system is required to operate in a high radiation field. Therefore, a small 10 mm /spl times/10 mm/spl times/5 mm CZT and 13mm/spl times/15mm LaCl/sub 3/ detector are placed inside the center of a well-shielded 76 mm by 76 mm long NaI detector. So far, we have been able to successfully reduce Compton background by a factor of 3.7 to 4.0 for a /sup 137/Cs spectrum. In this work, we will discuss the performance of this detection system using both CZT and LaCl/sub 3/ detectors. The results are compared with MCNP calculations.

Si PIN diodes for detecting topsoil contamination

In some environmental cleanup applications, there is a need for utilizing Si PIN diodes to detect electrons, x-rays, and low-energy gamma rays with very good energy resolution. The advantage of these detectors in such particular applications when compared with others is the ease of the operation at room temperature and at much lower bias voltages. We are currently investigating the feasibility of using silicon PIN photodiodes to detect the x-rays of radioisotopes such as Cs, Eu, La, U, Th, Am, and Pu for monitoring and characterizing topsoil contamination. The design and development of this Si PIN diode array will be discussed and the results of tests and its overall performance will be presented.

Handheld device for simultaneous monitoring of fast neutrons and gamma rays

Currently at the INEEL, a handheld device is being developed to measure fast neutrons and gamma rays using a single detector instead of a previous two detector system. The handheld detection system presented here uses a single 1/2 inch (diameter) by 1/2 inch (long) liquid scintillator detector (BC501). This means the detection system can be made smaller, lighter, less expensive, and is expected to be more sensitive than the original system. A smaller and lighter device makes it possible to be used in several applications such as customs inspection, border security, environmental radiation monitoring, and so on. The use of only one detector requires that the neutrons and gamma rays be distinguished by the shape of their pulses in the detector. Two methods of pulse shape discrimination (PSD) are: presented here, charge integration and crossover timing. Figures of merit were calculated for both methods for a threshold energy range of 50 to 600 keV. Results show that the crossover method gives much better PSD for electron energy of 100 keV and lower, whereas the charge integration method leads to better separation above 100 keV. However, the neutrons and gamma rays are totally separated for energies of 100 keV and above in both techniques. We are currently designing a miniaturized electronic system to be incorporated in the handheld device.