Photon Induced Positron Annihilation Research Articles

Photon-induced positron annihilation lifetime spectroscopy using ultrashort laser-Compton-scattered gamma-ray pulses

High-energy ultrashort gamma-ray pulses can be generated via laser Compton scattering with 90° collisions at the UVSOR-II electron storage ring. As an applied study of ultrashort gamma-ray pulses, a new photon-induced positron annihilation lifetime spectroscopy approach has been developed. Ultrashort gamma-ray pulses with a maximum energy of 6.6 MeV and pulse width of 2.2 ps created positrons throughout bulk lead via pair production. Annihilation gamma rays were detected by a BaF2 scintillator mounted on a photomultiplier tube. A positron lifetime spectrum was obtained by measuring the time difference between the RF frequency of the electron storage ring and the detection time of the annihilation gamma rays. We calculated the response of the BaF2 scintillator and the time jitter caused by the variation in the total path length of the ultrashort gamma-ray pulses, annihilation gamma rays, and scintillation light using a Monte Carlo simulation code. The positron lifetime for bulk lead was successfully measured.

Photon-induced positron annihilation lifetime spectroscopy using an S-band compact electron linac

A new photon-induced positron annihilation lifetime spectroscopy approach has been developed using an S-band compact electron linac at the National Institute of Advanced Industrial Science and Technology (AIST). The high energy (<42MeV), intense (105 photons pulse−1), and ultra-short pulse (3ps pulse width) photon beam creates positrons throughout an entire sample via pair production. A positron lifetime spectrum can be obtained by measuring the time difference between the accelerator's RF frequency and the detection time of the annihilation gamma rays. The positron lifetimes for lead and yttria-stabilized zirconia samples have been successfully measured.

Photon induced positron annihilation spectroscopy: A nondestructive method for assay of defects in large engineering materials

This paper describes a new methodology for volumetric assay of defects in large engineering materials nondestructively. It utilizes high energy photons produced by nuclear reaction to create positrons in situ whose fate is followed using conventional positron spectroscopic techniques. The photon induced positron annihilation (PIPA) spectroscopy system has been set-up using a Folded Tandem Ion Accelerator (FOTIA). Possibility of using prompt γ-rays produced in nuclear reactions 27Al( 1H,γ) 28Si and 19F( 1H,αγ) 16O has been examined. The reaction 19F( 1H,αγ) 16O is seen to provide higher photon flux (and positron yield) and measurements have been carried out in large samples of metals and polymers. We could establish good sensitivity of the technique as well as reproducibility in a number of measurements. This technique has been used to carry out defect studies in cold worked zircaloy-2 plates. The measured S-parameter, indicative of defect concentration, was seen to correlate well with the measured residual stress using X-ray technique. The results were validated by γ-induced positron annihilation lifetime measurements at ELBE LINAC based GiPS facility.

Photon-induced positron annihilation for standoff bomb detection

We describe an approach to detect improvised explosive devices (IEDs) by using photon-induced positron annihilation radiation (PIPAR). This system relies on back-scattered γ photons from the target and surrounding objects following exposure to high energy X-rays from a betatron. In this work we simulate the use of Bremsstrahlung source operating at 3.5 MeV, with a scintillation detector, working in PIPAR mode, in order to reduce noise produced by undesired back-scattering from the surrounding objects. In this paper, we describe the basic imaging method and preliminary results on simulating a suitable betatron source. Two types of X-ray filters copper (Cu) and aluminium (Al), have been used in the simulation to observe their differences in the deposited energy spectrum in the iron target. It was found that the use of iron target in conjunction with 2 mm Al filter is capable of detecting annihilation γ photons. An initiated experiment with an interlaced source also shows promise.

Detection of chemical explosives using multiple photon signatures

A template-matching procedure is being investigated for rapid detection of improvised explosive devices at standoff distances. Photon-scattered and photon-induced positron annihilation radiation responses are being studied as a part of a signature-based radiation scanning approach. Back-streaming radiation responses, called signatures, are compared to templates, which are collections of the same signatures if the interrogated volume contained a significant amount of explosive. Experiments have been conducted that show that explosive surrogates (fertilizers) can be distinguished from several inert materials.

Ionizing photon methods for standoff bomb detection

We consider a method that uses multiple photon-scatter and photon-induced positron annihilation radiation (PIPAR) responses in a template-matching procedure to assist in rapid standoff detection of improvised explosive devices (IEDs). The procedure is shown in a simulation study to be able to distinguish an explosive surrogate (fertilizer) from several inert materials, and thus the method may prove useful as part of a multidimensional approach in detecting hidden chemical explosives.

Photon-induced positron annihilation radiation (PIPAR) — A novel gamma-ray imaging technique for radiographically dense materials

A discussion is presented of some fundamental limitations of the Compton back-scattering technique for imaging radiographically dense materials. These include the low probability of Compton back-scattering for high energy (> 1 MeV) photons, the low energy (and hence high attenuation) of the scattered radiation (≤ 225 keV) at large angles of scattering and the invariable presence of a large multiple scattering background superimposed on the single scattering component. A novel radiographic technique—photon-induced positron annihilation radiation (PIPAR)—is described and is shown to avoid the above limitations. It thus extends significantly the depth range of materials which may be investigated with gamma rays in the reflection geometry. Preliminary experimental results showing the feasibility of PIPAR imaging are presented here for the first time. These were obtained with megavoltage radiation from a linear accelerator exciting positrons in elemental samples through the pair production effect. The 511 keV annihilation line was extracted from the back-scattered radiation using a plastic scintillator detector and a difference filter technique. The experimental arrangement is described and potential applications are briefly discussed.