MeV Γ-rays Research Articles

Hadron and nuclear physics with inverse compton gamma-rays at SPring-8

A new facility for GeV γ-ray beams in an energy range of 1.5–2.4 GeV has been constructed for developing hadron physics at SPring-8. GeV γ-rays are produced via the inverse Compton scattering process, and are used to study the sub-nucleonic structure of nucleon via the productions of φ and K + mesons. The recent experimental results to observe φ and K + mesons are discussed to look for the physics in relation to strangeness quarks in baryon resonances. A new beam line for MeV γ-rays at SPring-8 to give new possibilities for the studies of the weak-strong coupling effects in nuclear mediums through the observation of parity violation is also discussed.

Production and dosimetry of [ 14O]water for PET activation studies

[ 14O]water was produced by the 14N(p,n) 14O reaction in quantities greater than 80 mCi (EOB). The carbon-11 impurity in the final product was approximately 0.003±0.002% of 14O activity at EOB. A factor of 0.5±0.02 was obtained to correct the dose calibrator for the additional 2.313 MeV γ-ray. The effective dose equivalent was calculated for 14O and 15O using MIRDOSE, and the 14O dose was found to be ≈70% of that for 15O. For scanner performance based on noise equivalent count measurements, the peak activity concentration for 14O was 30% lower than that for 15O. At their peak activity concentrations the noise equivalent count rate for 14O was found to be about 13% less than that for 15O.

Frontier of Quark-Nuclear Physics at SPring-8 and Nuclear Data

A new facility for GeV γ-ray beams in an energy range of 1.5~3.5 GeV has been constructed for developing physics with photo-nuclear reactions at SPring-8. The GeV γ-rays are produced via the inverse Compton scattering process, and are used to study the sub-nucleonic structure of the nucleon via the productions of ϕ and K + mesons. This SPring-8 project offers an unique opportunity to study the nucleon structure in view of the quark physics. The recent experimental results to observe ϕ and K + mesons are discussed to look for the physics in relation to strangeness quarks in nucleon. A new beam line for MeV γ-rays at SPring-8 to give new possibilities for the basic science, astrophysics, and nuclear structure studies is discussed.

The yields, branching ratios and angular distributions of 6–7 MeV photons produced in the 19F(p, αγ) 16O reaction

The yields and branching ratios of 6.13, 6.92 and 7.12 MeV photons produced in the 19F(p, áγ) 16O reaction were measured for incident proton energies between 340.46 and 3490 keV. The experimental data were recorded and analysed to show photon features. The branching ratios of 6.13, 6.92 and 7.12 MeV γ-rays are different for different incident proton energies. The maximum yield of 6–7 MeV γ-rays was found at E p=2.63 MeV. The angular distributions for 6.13 and 7.12 MeV γ-rays in the E p=340.46 keV resonance were also measured and show to be isotropic within experimental uncertainty.

Irradiation Effects on Diagnostic Components for ITER.

Irradiation tests on many diagnostic components have been carried out as a part of the R&D program of the ITER Engineering Design Activities (EDA). Five kinds of ITER round robin fibers were irradiated in JMTR and60Co γ-rays. Induced transmission loss of those fibers are much smaller than that of pure SiO2 core fiber. Especially, KU-H2G from Russian Federation and F-doped fibers from Japan have rather good radiation hardness even in the visible range. Those fibers might be available in the diagnostic port of ITER. The transmissivity of KU-1 quartz, which is a candidate of the window material for UV and visible spectroscopy in ITER, was measured under the irradiation of 14 MeV neutrons and γ-rays in the UV range (200 - 400 nm). Significant transmission loss was observed in the wavelength range of 200-300 nm. The Mica substrate bolometer was irradiated in JMTR during three irradiation cycles. Total neutron fluence was about 1×1024 n/m2 which was equivalent to 0.1 dpa. Significant increase in the meander resistance was observed, which was causedby the nuclear transmutation of gold into mercury. The use of gold meanders might be problematic in ITER.

A new positron lifetime spectrometer using a fast digital oscilloscope and BaF 2 scintillators

A new positron lifetime spectrometer has been constructed and tested. It consists of a state-of-the-art digital oscilloscope (LeCroy Wavepro 960) and scintillation detectors based on Hamamatsu H3378 (R2083Q) photomultiplier tubes and BaF 2 scintillators. A very good time resolution is obtained with scintillators of commonly used sizes (28 mm in diameter, 10–20 mm thick) and wide energy window settings (40–50%). The time resolution of 144 ps full-width at half-maximum (FWHM) is achieved for the positron lifetime measurement, in which time differences are measured between the arrivals of a 1.27 MeV γ-ray from 22Na and one of the two positron annihilation γ-rays of 0.511 MeV. The time resolution is further improved with a ‘double-stop’ setup, where timing information carried by the positron annihilation γ-ray pair is combined to determine the time of the annihilation. The time resolution with this setup is 119 ps FWHM. This improvement is interpreted in terms of the energy deposit in the scintillation detectors by γ-rays. Applications of the new spectrometer to other scintillation timing measurements are also described.

The 16N calibration source for the Sudbury Neutrino Observatory

A calibration source using γ-rays from 16N ( t 1/2=7.13 s) β-decay has been developed for the Sudbury Neutrino Observatory (SNO) for the purpose of energy and other calibrations. The 16N is produced via the (n,p) reaction on 16O in the form of CO 2 gas using 14-MeV neutrons from a commercially available Deuterium-Tritium (DT) generator. The 16N is produced in a shielding pit in a utility room near the SNO cavity and transferred to the water volumes (D 2O or H 2O) in a CO 2 gas stream via small diameter capillary tubing. The bulk of the activity decays in a decay/trigger chamber designed to block the energetic β-particles yet permit the primary branch 6.13 MeV γ-rays to exit. Detection of the coincident β-particles with plastic scintillator lining the walls of the decay chamber volume provides a tag for the SNO electronics. This paper gives details of the production, transfer, and triggering systems for this source along with a discussion of the source γ-ray output and performance.

An 26Al target for (n,p) and (n,α) cross-section measurements

The radionuclide 26Al plays an important role in astrophysics. It can be detected via the 1.8 MeV γ-ray it emits, providing information on stellar nucleosynthesis processes using maps of the universe made by γ-ray telescopes. In addition, the decay of 26Al to 26Mg in meteorites producing anomalous 26/24Mg ratios gives clues to the origin of the solar system. New studies of the 26Al(n,p) 26Mg and 26Al(n,α) 23Na destruction mechanisms required an 26Al target containing significantly more 26Al than that previously used. This target was prepared by molecular plating from isopropanol onto a nickel foil substrate with a yield close to 100%. The total number of 26Al atoms, determined by γ-spectrometry, was (2.6±0.2)×10 17, corresponding to 11.2±1.0 μg (expanded uncertainty, coverage factor k=2). The areal density was 0.37 μg/cm 2. Measurements of (n,p) and (n,α) cross-sections in a thermal neutron beam exhibited sufficient resolution of the p- and α-peaks to allow detection of a number of new transitions.

Identification of the 10Li ground state

Abstract The proton-stripping reaction from a 11Be radioactive beam incident on a beryllium target demonstrates that only (7±3)% of the 9Li residues in the reaction are in coincidence with the 2.7 MeV γ-ray corresponding to the 9Li first excited state. This implies that the previously observed low-energy neutrons from the decay of the unbound nucleus 10Li represent a direct l=0 transition to the 9Li ground state. Consequently, neutron-unbound 10Li is proven to have the same parity inversion as occurs in the case of 11Be with a 1 s 1 2 intruder state below the natural parity 0 p 1 2 state.

Response calculation of a stacked CdZnTe detector for 16N γ-ray measurement

A stacked CdZnTe semiconductor detector, which is able to detect the 6.13 MeV γ-rays from 16N, was prototyped and the response calculation was carried out by a Monte-Carlo simulation. The detector response was simulated by using the electron and photon transport code, EGS4 and taking into account the carrier trapping phenomena. The results of the response calculation agreed with the experimental data from the checking source of 137Cs and 60Co. The prototype's response and sensitivity to 16N were calculated by simulating an incident energy of 6.13 MeV . The source spectra were unfolded with the detector's response function obtained by simulation, and it indicated that the incident γ-ray energy and its intensity ratio was identified. We have acquired the potential to measure the γ-ray energy in the high energy region about 6 MeV with the stacked CdZnTe detector.

On-line reconstruction of low boron concentrations by in vivoγ-ray spectroscopy for BNCT

Boron neutron capture therapy (BNCT) is a radiationtherapy in which the neutron capture reaction of 10B is used forthe selective destruction of tumours. At the High Flux Reactor (HFR) inPetten, a therapy facility with an epithermal neutron beam has been built. Inthe first instance, patients with brain tumours will be treated. The dosesdelivered to the tumour and to the healthy tissue depend on the thermalneutron fluence and on the boron concentrations in these regions. Anaccurate determination of the patient dose during therapy requiresknowledge of these time-dependent concentrations. For this reason, aγ-ray telescope system, together with a reconstructionformalism, have been developed. By using a γ-ray detector in atelescope configuration, boron neutron capture γ-rays of 478 keVemitted by a small specific region can be detected. The reconstructionformalism can calculate absolute boron concentrations using themeasured boron γ-ray detection rates. Besides the boronγ-rays, a large component of 2.2 MeV γ-rays emitted atthermal neutron capture in hydrogen is measured. Since the hydrogendistribution is almost homogeneous within the head, this component canserve as a measure of the total number of thermal neutrons in theobserved volume. By using the hydrogen γ-ray detection rate fornormalization of the boron concentration, the reconstruction tooleliminates the greater part of the influence of the inhomogeneity ofthe thermal neutron distribution. MCNP calculations are used as a toolfor the optimization of the detector configuration.Experiments on a head phantom with 5 ppm 10B in healthy tissueshowed that boron detection with a standard deviation of 3% requires aminimum measuring time of 2 min live time. From two position-dependentmeasurements, boron concentrations in two compartments(healthy tissue and tumour) can be determined. The reconstruction ofthe boron concentration in healthy tissue can be done with a standarddeviation of 6%. The γ-ray telescope can also be used forin vivo dosimetry.

Prototype of the Stacked CdZnTe Semiconductor Detector for <sup>16</sup>N Measurement

The prototype model of the stacked CdZnTe semiconductor detector, which is able to measure the 6.13MeV γ-ray from 16N, was fabricated. The prototype's response calculation was carried out by Monte-Carlo method. The result of the response calculation agreed with the experiment data of check sources of 137Cs and 60Co, and 16N which was measured at vicinity of the primary cooling water pipe of the nuclear reactor. The source spectra were unfolded with detector's response function obtained by simulation, and it is indicated that the incident γ-ray energy and its intensity ratio was identified and that the energy of 6MeV γ-ray could be measured by the prototype of the stacked detector.

Evaluation of a Compton scattering camera using 3-D position sensitive CdZnTe detectors

A CZT Compton Camera (CCC) is being built using two three-dimensional (3-D) position-sensitive CZT detectors. Expected system performance was analyzed by analytical and Monte Carlo approaches. Based on the measurement of detector energy and position resolution, the expected angular resolution is ∼3° and ∼2° for a ±30° FOV for 511 keV and 1 MeV γ-rays, respectively. The intrinsic efficiency for a point source 10 cm from the first detector surface ranges from 1.5×10 −4 to 8.8×10 −6 for 500 keV–3 MeV.

Ｘ線材料強度 共鳴核反応分析法によるＢＣＮ膜の水素量測定

Hydrogen is a very common contaminant in carbon films. It can strongly influence on mechanical, physical and chemical properties of the films. The analysis of hydrogen is therefore a crucial problem produce the films with the properties required. Ion beam techniques using nuclear reactions are effective for the quantitative determination of hydrogen concentration. A specially designed spectrometer is employed for the detailed determination of hydrogen concentrations by detecting 4.43MeV γ-rays from the resonant nuclear reactions 1H(15N, αγ)12C at the 6.385MeV. In this study, the BCN films were formed on silicon substrate by ion beam assisted deposition (IBAD), in which boron and carbon were deposited by electron beam heating of B4C solid and nitrogen was supplied by ion implantation simultaneously. The concentrations of hydrogen in BCN films were measured using RNRA. The mechanical properties of BCN films were evaluated using an ultra-micro-hardness tester. It was confiremed that the hardness of BCN films increased with increasing the concentration of hydrogen.

Measurement of 15 MeV γ-rays with the Ge cluster detectors of EUROBALL

A measurement of the response to 15.1 MeV γ-rays has been made for the Ge cluster detectors in the EUROBALL array. Each cluster detector consists of seven germanium capsules surrounded by a single anticompton shield of BGO. The reaction D( 11B,γ) 12C+n at E beam =19.1 MeV has been employed. The “adding-back” of signals simultaneously present in the capsules composing each cluster detector has been made on an event by event basis. The intensity in full-energy peak increases by a factor of three as compared to that of the spectrum obtained by summing the individual spectra of the 7 capsules. The pulse height to energy conversion is found to be very linear from few hundreds keV to 15 MeV. The efficiency is discussed relative to that of large volume BaF 2 scintillators.

Thick target photon yields and angular distributions for the 19F(p,αγ) 16O source reaction at incident proton energies between 1.5 and 4.0 MeV

The absolute thick target yield of 6.129, 6.917 and 7.116 MeV γ-rays produced from the 19F(p,αγ) 16O source reaction has been measured for incident proton energies between 1.5 and 4.0 MeV. The angular distributions of the respective γ-lines have been determined for incident proton energies of 2.0 and 3.0 MeV. The experiments were performed at the 4.5 MV Tandem Van der Graaff accelerator at the Ohio University Edwards Accelerator Laboratory in Athens, Ohio, using a thick CaF 2 target and a 7.62 cm×7.62 cm Na(I) scintillation detector. The Monte Carlo code MCNP was used to calculate detector response functions for the three individual γ-rays. A least-squares fit of these functions to a selected region in the pulse height spectrum was carried out to determine the relative intensities of these γ-rays. The uncertainty in the fluence determination is based on the χ 2 of the fit, the uncertainty in the response functions, the statistics of the data, and the uncertainty in the recording of the proton charge. A maximum photon yield of 1.316×10 7 γ/μC/sr (at 90°) was determined for the sum of these three γ-rays at the highest incident proton energy of 4.0 MeV. The contribution of the individual lines to the total photon yield depends strongly on the incident proton energy. The angular distributions are isotropic to within 15%.

Vibrational and thermal noise reduction for cryogenic detectors

In this paper we present the excellent results obtained by mechanical decoupling of our thermal detectors from the cryostat. The starting point of this work is the necessity to improve the performances of thermal detectors and, besides, to eliminate the non-constant noise resulting from the overall cryogenic facility; this second point results to be crucial for rare-events experiments and the fundamental task for Dark Matter search. Tested on our bolometer, consisting of a 750 g tellurium oxide absorber coupled with an NTD thermistor and operated at ∼9 mK in an Oxford 200 dilution refrigerator, this powerful technique can, moreover, provide advantages for a large variety of thermal detectors. A good energy resolution of 3.9 keV FWHM was obtained for 2.615 MeV γ-rays. The 4.2 keV average FWHM resolution for the 5407 keV 210 Po α decay line is the best ever obtained for α-particles with any type of detector.

Space VLBI observations of southern hemisphere gamma-ray and non-gamma-ray AGN: First results for PKS 0637-752

Abstract We present the first results from our VSOP proposal, “γ-ray loud and quiet AGN with VSOP and SHEVE at 5 GHz”. This project is aimed at determining what, if anything, differentiates γ-ray-identified radio sources from similar strong, flat-spectrum radio sources which have not been identified as sources of greater than 100 MeV γ-rays. Five VSOP observations have been successfully completed as part of this project during VSOP AO1. One observation has been correlated thus far, a 4.970 GHz observation of PKS 0637-752 from 1997 November 21. We present the VSOP image for PKS 0637-752 and make comparisons between the space VLBI image and ground-based VLBI and Australia Telescope Compact Array (ATCA) images, as well as present ATCA flux density monitoring at 4.8 GHz. A brightness temperature for PKS 0637-752 of 0.7 × 1012 K has been determined from the VSOP data and a tentative apparent superluminal speed, from comparison to the ground-based VLBI image, of ∼9c.

Liquid deuteromethane pulse ionization chamber

The serviceability of a pulse ionization chamber filled with liquid deuteromethane (LCD 4) is confirmed experimentally. Deuteromethane with a level of electronegative impurities of 3 × 10 −9 equiv. O 2 has been obtained using Ni/SiO 2 adsorbent. It is shown that for electric fields up to 3kV/cm, the electronic properties of LCD 4 are close to those of LCH 4. The ionization chamber shows an energy resolution of 14%(FWHM) when detecting 1.2 MeV γ-rays.

Serum aluminum determination by instrumental neutron activation analysis in long-term haemodialysis patients

Serum aluminum levels were determined by instrumental neutron activation analysis in 31 patients undergoing long-term haemodialysis. Aluminum-28 1.778 MeV (T1/2=2.24 min) γ-rays produced by the thermal neutron reaction27Al(n,γ)28Al were detected. Successive irradiation of the samples at epithermal neutron fluence was performed to correct for the interference from the fast neutron reaction31P(n,α)28Al. Serum aluminum level in this group of subjects was adequately represented by a lognormal distribution with a mean and variance of 16.5 μg/l and 16.8 μg/l, respectively. The results obtained were found to be in agreement with serum aluminum determination performed by electrothermal atomic absorption spectrophotometry (r2=0.97). Instrumental neutron activation can provide a rapid technique to routinely monitor long-term haemodialysis patients in order to identify individuals at greater risk to develop aluminum toxicity.