J. Henniger

The program StopPow – A useful tool for computation of energy loss and range of light ions in SSNTDs

Abstract Energy loss along particle trajectories and ranges of light ions are needed for theoretical characterisation of tracks in solid state nuclear track detectors (SSNTDs). Computation of these data is possible using ion transport programs, e.g., the well-known TRIM program. Derived quantities necessary for the simulation of the track formation process can be calculated by these programs too. The practical use is, however, limited by the time-consuming data processing that the user has to perform. Therefore, the program StopPow was developed based on algorithms analogous to TRIM, but yielding direct output of interesting quantities such as restricted energy loss (REL) for different cut-off energies of delta electrons or energy shift due to ion passage through material layers of different thicknesses. Tests of the StopPow program were conducted by comparison of exemplary results with TRIM and International Commission on Radiation Measurements and Units (ICRU) data as well as with experimental results.

Neutron response calculation on the basis of variable track etch rates along the secondary particle trajectories in CR-39

Abstract The calculation of the response of CR-39 detectors exposed to neutrons is of high importance for their dosimetric application. A computer code system has been developed for this purpose. Whereas the generation of secondary charged particles is carried out using non-analogue Monte-Carlo techniques with variance reduction the simulation of the track formation process is treated without any free parameter starting from the etch rate ratio V(REL) only. Results are given for the contribution of recoil protons to the response as a function of the neutron energy and angle of incidence. Furthermore, the influence of an external radiator has been studied. The comparison of the calculated values with experimental data confirm the reliability of the track etch model applied.

The evaluation of CaF2:Mn-polyethylene detectors with the aid of the optically stimulated luminescence (OSL)

Abstract A serious problem in using TL detectors for neutron dosimetry is their low sensitivity to fast neutrons. Therefore, radiator-detector combinations are employed. But in this case the restricted temperature stability of the radiator material is disadvantageous. This difficulty can be overcome by using the optically stimulated luminescence (OSL). The production of suitable detectors for OSL dosimetry and a convenient evaluation equipment are described. The results given for CaF2:Mn-polyethylene detectors show that OSL evaluation is useful for dosimetry in mixed neutron gamma fields.

Calculation of the neutron sensitivity of TL detectors

Abstract A procedure is described for the calculation of the sensitivity of TL detectors in neutron radiation fields. Since in neutron TL dosimeters secondary particles of different types arise at different locations, it is therefore appropriate to consider single components for the calculation of the sensitivity. The following components are taken into account: the interaction of the primary neutrons with the TL material, secondary particles coming out of a radiator, (n, γ)-reactions in the body and the interaction of the albedo neutrons with the TL material. The fundamental steps in the procedure for the calculation of the neutron sensitivity of TL detectors are (a) finding the relation between detector reading and dose through a 60Co gamma calibration, (b) calculation of the dose distribution in L for the different charged secondaries, (c) calculation of the TL effective dose by means of the relative light conversion factor n(L), (d) to get from this dose a value for the detector reading according to the calibration (a). Results are given for CaSO4 combined with a polyethylene (PE) radiator, CaF2 embedded in polytetrafluorethylene (PTFE) and LiF.

Experimental determination of relative light conversion factors of TLD-100 for protons with energies from 2.0 to 9.0 MeV

Abstract The efficiency of thermoluminescent (TL) detectors to heavy charged particles is described by the so-called light conversion factor η. Relative light conversion factors for protons, alphas and heavier recoils are needed for the calculation of the neutron sensitivity of TL detectors. Such light conversion factors can be determined experimentally. In this paper a method is presented for the experimental determination of relative light conversion factors. Using the experimental arrangement described, relative light conversion factors for LiF material (TLD-100) for protons were determined. In LiF the relative main peak (peak V) efficiency is always lower than 1. It increases with increasing proton energy whereas the relative efficiency of the high temperature peak (peak VI) shows an opposite dependence on the proton energy. Relative light conversion factors for peak VI clearly exceed 1.

Dose reduction in computed tomography: the effect of eye and testicle shielding on radiation dose measured in patients with beryllium oxide-based optically stimulated luminescence dosimetry

The aim of this study was to assess the effect of eye and testicle shielding on radiation dose to the lens and the testes of patients undergoing CT examinations. Fifty-one male patients underwent CT twice with identical protocols initially without, the second time with protective garments. Doses to the testes and the lenses were recorded with beryllium oxide-based dosimeters. The dose to the testes and lenses from CT exposure was reduced by 96.2% ± 1.7% and 28.2% ± 18.5%, when testicle and eye shielding was used, respectively. The effect of the eye shielding on the eye lens dose was found to depend on the x-ray tube position when the eye is primarily exposed during the scan. The maximum eye lens dose reduction achieved was found to be 43.2% ± 6.5% corresponding to the anterior position of the tube. A significant correlation between the patient’s body mass index and dose exposure could not be found. Eye and testicle shields, apart from being inexpensive and easy to use, were proven to be effective in reducing eye lens and testicle radiation dose burden from CT exposures.

Scintillation properties of the YVO4:Eu3+ compound in powder form: its application to dosimetry in radiation fields produced by pulsed mega-voltage photon beams

The investigation of scintillation properties of europium doped yttrium orthovanadate shows the suitability of this material for fiber-based dose rate measurements. All measurements were carried out with a 6 MV Varian linear accelerator. The temperature dependence of the signal is lower than that of the plastic scintillators reported so far. By measuring the afterglow of probes between Linac-pulses, the signal due to the stem effect can be successfully eliminated. Comparison of depth dose profiles in a water phantom for radiation field dimensions between 1 x 1 cm(2) and 10 x 10 cm(2) shows that the probes are suitable for small fields having dimensions up to 1 x 1 cm(2). The high light yield of probes having dimensions of 1 mm opens up the possibility for their use in spatially confined radiation fields, such as in intensity-modulated radiotherapy (IMRT) and volume-modulated radiation therapy (VMAT).

LET dependence of the TL response and range measurements of heavy charged particles in TL detectors

Abstract For LiF : Mg, Ti and CaF 2 : Mn powder as well as CaF 2 : Mn-PTFE (30 μm thick) the relative sensitivity was measured as a function of LET. For range measurements of heavy charged particles in TL detectors a method using a SSNTD has shown to be suitable.

Radioluminescence of red-emitting Eu-doped phosphors for fiberoptic dosimetry

Fiberoptic dosimetry (FOD) technique has become an attractive method for real-time dosimetry. Al(2)O(3):Cis one of the most used radioluminescence materials for FOD due to its high efficiency but it presents the drawback of emitting in the spectral region, where spurious luminescence is also important. Optical filtering is the simplest technique to remove spurious luminescence, but is useful when red-emitting scintillators are employed. In this work, the feasibility of using red-emitting Eu-doped phosphors as FOD scintillators has been investigated.

Calculation and experimental determination of the fast neutron sensitivity of OSL detectors with hydrogen containing radiators

Abstract Detectors based on optically stimulated luminescence are useful for fast neutron dosimetry. For this one needs the neutron sensitivity of these detectors. We describe a procedure for the calculation of the neutron sensitivity. For CaF2:Mn embedded in polyethylene the calculated values are compared with experimentally determined neutron sensitivities. There is good agreement.