1 / 17

Neutron Background Study

Neutron Background Study. Gary Bower Oct 4, 2004 Babar simulation meeting. Warning. This is the opposite of finished work. It is an initial exploration of a concept. Some items that follow are intentionally simplified. Some items may unintentionally be incorrect.

beau-serrano
Download Presentation

Neutron Background Study

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Neutron Background Study Gary Bower Oct 4, 2004 Babar simulation meeting

  2. Warning • This is the opposite of finished work. • It is an initial exploration of a concept. • Some items that follow are intentionally simplified. • Some items may unintentionally be incorrect. • I am on a learning curve. Neutrons in PEP/Babar - Bower

  3. Introduction • Many ways to present this information. • Will skip the generalities and immediately go into a concrete problem discussion. • The initial goal is to determine the neutron flux at the B1 magnets for Mike Sullivan. • Will discuss an approach to doing this. Neutrons in PEP/Babar - Bower

  4. A crude model • 8 GeV beam e- hits Q2 magnet. • e- brems to 4 GeV e- and 4 GeV gamma. • 4 GeV gamma pair produces a 2 GeV e+ and e-. • Cascade to ~400 x 20 MeV es and gammas. • Giant Dipole Resonance (GDR) captures 1.5%. • GDR decays to a few multi-MeV neutrons. • Neutrons travel and thermalize down to a few eV. • Nuclear capture or fission. • Decay emitting detectable radiation. Neutrons in PEP/Babar - Bower

  5. Model notes • Each 8 GeV beam e- produces ~10-20 neutrons. • EM shower is directed. • GDR neutron “shower” is isotropic. • The neutrons travel far beyond the zone of the original EM shower. Neutrons in PEP/Babar - Bower

  6. Mike’s problem • Want’s to build sumarium-cobalt B1 magnets. • Neutron + sumarium decreases magnetic moment of sumarium nucleus. • What is the neutron flux at each B1? Neutrons in PEP/Babar - Bower

  7. Simulation based solution to Mike’s problem • Do a simulation of 8 GeV e- on Q2 and find the neutron flux at each B1 per e-. • Problem 1: Is the simulation correct? • Problem 2: What is absolute e- rate on Q2? Neutrons in PEP/Babar - Bower

  8. Jerry Vavra’s breakthrough • Jerry developed a diagnostic neutron detector. • He deployed two in Babar. • The neutron flux in each detector varied with time but their ratio was constant!! • This strongly suggests neutrons are created by a single accelerator process that varies in intensity. • Postulate a single neutron source location. • and assume the physics model in slide 2. • and use the neutron flux ratio. • to deduce the distance of the neutron source from the two detectors. • Answer: outgoing Q2. Neutrons in PEP/Babar - Bower

  9. Data based solution to Mike’s problem • Using the model of slide 2 + Jerry’s data + Q2 as the neutron source we can calculate the absolute flux at both B1 magnets. • Problem 3: Is the model correct? Neutrons in PEP/Babar - Bower

  10. Putting it together • We have two solutions but with three problems. • We can put the two solutions together to solve the three problems. Neutrons in PEP/Babar - Bower

  11. Solutions to problems • Problem 1: Is the simulation correct? • Answer 1: Yes, if it predicts Jerry’s flux ratios at his detectors. • Problem 2: What is e- rate on Q2? • Answer 2: Use absolute neutron flux rates on Jerry’s detectors to get flux at the B1s. • Problem 3: Is the model correct? • Answer 3: Yes, if it agrees with simulation. Neutrons in PEP/Babar - Bower

  12. Many caveats • Jerry has found that the neutron flux varies with the lumi term – reinforces the idea of beam e- on something near the IP. • Two detectors do not justify the assumption of a localized neutron source. Need three. • Perhaps the neutron source is not localized. • Also need three detectors to truly validate model. • To be a magnet problem the neutrons must be thermalized. Neutrons in PEP/Babar - Bower

  13. 1st crude calculation of flux on B1s • Assume source is at z = +3m. • Detector D1 is at z = +3.65m. • Thermalized flux at D1 = 8 Hz. • Volume of D1 = 10cc. • 1Hz/cc at 3.65m due to source at +3m. • Flux at +1m = 1*(0.65/2)**2 = 0.1 Hz/cc. • Flux at -1m = 1*(0.65/4)**2 = 0.03 Hz/cc. Neutrons in PEP/Babar - Bower

  14. Initial To Do List • Model Jerry’s detectors in G4 – validate. • Simulate in Babar a GDR neutron source at +3m. • Does it gives Jerry’s flux ratios? • What is the flux at each B1? • This list is simple but interpreting and refining the results will be involved and will lead naturally to more things to do. Neutrons in PEP/Babar - Bower

  15. Further possible study items • Soon will have data from 3rd detector and also have neutron data in DIRC. • Is all the data consistent with the model and the simulation? • Is the neutron source extended? • How good is the G4 simulation? Compare special cases with Fluka, G3? • Compare G4 with E166 data. • Test beam studies at FFTB. Neutrons in PEP/Babar - Bower

  16. Propitious time for this study • G4 team is active and we can interact with them. • Babar/PEP extension team is active. • Jerry’s detector program is active. • Mike’s magnet question is a focused and important question to guide initial work. • E166 may also have neutron problem. • E166 DAQ easily adapted to test beam study with Jerry’s detectors. Neutrons in PEP/Babar - Bower

  17. Summary • Sketched out an approach to answering Mike’s magnet question. • These studies provide a comparison of G4 neutron physics simulations with a variety of data. • This leads naturally to further studies regarding possible neutron problems in Babar. Neutrons in PEP/Babar - Bower

More Related