Environmental Radiation Resulting from the Experimental Program at JLab. January March Pavel Degtiarenko. Radiation Control Group Note 04-01

Transcription

1 Environmental Radiation Resulting from the Experimental Program at JLab January March 4 Pavel Degtiarenko Radiation Control Group Note 4-1 Distribution MS 7A: F. Dylla MS 1A: S. Chattopadhyay A. Hutton W. Oren C. Rode MS 1A3: J. Murphy MS 1H: H. Areti V. Burkert L. Cardman K. DeJager R. Ent D. Skopik MS 1K: R. Whitney MS 8H: L. Even C. Ficklen MS 5A: D. Dotson J. Jackson G. Walker M. Washington K. Welch MS 58: C. Reece MS 85A: S. Suhring MS 5A: E. Abkemeier R. May P. Degtiarenko

2 Rad Con Group Note 4-1 April 4 Environmental Radiation Resulting from the Experimental Program at JLab January March 4 Pavel Degtiarenko Points of note: Boundary dose accumulation due to CEBAF operations in the first quarter of 4 was very small, and less than conservatively estimated Radiation Budget. The projected total year 4 boundary dose accumulation is estimated to be about 9 mrem, below the 1-mrem administrative design goal. The release of tritium, generated mostly in the beam dump cooling water in the experimental halls, is.5 curie in the first quarter. 1. Hall A and Hall C Experiments The experimental program scheduled for the first quarter of 4 is set out as Table 1. Six Radiation Boundary Monitors (RBM-1 to RBM-6) whose positions are shown in Figure 1 monitored the radiation at the CEBAF boundary. Two Radiation Monitors (RM-48 and RM-47) have been installed at the top of Hall A and Hall C roofs as indicated in the same figure. RM-44 and RM-45 shown in Figure monitored the dose rates inside the Halls. Figures 3 and 4 illustrate running conditions in Halls A and C in this period. Hourly average beam energy and current are shown. The data are collected by the Radiation Control Group EPICS data retrieval system. The lower portions of the figures show the neutron dose rates measured inside the Halls and at the top of the Hall roofs. Neutron dose rates inside and at the rooftop of the halls normalized to 1µA beam current are shown in Figure 5. Figure 6 presents ratios of measured neutron dose rate to the dose rate measured by the ion chamber detectors in the Radiation Monitors, sensitive to charged particles and gamma radiation.. Measurement of Boundary Dose Rates The techniques for neutron and photon detection, detector calibration, data acquisition and analysis are discussed in earlier Rad. Con. reports; no major changes have been made in the hardware and the procedures. RBM-3 is the closest to the end stations. It represents the maximum dose at CEBAF boundary when Hall C is operating at a significant beam current. However, when Hall A operations are the main source of the boundary dose, the dose at RBM- position may become comparable and even larger than the dose at RBM-3. In the first quarter the dose rate at RBM-3 was larger than at RBM-. Thus RBM-3 data are reported as the measure of the maximum dose accumulation at the boundary.

3 3. Discussion of Results The technical illustrations of neutron data analysis are given in Figures 7-1. Figure 11 presents time dependence of neutron dose accumulation at different RBM positions in the first quarter. The photon doses are difficult to measure at the present low level of radiation produced at CEBAF. Expected photon signals are at a level lower than 1% of natural background, which is varying. This time we used the previous results measured at higher dose rates, and assumed the photon dose at the boundary as 5% of neutron dose. More sensitive scintillation detectors for photon and charged particle dose measurement are installed at RBM-3, and at RBM-6, but their readings are not used in the analysis due to the fact that the dose rates produced at the boundary were still below lower level of the detector sensitivity. The results for the passive (fission track) neutron monitors at the various monitor stations are given in the table below. The upper portion of the table shows raw data for all detectors (errors are 1σ). Only three detectors measured doses in the field in this quarter; RBM-1 reading was used as background. Monitor at Position 1-st quart. 3 (mrem) RBM-1 neutrons.53 +/-.15 RBM- neutrons.47 +/-.15 RBM-3 neutrons.83 +/-.15 RBM-4 neutrons n/a RBM-5 neutrons n/a RBM-6 neutrons n/a Backgr. neutrons n/a -nd quart. 3 (mrem) 3-rd quart. 3 (mrem) 4-th quart. 3 (mrem) Total (mrem) Result RBM-3 - Backgr(n).33 +/ /-. RBM-3 result(n+γ).41 +/ /-.5 The errors shown are estimated using a combination of the statistical errors in the number of fission tracks detected and the average calibration coefficient. Figure 1 presents time dependence of the dose accumulation at RBM-3 position through the year 4, measured by RBM-3 (neutrons plus gamma). 4. Radiation Budget Calculations vs. Measurements Figure 1 also tracks the budget calculations based on a very simplified model whereby the total radiation budget for an experiment is uniformly assigned over the total experiment period and each experiment is summed over the whole year. Each experiment is assumed to have utilized 1% of its scheduled beam time on planned target setups. The experimental schedule is taken from the JLab WWW site. The Radiation Budget estimate for the year is about 9% of the annual design goal. Figure 13 shows the history of boundary dose accumulation at JLab in the past years of operation and its projection into the future. The plot helps to explain why and how we use the process of Radiation Budgeting at JLab to keep annual boundary dose accumulation below the set administrative limit of 1 mrem. 3

4 5. Tritium Discharge High power beam dump operation is the source of tritium in the beam dump cooling water in the experimental halls A and C. To manage the tritium contamination, periodic discharges of tritiated water are performed during the year in accordance with the current JLab discharge permit. Figure 14 illustrates the process by showing the series of tritium concentration measurements in Hall A and Hall C, together with the cumulative beam dump tritium discharge plot (thick line). For reference, the total beam energy delivered to the beam dumps is shown in the plot. The total amount of tritium discharged in the first quarter from the beam dump cooling water is.5 Ci. 6. Conclusions The boundary dose accumulation for the first quarter of 4 for the position RBM-3 is given below: Period Jan Mar 4 Neutron (mrem).1 +/-.1 Photon (mrem). +/-.1 Neutron + Photon (mrem).1 +/-. Apr Jun 4 Jul Sep 4 Oct Dec 4 Totals.1 +/-.1. +/ /-. The yearly boundary dose accumulation is expected to be about 9 mrem, below the 1-mrem design goal. The total release of tritium measured in the first quarter of 4, generated mostly in the beam dump cooling water in the experimental halls, is about.5 curie, below the 5-curie yearly release limit. Acknowledgements The Radiation Control Group report has been prepared with the help of Dan Dotson, Melvin Washington, and David Hamlette who provided radiation monitors hardware operation, tests and calibration. David Hamlette, George Walker and Keith Welch set up measurements and obtained results with the fission track neutron detectors. George Walker and Dan Dotson provided data on the tritium concentration and discharge rates. 4

5 Table 1. Accelerator schedule in January March 4. Updated February 7, 4 Date Weekday Accelerator Hall A Hall A Hall B Hall B Hall C Hall C Priority GeV/pass/Pol Experiment GeV/µA Experiment GeV/nA Experiment GeV/µA Hall 1/1/4 Thursday New Year's 1//4 Friday Holiday 1/3/4 Saturday Holiday 1/4/4 Sunday Holiday 1/5/4 Monday Down 1/6/4 Tuesday Restore 1/7/4 Wednesday Restore 1/8/4 Thursday Restore 1/9/4 Friday.99 E94-17 Com 4.16/1 eg 5.6/5 A 1/1/4 Saturday.99 E94-17 Com 4.16/1 eg 5.6/5 G Eng. Run 3.6/4/p A/C/B 1/11/4 Sunday.99 E /1 eg 5.6/5 G Eng. Run 3.6/4/p A/C/B 1/1/4 Monday.99 Hypernuclear 4.16/1 eg 5.6/5 G Eng. Run 3.6/4/p A/C/B 1/13/4 Tuesday.99 E /1 eg 5.6/5 G Eng. Run 3.6/4/p C/B/A 1/14/4 Wednesday.99 E /1 eg 5.6/5 G Eng. Run 3.6/4/p C/B/A 1/15/4 Thursday.99 E /1 eg 5.6/5 G Eng. Run 3.6/4/p C/B/A 1/16/4 Friday.99 E /1 eg 5.6/5 G Eng. Run 3.6/4/p C/B/A 1/17/4 Saturday.99 E /1 eg 5.6/5 G Eng. Run 3.6/4/p C/B/A 1/18/4 Sunday.99 E /1 eg 5.6/5 G Eng. Run 3.6/4/p C/B/A 1/19/4 Monday.99 E /1 eg 5.6/5 G Eng. Run 3.6/4/p C/B/A 1//4 Tuesday.99 E /1 eg 5.6/5 G Eng. Run 3.6/4/p C/B/A 1/1/4 Wednesday.99 E /1 eg 5.6/5 G Eng. Run 3.6/4/p C/B/A 1//4 Thursday.99 E /1 eg 5.6/5 G Eng. Run 3.6/4/p B/A/C 1/3/4 Friday.99 E /1 eg 5.6/5 G Eng. Run 3.6/4/p B/A/C 1/4/4 Saturday.99 E /1 eg 5.6/5 G Eng. Run 3.6/4/p B/A/C 1/5/4 Sunday.99 E /1 eg 5.6/5 G Eng. Run 3.6/4/p B/A/C 1/6/4 Monday.99 E /1 eg 5.6/5 G Eng. Run 3.6/4/p B/A/C 1/7/4 Tuesday.99 E /1 eg 5.6/5 G Eng. Run 3.6/4/p C/A/B 1/8/4 Wednesday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C/B 1/9/4 Thursday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C/B 1/3/4 Friday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C/B 1/31/4 Saturday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C/B 5

6 Table 1. Accelerator schedule in January March 4 (continued). Updated February 7, 4 Date Weekday Accelerator Hall A Hall A Hall B Hall B Hall C Hall C Priority GeV/pass/Pol Experiment GeV/µA Experiment GeV/nA Experiment GeV/µA Hall /1/4 Sunday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C/B //4 Monday Maintenance /3/4 Tuesday Maintenance /4/4 Wednesday Restore /5/4 Thursday Restore /6/4 Friday.99 MagnetRepairs eg 5.6/5 G Eng. Run B/C /7/4 Saturday.99 MagnetRepairs eg 5.6/5 G Eng. Run B/C /8/4 Sunday.99 MagnetRepairs eg 5.6/5 G Eng. Run B/C /9/4 Monday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C /1/4 Tuesday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C /11/4 Wednesday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C /1/4 Thursday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C /13/4 Friday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C /14/4 Saturday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C /15/4 Sunday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C /16/4 Monday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p B /17/4 Tuesday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p B /18/4 Wednesday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p B /19/4 Thursday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p B //4 Friday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p B /1/4 Saturday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p B //4 Sunday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C /3/4 Monday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C /4/4 Tuesday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C /5/4 Wednesday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C /6/4 Thursday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C /7/4 Friday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C /8/4 Saturday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p B /9/4 Sunday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p B 6

7 Table 1. Accelerator schedule in January March 4 (continued). Updated February 7, 4 Date Weekday Accelerator Hall A Hall A Hall B Hall B Hall C Hall C Priority GeV/pass/Pol Experiment GeV/µA Experiment GeV/nA Experiment GeV/µA Hall 3/1/4 Monday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p B 3//4 Tuesday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p B 3/3/4 Wednesday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p B 3/4/4 Thursday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C 3/5/4 Friday.99 MagnetRepairs eg 5.6/5 G Eng. Run 3.6/4/p C 3/6/4 Saturday.99 MagnetRepairs Det. Calib. 5.6/5 G Eng. Run 3.6/4/p C 3/7/4 Sunday.99 MagnetRepairs Det. Calib. 5.6/5 G Eng. Run 3.6/4/p C 3/8/4 Monday Maintenance MagnetRepairs Install g1 3/9/4 Tuesday Maintenance MagnetRepairs Install g1 3/1/4 Wednesday Maintenance MagnetRepairs Install g1 3/11/4 Thursday Restore MagnetRepairs Install g1 3/1/4 Friday Restore MagnetRepairs 3/13/4 Saturday.746 MagnetRepairs g /5 G Forward 3.6/4/p C 3/14/4 Sunday.746 MagnetRepairs Pentaquark 3.767/5 G Forward 3.6/4/p C 3/15/4 Monday.746 MagnetRepairs g /5 G Forward 3.6/4/p B 3/16/4 Tuesday.746 MagnetRepairs g /5 G Forward 3.6/4/p B 3/17/4 Wednesday.746 MagnetRepairs g /5 G Forward 3.6/4/p C 3/18/4 Thursday.746 MagnetRepairs g /5 G Forward 3.6/4/p C 3/19/4 Friday.746 MagnetRepairs g /5 G Forward 3.6/4/p C 3//4 Saturday.746 MagnetRepairs g /5 G Forward 3.6/4/p C 3/1/4 Sunday.746 MagnetRepairs g /5 G Forward 3.6/4/p C 3//4 Monday.746 MagnetRepairs g /5 G Forward 3.6/4/p C 3/3/4 Tuesday.746 MagnetRepairs g /5 G Forward 3.6/4/p C 3/4/4 Wednesday.746 MagnetRepairs g /5 G Forward 3.6/4/p B 3/5/4 Thursday.746 MagnetRepairs g /5 G Forward 3.6/4/p B 3/6/4 Friday.746 MagnetRepairs g /5 G Forward 3.6/4/p B 3/7/4 Saturday.746 MagnetRepairs g /5 G Forward 3.6/4/p B 3/8/4 Sunday.746 MagnetRepairs g /5 G Forward 3.6/4/p B 3/9/4 Monday.746 MagnetRepairs g /5 G Forward 3.6/4/p B 3/3/4 Tuesday.746 MagnetRepairs g /5 G Forward 3.6/4/p B 3/31/4 Wednesday.746 MagnetRepairs g /5 G Forward 3.6/4/p C 7

8 FIGURES FIG. 1. CEBAF site schematic with Radiation Boundary Monitor (RBM) positions shown (RB1 to RB6 in the figure). 8

9 FIG.. Schematic of end stations showing locations of Hall radiation monitors. Radiation Monitors RM48 and RM47 shown are located at the top of Hall A and Hall C roofs. RM44 and RM45 are positioned inside the halls. 9

10 Hall A data: January - March, 4 E A (GeV) Jan Beam Energy Feb Mar 1 Beam Current I A (µa) 5 H RM44 n (mrem/h) H RM48 n (mrem/h) Neutron Dose Rate Inside Hall A Neutron Dose Rate Top of Hall A roof Hours in the year for the period Jan 1 through Mar 31, 4 FIG. 3. Upper two figures: Hall A electron beam energy and current (hourly averages) as a function of time, measured in hours starting on Jan 1, 4. Hours with E A =, and no beam current data, indicate absence of the energy and current information in the database. Lower two figures: the neutron dose rate measured in the hall, and at the top of Hall A roof (Radiation Monitors RM44 and RM48). Dots denote all hours in the period, circles correspond to the hours when average current in Hall A was reported to be above µa. 1

11 Hall C data: January - March, Jan Feb Mar E C (GeV) 6 4 Beam Energy 6 Beam Current I C (µa) 4 H RM45 n (mrem/h) Neutron Dose Rate Inside Hall C H RM47 n (mrem/h) Neutron Dose Rate Top of Hall C roof Hours in the year for the period Jan 1 through Mar 31, 4 FIG. 4. Same as Figure 3 for Hall C, together with the data from the Hall C Radiation Monitors RM45 and RM47. Dots denote all hours in the period, circles correspond to the hours when average current in Hall C was reported to be above µa. 11

12 Neutron Dose Rates per Beam Current H RM44 n (mrem/h)/i A Jan Inside Hall A (per 1 µa) Feb Mar H RM48 n (mrem/h)/i A.4. Top of Hall A roof (per 1 µa) H RM45 n (mrem/h)/i C Inside Hall C (per 1 µa) H RM47 n (mrem/h)/i C 1 Top of Hall C roof (per 1 µa) Hours in the year for the period Jan 1 through Mar 31, 4 FIG. 5. Hourly averaged neutron dose rates measured inside halls and at the top of hall roofs, normalized per 1 µa beam current delivered into the halls. Top two figures: Hall A, lower two figures: Hall C. Dots denote all hours in the period, circles correspond to the hours when average current was reported to be above µa in Hall A, and above µa in Hall C. 1

13 H H H H RM44 n/h Ion Ch. RM48 n/h Ion Ch. RM45 n/h Ion Ch. RM47 n/h Ion Ch. RM47 RM45 RM48 RM Neutron to Ion Chamber dose ratios Jan Inside Hall A Top of Hall A roof Inside Hall C Top of Hall C roof Feb Mar Hours in the year for the period Jan 1 through Mar 31, 4 FIG. 6. Hourly averaged neutron to ion chambers dose rate ratios measured inside halls and at the top of hall roofs. Top two figures: Hall A, lower two figures: Hall C. Dots denote all hours in the period, circles correspond to the hours when average current was reported to be above µa in Hall A, and above µa in Hall C. 13

14 Neutron hourly dose at RBM Jan Feb Mar 8 Dose rate (µrem/hour) 6 4 Average dose rate measured Average dose rate design goal Hours in the year for the period Jan 1 through Mar 31, 4 FIG. 7. The neutron dose rate measured hourly with the radiation boundary monitor RBM-3 as a function of time in the first quarter. Background subtracted. Solid line shows yearly average dose rate design limit; the dashed line shows the average neutron dose rate measured in the first quarter. 14

15 Neutron hourly dose at RBM Jan Feb Mar 8 Dose rate (µrem/hour) 6 4 Average dose rate measured Average dose rate design goal Hours in the year for the period Jan 1 through Mar 31, 4 FIG. 8. The neutron dose rate measured hourly with the radiation boundary monitor RBM- as a function of time in the first quarter. Background subtracted. Solid line shows yearly average dose rate design limit; the dashed line shows the average neutron dose rate measured in the first quarter. 15

16 Neutron hourly dose at RBM Jan Feb Mar 8 Dose rate (µrem/hour) 6 4 Average dose rate measured Average dose rate design goal Hours in the year for the period Jan 1 through Mar 31, 4 FIG. 9. The neutron dose rate measured hourly with the radiation boundary monitor RBM-5 as a function of time in the first quarter. Background subtracted. Solid line shows yearly average dose rate design limit; the dashed line shows the average neutron dose rate measured in the first quarter. 16

17 Neutron dose rate (8 hour average) Jan Feb Mar 8 RBM-3 RBM- Dose rate (µrem/hour) 6 4 Average dose rate design goal RBM-1 RBM Hours in the year for the period Jan 1 through Mar 31, 4 FIG. 1. The neutron dose rate (8-hour average) as a function of time in the first quarter for the boundary monitors RBM-1, RBM-, RBM-3, and RBM-5. Background subtracted. Solid line shows yearly average dose rate design limit. 17

18 Neutron dose accumulation at the boundary monitors Jan Background subtracted Feb RBM-3:.99±.9 mrem RBM-:.57±.14 mrem Mar RBM-1:.6±.8 mrem 1 RBM-5:.1±.1 mrem Accumulated dose (mrem) Hours in the year for the period Jan 1 through Mar 31, 4 FIG. 11. The accumulation of neutron dose due to CEBAF operations at RBM positions 1,, 3, and 5, as a function of time in the first quarter, 4. The integrals with the estimated statistical errors are shown. 18

19 Total dose accumulation at JLab boundary monitor RBM-3 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 1 Accumulated dose (mrem) Design goal for the year: less than 1 mrem Measured dose net of background RBM data 1st Q:.1 mrem Experiments Hall C: Hall A: Fission Track data Total estimated dose (Rad. Budget) Hours in the year for the period Jan 1 through Dec 31, 4 FIG. 1. Total dose accumulation due to CEBAF operations at RBM-3 position as a function of time in the year 4. The measured RBM-3 accumulated dose is shown by the thick solid line. The quarterly values are shown by the open circles with error bars, and by the dashed horizontal lines. Open diamonds show the dose measured by fission track detectors at the same RBM position. Thin-line triangles attached to the abscissa represent radiation budget estimates of the dose accumulation resulting from a particular experiment. The simplest model of a constant dose rate between scheduled start time and end time of an experiment is used. Extended intermissions are taken into account. All experiments scheduled to run in 4 are presented, and the integral estimated dose (Rad. Budget) produced by all of the experiments is shown by the solid line. 19

20 Yearly dose accumulation at JLab boundary 14 Accumulated dose (mrem) Radiation Budget estimates Design goal for a year: less than 1 mrem Boundary Monitor data Calendar year FIG. 13. Yearly boundary dose accumulation due to CEBAF operations for the period starting in 1996 through the first quarter of 4. Open circles show the measured dose accumulated during each calendar year. Error bars indicate 3% estimated systematic error of the measured value. Thick solid lines show accumulation of the dose as a function of time in the corresponding year. Thin-line gaps between thick portions of the lines indicate that only integral dose measurement data were available. No differential data is given for Thin solid lines ending with open squares show the integral estimated boundary dose produced by all experiments planned to run in the corresponding year, including experiments scheduled to run in 4. Every estimate is made before the actual run time. Dash-dotted line illustrates the design goal not to exceed 1 mrem yearly dose accumulation at the boundary.

21 Tritium concentration and discharge. Beam energy delivered..6 Jan Feb Mar.5 Beam energy delivered to the dumps (1 1 J).4 Hall C: Joules.3. Hall A: Joules 3 H cumulative discharge (Ci). Total:.5 Ci.1 3 H in dump water (µci/ml) Hall C Hall A Hours in the year for the period Jan 1 through Mar 31, 4 FIG. 14. Tritium concentration as measured in the beam dump water at Hall A (open circles connected by thin solid line), and Hall C (open squares connected by thin dashed line). The scale is µci/ml. Cumulative amount of tritium released to the HRSD sewer in accordance with the current JLab discharge permit during the first quarter (thick solid line). The scale is in Curie. The total amount of tritium discharged is.5 Ci. Thin dotted and dash-dotted lines show the integral energy delivered to the dumps with the electron beams. The scale units are terajoules. The total energy delivered during the first quarter is about 17 gigajoules to the Hall A dump, and 39 gigajoules to the Hall C dump. 1