Unfolding of 239Pu-Be and 252Cf neutron energy spectra using passive multi-layer neutron spectrometer.

In the study, the passive multi-layer neutron spectrometer, based on thermoluminescence detectors, was tested in a calibration laboratory with 239Pu-Be and 252Cf isotopic sources. MCNP code was used for the calculation of the response functions for the neutron energy range from 1 meV to 100 MeV. It was also utilised for initial guess spectra calculations. Deconvolution was performed with MAXED and GRAVEL deconvolution codes resulting in the neutron spectra defined at the measuring point in the calibration laboratory.

Investigation of 252Cf sources with a Ge gamma-ray detector.

This study investigated the feasibility of combining high-resolution gamma-ray spectroscopy with the simulation capabilities of the Nucleonica Nuclear Science Portal with the aim to determine the properties of Cf sources. In this contribution, we present the results for a 20-month-old and a 49-year-old Cf source. In particular, the question arises whether the neutron emission rate can be determined using gamma-ray spectroscopy.

Observation of a Nuclear Recoil Peak at the 100 eV Scale Induced by Neutron Capture.

Coherent elastic neutrino-nucleus scattering and low-mass dark matter detectors rely crucially on the understanding of their response to nuclear recoils. We report the first observation of a nuclear recoil peak at around 112 eV induced by neutron capture. The measurement was performed with a CaWO_{4} cryogenic detector from the NUCLEUS experiment exposed to a ^{252}Cf source placed in a compact moderator. We identify the expected peak structure from the single-γ de-excitation of ^{183}W with 3σ and its origin by neutron capture with 6σ significance. This result demonstrates a new method for precise, in situ, and nonintrusive calibration of low-threshold experiments.

THE NATIONAL RESEARCH COUNCIL OF CANADA MANGANESE BATH SYSTEM.

The manganese salt bath is considered a primary standard for determining the absolute emission rate of radionuclide neutron sources. The National Research Council of Canada has recently revived its manganese salt bath and a full description of the system is given here. The physical characteristics of the bath, as well as the methods for determining the efficiency of the bath system and the induced activity in the bath, are described. An in-depth analysis of the fraction of neutrons captured in the manganese and the correction factor for neutron losses is also provided. Finally, the results of emission rate measurements of four different sources, complete with an uncertainty budget, are given. The emission rates of three americium-beryllium neutron sources and one californium-252 neutron source were found to agree with the known values, within a standard uncertainty of 1.7%.

Development of a Fission Neutron Spectrum from a D-T Neutron Generator by Spectrum Subtraction Technique.

ABSTRACT: Californium-252 (252Cf) is considered essential by the National Institute of Standards and Technology for the calibration of neutron instrumentation and dosimetry. Californium-252 has a relatively short half-life of 2.645 y; consequently, it must be replaced frequently to produce an adequate neutron flux for calibration. The user community is currently looking for a replacement for 252Cf. The patented technology described herein has a high probability of being that replacement. A preferred method to replace 252Cf would use an affordable and easily maintained neutron source that generates neutrons in an energy spectrum as close to that of 252Cf as possible. Deuterium-tritium (D-T) neutron generators are both affordable and easily maintained, which makes them highly attractive for replacing 252Cf. The patented technology discussed in this paper simulates the 252Cf fission spectrum through a D-T neutron generator by using spectral subtraction. The primary spectrum is built using principally (n,xn) and (n,n') reactions in a variety of materials. In conjunction with the primary spectrum, an engineered background spectrum is generated using a second set of materials. This engineered background spectrum corrects for differences between the primary and desired spectra. This subtraction technique generates a spectrum very similar to 252Cf while maintaining a reasonable flux. Further, by choosing different scattering materials, any fission spectrum can be matched, including the thermal and epithermal components. This flexibility expands the potential use of this technology beyond simulating 252Cf to any desired neutron spectrum below 14 MeV.

Assessment of Cs-137, Am-241, and Cf-252 in Well Logging.

ABSTRACT: This paper assesses radiation exposures resulting from 137Cs, 241Am, and 252Cf during well logging incidents. Based on a hypothetical rupture incident, the computer code RESRAD-OFFSITE is run for both offsite and onsite exposure locations. The absorbed doses are compared among three radioactive sources. The adverse health and environmental impact of 241Am is higher than the impact from the other two radioactive sources (137Cs and 252Cf) due to its relatively long half-life and radioactive progeny. The serious impact of 241Am will appear many years after its abandonment depending on its initial activity in the soil. For offsite, the highest maximum dose is due to 241Am (6.18 mSv y-1), which is more than 22 times the maximum doses from 137Cs and 252Cf. For onsite, the highest maximum doses are due to 241Am (121 mSv y-1), which is more than twice the maximum doses from 137Cs and 252Cf. For offsite and onsite, the dominant pathway for 137Cs is direct radiation from soil, the dominant pathway for 241Am is drinking water followed by plant ingestion, and the dominant pathway for 252Cf is direct radiation from soil. Doses from 137Cs and 252Cf are mainly impacted by the contamination on the surface. For 241Am, the opposite is true. Americium-241 doses are mainly impacted by the contamination below the surface. Based on these findings, the exposure impact for replacing an 241Am neutron source for well logging with 252Cf is assessed.

Dosimetric effects of composition, location and size of tissue heterogeneities on 252Cf neutron brachytherapy.

The purpose of this study is to evaluate the effect of tissue heterogeneities on dose distribution in Californium-252(252Cf) neutron brachytherapy. The effect of location and size of heterogeneity on dose distribution was also evaluated. Neutron and photon dose rate distributions were determined in a water phantom in presence of air, lung, soft tissue and bone heterogeneities using MCNPX code. To benchmark the Monte Carlo simulation of the 252Cf source, air kerma strength(SKN), dose rate constant (ɅN) and radial dose function (gN(r)) were calculated and compared with previously reported data. Results showed a considerable reduction of neutron dose rate (up to 66%) inside heterogeneities, especially in air and bone heterogeneities, while the reduction of total photon dose rate was found less significant (up to 10%). In the presence of a heterogeneity, dose rate, fluence and energy spectrum were significantly different with respect to the homogenous phantom. The contribution of photon dose to the total dose in the presence of air and bone was dominant, compared to the neutron dose, whereas this photon contribution was reduced after passing the heterogeneity. As the bone heterogeneity size was increased from 1 × 1 × 1 cm3 to 1 × 3 × 1 cm3, the total dose and neutron energy fluence decreased of about 50% and 70%, respectively.

Relative Biological Effectiveness and Non-Poissonian Distribution of Dicentric Chromosome Aberrations following Californium-252 Neutron Exposures of Human Peripheral Blood Lymphocytes.

Cells exposed to fast neutrons often exhibit a non-Poisson distribution of chromosome aberrations due to the high ionization density of the secondary reaction products. However, it is unknown whether lymphocytes exposed to californium-252 (252Cf) spectrum neutrons, of mean energy 2.1 MeV, demonstrate this same dispersion effect at low doses. Furthermore, there is no consensus regarding the relative biological effectiveness (RBE) of 252Cf neutrons. Dicentric and ring chromosome formations were assessed in human peripheral blood lymphocytes irradiated at doses of 12-135 mGy. The number of aberrations observed were tested for adherence to a Poisson distribution and the maximum low-dose relative biological effectiveness (RBEM) was also assessed. When 252Cf-irradiated lymphocytes were examined along with previously published cesium-137 (137Cs) data, RBEM values of 15.0 ± 2.2 and 25.7 ± 3.8 were found for the neutron-plus-photon and neutron-only dose components, respectively. Four of the five dose points were found to exhibit the expected, or close to the expected non-Poisson over-dispersion of aberrations. Thus, even at low doses of 252Cf fast neutrons, when sufficient lymphocyte nuclei are scored, chromosome aberration clustering can be observed.

External beam radiotherapy with or without californium-252 neutron brachytherapy for treatment of recurrence after definitive chemoradiotherapy.

We aimed to evaluate the application of external beam radiotherapy (EBRT) combined with californium-252 (252Cf) neutron intraluminal brachytherapy (NBT) in patients with local recurrent esophageal cancer after definitive chemoradiotherapy (CRT). Sixty-two patients with local recurrent esophageal squamous cell carcinoma after definitive CRT were retrospectively analyzed; 31 patients underwent NBT+EBRT, and 31 received EBRT alone. The response rate; 1-, 2-, and 3-year overall survival rates; and adverse event occurrence rates were compared between these two patient groups. The response rate was 83.87% (26/31) in the NBT+EBRT group and 67.74% (21/31) in the EBRT group (p < 0.001). The 1-, 2-, and 3-year overall survival rates were 80.6%, 32.3%, and 6.5%, respectively, in the EBRT group, with a median survival time of 18 months. The 1-, 2-, and 3-year overall survival rates were 83.8%, 41.9%, and 6.9%, respectively, in the NBT+EBRT group, with a median survival time of 19 months. The differences between the groups were not significant (p = 0.352). Regarding acute toxicity, no incidences of fistula or massive bleeding were observed during the treatment period. The incidences of severe and late complications were not significantly different between the two groups (p = 0.080). However, the causes of death for all patients differed between the groups. Our data indicate that 252Cf-NBT+EBRT produces favorable local control for patients with local recurrent esophageal cancer after CRT, with tolerable side effects.

[Operative efficacy of 13 malignant uterine tumors after Cf-252 intracavitary irradiation].

Objective: To investigate the surgical therapeutic efficacy of uterine tumors patients underwent Cf-252 neutron intra-cavity and external radiotherapy, and evaluate the application value of Cf-252 neutron radiotherapy. Methods: Thirteen cases of uterine tumor with local suspicious lesions or poor prognostic factors after CF-252 neutron intracavity and external radiotherapy were treated with surgery. Among them, 12 cases underwent extrafascial hysterectomy, 1 case underwent extensive hysterectomy and lymphadenectomy. The postoperative pathology and follow-up results were used to evaluate the efficacy. Results: Nine cases showed severe response to radiotherapy in postoperative cervical pathological tissues without residual tumor, and survived for more than 3-14 years, the median survival time was 8 years. All of 4 cases with residual tumor died within 1 year. Delayed healing of vaginal wounds occurred in 3 of the 12 cases. Conclusions: Cf-252 is a good brachytherapy source. The cervical tissue shows severe response to radiotherapy and prolonged healing time of vaginal wound is observed in some cases after CF-252 radiotherapy. To those uterine tumor patients with local suspicious lesions or poor prognostic factors after CF-252 neutron intracavity and external radiotherapy, extrafascial hysterectomy is a safe and feasible treatment method.

EXPERIMENTAL DETERMINATION OF ANISOTROPIC EMISSION OF NEUTRONS FROM 252CF NEUTRON SOURCE WITH THE SPHERICAL PROTECTION CASE.

The anisotropic emission of neutrons from a cylindrical X1 252Cf source with the spherical external casing was experimentally determined. The influence of metal materials and shapes of the external casing to the anisotropy factor, FI(θ), was assessed by the Monte Carlo calculation, before performing the measurement. The results of the calculation implied that light- and spherical-shaped external casing decreases the anisotropic emission of neutrons from a cylindrical source and the nature of the material does not affect the anisotropic emission to a large extent. The experimental results obtained when a spherical-shaped aluminum protection case was employed also revealed that the anisotropy factor was close to 1.0 with a wide zenith angle range. Considering the source handling and measures against mechanical impact to the source, we designed an SUS304-made spherical protection case for a renovated source delivering apparatus. With the SUS304-made spherical protection case, the measured anisotropy factor FI(90) was determined to be 1.002 ± 0.002 (k = 1). Results from the experiments also indicated that the measured anisotropy factor has a flat distribution from 55 to 125° with zenith angle.

Effects of chronic exposure to a mixed field of neutrons and photons on behavioral and cognitive performance in mice.

To simulate the space radiation environment astronauts are exposed to, most studies involve acute exposures but during a space mission there will be chronic (long-lasting) exposures. To address this knowledge gap, a neutron irradiator using a 252Cf (252Californium) source was used to generate a mixed field of neutrons and photons to simulate chronic, low dose rate exposures to high LET radiation. In the present study, we assessed the effects chronic neutron exposure starting at 60 days of age on behavioral and cognitive performance of BALB/c female and C3H male mice at 600 and 700 days of age as part of an opportunistic study that took advantage of the availability of neutron and sham-irradiated mice from a radiation carcinogenesis experiment. There were profound dose- and time point-dependent effects of chronic neutron exposure. At the 600-day time point, irradiated BALB/c female mice showed improved nest building at all three doses. At the 700-day, but not 600-day, time point slightly but significantly increased body weights were seen in C3H male mice exposed to 0.118 Gy. At the 600-day time point BALB/c female mice irradiated with 0.2 Gy did, like sham-irradiated, not show preferential exploration of the novel object that was seen in mice irradiated with 0.118 or 0.4 Gy. In C3H male mice exposed to 0.4 Gy and at the 600-day time point, increased measures of anxiety were observed on days 1 and 2 in the open field. Thus, different outcome measures show distinct dose-response relationships, with some anticipated to worsen performance during space missions, like increased measures of anxiety, while other anticipated to enhance performance, such as increased nest building and object recognition.

IMPROVEMENT OF GAMMA-RAY SUBTRACTION PROCEDURE FOR A CURRENT-MODE NEUTRON DETECTOR WITH A PAIR OF 6Li- AND 7Li-GLASS SCINTILLATORS.

A current-mode neutron detector with a pair of 6Li- and 7Li-glass scintillators has been developed to measure high-flux neutrons in a boron neutron capture therapy field. Neutrons are basically measured by subtracting gamma-ray component using current outputs from the 7Li-glass scintillator. In the present study, the difference in the gamma-ray sensitivity between the 6Li- and 7Li-glass scintillators and the neutron sensitivity for the 7Li-glass scintillator due to the 6Li contamination were also considered to improve the gamma-ray subtraction precision. The gamma-ray subtraction procedure was experimentally investigated in thermal neutron fields with 252Cf and 241Am-Be neutron sources, which have different gamma-ray intensities per unit neutron fluence. A linear relation between neutron fluence and current output was obtained for the neutron detector in the two types of thermal neutron fields with different gamma-ray intensities. It was found that the gamma-ray subtraction procedure is useful for current-mode neutron detectors.

ESTIMATION OF THE ANISOTROPY EMISSION OF LPN/CIEMAT NEUTRON SOURCES: EFFECT OF HEAVY CAPSULE HOLDERS.

In order to estimate the anisotropy emission of 241Am-Be and 252Cf neutron sources from the Spanish Neutron Standards Laboratory (LPN/CIEMAT) detailed models of sources capsules and capsule holders were designed with the MCNPX code. Simulations of the sources inside the capsules without the capsule holders were done to validate the MC model by comparison with experimental results provided by other authors. After that, the capsule holders were incorporated to the simulation. In general, a good agreement has been found between measurements and our calculations. Results show the additional encapsulations have significant influence on anisotropy factors, energy spectra and dose rates.

Study on the Relationship between Seed Absorbed Dose and Seed Composition of 252Cf Neutron Source Irradiated Bean Seed.

This study aims to further identify the biological effects of neutron-irradiated plants and provides insights into the mutation breeding of such plants. In this study, the neutron irradiation device designed by our institute was used to analyze the relationship between the seed components in different legume crops and their neutron absorption dose rate, fission gamma absorption dose rate, and induced gamma absorption dose rate. The results show that the effect sizes of the components on the neutron absorbed dose rate are as follows: ash > fat > moisture > carbohydrate > protein. The effect sizes of the components on the absorbed dose rate of fission gamma are as follows: ash > moisture > fat > carbohydrate > protein. There is a positive correlation between fission gamma absorbed dose rate and the weight of ash, water and fat, while a negative correlation with carbohydrate and protein. However, the linear relationship between each component and the absorbed dose rate of induced gamma is not significant, this needs to be identified by further researches. Based on the results of the present study, we conclude that the neutron absorbed dose can be calculated without taking into account the fat composition of bean crop seeds (except for soybean seeds) in the process of mutation breeding induced by radiation. In special cases where the accuracy requirement of the dose rate is not high, it is possible to use protein instead of legume crop seeds for neutron absorption dose calculations.

THE DETERMINATION OF NEUTRON FLUENCE TO ABSORBED DOSE CONVERSION COEFFICIENTS AND RELATIVE BIOLOGICAL EFFECT BASED ON MICRODOSIMETRY MEASUREMENTS.

A tissue-equivalent proportional counter (TEPC) is a reference detector to measure microdosimetric quantities. A conventional spherical TEPC and a novel TEPC based on a ceramic thick gas electron multiplier (THGEM) foil were developed to carry out microdosimetric measurements of lineal energy spectra in monoenergetic and 252Cf/241Am-Be neutron radiation fields, and the absorbed dose values had been derived. In order to go further in radiobiology and therapy, the fluence to absorbed dose conversion coefficients in neutron fields were also determined. According to the dose distribution in lineal energy, the neutron relative biological effect (RBE) values were also calculated using an empirical procedure applying biological weighting functions.

Second primary malignancies after high-dose-rate 60Co photon or 252Cf neutron brachytherapy in conjunction with external-beam radiotherapy for endometrial cancer.

PURPOSE: Second primary malignancies (SPMs) may occur in organs after radiotherapy (RT). This study aimed to determine the rate and distribution of SPMs for photon- or neutron-emitting radiotherapy sources for patients treated for primary endometrial cancer. METHODS AND MATERIALS: The cohort comprised 426 patients with 5334 patient-years of observation. Patients were treated by different methods of RT from 1990 to 2000. Patients received postoperative 60Co external-beam radiotherapy (43.4%), external-beam radiotherapy + high-dose-rate (HDR) intracavitary brachytherapy with 60Co or 252Cf (42.3%), or HDR intracavitary brachytherapy alone with 60Co or 252Cf (14.3%). RESULTS: Over a 25-year period, 47 SPMs were observed (21 for HDR 60Co and 26 for HDR 252Cf). SPMs were observed for 13 patients in the high-intermediate risk group for each radiation source. Patients treated with 60Co developed SPMs in the urinary tract (1.2%) and in lymphoid/hematopoietic tissues (1.2%). Only three SPM cases (0.7%) were observed in digestive tract. In comparison, the patient group treated with 252Cf developed SPMs in the digestive tract (1.4%) with the majority in the colon (1.2%), urinary tract (0.9%) primarily the kidneys, and vulva (0.7%). All other SPMs (4.9%) were in the low-risk group. Of these, SPMs in the skin were most prevalent (1.6%) for 60Co, and breast (1.6%) for 252Cf, but believed to be caused by factors other than treatment. SPM incidence in the digestive and urinary tracts were similar (2.1%), regardless of radiation source. CONCLUSIONS: For followup at 25 years, 47 SPMs were observed with no differences in the high-intermediate risk group depending on the RT source.

EXPERIMENTAL AND COMPUTATIONAL EVALUATION OF EFFECTIVE CENTRE FROM A LONG COUNTER AT NEUTRON METROLOGY LABORATORY IN BRAZIL.

A long counter detector was manufactured by the Institute of Advanced Studies (IEAV) and was characterised in the neutron low scattering room at Brazilian National Ionising Radiation Metrology Laboratory (LNMRI/IRD) to deploy a secondary Standard for neutron fluence. The effective centre was measured experimentally with 252Cf+D2O, 252Cf, 241AmBe and 238PuBe neutron sources, having average energies from 0.55 to 4.16 MeV. The experimental arrangement and detector construction were carefully reproduced in Monte Carlo simulations, and the computational results were found to be in good agreement with those from experiment.

REFERENCE NEUTRON FIELDS IN CALIBRATION LABORATORY; SIMPLE DOSIMETRIC PARAMETERS AND THEIR CHANGES IN TIME.

The calibration laboratory revises periodically the dosimetric properties of its calibration fields. For reference neutron fields based on radionuclide sources, it is due to presence of isotopic impurities in the source ingredients. Consequently, in long term, the admixtures and their decay products become significant. Neglecting the impact of such effect leads to inconsistencies between the neutron emission rate observed during the measurements and the emission rate derived from the decay curve of the main isotope. In the Radiation Protection Measurements Laboratory at the National Centre for Nuclear Research the neutron fields of the bare sources of 252Cf, 241AmBe and 239PuBe have been examined for nearly 30 years, regularly, in fixed geometry. Additionally, at the particular point of a calibration bench, determination of neutron fluence rate, ambient dose equivalent rate and its scattered component, total neutron and gamma dose rate, gamma to total dose ratio, radiation quality factor and total tissue kerma are occasionally determined. In this article, we would like to present recently achieved results and their comparison with the measurement data formerly presented. The growth of the neutron emission of 239PuBe source, as well as discrepancies between the decay curves of relevant isotopes and the emission rate of 252Cf and 241AmBe will be presented.