Kamland radioassay progress in the united states
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KamLAND Radioassay Progress in the United States. Lawrence Berkeley National Laboratory with University of Alabama California Institute of Technology University of Tennessee. Low Background Counting. Balloon Film. Goal: Assay radioimpurities in KamLAND construction materials.

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KamLAND Radioassay Progress in the United States

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Kamland radioassay progress in the united states

KamLAND Radioassay Progress in the United States

Lawrence Berkeley National Laboratory

with

University of Alabama

California Institute of Technology

University of Tennessee


Low background counting

Low Background Counting

Balloon Film

  • Goal: Assay radioimpurities in KamLAND

  • construction materials.

  • Identify KamLAND background problems.

  • Method: U/Th daughter and 40K gamma detection

  • by optimized Germanium detectors.

  • Only method to verify equilibrium in daughters!

  • Activity: over 30 samples measured in the past

  • year. A sample of most KamLAND

  • construction materials is catalogued

  • for possible future assay.

  • Some Results:U (ppb)Th (ppb)40K (ppb)

  • Balloon Film<3 <3 1.0+/-0.2

  • Balloon Ropes<1 <3 0.8+/-0.3

  • Cable Guides<4 <9 49+/-3

  • Chimney Steel0.6+-0.2 2.0+-0.5 <0.1

  • (60Co26+/-2 mBq/kg)

Ge Detector

KamLAND balloon film inside

the Low Background Detector

at Caltech


Activation analysis of kamland scintillator

Activation Analysis of KamLAND Scintillator

Goal: Reliable, Independent monitor of Purity and Backgrounds

  • Collection of Scintillator

    • Ship samples to US

  • Preconcentration

    • Remove Reactor-unfriendly organics

  • Irradiation at Reactor (ORNL/MITR)

  • Post-chemistry

    • Separate “Signal” isotopes from “Background”

  • g-b Counting(HPGe + Scintillator)

  • Analysis and Results

Clean

Hot


Neutron activation analysis

Neutron Activation Analysis

KamLAND Scintillator purity needs are stringent!

Reactor ( solar) experiment requirements are

K<10-10 (10–14)g/g Th<10-14 (10-16) g/g U<10-14(10-16) g/g

Activation Analysis Goals:

  • Verify scintillator component purity for reactor neutrino phase

  • Study purification schemes for solar neutrino experiment.

    Why Activation Analysis?

  • Direct counting not feasible: <10-14g/g U gives 0.01 decay/day/kg

  • Mass spectroscopy ultimately limited by chemical blank values.

  • Neutron capture cross sections and lifetimes are reasonable:

    41K + n 1.3b42K(12.4 h) β-42Ca

    232Th + n 6.5b 233Th(22.3 m) β-233Pa(27 d) β-233U

    238U + n 2.4b239U(23.5 m) β-239Np(2.4 d) β-239Pu


Technical issues at irradiation facilities

Technical Issues at Irradiation Facilities

  • Technical Challenges: Pressure build-up through out-gassing of organic samples in high neutron flux environment.

  • Solutions:

    • Oak Ridge: Irradiate ashed samples. Utilize pneumatic sample insertion and long-term irradiation at highest-flux. Retention efficiency for U experimentally demonstrated through tracer experiments.

    • MIT: Irradiate smaller samples e.g. PPO

      Develop liquidirradiation facility (Engineering Proposal by MIT)

      Reactor irradiation fees are also significant! Optimize samples for efficiency.


Activation analysis procedures

Activation Analysis: Procedures

Significant technical progress in the past year towards routine analysis of KamLAND scintillator!

  • High sensitivity analysis:

    Slowly evaporate scintillator to PPO residue.Ash residue in synthetic quartz.

  • Faster, lower sensitivity analysis:

    Irradiate ~2g of PPO in plastic vials in the MIT reactor.

  • Detection of 233Pa and 239Np by gamma ray spectroscopy with shielded Ge detectors.

  • Use gamma peak energies and decay times to identify target isotopes.

    Test irradiations show promising sensitivity and identify challenges!

  • KamLAND scintillator analyzed :

    U < 10-13g/g Th~2x10-13g/g

  • Primary limit on sensitivity comes from side activity interference, including 24Na and 82Br


Activation analysis 232 th in kamland scintillator

Activation Analysis: 232Th in KamLAND Scintillator

232Th + n 233Th

233Pa( 39 days mean life)

233U+b+gs (311 keV)

NAA Result:

~2x10-13gTh/g

(ICPMS: 4x10-13 gTh/g)

Test data showed NAA sensitivity may easily extend below 10-15 g/g through side activity background reduction.

233Pa

Ge spectrum from activated scintillator

The 233Pa peak at 311 keV can be seen.

Background reduction would enhance

sensitivity by 2 orders of magnitude.


Radiochemistry improvements

Radiochemistry Improvements

  • October 2000 data showed that 239Np/ 233Pa detection is limited

  • by interfering backgrounds: 24Na, 82Br, 65Zn, 51Cr…

  • Solve this with chemical separation techniques!

  • Techniques and Results:

  • Actinide Absorbing Resin:

  • Digest sample in nitric acid and pour through a column of Actinide resin.

  • Np/Pa Efficiency~95% Typical Background rejection: x5-1000.

  • Tri-butyl Phosphate:

  • Digest sample in nitric acid and mix with Np/Pa absorbing organic liquid

  • tri-butyl phosphate. Count the TBP in a β-γ coincidence spectrometer.

  • Np/Pa Efficiency~90% Typical Background rejection: x10

  • Chloroplatinic Acid:

  • Digest sample in HCl6Pt, evaporate, rinse salt with ethanol, and count.

  • K Efficiency>40% 24Na rejection >10.

  • March 2001: U/Th/K Sensitivity gain of ~100!


Further improvements new detectors

Further Improvements: New Detectors

A new ultra low background

Germanium detector was

added to our capabilities in

Time for PPO counting,

March `01.

The high efficiency detector

improves statistics of the

counting considerably.

Ultra low activity materials

were carefully selected for

its construction.

The shielding hut of the new

detector.


Ppo purity verification

PPO Purity Verification

  • December – April 2001, NAA was first employed to monitor radiopurity of final Packard PPO production.

  • Sensitivity Goals: At 1.5 g PPO per liter scintillator,

  • 5ppt PPO impurity yields 1x10-14 g/g impurity in scintillator

  • January 2001: irradiation of small batches of

  • PPOs for first pass testing

  • Result: 5 test lots of PPO proven <500 ppt U/Th

  • March 2001: focused irradiation of one of final lots

  • for KamLAND (Lot 21-634)

  • Radiochemical techniques employed for further sensitivity.

  • Result: < 2.2 ppt Uranium in PPO

  • < 7.7 ppt Thorium in PPO

  • < 8.4 ppt Potassium-40 in PPO

  • The limits reach the required tolerance of the reactor experiment.

  • Further study of the final PPO lots continues.


Kamland radioassay progress in the united states

Ge detector spectrum from activated KamLAND PPO:The three spectra compare the spectra before radiochemistry(purple), the spectra after extraction ( actinide ion column)(red), and the ambient detector background(blue).The bottom plot shows a closeup of the 233Pa peak region.


Future direction coincidence counting

Future Direction: Coincidence Counting

Delayed β-γ-e- decay signatures may offer further

sensitivity. Spectrometers for this have been built.

239Np Decay

Data from a feasibility study with a

239Np source. The TDC measures the

delay between a β and conversion e-

A Schematic coincidence

detection spectrometer


Mass spectroscopy

Mass Spectroscopy

  • We are also investigating mass spectroscopic analysis for

  • KamLAND. It provides

  • a faster, but less sensitive, analysis technique than NAA,

  • an optimal technique for studying water, e.g. from

  • the KamLAND scintillator purification system.

  • Progress:In Dec.-Feb. 2001, a technique for preparing PPO

  • for ICP-MS was developed. Studies to

  • improve sensitivity are continuing.

  • Selected Results:

  • KamLAND “test” Scintillator 0.2ppt U, 0.4 ppt Th

  • Dojindo PPO ( a final lot for KamLAND) <100ppt U/Th

  • Other PPOs compared (Acros, EMScience, Aldrich,

  • Alfa Aesar). Packard, Dojindo PPO confirmed best.


Accomplishments

Accomplishments

  • We have established the basic counting equipment and reactor agreements necessary to analyze activated samples.

  • We have developed clean procedures and equipment for preparing samples for analysis.

  • We have demonstrated feasibility of analyzing organic samples and proven our proficiency in this technique.

  • We have developed the analysis sensitivity to the level

    required for the KamLAND reactor experiment.

  • We have already contributed to the experiment by verifying the purity of test scintillator and the first KamLAND PPO productions.


Directions i

Directions: I

  • We will begin detailed study of KamLAND PPO, oil, and scintillator to understand its purity and the purification process in general in time for the start of the reactor experiment.

    Equipment and procedures for sample transport

    to the United States are now in place.

    Operating costs in reactor irradiation fees, hazardous sample shipment from Japan, and clean materials will be substantial!


Directions ii

Directions II

  • We will continue to upgrade the sensitivity of the analysis techniques pushing towards the requirements of the solar experiment.

  • Simulations usingthe exterior material radioassay show that the KamLAND solar experiment is still limited by scintillator purity.

  • Further background reduction through radiochemistry is achievable.

  • Equipment can be established at the MIT reactor to process samples soon after irradiation, reducing sample cooling delays.

  • Longer irradiation times (12 hours) have been approved MIT.

  • Upgrade the basic existing clean room and detector equipment for lower blank and higher sensitivity.

  • A direct liquid irradiation facility with very low blank is under discussion at the MIT reactor.


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