Neutron spectrometer for fast nuclear reactors

In this paper we describe the development and first tests of a neutron spectrometer designed for high flux environments, such as the ones found in fast nuclear reactors. The spectrometer is based on the conversion of neutrons impinging on $^6$Li into $\alpha$ and $t$ whose total energy comprises the initial neutron energy and the reaction $Q$-value. The $^6$LiF layer is sandwiched between two CVD diamond detectors, which measure the two reaction products in coincidence. The spectrometer was calibrated at two neutron energies in well known thermal and 3 MeV neutron fluxes. The measured neutron detection efficiency varies from 4.2$\times 10^{-4}$ to 3.5$\times 10^{-8}$ for thermal and 3 MeV neutrons, respectively. These values are in agreement with Geant4 simulations and close to simple estimates based on the knowledge of the $^6$Li(n,$\alpha$)$t$ cross section. The energy resolution of the spectrometer was found to be better than 100 keV when using 5 m cables between the detector and the preamplifiers.Comment: submitted to NI

The developmental pathways of preschool children with acute lymphoblastic leukemia: communicative and social sequelae one year after treatment

Early childhood is considered to be a period of rapid development, with the acquisition of abilities predicting future positive school competences. Motor, cognitive, and social diculties related to cancer therapies heavily impact the development of children with cancer. This study focused on two main aims: To assess the developmental pathways of preschool children with acute lymphoblastic leukemia one year post-treatment and to compare these abilities both with those of a control group of healthy peers and with Italian norms. Forty-four children and their families, recruited through the Hematology-Oncologic Clinic of the Department of Child andWoman Health (University of Padua), agreed to participate in this study. The children\u2019s mean age was 4.52 years (SD = 0.94, range = 2.5\u20136 years), equally distributed by gender, all diagnosed with acute lymphoblastic leukemia. Matched healthy peers were recruited through pediatricians\u2019 ambulatories. Each family was interviewed adopting the Vineland adaptive behavior scales. Paired sampleWilcoxon tests revealed that children were reported to have significantly more developmental diculties than their healthy peers. When compared with Italian norms, they scored particularly low in verbal competence, social, and coping skills. No significant association was found between treatment variables and developmental abilities. These findings suggest that the creation of specialized interventions, both for parents and children, may fill the possible delays in children\u2019s development probably due to stress, lack of adequate stimulation, or dicult adaptation

Search for Neutron Flux Generation in a Plasma Discharge Electrolytic Cell

Following some recent unexpected hints of neutron production in setups like high-voltage atmospheric discharges and plasma discharges in electrolytic cells, we present a measurement of the neutron flux in a configuration similar to the latter. We use two different types of neutron detectors, poly-allyl-diglicol-carbonate (PADC, aka CR-39) tracers and Indium disks. At 95% C.L. we provide an upper limit of 1.5 neutrons cm^-2 s^-1 for the thermal neutron flux at ~5 cm from the center of the cell. Allowing for a higher energy neutron component the largest allowed flux is 64 neutrons cm^-2 s^-1. This upper limit is two orders of magnitude smaller than what previously claimed in an electrolytic cell plasma discharge experiment. Furthermore the behavior of the CR-39 is discussed to point our possible sources of spurious signals.Comment: 4 pages, 3 figure

Health-related quality of life in AYA cancer survivors who underwent HSCT compared with healthy peers

This\ue002study\ue002was\ue002aimed\ue002at\ue002comparing\ue002adolescent\ue002and\ue002young\ue002adult\ue002(AYA)\ue002Hematopoietic\ue002 Stem Cell Transplantation (HSCT) paediatric cancer survivors and a control group of healthy peers in terms of Health- Related Quality of Life (HRQOL) and frequency of posttraumatic\ue002stress\ue002symptoms\ue002(PTSS).\ue002The\ue002participants\ue002were\ue00232\ue002AYA\ue002HSCT\ue002survi- vors and 28 matched healthy peers. The survivors were, on average, 19.4 years old (SD = 3.8), with an average age of 8.1 years (SD = 4.3) at diagnosis, and with a mean time, since treatment was completed, of 8.5 years (SD = 3.2). The majority of survi- vors (78.1%) did not show clinical PTSS, with intrusion symptoms most frequently reported in those who had undergone autologous HSCT (F = 3.3; df = 2; p = 0.05) and relapse presence in their treatment associated with more PTSS avoidance symptoms (r = 0.4; p\ue002=\ue0020.002).\ue002Women\ue002reported\ue002more\ue002problems\ue002in\ue002the\ue002SF-\ue00236\ue002pain\ue002scale\ue002(t = 2.1; df = 31; p\ue002=\ue0020.04)\ue002than\ue002men.\ue002Additionally,\ue00287.5%\ue002of\ue002survivors\ue002fell\ue002below\ue002the\ue00225th\ue002per- centile\ue002in\ue002the\ue002SF-\ue00236\ue002general\ue002well-\ue002being\ue002scale,\ue002and\ue00270.8%\ue002had\ue002the\ue002same\ue002trend\ue002for\ue002the\ue002 SF-\ue00236\ue002fatigue\ue002scale.\ue002Survivors\ue002reported\ue002better\ue002emotional\ue002well-\ue002being\ue002(t\ue002=\ue0022.6,\ue002df = 27, p = 0.01) and fewer limitations than their healthy peers (t = 2.5, df = 27, p = 0.02), while they perceived a lower life satisfaction referring to the past (t\ue002=\ue002 122.8,\ue002df = 27, p = 0.009)

Silicon Photo-Multiplier radiation hardness tests with a beam controlled neutron source

We report radiation hardness tests performed at the Frascati Neutron Generator on silicon Photo-Multipliers, semiconductor photon detectors built from a square matrix of avalanche photo-diodes on a silicon substrate. Several samples from different manufacturers have been irradiated integrating up to 7x10^10 1-MeV-equivalent neutrons per cm^2. Detector performances have been recorded during the neutron irradiation and a gradual deterioration of their properties was found to happen already after an integrated fluence of the order of 10^8 1-MeV-equivalent neutrons per cm^2.Comment: 7 pages, 6 figures, Submitted to Nucl. Inst. Meth.

Trapping and detrapping effects in high-quality chemical-vapor-deposition diamond films: Pulse shape analysis of diamond particle detectors

An analysis of the time evolution of the response of diamond particle detectors is carried out, using as a probe 5.5 MeV α particles impinging on high-quality diamond films grown by microwave chemical vapor deposition (CVD). Both the amplitude and the time evolution of the pulses are shown to change drastically when the detector is preirradiated with β particles (pumping), a slow component developing after pumping, indicating carriers trapping and releasing (detrapping). Pulse shapes obtained for positive and negative detector polarities are compared in both the as-grown and pumped states. The presence of at least two trapping centers for holes is necessary to explain the results, the shallower having an activation energy of about 0.3 eV. The effects of pumping are clarified, and the different role played by electrons and holes is evidenced. We modify a previous model for trapping-detrapping behavior originally applied to Si(Li) detectors to describe the more complex behavior of CVD diamond detectors, and develop a computer simulation based on it. The simulated pulse shapes agree very well with experiment with reasonable values of the physical parameters involved, making this technique helpful for studying and identifying defects which are responsible for limitation of the efficiency of CVD diamond particle detectors. Field-assisted detrapping seems to take place for fields of about 104 V/cm

Systematic study of the normal and pumped state of high efficiency diamond particle detectors grown by chemical vapor deposition

The efficiency and charge collection distance (CCD) of nuclear particle detectors based on high quality diamond films grown by chemical vapor deposition (CVD) have been systematically studied as a function of the methane content in the growth gas mixture and for varying film thickness. The effects of preirradiation with β particles (pumping) have been thoroughly studied. The results fully support a recently proposed model [Marinelli et al., Appl. Phys. Lett. 75, 3216 (1999)] discussing the role of in-grain defects and grain boundaries in determining the charge collection spectra of CVD diamond films both in the normal and in the pumped state. The model allows us to quantitatively explain the dependence of CCD and efficiency on film thickness, giving a microscopic picture of the effects of preirradiation with ionizing radiation in CVD diamond films. The highest average CCD obtained is 145 μm in a 160 μm thick detector (corresponding to about 50% average efficiency), while the maximum value (about 70% efficiency) is close to 370 μm. In addition, CCD is shown to be higher than film thickness and to monotonically increase with thickness, indicating margins for further improvements. © 2001 American Institute of Physics