Summary of P6 Problem: Iron Sphere Experiment

Transcription

1 Uncertainty Assessment in Comutational Dosimetry: A comarison of Aroaches Summary of P6 Problem: Iron Shere Exeriment Presentation and Evaluation of Solutions with Conclusions for Future SINBAD Comilations I. Kodeli IAEA reresentative at OECD/NEA DB, Issy-les-Moulineaux, France SINBAD Benchmarks using TOF technique Reactor Shielding IPPE Th shell with 14 MeV and Cf-252 source neutrons Fusion Neutronics Shielding Nickel Shere (OKTAVIAN) Iron Shere (OKTAVIAN) Aluminium Shere (OKTAVIAN) Silicon Shere (OKTAVIAN) Tungsten Shere (OKTAVIAN) FNS Liquid Oxygen FNS Skyshine FNS Dogleg Duct Streaming IPPE Vanadium Shells IPPE Iron Shells Accelerator Shielding RIKEN Quasi-monoenergetic Neutron Field in MeV Energy Range HIMAC High energy Neutron (<800 MeV) Measurements in Iron HIMAC High energy Neutron (<800 MeV) Measurements in Concrete MSU exeriment with He & C ions on Al target Neutron Sectra Generated by 590-MeV Protons on a Thick Pb Target I. Kodeli: Summary of P6 Problem: Iron Shere Exeriment P6 - Neutron Sectra from Iron Sheres 14 MeV facility at IPPE, Obninsk, Russia TOF exeriments: detector time resolution, multile scattering, flight ath, neutron source from D-T reaction, conversion between time-of-arrival and energy sectra... I. Kodeli: Summary of P6 Problem: Iron Shere Exeriment 1

2 P6 - Iron Shere Exeriments Source: 280 kev deuterons injected to TiT target located in center of Fe sheres. ~14 MeV n roduced by T(d,n). 5 iron sheres with wall thicknesses cm. Energy and TOF sectra Tasks: Calculate neutron leakage sectra for different iron shells. For larger shells comare the sectra obtained using time indeendent and time deendent transort calculations; Aly resonse function to account for resolution broadening and collimator scattering; Estimate the uncertainties in the calculated neutron sectra. Verify if the agreement between the calculation and exeriment is within the overall uncertainties. I. Kodeli: Summary of P6 Problem: Iron Shere Exeriment Objectives Test the skills of the articiants in the use of the comuter codes and the nuclear data; Obtain feedback information on how suitable the information contained in SINBAD is for the nowadays users and comuter codes. Provide guidance for the future SINBAD comilations in order to facilitate the use of exerimental data, and to deduce maximum information from the measurements. I. Kodeli: Summary of P6 Problem: Iron Shere Exeriment IPPE - Fe # 1 Shere Returned Solutions Neutron sectrum/ U Leakage sectra (n/mev) E-3 1E-4 Ex IJS JEFF nea JEFF IJS ENDF G H Energy (MeV) IPPE-Fe shere #5 Ex. sh.#5 MCNP5 IJS JEFF IJS ENDF G H (E) H (T) Altogether three solutions were received from the articiants, all using MCNP codes. Although the modelling of the geometry and the transort calculations themselves seemed not to cause roblems to the articiants, the whole roblem was found rather demanding, osing difficulties in the hysical interretation of the measurements and the comutational results. Two of the received solutions were not comlete since many hysical effects were not addressed roerly or not at all. Energy (MeV) I. Kodeli: Summary of P6 Problem: Iron Shere Exeriment 2

3 IPPE - Fe # 1 Shere Solutions Neutron sectrum/ U Ex IJS JEFF nea JEFF IJS collimator IPPE-Fe shere # Energy (MeV) 1 On the other hand, one solution received is very comlete, with detailed study of major effects and some uncertainties involved in the measurements and the interretation. Leakage sectra (n/mev) E-3 Ex. sh.#5 MCNP5 IJS JEFF IJS ENDF Energy (MeV) I. Kodeli: Summary of P6 Problem: Iron Shere Exeriment Conclusions - Several articiants found the hysical interretation of the exercise difficult, articularly the detector resonse function was not used roerly in 2 cases;; - Modification (simlification of hysics) in the SINBAD benchmark descrition would facilitate the use of the data; - Exlicit modelisation of the collimator and roviding TOF sectra in addition to the energy sectra could make the life of the users much easier. If the collimator is included in the comutational model, the MCNP results (using 4-ns Gaussian broadening), could be comared directly with the measured TOA sectra, without needing any resonse function, nor TOA-Energy transformation. Detailed information on collimator and detector system would be required in the latter case. I. Kodeli: Summary of P6 Problem: Iron Shere Exeriment Faculty of Science Institute of Nuclear and Particle Physics, Radiation Physics Grou P8 Sensitivity Study of a Recoil- Proton Telescoe Detector J. Posselt 1, J. Henniger 1 and B.R.L. Siebert 2 1 ) TU Dresden 2 ) retired senior researcher, PTB Braunschweig Bologna, October 10 th,

4 Detector Geometry, General assumtions (see P1): y z x n n θ olyethylene dead layer E stage E stage first collission effects m = m, isotroic n scattering in CM µ = cos( θ ) f µ 2 ( ) 1 ( + 1K 0) = 0 (0K 1) E = E cos ( θ ) = E µ 2 2 n n Different ways of sensitivity analysis 1 Simle deterministic aroach 2 3D Monte Carlo calculations with AMOS a) simle model (straight lines, energy range tables) b) realistic model (curved trajectories, energy and range straggling) Deterministic Aroach 0 * 2 N( En) = A Φ Σ e( En) z H (, zen, µ )dµ * Z ( En ) 1, x 0, Heaviside Function H() x = 0, otherwise. A area of the exosed converter surface Σ e cross section density for roton generation. hysical dimensions and neutron energy fixed with given tolerances cross sections densities Σ t (CH 2 ) and Σ e (H), well known microscoic cross sections stoing owers res. energy range functions StoPow or SRIM tables differences max. 1% absolute values vary by max. ±3% for the resent targets (PE, Ti and Si) * Z ( K ) contains the thickness of dead layer RΦ En = A Σ En * Z E e n and E-stage etc. as additional arameters. ( ) ( ) ( ) Sensitivity coefficients: c RΦ( En) RΦ( En) = = A A other terms analog A w ( R ( E )) = w ( A) + w ( Σ ) + w ( Z ( E )) * Φ n e n 4

5 E kev Evaluation of Uncertainties w(a) analytical w(σ e ) analytical w(z * ) numerical w(r Φ ) seems good for estimating the uncertain-ties in energies, areas, thicknesses and cross section densities their influence with on the resonse decreases with increasing energy - but is the imlied transort model correct? 3D Monte Carlo calculations with AMOS n olyethylene simle Model n olyethylene realistic Model y z x θ dead layer E stage y z x θ dead layer E stage E stage E stage Sensitivity E n R Φ - simle R Φ - realistic 680 kev 996 kev 1306 kev cm² cm² cm² cm² cm² cm² 5

6 Summary Comarison of simle and realistic MC calculations show that the simle model overestimates R Φ For high energies the simle model is satisfying and the deterministic uncertainty calculation is alicable For low energies there are major differences between simle and realistic model. Hence, the alicability of the deterministic uncertainty calculation has to be questioned Conclusions The simle deterministic aroach is good for analyzing the influence of neutron energies, layer thicknesses and nuclear res. atomic data on detector resonse Monte Carlo calculations allow to discuss all arameters including 3D effects Further investigations by realistic Monte Carlo simulations are necessary for final evaluation Summary - Problem P7: Energy Resonse Characteristics of a MOSFET Radiation Detector Robert A. Price Detectors and Nuclear Science Laboratory (DENSL) The City University London r.rice@city.ac.uk 6

7 National requirements to erform in vivo atient dosimetry (eg Council Directive 97/43/euratom, UK cancer standards, etc) Should form art of QA rocedures of an oncology deartment Ergo a need for simle high-fidelity system Reality: - no system exists for brachytheray QA Develoed non-encasulated semiconductors (MOSFETs) Used micro-electronics fabrication rocesses Custom designed layered flex Layer 1 Layer 2 Field oxide Thickness = 1.5 µm Metallization thickness = 1µm Field oxide Thickness = 1.5 µm Region 1: 250 µm lid 29% Ni, 17% C0, 54% Fe Region 2: 250 µm vacuum Region 3: 0.2 µm thick assivation Si 3N 4 P + - source 500 µm Substrate Gate, thickness = 0.4 µm. Width = 800 µm Length = 50 µm P + - drain Region 4: 1 µm thick aluminium contact Region 5: 0.4 µm thick gate oxide SiO 2 1 Calculate the energy resonse function (for caed and uncaed systems) 2 Consider the effects of uncertainties in the comosition of the device: a) 20% in thickness of region 1 b) 20 % in Ni roortion of region 1 c) 20% in Ag in region 7 d) 200% underestimate of region 8 thickness e) sensitivity to lateral extent Region 6: 500 µm thick silicon substrate - Si Region 7: 250 µm adhesive 80% Ag, 20% SiO 2 Region 8: 1.5 µm Au attach ad A Region 9: 2 µm Ni attach ad B Region 10: 0.2 mm attach ad C - 90% W, 10% Cu Region 11: 1000 µm Al 2O 3, base 7

8 Particiant A Particiant B Particiant C Particiant D MCNP PENELOPE GEANT 4 FLUKA FOTELP Particiant C: Question 1 results. energy of the source(ev) energy deosited at gox (kev) Absorbed dose (arb units) Photon energy kev Plotted from data rovided Particiant D: Question 1 results. Particiant A Particiant B Particiant C Particiant D MCNP 52 kev 52 kev PENELOPE 42 kev GEANT 4 FLUKA 56 kev 55 kev FOTELP 52 kev Author results: MCNP - 55 kev, Peneloe, 54 kev, ex. 55 kev (rov.) 8

9 Percentagechange in dose Nondimnsional area Only articiant A investigated the effect of geometric truncation! Results shown are from the author s solution - Particiant A solution is consistent. Similarly, only one articiant (exlicitly) discussed the effect of varying code arameters - Particiant B. Although discussions with articiant A indicate that this grou also investigated this. Comonents of sensitivity from roblem secification layer thickness comosition kerma calculation data / assumtions osition in energy of maximum geometrical truncation cross-sections code sace etc Only one grou (A) rovided a sensitivity analysis % Author s sensitivity analysis % Conclusions - Whilst all articiants clearly understood the nature of the roblem only one grou (A) rovided solutions and justifications for all arts. - Secifically, only one grou (A) attemted a sensitivity analysis of the data. - two of the four grous used only one code and then didn t test the validity of the code limitations and assumtions for the given roblem. - Only one grou reorted investigations ertaining to their geometric simlifications and demonstrated a clear effect on the results. - Presentation of results from one grou seemed to suggest a lack of self reflection - ie a naive belief in the comutational results. 9