keV Peak Research Articles

Generation of bright attosecond x-ray pulse trains via Thomson scattering from laser-plasma accelerators.

Generation of attosecond x-ray pulse attracts more and more attention within the advanced light source user community due to its potentially wide applications. Here we propose an all-optical scheme to generate bright, attosecond hard x-ray pulse trains by Thomson backscattering of similarly structured electron beams produced in a vacuum channel by a tightly focused laser pulse. Design parameters for a proof-of-concept experiment are presented and demonstrated by using a particle-in-cell code and a four-dimensional laser-Compton scattering simulation code to model both the laser-based electron acceleration and Thomson scattering processes. Trains of 200 attosecond duration hard x-ray pulses holding stable longitudinal spacing with photon energies approaching 50 keV and maximum achievable peak brightness up to 1020 photons/s/mm2/mrad2/0.1%BW for each micro-bunch are observed. The suggested physical scheme for attosecond x-ray pulse trains generation may directly access the fastest time scales relevant to electron dynamics in atoms, molecules and materials.

A recommendation for revised dose calibrator measurement procedures for 89Zr and 124I.

Because of their chemical properties and multiday half lives, iodine-124 and zirconium-89 are being used in a growing number of PET imaging studies. Some aspects of their quantitation, however, still need attention. For 89Zr the PET images should, in principle, be as quantitatively accurate as similarly reconstructed 18F measurements. We found, however, that images of a 20 cm well calibration phantom containing 89Zr underestimated the activity by approximately 10% relative to a dose calibrator measurement (Capintec CRC-15R) using a published calibration setting number of 465. PET images of 124I, in contrast, are complicated by the contribution of decays in cascade that add spurious coincident events to the PET data. When these cascade coincidences are properly accounted for, quantitatively accurate images should be possible. We found, however, that even with this correction we still encountered what appeared to be a large variability in the accuracy of the PET images when compared to dose calibrator measurements made using the calibration setting number, 570, recommended by Capintec. We derive new calibration setting numbers for 89Zr and 124I based on their 511 keV photon peaks as measured on an HPGe detector. The peaks were calibrated relative to an 18F standard, the activity level of which was precisely measured in a dose calibrator under well-defined measurement conditions. When measuring 89Zr on a Capintec CRC-15R we propose the use of calibration setting number 517. And for 124I, we recommend the use of a copper filter surrounding the sample and the use of calibration setting number 494. The new dose calibrator measurement procedures we propose will result in more consistent and accurate radioactivity measurements of 89Zr and 124I. These and other positron emitting radionuclides can be accurately calibrated relative to 18F based on measurements of their 511 keV peaks and knowledge of their relative positron abundances.

Characterization of Uranium in Bituminized Radioactive Waste Drums by<newline/>Self-Induced X-Ray Fluorescence

This paper reports the experimental qualification of an original uranium characterization method based on fluorescence X-rays induced by the spontaneous gamma emission of bituminized radioactive waste drums. The main 661.7 keV gamma ray following the 137Cs decay produces by Compton scattering in the bituminized matrix an intense photon continuum around 100 keV, i.e. in the uranium X-ray fluorescence region. “Self-induced” X-rays produced without using an external source allow a quantitative assessment of uranium as 137Cs and uranium are homogeneously mixed and distributed in the bituminized matrix. The paper presents the experimental qualification of the method with real waste drums, showing a detection limit well below 1 kg of uranium in 20 min acquisitions while the usual gamma rays of 235U (185 keV) or 238U (1001 keV of 234mPa in the radioactive decay chain) are not detected. The relative uncertainty on the uranium mass assessed by self-induced X-ray fluorescence (SXRF) is about 50%, with a 95% confidence level, taking into account the correction of photon attenuation in the waste matrix. This last indeed contains high atomic numbers elements like uranium, but also barium, in quantities which are not known for each drum. Attenuation is estimated thanks to the peak-to-Compton ratio to limit the corresponding uncertainty. The SXRF uranium masses measured in the real drums are in good agreement with long gamma-ray spectroscopy measurements (1001 keV peak) or with radiochemical analyses.

Using the 186-keV peak for 226Ra activity concentration determination in Hungarian coal-slag samples by gamma-ray spectroscopy

The uranium isotopic abundance and the 238U–226Ra secular equilibrium were determined in nine Hungarian coal slag samples. The 226Ra activity concentration was measured based on the radon decay products and also the 226Ra peak at 186 keV. Secular equilibrium existed in eight samples, whereas one sample showed a slight disequilibrium. The direct and fast measurement using only the 186 keV peak was validated which can be used after measuring the uranium isotopic ratio and verifying the 238U–226Ra secular equilibrium. This method can be used to measure the 226Ra content of high number of samples from the same geochemical background.

Development of a Prototype Detector Using APD-Arrays Coupled With Pixelized Ce:GAGG Scintillator for High Resolution Radiation Imaging

A novel digital PET scanner based on Time over Threshold method is developed. The positron emission tomography (PET) is composed of 144channel Ce:Gd3Al2Ga3O12 (GAGG)-Avaranche photodiode (APD) detector arrays individually coupled with custom designed Time over Threshold (ToT) application-specific integrated circuit (ASIC) to realize the high count rate and good spatial resolution. Such an imaging system provides a simple front-end circuit and flexible digital signal processing like multiplexing such as a pulse train method. The measured energy resolution of the detector system was 6.7% for the 511 keV peak, and 4.25 ns time resolution was measured with a single detector module. The measured spatial resolution for a point source was 1.37 mm FWHM for our initial data with a columnar 22Na source.

Cd$_{0.9}$Zn$_{0.1}$Te Crystal Growth and Fabrication of Large Volume Single-Polarity Charge Sensing Gamma Detectors

Detector grade Cd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.9</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.1</sub> Te single crystals were grown using a tellurium solvent method. Single crystal blocks of volume ~1 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> were prepared for detector fabrication and characterization. The grown crystals were characterized using infra-red transmission imaging and Pockel's effect measurements. Two detectors in single-polarity charge sensing configurations viz., small pixel, and virtual Frisch grid were fabricated on two crystals obtained from the same section of the ingot. Current-voltage measurements performed in planar configuration exhibited a very low leakage current of ~5 nA at 1000 V and resistivities of the order of 8.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> Ω·cm. Electron drift mobilities of the order of 840 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V.s and electron mobility-lifetime products of the order of 2.7×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V were calculated from alpha spectroscopy using detectors in planar configuration. The small pixel and the virtual Frisch grid detector showed similar energy resolution of 3.7% for 662 keV gamma rays however, the virtual Frisch grid configuration revealed a better overall performance with a peak-to-Compton ratio of 2.8. A digital spectrometer and related software has been developed using a digitizer card and used to employ offline correction schemes to compensate for the charge loss effects, resulting in significant improvement of the 662 keV peak resolution (1.8% as compared to 3.7% without correction) obtained in the case of small pixel detector.

HPGe 검출기를 사용한 감마분광분석계의 점검선원 개발

A simple laboratory-made radioactive source to check the integrity of a gamma spectrometry system with HPGe detector was developed. The check source consists of radium-riched soil which was ground in size of less than 0.154mm and contained in air tight cylinderical vial, and provides photons with 12 distinct energies. The spectra of the check source were measured once a month during one year, analyzed the charactreictics of their peaks. When the gamma spectrometry system was in normal state, the areas and FWHMs of the gamma rays with more than 3% gamma emission rate in radium and its decay products was constant within standard deviation 2% and 3%, respectively, except 77 keV peak. And it was found that this check source can play a sufficient role to check the integrity of a gamma spectrometry system using 10 peaks in the range of 77 to 2202 keV.

SU-E-CAMPUS-J-06: Development of a Tumor Blood Flow Measurement System for Proton Therapy Patients

Purpose: To develop a tumor blood flow rate measurement system utilizing positron emission after proton therapy for potential evaluation of the efficacy of radiotherapy, concurrent chemotherapy and/or antiangiogenesis therapy of proton therapy patients. Method: Daily proton treatment generates positron emission nuclei, i.e., 15O, 13N and 11C inside the treated volume of patients. In‐room measurement of activities of 15O as a function of time right after proton treatment can directly measure tumor blood flow rate due to the biological washout characteristics. A pair of NaI2 detectors and coincidence detection electronics were obtained. The NaI2 detectors were mounted on a modified C‐arm for good axial alignment and flexible isocentric rotation. The detector energy spectrum was calibrated using 60Co, 137Cs and 22Na sources. The energy window was set for 511 keV peaks. Current system is not optimized for collimation and shielding. The system performance was evaluated using 18F‐FDG. Proton irradiated water and/or ice were also measured for positron emission activity and the acquired data were analyzed. Detector shielding and collimation is under construction. IRB approval for proton patient blood flow rate measurement was obtained for evaluation of their tumor blood flow rates and changes over treatment course. Results: The C‐arm based detector platform demonstrated precise alignment and great flexibility for different treatment sites. The 18F‐FDG decay measurement using the system showed the measured half life is within 16s of the theoretical value. Activity measurement of proton irradiated water and ice showed about 10s half life difference between the measured and theoretical value. This was potentially due to the activation inside the water/ice container and lack of detector collimation and shielding. Conclusions: A non‐invasive in‐room tumor blood flow rate measurement system for proton therapy patients is under development. The preliminary data is reported. American Cancer Society Chris DiMarco Institutional Research Grant

X-ray source motion along the loop in two solar flares

We explore the 3-8 keV X-ray source motion along the loop legs in two solar flares observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) on August 12 and November 28, 2002. Firstly, an artificial loop is constructed to have an outline with a fixed width wide enough to cover the X-ray sources at an energy band between 3-60 keV and at various times. Secondly, RHESSI images are reconstructed at 15 energy bands with an 8 s integration window but 1 s cadence. Thirdly, the X-ray source motions are traced from the brightness distribution along the flare loop. We find that these two events tend to start as a single source at 3-8 keV around the loop top, and then separate into two which move downward along the loop legs. These two almost reach the feet of the loop at the hard X-ray (i.e. at 25-50 keV) peak. After that, the two sources move back upward to the loop top and merge together at the same position where they began. The typical timescale is about similar to 70 s, and the maximum speed can reach 1000 km s(-1). Such a downward-to-upward motion along the loop is rarely seen in the observations, and it seems to be consistent with the density evolution at the loop top, first decreasing after heating and then increasing due to evaporation.

First Performance Results of Ce:GAGG Scintillation Crystals With Silicon Photomultipliers

A new single-crystal Cerium doped Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">123</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> (GAGG) scintillation crystal with high luminosity, high density and relatively fast decay time has successfully been grown. We report on the first performance results of the new GAGG scintillation crystal read out with silicon photomultipliers (SiPM) from Hamamatsu (MPPC) and FBK. The best energy resolution (511 keV peak of Ge-68) of 7.9% was attained with GAGG coupled to MPPC and 9.0% with the FBK SiPM after correcting for non-linearity. On the other hand, the best coincidence resolving time (FWHM) of polished 3 × 3 × 5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and 3 × 3 × 20mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> crystals were 464 ±12 ps and 577 ±22 ps for GAGG crystals compared to 179 ±8 ps and 214 ±6 ps for LYSO crystals respectively with MPPCs. The rise time of GAGG was measured to be 200 ps (75%) and 6 ns (25%) while the decay time was 140 ns (92%), 500 ns (7.7%) 6000 ns (0.3%).

Biparametric analyses of charge trapping in Cd0.9Zn0.1Te based virtual Frisch grid detectors

Detector grade Cd0.9Zn0.1Te (CZT) single crystals were grown from zone refined Cd, Zn, and Te (∼7 N) precursor materials, using a tellurium solvent method. Detectors with virtual Frisch grid configuration were fabricated using these crystals. I-V measurements revealed low leakage currents at room-temperature, ∼11 nA for one such detector D1 and ∼8 nA for another detector D2 at 1100 V. The spectroscopic performances of the two CZT virtual Frisch grid detectors have been evaluated and compared for high energy gamma ray detection. Detector D1 showed a well-resolved pulse-height spectrum with an energy resolution of ∼1.6% for the 662 keV gamma rays. Detector D2 also showed a distinct 662 keV peak but with a broader pulse-height distribution. A digital biparametric correlation study of the depth of interaction and energy deposited by the 662 keV gamma rays was carried out. A different kind of correlation pattern from that observed normally for hole trapping was noticed in the case of detector D2. Correlation of results from thermally stimulated current measurement studies suggested that the anomalous biparametric correlation pattern was due to the trapping of holes but modified by the virtual Frisch grid effect. The results also suggested that the effect of electron trapping could not be ruled out either. Finally, a digital correction scheme was applied to recover the 137Cs spectrum from the effect of charge loss.

Implementation of a preamplifier-amplifier system for radiation detectors used in Mössbauer spectroscopy

We report the assembly and testing of a preamplification and amplification system for pulses produced by gaseous radiation detectors commonly used in Mossbauer spectroscopy. The system is composed by a pair of commercial integrated circuits A203 and A206, which operate as charge sensitive preamplifier-shaping amplifier and linear amplifier-low level discriminator, respectively. The integrated circuits were interconnected in the unipolar output mode and placed inside a metallic shielding, which prevents noise amplification for a suitable signal-noise ratio. The system was tested by irradiating a proportional counter LND-45431 with characteristic X rays of 6.3 keV and gamma rays of 14.4 keV emitted by a Mossbauer radioactive source of 57Co (Rh). Unipolar pulses with Gaussian profile were obtained at the output of the linear amplifier, whose amplitudes were close to 0.4 V for 6.3 keV X rays and 1.4 V for 14.4 keV gamma rays. Pulse height spectra showed that the system allows a satisfactory identification of the X-rays and gamma rays emitted by the 57Co source, giving the possibility to make a good selection of the 14.4 keV peak for having a suitable signal-noise ratio in the Mossbauer spectra. Absorption percentages of 14 % were found by taking the Mossbauer spectra of a natural iron absorber. The assembly and tests of the system are presented through this paper.

La spectrométrie de masse peut-elle tout faire ?

In this work a method for the evaluation of the activity when a point source containing 60Co is located in an unknown position within a sample is developed. The method can be applied if the count rate in the 2505 keV sum peak has an acceptable uncertainty. It is based on the correlation between the apparent efficiency for the 1173 keV peak and the ratio of the count rate in the sum peak of 2505 keV and in the 1332 keV peak. The correlation was observed in the measurements of a 60Co point source located in various positions in a soil sample. The measurements were done with a 47% efficiency n-type HPGe detector. The correlation is also observed in the measurements and simulations done with a Compton-suppressed spectrometer having a 100% n-type HPGe detector. The results obtained with the proposed method are less affected by the uncertainty of the position of the point source than the results obtained using the standard methods of activity evaluation.

Fast procedure for self-absorption correction for low γ energy radionuclide 210Pb determination in solid environmental samples.

Low-energy X and γ radiations (for example of 210Pb: E γ = 46.5 keV) are effectively self-absorbed even in thin environmental samples, including air filters with captured dust or contaminated soil, as well as in bottom sediment matrixes with limited quantities of the samples. In this paper, a simple method for the direct analysis of 210Pb (T 1/2 = 22.3 years) by gamma-ray spectrometry in environmental samples with self-absorption correction is described. The method is based on the comparison of two γ peak activities coming from other natural radionuclides, usually present in environmental samples. We have analyzed the dependence of the self-absorption correction factor for the 210Pb activity on the activity ratios of 911 and 209 keV peaks and 609 and 295 keV peaks coming from nuclides of 238U or 232Th rows, present in typical environmental samples.

X-RAY PROPER MOTIONS AND SHOCK SPEEDS ALONG THE NORTHWEST RIM OF SN 1006

We report the results of an X-ray proper motion measurement for the NW rim of SN1006, carried out by comparing Chandra observations from 2001 and 2012. The NW limb has predominantly thermal X-ray emission, and it is the only location in SN1006 with significant optical emission: a thin, Balmer-dominated filament. For most of the NW rim, the proper motion is about 0.30 arcsec/yr, essentially the same as has been measured from the H-alpha filament. Isolated regions of the NW limb are dominated by nonthermal emission, and here the proper motion is much higher, 0.49 arcsec/yr, close to the value measured in X-rays along the much brighter NE limb, where the X-rays are overwhelmingly nonthermal. At the 2.2 kpc distance to SN1006, the proper motions imply shock velocities of about 3000 km/s and 5000 km/s in the thermal and nonthermal regions, respectively. A lower velocity behind the H-alpha filament is consistent with the picture that SN1006 is encountering denser gas in the NW, as is also suggested by its overall morphology. In the thermally-dominated portion of the X-ray shell, we also see an offset in the radial profiles at different energies; the 0.5-0.6 keV peak dominated by O VII is closer to the shock front than that of the 0.8-3 keV emission--due to the longer times for heavier elements to reach ionization states where they produce strong X-ray emission.

A peculiar thermonuclear X-ray burst from the transiently accreting neutron star SAX J1810.8–2609

AbstractWe report on a thermonuclear (type-I) X-ray burst that was detected from the neutron star low-mass X-ray binary SAX J1810.8–2609 in 2007 with Swift. This event was longer (≃20 min) and more energetic (a radiated energy of Eb≃6.5×1039 erg) than other X-ray bursts observed from this source. A possible explanation for the peculiar properties is that the X-ray burst occurred during the early stage of the outburst when the neutron star was relatively cold, which allows for the accumulation of a thicker layer of fuel. We also report on a new accretion outburst of SAX J1810.8–2609 that was observed with MAXI and Swift in 2012. The outburst had a duration of ≃17 days and reached a 2–10 keV peak luminosity of ≃ 3 × 1037 (D/5.7 kpc)2 erg s−1. This is a factor &gt;10 more luminous than the two previous outbursts observed from the source, and classifies it as a bright rather than a faint X-ray transient.

New knowledge about the bremsstrahlung image of strontium-89 with the scintillation camera

Strontium-89 ((89)Sr) chloride has been used to treat metastases in bone. A method to visualize the distribution of (89)Sr chloride with a scintillation camera was developed in 1996. Studies using bremsstrahlung imaging have shown that (89)Sr accumulates in bone and that the bremsstrahlung generated from biological tissue surrounding bone does not exceed 30 keV. However, it was not clear how low-energy bremsstrahlung from bone can produce peak energy levels of around 75 keV. We speculate that a different (unidentified) factor is involved. The energy spectrum of an (89)Sr source was acquired with a scintillation camera with or without a low-to-medium-energy general-purpose collimator. The energy window was set at 20-650 keV for 4 windows. A 50-mm thick acrylic block was placed between the scintillation camera and the (89)Sr source to exclude the effects of bremsstrahlung. The energy spectrum of (89)Sr covered with lead was acquired using the scintillation camera without a collimator. With the collimator the energy spectrum curve was similar to that without the 50 mm of acrylic. The energy spectrum curve showed peaks at about 75, 170, and 520 keV. Without the collimator the energy spectrum showed a similar curve but no peak at 75 keV peak. The curve was similar to that obtained with the scintillation camera and the collimator; however, the curve obtained when the (89)Sr source had been placed in a lead container was similar to that obtained when the source was unshielded, and the collimator was not attached to the scintillation camera. If bremsstrahlung of (89)Sr produces an image, a low-energy spectrum region should decrease when acrylic is placed between the (89)Sr source and the scintillation camera. However, similar curves were obtained both with the acrylic in place and without the acrylic. Therefore, we believe that the radiation detected by the scintillation camera was not bremsstrahlung due to the beta rays of (89)Sr. Most (89)Sr preparations are contaminated by (85)Sr, and most of the gamma ray energy of (85)Sr is 514 keV. The scintillation camera detected the characteristic X-ray energy of about 75 keV from the materials of the collimator (lead and others) through interaction with the gamma rays of (85)Sr.

Solution growth of In-doped CdMnTe crystals by the vertical Bridgman method with the ACRT technique

Cd1−xMnxTe (CdMnTe) crystals were grown by the solution technique using Te as a solvent and the growth was performed in a vertical Bridgman arrangement with the accelerated crucible rotation technique (ACRT). Ingot in the diameter of 30mm and length of 60mm was obtained. As-grown crystals showed a resistivity of 2.065×1010Ωcm and mobility life time product of electrons of 1.61×10−3cm2V−1. PL spectrum and IR transmittance measurements revealed that the as-grown CdMnTe possessed high crystalline quality. A CdMnTe detector was fabricated with planar configuration structure, which showed a resolution of 12.51% of the 241Am at 59.5keV peak. In conclusion, the Te solution vertical Bridgman technique was proved to be a practical way to effectively reduce the twins in CdMnTe crystal and to produce high quality detector-grade CdMnTe crystal with good spectroscopic performance.

Enhanced keV peak power and yield using twisted pair “cables” in a z-pinch

Individual wires in a z-pinch were replaced with twisted pair “cables” of similar linear mass on the COBRA pulsed power generator, resulting in peak power and yield increases in radiation above 1 keV. A cable is defined here as two or more fine wires twisted together to form a continuous strand with a wavelength (λt) dependent on the twists per unit length. The magnitude of λt appears to play a strong role in these increases, with the largest gains found for a λt of ≈0.75 mm.

SU-E-T-482: A More Accurate Bare 12 5I Spectrum.

To compare measured energy spectra of 125 I brachytherapy seeds with Monte Carlo calculated energy spectra when using the bare 125 I energy spectrum recommended by TG43 and the one presented in NCRP Report 58 and to determine the impact of these different spectra on the calculation of the dose rate constant. The energy spectrum, absorbed dose at 1 cm on the bisector and air kerma strength of 10 different 125 I seeds were calculated using the EGSnrc BrachyDose Monte Carlo code. Energy bin width was 0.2 keV. The simulations were done with the bare 125 I energy spectrum recommended by TG43 or NCRP Report 58. Statistical uncertainties for the energy spectra were 0.02% and 0.1% or less for the other clinical parameters. Results are compared with published measuredvalues. There is close agreement between the measured and calculated branching ratio generated by 125 I seeds when simulated using the spectrum presented in NCRP58. However, for all seeds a 7% lower value is observed in the 31 keV peak when using data suggested by TG43. On the other hand, differences in the average energy, air kerma, absorbed dose and dose rate constant are undetectable (less than statistical uncertainty, <0.1%) when performed with either spectrum. For dosimetric parameter calculations, the bare 125 I energy spectra presented in TG43 and NCRP58 produce indistinguishable results. However, for branching ratio investigation purposes, there is a clear difference in the 31 keV peak between values obtained using the different 125 I bare energy spectra. Measured 125 I branching ratios are in close agreement with those calculated using the bare 125 I energy spectrum presented in NCRP58. Reassessment of the bare 125 I energy spectrum recommended in TG43 is suggested.