Gd Loading in Water

Mark Vagins

University of California, Irvine

Homestake Detector Meeting @ FermilabOctober 12, 2007

Based on work we first did in 2002 here at Fermilab, John Beacom and I wrote the original GADZOOKS!

(Gadolinium Antineutrino Detector Zealously Outperforming Old Kamiokande, Super!)

paper in late 2003. It was published the following year: [Beacom and Vagins, Phys. Rev. Lett., 93:171101, 2004]

In a nutshell, we proposed a way to tag neutrons produced by the inverse beta process (from

supernovae, reactors, etc.) in light water:

e + p e+ + n (=~4cm, =~20s)

At the 100’s of kton scale and beyond, the only way to see neutrons is a solute mixed into the water...

Much beyond the kiloton scale, you can forget about liquid scintillator, 3He counters, or heavy water!

Water solubleGdCl3 or Gd(NO3)3

should do the trick!

They’re (recently) affordable, have

low toxicity and reactivity, and once dissolved

are quite transparent.

All of the events in the present SK low energy analyses are singles in time and space.

And this rate is actually very low… just three events per cubic meter per year.

0.1% Gd gives>90% efficiency

for n capture

In Super-K this means ~100 tons of water soluble

GdCl3 or Gd(NO3)3

Gadolinium has1500X the n capturecross section of Cl

But, um, didn’t you just say 100 tons?What’s that going to cost?

In 1984: $4000/kg $400,000,000In 1993: $485/kg $48,500,000In 1999: $115/kg $11,500,000

In 2007: $5/kg $500,000

This positron/neutron capture coincidence technique is readily scalable to megaton class detectors at ~1% of

their total construction cost, with one important caveat:

In order to be both big and sensitive, ~40% photocathode coverage (or the equivalent in terms of photon collection)

is required in at least part of the detector.

Hyper-KHyper-K

UNO M3UNO M3

MEMPHYSMEMPHYS

As an example: adding 100 tons of soluble Gd to Super-K would provide at least two brand-new signals:

2) Discovery of the diffuse supernova neutrino background [DSNB],

also known as the “relic” supernova neutrinos

(~5 events per year)

1)Precision measurements of the neutrinos from all of

Japan’s power reactors(~5,000 events per year)

Will improve world average precision of m2

12 by 7X

Here’s what the coincident signals in Super-K-III with GdCl3 or Gd(NO3)3 will look like (energy

resolution is applied):

Most modernDSNB range

In addition to our two guaranteed new signals,it is likely that adding gadolinium to SK-III will

provide a variety of other interesting possibilities:

• Sensitivity to very late-time black hole formation • Full de-convolution of a galactic supernova’s signals• Early warning of an approaching SN burst • (Free) proton decay background reduction • New long-baseline flux normalization for T2K• Matter- vs. antimatter-enhanced atmospheric samples(?)

How good a job can Super-K do - by itself - on the solar neutrino parameters?

= ~3 years with gadolinium

= 4.1 live years of data without gadolinium

KamLAND alone

SK + SNO + KamLAND

SK + SNO + Ga + Cl + KamLAND (all of the world’s data)

~3 years of GADZOOKS! (by itself)

Our proposal has definitely been getting some attention:

At NNN05, before I had evengiven my talk, John Ellis suddenly

stood up and demanded of the SK people in attendance:

Why haven’tyou guys put gadolinium inSuper-K yet?

As I told him, studiesare under way…

…since we need to know the answers to the following questions:

• What does gadolinium do the Super-K tank materials?

• Will the resulting water transparency be acceptable?

• How will we filter the SK water but retain gadolinium?

Gadolinium R&D

The total AmericanR&D funding for this

gadolinium-in-water project has reached $400,000, withadditional support coming

from Japan.

So, can we make it work?

Over the last four years there have been a large number ofGdCl3-related R&D studies carried out in the US and Japan:

What we really want is selective filtration.

Adding nanofiltration (NF) to ultrafiltration (UF) and reverse osmosis (RO)

could make this possible.

}

Ultrafilter Nanofilter

DI/RO

Impurities to drain(RO Reject)

Pure water(RO/DI product) plus GdCl3 or Gd(NO3)3 back to detector

Pure waterplus GdCl3 or Gd(NO3)3 from detector

GdCl3 or Gd(NO3)3 (NF Reject)

Water “Band-pass Filter”

[Undergoing testing at UCI]

GdCl3 or Gd(NO3)3 plus smaller impurities (UF Product)

Impurities smaller than GdCl3 or Gd(NO3)3 (NF Product)

Impurities larger than GdCl3

or Gd(NO3)3 (UF Reject)

On another R&D front, gadolinium has unusually strong magnetic properties – hence its widespread use

as a contrasting agent in MRI scans:

Substance Magnetic Susceptibility

Gadolinium +185,000

Iron Chloride +14,750

Copper Chloride

+2,370

Iron Sulfide +1,074

Copper Oxide -20

So - if funding allowed - it would be great to investigate using magnetic fields as a selective gadolinium filter.

Method 1: Low Intensity Magnetic Separation

Method 2: High Gradient Magnetic Separation

6.5 m

Laser Pointers/N2 Dye Laser

Depth

Nor

mal

ized

Ligh

t In

tens

ityIS/PD

Water with Gd(NO 3) 3

IS/PD

IDEAL: Irvine Device Evaluating Attenuation Length

This is an upgradeof a 1-meter long

device successfullyused for IMB[UCI High Bay Building]

Violet Attenuation Curve

y = 9.1857e-0.0057x

0

1

2

3

4

5

6

7

8

9

0 1 2 3 4 5 6 7depth [m]

rela

tive

lig

ht

po

wer

Attenuation CurvesAttenuation Curves

Data taken September 2007in pure water

[plots by M. Smy]

Preliminary Measurement (Pure Water)Preliminary Measurement (Pure Water)

[plot by M. Smy]

Encouraging, but errors are yet to be determined. Will 7 meters of vertical pipe be enough? We’ll need to measure changes of less than 1% in very clear (~100 m ~95 m absorption length) water.

A longer lever-arm would be nice…but where to do it?

Hmmmmm… 40 m

That’s it for now…